Bss functions and paramaters

© Copyright 2002 AIRCOM International Ltd All rights reserved AIRCOM Training is committed to providing our customers with quality instructor led Telecommunications Training. This documentation is protected by copyright. No part of the contents of this documentation may be reproduced in any form, or by any means, without the prior written consent of AIRCOM International. Document Number: P/TR/003/P035/1.0a This manual prepared by: AIRCOM International

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BS

GSM PRE LAUNCH
S Functions and Parameters
http://www.aircom.co.uk/

Table of Contents

PART 1 – OPTIMISATION PROCESSES 1. Introduction to BSS Parameter Optimisation

1.1 Introduction ....................................................................................................... 1 1.2 What is the BSS? ............................................................................................... 2 1.3 What are BSS Parameters?................................................................................ 3 1.4 What is Optimisation? ....................................................................................... 5

2. The GSM Optimisation Process

2.1 Introduction ....................................................................................................... 7 2.2 The Purpose of Optimisation............................................................................. 8 2.3 The Reasons for Optimisation ........................................................................... 9 2.4 The Benefits of Optimisation .......................................................................... 10 2.5 Outline GSM Optimisation Process ................................................................ 11

3. BSS Parameter Review

3.1 Introduction ..................................................................................................... 15 3.2 BSS Parameter Review Process ...................................................................... 16 3.3 Database Consistency and Change Control..................................................... 17 3.4 BSS Configuration Parameter Sets.................................................................. 17 3.5 BSS Configuration Parameter Types............................................................... 18 3.6 Adjusting BSS Configuration Parameters ....................................................... 20

PART 2 – COMMON SITE/CELL PARAMETERS 4. Network Identifier Parameters

4.1 Introduction ..................................................................................................... 23 4.2 Subscriber Indentifiers..................................................................................... 24 4.3 Equipment Indentifiers .................................................................................... 26 4.4 Call Number Indentifiers................................................................................. 28 4.5 Call Routing Indentifiers ................................................................................. 29

5. Common Site and Cell Parameters

5.1 Introduction ..................................................................................................... 33 5.2 Cell Indentifiers ............................................................................................... 34 5.3 Cell Functions................................................................................................... 35 5.4 Cell Channel Configurations ........................................................................... 36

GSM BSS Functions and Parameter Optimisation © AIRCOM International 2002 i

PART 3 – IDLE MODE FUNCTIONS AND PARAMETERS 6. Network Access

6.1 Introduction .................................................................................................... 39 6.2 Network Access Procedures ............................................................................ 40 6.3 Key Network Access Parameters .................................................................... 43

7. BCCH Allocation Lists and Idle Mode Measurements

7.1 Introduction ..................................................................................................... 47 7.2 Generic Neighbour List Functionality............................................................. 48 7.3 Idle Mode Cell Measurements......................................................................... 51 7.4 Key Neighbour Relation Parameters ............................................................... 53

8. Cell Selection/Reselection 8.1 Introduction .................................................................................................... 55 8.2 Cell Selection Procedures................................................................................ 56 8.3 Cell Reselection Procedures ............................................................................ 57 8.4 Summary of Key Cell Selection/Reselection Parameters ............................... 62 Self Assessment Exercises .............................................................................. 65

9. Location Management and Paging Requirements

9.1 Introduction .................................................................................................... 67 9.2 Location Management Procedures .................................................................. 68 9.3 Paging Procedures ........................................................................................... 71 9.4 Calculations Using Paging Parameters............................................................ 73 9.5 Key Paging Parameters.................................................................................... 74 9.5 Key Location Management Parameters........................................................... 77 Self Assessment Exercises .............................................................................. 79

10. Frequency Hopping

10.1 Introduction ................................................................................................... 81 10.2 Frequency Hopping Procedures .................................................................... 82 10.3 Key Frequency Hopping Parameters............................................................. 87

ii GSM PRE LAUNCH - BSS Functions and Parameters © AIRCOM International 2002

PART 4 – DEDICATED MODE FUNCTIONS AND PARAMETERS 11. Dedicated Mode Cell Measurements

11.1 Introduction .................................................................................................. 89 11.2 Dedicated Mode Cell Measurement Procedures and Parameters.................. 90

12. Power Control

12.1 Introduction ................................................................................................... 99 12.2 Power Control Functions............................................................................. 100 12.3 Adaptive Power Control .............................................................................. 103 12.4 Discontinuous Transmission (DTX)............................................................ 107 12.5 Discontinuous Reception (DRX)................................................................. 109 12.6 Summary of Key Power Control Parameters .............................................. 111 Self Assessment Exercises ............................................................................ 15

13. Adaptive Frame Alignment

13.1 Introduction ................................................................................................. 117 13.2 Timing Advance Procedures ....................................................................... 118 13.3 Extended Cell Range ................................................................................... 119 13.4 Key Timing Advance Parameters................................................................ 120

14. Handover

14.1 Introduction ................................................................................................. 123 14.2 Handover Procedures................................................................................... 125 14.3 Key Handover Parameters........................................................................... 129 Self Assessment Exercises .......................................................................... 133

Appendix A - Vendor Parameter Table Appendix B - Answers to Self-Assessment Exercises Appendix C - Glossary of Terms

GSM BSS Functions and Parameter Optimisation © AIRCOM International 2002 iii

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iv GSM PRE LAUNCH - BSS Functions and Parameters

© AIRCOM International 2002

Course Objectives and Structure The objectives of the BSS Functions and Parameter Optimisation Course are to enable the delegate to:

• Understand the meaning of the terms ‘BSS’, ‘parameters’ and ‘optimisation’ in the context of GSM networks important for Network Pre launch Optimisation

• Be able to describe the GSM Optimisation process and, in particular, the purpose of the BSS parameter review within this process.

• Be familiar with the purpose and structure of network and cell identifier parameters and the parameters that control air-interface channel configurations

• Be familiar with the functionality and parameters that control the following Idle Mode functions: • BSS mobile access functions and the key controlling parameters • Idle mode cell measurement functions and the key controlling parameters • Cell selection and reselection functions and the key controlling parameters • Paging mode functions and the key controlling parameters • Location management functions and the key controlling parameters

• Be familiar with the functionality and parameters that control the following Dedicated Mode functions: • Dedicated mode cell measurement functions and the key controlling parameters • Power control functions and the key controlling parameters • Frequency hopping functions and the key controlling parameters • Handover functions and the key controlling parameters • Adaptive frame alignment functions and the key controlling parameters

PART 1 - Introduction to BSS Parameter Optimisation

PART 2 – Common Site / Cell Parameters

PART 3 – Idle Mode Functions and Parameters

PART 4 – Dedicated Mode Functions and Parameters

Course OutlineCourse Outline

GSM BSS Functions and Parameter Optimisation © AIRCOM International 2002 v


PART 2 - Common Parameters

4. Network Identifier Parameters

5. Common Site and Cell Parameters

6. Network Access

PART 1 - Introduction

1. Course Introduction



PART 3 – Idle Mode

7. BCCH Allocations Lists and Idle Mode Measurements

8. Cell Selection / Reselection

9. Location Management andPaging Requirements



PART 4 – Dedicated Mode

11. Dedicated Mode Cell Measurements

12. Power Control


14. Handover Requirements

vi © AIRCOM International 2002

GSM PRE LAUNCH - BSS Functions and Parameters

1. Introduction to BSS Parameter Optimisation

GSM BSS Functions and Parameter Optimisation © AIRCOM International 2002 1


_____________________________________________________________________ 1.1 Introduction

This section provides an introduction to the course by analysing the title of the course i.e. it describes what is meant, in the context of this course, by:

• The BSS • Parameters • Optimisation


2 GSM BSS Functions and Parameter Optimisation


_____________________________________________________________________ 1.2 What is the BSS?

1.2.1 THE BSS COMPONENTS OF THE GSM NETWORK

GSM Architecture OverviewGSM Architecture Overview

BTSBTS BSCBSC

HLRHLR

MSCMSC AuCAuC

EIREIR

PSTNPSTN

TRXTRX

Air Interface Air Interface (Um)(Um)

BSSBSS

OMCOMC

A Interface A Interface AbisAbis Interface Interface

MSMS

MSMS

MSMS

VLRVLR

NSSNSS

The Base Station SubThe Base Station Sub--System (BSS)System (BSS)• The BSS comprises:

• Base Station Controller (BSC) • One or more Base Transceiver Stations (BTSs)

• The purpose of the BTS is to:• provide radio access to the mobile stations• manage the radio access aspects of the system

• BTS contains: • Radio Transmitter/Receiver (TRX)• Signal processing and control equipment• Antennas and feeder cables

• The BSC:• allocates a channel for the duration of a call • maintains the call:

– monitors quality– controls the power transmitted by the BTS or MS– generates a handover to another cell when required

• Siting of the BTS is crucial to the provision of acceptable radio coverage

BSCBSC

BTS

BTS

BTS

BSSBSS

BTS



The Base Station System (BSS) is the system of base station equipments (transceivers, controllers, etc) which is viewed by the MSC through a single A-interface as being the entity responsible for communicating with Mobile Stations in a certain area. The radio equipment of a BSS may support one or more cells. The BSS consists of one Base Station Controller (BSC) and one or more Base Transceiver Station (BTS). Where multiple BTSs exist, an A-bis interface is implemented between the BSC and each BTS.

BSS Network TopologiesBSS Network Topologies

• Chain: cheap, easy to implement• One link failure isolates several BTSs

• Ring: Redundancy gives some protection if a link fails

• More difficult to roll-out and extend• ring must be closed

• Star: most popular configuration for first GSM systems

• Expensive as each BTS has its own link• One link failure always results in loss of BTS

BSC

BSC

BSC

Base stations are linked to the parent BSC in one of several standard network topologies. The actual physical link may be microwave, optical fibre or cable. Planning of these links may be done using a software application such as AIRCOM’s Connect planning tool.

_____________________________________________________________________ 1.3 What are Parameters?

Mobile network parameters are generally database settings or hardware switches within a network element that are used to control the functionality of that element. There are many types of parameters but can be grouped into the classes described in this section:




What Are Parameters?What Are Parameters?

• Identifier Parameters• Uniquely identifies network elements

• Functional Parameters (Flags)• Enable/disable functions

• Timer Parameters• Time-dependant counters

• Counter Parameters• Event-dependant counters

• Threshold Parameters• Define operating limits

• Measurement Parameters• Stores measured values

1.3.1 IDENTIFIER PARAMETERS Identifier parameters are those that identify a specific element or functional area in the network. 1.3.2 FUNCTIONAL PARAMETERS Functional parameters are those that are used to turn on or off specific functions within a network entity. Hence there are generally in one of two states:

• On. Function has been activated

• Off. Function is available but inactive. 1.3.3 TIMER PARAMETERS Timers are used to control the time period for which a certain condition exists. They are always in one of three states:

• Off/Reset. The timer is set to 0 and is inactive

• Counting. An event has occurred that has caused the timer to start incrementing.

• Expired. The timer has reached a pre-determined value and has expired, generally triggering a new event.



1.3.4 COUNTER PARAMETERS Counter parameters are similar to timers in that they can be in one of the same three states at any one time. However, whereas timers increment on a time basis (e.g. every second), counters increment on an event basis i.e. every time a specific event occurs. They can be linked to a threshold, beyond which a subsequent event can be triggered 1.3.5 THRESHOLD PARAMETERS These are values which, when exceeded above or below, will trigger and event. Threshold parameters can either be:

• Fixed. For example, designed into the hardware

• Variable. Set by operator to meet specific local operating conditions. 1.3.6 MEASUREMENT PARAMETERS These are parameters that stores measured values or averages of measured values. For example, power level measurements.

_____________________________________________________________________ 1.4 What is Optimisation?

The goal of optimisation is to ensure the network is operating at optimum efficiency within the defined quality of service constraints.

What is Optimisation?What is Optimisation?

• Dictionary Definition:

‘Determining the best compromise between potentially conflictingrequirements in order to plan and implement an activity with maximum efficiency.’

• Mobile Radio Definition:

‘The identification and rectification of performance affecting problems within the constraints of an existing network infrastructure in order to maximise its efficiency.’




This is achieved by implementing corrective action and procedures to rectify network problems identified though analysis of performance management monitoring parameters. The reason this optimisation process is carried out is to:

• Maintain or improve quality of service • Reduce churn rate by retaining existing customers • Attract new customers.

Section 1 Section 1 -- SummarySummary• In this section the following topics have been covered:

• What is the BSS in a GSN Network

• Basic BSS topologies

• What is meant by ‘Parameters’

• What is meant by ‘Optimisation’



2. GSM Optimisation Process

_____________________________________________________________________ 2.1 Introduction

This section of the course reviews the purpose and goals of optimisation in a GSM network. It looks at the generic GSM optimisation process in order to identify the point in the process at which it is recommended that BSS parameter changes take place. It should be noted that the optimisation process is dependant upon a number variables and, as such the process may vary from organisation to organisation.

GSM OptimisationGSM Optimisation

No prescribed methodology

Often network architecture dependant

Often vendor equipment-dependant

Often engineer-experience dependant

Optimisation is an art as much as a science

A ‘tool-box’ approach




_____________________________________________________________________ 2.2 The Purpose of Optimisation

Purpose of OptimisationPurpose of Optimisation

• To correct identified performance shortfalls

• To ensure network performance remains within QoS constraints

• To make an existing network more efficient

The essential purpose of optimising a network is to improve the current overall quality of a mobile network. This quality improvement can be achieved by addressing one or a combination of the following: • To correct identified performance shortfalls. These shortfalls are identified through

continual monitoring of the defined network Key Performance Indicators (KPIs) or through customer complaints.

• To ensure network performance remains within QoS constraints. When a network is

initially designed, one of the key planning constraints is the Quality of Service (QoS) to be offered to customers. It is beholden upon the operator to maintain or improve the QoS levels advertised and offered to customers.

• To make a network more efficient. It may become necessary to try and increase the

revenue being generated by the network with minimum further investment. This can only be achieved by efficiency improvements within the existing network infrastructure.



_____________________________________________________________________ 2.3 The Reasons for Optimisation

There are a number of reasons for the instigation of an optimisation process:

• After completion of network rollout where monitoring of KPIs indicates that problems are occurring due to incorrect initial planning assumptions.

• On implementation of a new service (e.g. SMS/GPRS) in an attempt to introduce the new service with minimum impact on existing service levels and with minimum additional infrastructure investment.

• As a result of problems identified through a Network Audit.

• As a result of on-going performance monitoring where faults or performance

degradation trends have been identified.

• Where a new business case has been generated to increase the network performance above original targets without additional infrastructure investment in order to boost Return On Investment (ROI).

• When it has been decided that certain operating parameters are to be changed e.g. a

change to the offered Grade of Service from 2% to 1.5%.

Reasons for OptimisationReasons for Optimisation

• Correct identified post-roll-out inefficiencies

• Preparation for new service implementation

• Correct identified Network Audit performance deficiencies

• Correct identified KPI performance monitoring degradation

• Improve network efficiency to meet business requirements

• Deliberate change in network operating parameters




_____________________________________________________________________ 2.4 Benefits of Optimisation

Successful network optimisation should accrue the following benefits:

• Maintain or improve existing quality of service

• Reduce churn rate by retaining existing customers

• Attract new customers through offering better services and/or grade of service, achievable through efficient network performance.

• Maximise revenue generating services by maximising efficiency of functional network

elements.

Benefits of OptimisationBenefits of Optimisation

• Maintain/improve QoS

• Reduce churn rate

• Attract new customers

• Maximise revenue-generating service

• Maximize efficiency of network functional elements

Vendors are continually seeking ways of maximising revenue generation with minimum additional investment. One way of achieving this is to identify areas where the network is not operating at peek efficiency and making adjustments for improvement. For example, over capacity may exist in certain areas allowing for a possible removal of TRXs. Alternatively, congestion may exist in certain areas and by prudent optimisation, additional capacity can be generated with no additional infrastructure investment. The Vendor may wish to add new services to the network (such as HSCSD/GPRS) in order to attract more customers and/or increase revenue generation. This may generate an increased requirement for network capacity either in terms of additional customers or an average increase in traffic per existing customer. Network optimisation may enable these services to be introduced with minimal additional infrastructure investment to meet the increased capacity demand.



It may be that the original network design was based on flawed information and as a result the network is not performing as originally envisaged. Alternatively, information on which the network design was based has subsequently changed, requiring a change to the network configuration. For example, a new airport or shopping mall has been built creating unforeseen congestion in a particular part of the network.

_____________________________________________________________________ 2.5 Outline Optimisation Process

2.5.1 PERFORMANCE MANAGEMENT AND OPTIMISATION

Performance Management CyclePerformance Management Cycle

Monitor Network

Analyse Data

Yes

Identify Problems

Implement Changes

No

Initial Network Design and

Implementation

Performance Management

Optimisation

QoS Targets

Met?

Optimisation can form part of the performance management process. The objective of the radio network optimisation is to extract the optimum performance from the cellular network, at any given phase of its lifecycle. All cellular systems will be associated with continuous change, with new radio sites being introduced, old sites being enhanced and assigned additional frequencies, omni-directional sites being sectorised, new frequency plans being implemented in different regions, etc. The initial step in performance management is to define a set of QoS (Quality of Service) parameters such as dropped call rates and call success rates. Key metrics are derived from data collected from sources such as drive tests, statistical data, customer complaints and field engineer reports and are used to measure the performance of the network. These metrics are analysed and compared to the QoS targets in order to identify any performance degradation in the network. If problematic areas are identified from analysis of the network performance parameters, corrective processes and/or procedures are implemented to rectify the situation using one or a combination of techniques. This process of corrective actions is known as optimisation.




2.5.2 OUTLINE OPTIMISATION PROCESS

Outline Optimisation ProcessOutline Optimisation Process

Initial network design and roll-out phase

Monitoring/Network Audit Phase

Optimisation Activity Phase

Design Review and growth phase

2.5.3 NETWORK AUDIT PHASE OF OPTIMISATION

Network Audit Phase of OptimisationNetwork Audit Phase of Optimisation

Decide on KPIs, Measurement Strategy and Tools

Measure Performance, Establish Benchmark

Performance Review to Identify Major Performance

Affecting Issues

Decide on Strategy,Establish Action Plan Feedback from

Optimisation Activities

Start Optimisation Activity



The network audit phase serves two primary purposes:

• A review of existing network hardware and software (inc database) configurations to determine the both validity and consistency across the network.

• Analysis of data gathered from performance-related network monitoring in order to

identify weaknesses or sub-optimal operating performance levels. 2.5.3.1 Deciding on KPIs, Measurement Strategy and Tools This step in the process is normally only implemented when these elements do not exist within the network. A mature network should already have its KPIs and measurement strategy in place, together with tools to support this process. However, in such cases, part of the network audit process would be to validate these measurement counters and procedures. 2.5.3.2 Measuring Performance and Establishing Benchmarks In mature networks, benchmarks would have already been established. Measuring performance is an ongoing process. However, if a network audit is to carried out as an independent process, a review of existing performance parameters and benchmarks will be required to ensure their validity and applicability to the audit taking place. 2.5.3.3 Performance Review Having established benchmarks and validated performance parameters, a review of performance is carried out. A possible structure of such a review is as shown in the slide below. The performance Review is not intended to provide all the answers to all the problems, but to highlight the major issues and provide all the necessary background for further analysis, investigation and in-depth troubleshooting of the major performance-impacting problems in the network. It is important that any network performance audit should follow a methodical process and should be systematic in its approach to data collection.




2.5.4 ACTIVITY PHASE OF OPTIMISATION

Activity Phase of OptimisationActivity Phase of Optimisation

Start Optimisation Activity

Identify and Fix Hardware Problems Ongoing Performance Measurement

Process

Review Process and Results

Feedback to modify strategy decisions

BSS Database Parameters Review:

SettingsConsistency

Change Control

Design Review and Growth Plan

Identify and Fix Neighbour Problems

Identify and Fix Frequency Plan Problems

Network Audit ProceduresFeedback

to Audit

Procedures

Section Section 22 -- SummarySummary• In this section the following topics have been covered:

• The purpose of Optimisation

• The reasons for carrying out Optimisation

• The benefits of Optimisation

• The Performance Management Cycle

• An Optimisation Process

• The Network Audit phase of Optimisation

• The Activity Phase of Optimisation




_____________________________________________________________________ 3.1 Introduction

The BSS database parameter review is intended to review existing BSS database parameter settings in the light of performance measurement results, and recommend changes necessary to improve or optimise the performance of specific features




_____________________________________________________________________ 3.2 BSS Parameter Review Process

3.2.1 REVIEW DATABASE SETTING

BSS Configuration Parameter ReviewBSS Configuration Parameter Review

• Review current settings as related to performance measurement results• Recommend changes to improve/optimise performance of specific

features.• Review includes:

• Handover parameters, timers, thresholds and margins• Power control thresholds• Voting and average mechanisms for handover and power control• Call setup parameters to maximise resource utilisation• C1/C2 cell reselection parameters• Any vendor-specific advance traffic management algorithms

This review includes the following:

• Handover parameters, timers, thresholds and margins (including inter-layer and inter-band handovers where applicable).

• Power Control thresholds (power window settings, power up/down step size,

adaptive power control parameters, and so on).

• Voting and averaging mechanisms for handover and power control decisions.

• Call setup and handover timers to maximise resource utilisation and availability

• C1/C2 cell reselection parameters.

• Advanced traffic management algorithms (Congestion-based handovers, inter-band and inter-layer traffic distribution)



_____________________________________________________________________ 3.3 Database Consistency and Change Control

BSS Database Parameter ConsistencyBSS Database Parameter Consistency

• Within a network, different site types are defined (e.g. urban micro, rural macro etc) by a standard template

• Each site type database will comprise a default parameter set

• Each site may modify default set to suit local conditions

• Consistency of the default parameter sets should be checked across BSS types

• Change control management processes should be reviewed to ensure procedural consistency

Review of all BSS databases to identify inconsistencies and discrepancies, and a review of change control, datafill and database management processes. For example:

• Define pre-configured parameter templates for a variety of site types (micro, highway 2/2, urban 3/3/3, etc.).

• Identify sets of parameters allowed for optimisation on permissions basis (fully configurable permissions per BSC, region, etc).

• Check consistency of live network data against planned configuration.

_____________________________________________________________________ 3.4 BSS Configuration Parameter Sets

Each BSS performs in accordance with its software configuration. Generally, there will be a common set of default parameters for each BSS, for example, the handover algorithms. However, each BSS will be programmed with certain parameters which are tailored to suit specific actions, locations and/or applications. Examples of BTS-specific parameters include the cell ID and power output settings.




BSS Configuration Parameter SetsBSS Configuration Parameter Sets

• Each BSS operates in accordance with its software configuration

• All BSS are configured with certain standard default parameters

• Each BSS will have a subset of BSS-specific parameters• Potentially hundreds of configuration parameters• Many parameters are inter-dependant• Often vendor-specific abbreviations/acronyms used for same

parameter

The number of configurable BSS parameters run into their hundreds and are defined in two sources:

• ETSI GSM Recommendations. ETSI has defined a primary set of parameters which are listed in the GSM 12.04) document.

• Proprietary Parameters. These are additional parameters created by individual vendors to enhance the capabilities of their equipment when compared that of their competitors.

This multitude of parameters allows for very sophisticated control of the BSS behaviour. However, the complexity can also lead to problems:

• Many parameters are inter-related so changing one can have a corresponding effect on others.

• Many equipment manufacturers use different abbreviations or acronyms for the same GSM-recommended parameter, leading to potential confusion when a network comprises equipment for more than one manufacturer.

_____________________________________________________________________ 3.5 BSS Parameter Types

As mentioned above, the number of performance configuration parameters in a BSS runs into three figures. Within the scope of this overview course, the following provides an overview of the type of parameters stored:



BSS Configuration Parameter TypesBSS Configuration Parameter Types• Identifiers:

• CI, LAI, GCI, BSIC etc

• Channel Configuration:• TCH channels, Signalling channel configuration (e.g. CCCH)

• Timers:• Location Updates, C2 calculations etc

• Thresholds:• RxLev, RxQual for handover decisions etc

• Offsets:• Hysteresis for handovers etc

• Control Features:• SFH, DTX, DRX etc

3.5.1 IDENTIFIERS This includes such parameters as the Cell Identity (CI), Cell Global Identity (CGI) Location Area Identity (LAI) and Base Station Identity Code (BSIC) etc 3.5.2 CHANNEL CONFIGURATION PARAMETERS These parameters define the number of traffic channels and control channels. For example, the configuration of CCCH on the signalling channel (i.e. combined/non-combined multiframes). 3.5.3 TIMER PARAMETERS Timers are counters which are set at the start of a certain time period and count down. If an event has not happened by the time the counter reaches zero, an alternative action may be triggered. For example, the time periods between periodic location updates (T3212) or the penalty timer for C2 calculations (see Cell Reselection in Section 1 for details). 3.5.4 THRESHOLD PARAMETERS Thresholds are certain values which, when exceeded, trigger a certain event. For example, received signal strength or bit error rate thresholds which may trigger cell handovers. 3.5.5 OFFSET PARAMETERS Offsets are fixed values applied for the purposes of applying bias to certain actions. An example is the hysteresis bias value applied to BTS at location area boundaries.




3.5.6 CONTROL FEATURE PARAMETERS A number of parameter settings exist to identify the implementation of certain functions and features. Such features include Frequency Hopping, DTX etc

_____________________________________________________________________ 3.6 Adjusting BSS Configuration Parameters

Adjusting BSS Configuration ParametersAdjusting BSS Configuration Parameters

• Effected from:

• PC connected directly to hardware

• Remotely from OMC/NMC

• Can be individually addressed or broadcast

• May require hardware reset to effect change

• Be aware of hierarchical changes (MSC BSC BTS)

• Only implement during low-traffic periods

• Use test BSS where available

• Avoid simultaneous multiple parameter changes

It is normally possible to carry out parameter changes from:

• BSS – directly into the BSS database via a connected PC.

• OMC/NMC – Many OMC/NMC systems allow parameters to be transmitted to the BSS remotely including a broadcast capability where a specific parameter change needs to be transmitted to several network entities simultaneously.

Adjustment of parameters on live network elements should be deferred until low traffic periods in order to minimise any disruption to existing users. This is particularly important when a configuration change requires a hardware rest to become effective. A change BSC parameter is changes it may affect all BTSs associated with that BSC. Some network operators reserve a BSS for test purposes. This has the advantage of being able to assess the impact of a parameter change before making the adjustment to a live network. However, it is a non-revenue generating asset.



Making simultaneous multiple parameter changes should also be avoided where possible for two reasons:

• If an unexpected problem arises as a result of a multiple parameter change, it will be difficult to identify the specific parameter or parameter combination causing the problem.

• Similarly if a performance improvement is observed, it may be difficult to identify

which of the parameters are causing which part of the performance improvement.





• The BSS Parameter review process

• The importance of database consistency and control

• BSS configuration parameter sets

• BSS configuration parameter types

• Practical aspects of changing parameter settings

4. GSM Network Identifiers


4. GSM Network Identifiers _____________________________________________________________________ 4.1 Introduction

There are many identifiers used within the GSM system for establishing a unique identity for each of the network elements, areas and subscribers. Many of these identities are used as parameters for controlling the performance of network elements. This section of the course details the main GSM network identifiers so that the reader will be aware of their meaning and composition when referred to later in the course.

GSM Network Identifier ParametersGSM Network Identifier Parameters

• Subscriber Identifier Parameters:• IMSI / TMSI

• Equipment Identifiers:• IMEI

• Call Number Identifiers:• MSISDN

• Call Routing Identifiers:• LAC / LAI / MSRN




_____________________________________________________________________ 4.2 Subscriber Identifiers

4.2.1 INTERNATIONAL MOBILE SUBSCRIBER IDENTITY (IMSI)

International Mobile Subscriber Identifier (IMSI)International Mobile Subscriber Identifier (IMSI)

• Globally unique subscriber identity (15 digits max)• Comprises:

• Mobile Country Code (MCC)• Mobile Network Code (MNC) (operator)• Mobile Subscriber Identification Number (MSIN)

3 digits

MCC

9-10 digits

MSINMNC

2-3 digits

Example: 262 – Germany 01 – D1 Telekom 123456789

When a subscriber registers with a network operator, a unique subscriber IMSI identifier is issued and stored in the SIM of the MS. An MS can only function fully if it is operated with a valid SIM inserted into an <MS with a valid IMEI. 4.2.2 TEMPORARY MOBILE SUBSCRIBER IDENTITY (TMSI) A TMSI is used to protect the true identity (IMSI) of a subscriber. It is issued by and stored within a VLR (not in the HLR) when an IMSI attach takes place or a Location Area (LA) update takes place. At the MS it is stored in the MS’s SIM. The issued TMSI only has validity within a specific LA. Since the TMSI has only local significance (i.e. within the area controlled by a VLR), the structure and coding of it can be chosen by agreement between operator and manufacturer in order to meet local needs. The TMSI consists of 4 octets and is only be allocated in ciphered form. The network does not allocate a TMSI with all 32 bits equal to 1 as this indicates in the MS SIM that no valid TMSI is available.



Temporary Mobile Subscriber Identity (TMSI)Temporary Mobile Subscriber Identity (TMSI)

• Replaces IMSI• Unique only within a LA• Issued on IMSI attach and LA change (minimum)• Comprises 32-bits:

8 bits

Octet

8 bits

Octet

8 bits

Octet

8 bits

Octet

TMSI Parameter Settings (VLR)TMSI Parameter Settings (VLR)

NMobile SS Operation

NMobile Terminating USSD

NMobile Terminating SMS

NMobile Terminating Call

NMobile Originating SMS COUNTERS

NMobile Originating Call ALLOCATION

NPeriodic Location Update TMSI

YLocation Update

YIMSI Attach

YLocation Update New Visitor

RECPARAMETER




IMSI/TMSI Authentication Parameter SettingsIMSI/TMSI Authentication Parameter Settings

NMobile SS Operation NMobile Terminating USSD NMobile Terminating SMS

NMobile Terminating Call NMobile Originating SMS NMobile Originating Call COUNT

NPeriodic Location Update AUTHENTICATION

NLocation Update YIMSI Attach YLocation Update New Visitor

RECPARAMETER

_____________________________________________________________________ 4.3 Equipment Identifiers

4.3.1 INTERNATIONAL MOBILE EQUIPMENT IDENTITY (IMEI) The IMEI has been implemented in order to identify the presence of a specific mobile station equipment in the network, irrespective of the owning subscriber. Its main purpose is to identify stolen or technically incompatible mobile equipments The IMEI is incorporated in an MS module (not the SIM) which is contained within the MS equipment. The IMEI should be fixed on completion equipment production process and is generally resistant to casual tampering The IMEI is an internationally-unique serial number allocated to the MS hardware at the time of manufacture. It is registered by the network operator and (optionally) stored in the AuC for validation purposes.

The IMEI Software Version Number (IMEISV), is a 15 digit decimal number composed of four distinct elements:

• a 6 digit Type Approval Code (TAC); • a 2 digit Final Assembly Code (FAC); • a 6 digit Serial Number (SNR); and • a spare digit (sometimes used as a check digit (CD))



International Mobile Equipment Identifier (IMEI)International Mobile Equipment Identifier (IMEI)

• Globally unique MS equipment identity• Comprises:

• Type Approval Code (TAC) • (2-digit (49 = Germany) country code + 4-digit approval code )

• Final Assembly Code (FAC) • (Manufacturer: e.g. 10 & 20 = Nokia)

• Serial Number (SNR)• (unique 6-digit code)

• Spare digit• (default to 0)

6 digits

TAC

6 digits

SNRFAC

2 digits

Example: 495020 10 123456 7 (Access: *# 92702689 #)

X

1 digit

IMEI Check Parameters (VLR)IMEI Check Parameters (VLR)

BLOCKUnknown IMEI EffectTRACEGrey List EffectBLOCKBlack List Effect

NMobile SS Operation NMobile Terminating USSD NMobile Terminating SMS NMobile Originating SMS NMobile Terminating Call IMEI CHECKING ON….NMobile Originating Call NPeriodic Location Update

Y(10)Location Update YIMSI Attach YLocation Update New Visitor

RECPARAMETER




_____________________________________________________________________ 4.4 Call Number Identifiers

4.4.1 MOBILE SUBSCRIBER ISDN NUMBER (MSISDN) The MS international ISDN numbers are allocated from the CCITT Recommendation E.164 numbering plan. The number consists of:

• Country Code (CC) of the Country in which the MS is registered, followed by • National (significant) mobile number which consists of National Destination Code

(NDC) • Subscriber Number (SN).

For GSM applications, a National Destination Code is allocated to each GSM PLMN. In some countries more than one NDC may be required for each GSM PLMN. The composition of the MS international ISDN number should be such that it can be used as a global title address in the Signalling Connection Control Part (SCCP) of the SS7 protocol for routing messages to the MS’s HLR using the CC and NDC. If further routing information is required, it must be contained within the first few digits of the SN). A sub-address may be appended to an ISDN number for use in call set-up and in supplementary service operations The MSISDN represents the ‘true’ or ‘dialled’ number associated with the subscriber. It is assigned to the subscriber by the network operator at registration and is stored in the SIM. It is possible for an MS to hold multiple MSISDNs, each associated with a different service.

Mobile Subscriber ISDN Number (MSISDN)Mobile Subscriber ISDN Number (MSISDN)

• Identifies the global calling number• Comprises:

• Country Code (CC)• National Destination (area) Code (NDC) • Subscriber Number (SN)

3 digits

CC

9-10 digits

SNNDC

2-3 digits




_____________________________________________________________________ 4.5 Call Routing Identifiers

4.5.1 LOCATION AREA CODE (LAC)

Location Area Code (LAC)Location Area Code (LAC)

• Uniquely identifies a LA within a specific PLMN• Comprises 2 octets:

8 bits

Octet

8 bits

Octet

4.5.2 LOCATION AREA IDENTITY (LAI)

Location Area Identifier (LAI)Location Area Identifier (LAI)

• Globally unique Identity• Comprises:

• Mobile Country Code (MCC)• Mobile Network Code (MNC) (operator)• Location Area Code (LAC)

3 digits

MCC

2 octets

LACMNC

2-3 digits





Each Location Area within the PLMN has an associated internationally-unique identifier (LAI). The LAI is broadcast regularly by BTSs on the Broadcast Control Channel (BCCH), thus uniquely identifying each cell with an associated LA. The purpose of LAs is covered later in this course. 4.5.3 MOBILE SUBSCRIBER ROAMING NUMBER (MSRN) The MSRN is used to route calls directed to an MS. It has the same structure as international ISDN numbers in the area in which the roaming number isallocated, i.e.:

• the Country Code of the country in which the visitor location register is located; • the National Destination Code of the visitor GSM PLMN or numbering area; • a Subscriber Number with the appropriate structure for that numbering area.

The MSRN is a temporary, location-dependant ISDN number issued by the parent VLR to all MSs within its area of responsibility. It is stored in the VLR and associated HLR but not in the MS. The MSRN is used by the VLR-associated MSC for call routing within the MSC/VLR service area. On request from the GMSC via the HLR, the MSRN is temporarily allocated to an MS by the VLR with which the MS is registered. The MSRN is passed by the HLR to the GMSC for routing calls to the MS.

Mobile Subscriber Roaming Number (MSRN)Mobile Subscriber Roaming Number (MSRN)

• Unique routing identifier within a VLR area• Same structure as MSISDN for PSTN/ISDN routing• Comprises:

• Country Code (CC)• National Destination (area) Code (NDC) • Subscriber Number (SN)

3 digits

CC

9-10 digits

SNNDC

2-3 digits




Section 4 Section 4 -- SummarySummary

• Subscriber Identifiers:• IMSI / TMSI

• Equipment Identifiers:• IMEI / IMEISV

• Call Number Identifiers:• MSISDN

• Call Routing Identifiers:• LAC / LAI / MSRN

• In this section the following network identifiers were described:





5.. Common Cell Parameters


5. Common Cell Parameters _____________________________________________________________________ 5.1 Introduction

This section of the notes introduces parameters that have setting unique to a particular site or cell. These parameters include those relating to the cell identity, activated functions and channel configurations




_____________________________________________________________________ 5.2 Cell Identifiers

5.2.1 CELL IDENTITY (CI) AND GLOBAL CELL IDENTIFIER The CI an identifier assigned to each cell within a network. However, the CI is only unique within a specific Location Area. By adding the LAI to the CI, a globally-unique GCI is created.

Cell Identifier (CI) and Global CI (GCI)Cell Identifier (CI) and Global CI (GCI)

• CI:• Identity unique to a cell within a location area (LA)• Fixed Length of 2 octets:

8 bits

Octet

8 bits

Octet

Cell Identity(CI)

Location Area Identity (LAI)

• GCI:• Globally unique cell identity• Comprises LAI +CI

5.2.2 BASE STATION IDENTITY CODE (BSIC) The BSIC is a local colour code that allows an MS to distinguish between different neighbouring base stations. BSIC is a 6-bit length code structured as shown in the next diagram. Each BTS is issued with a unique identity, the BSIC and is used to distinguish between the same frequency being received from a different neighbouring BTS. In the definition of the NCC, care must be taken to ensure that the same NCC is not used in adjacent PLMNs that may use the same BCCH carrier frequencies in neighbouring areas.



Base Station Identity Code (BSIC)Base Station Identity Code (BSIC)

3 bits

Network Colour Code (NCC)

• Identity that allows an MS to distinguish between different neighbouring BTSs transmitting on the same frequency

• 6-bit code, therefore only 64 unique BSIC values• Structure:

Base StationColour Code (BCC)

3 bits

• Countries/Operators may have different NCCs allocated (e.g. UK = 2, France = 0, Ireland = 3, Italy = 2) (ETSI GSM 03.03)

• The BCC identifies the training sequence used by the BTS.• The NCC allows the MS to discriminate invalid BSICs

_____________________________________________________________________ 5.3 Cell Functions

Cell Function Implementation ExamplesCell Function Implementation Examples

• SMS Cell Broadcast (CBCH) Usage:• SMSCBUSE (Y/N) {Ericsson}

• HSCSD Usage• BTSHSCSD (Y/N) {Ericsson}• BSCHSCSD (Y/N) {Ericsson}




_____________________________________________________________________ 5.4 Cell Channel Configurations

Control Channel Configurations Control Channel Configurations

• On the downlink, CCCH consists of paging (PCH) and access grant (AGCH) messages

• A combined multiframe has only 3 CCCH blocks to allow for SDCCH and SACCH:

• A non-combined multiframe has 9 CCCH blocks:

• A complete paging or access grant message takes four bursts (timeslots),i.e. one CCCH block.

S BCCHF CCCH S CCCHF CCCH S SDCCH0F SF SF ISDCCH

1SDCCH

2SDCCH

3SACCH

0SACCH

1

S BCCHF CCCH S CCCHF CCCH S CCCHF CCCH S CCCHF CCCH S CCCHF CCCH I

ISACCH0

SACCH1

SDCCH0

SDCCH1

SDCCH2

SDCCH3

SDCCH4

SDCCH5

SDCCH6

SDCCH7

SACCH2

SACCH3 I I

Cell Channel Configuration ExamplesCell Channel Configuration Examples

• BCCH Frequency in Use:• BCCHFREQ (0-1023) {Siemens}• BCCHNO (0-1023) {Ericsson}

• BCCH Type:• BCCHTYPE (comb,ncomb) {Ericsson}

• CCCH Block Allocation• CCCH_CONF

• Reservation of CCCH blocks for AGCH• BS_AF_BLKS_RES



Control Channel ConfigurationControl Channel Configuration

TS0 (non-combined),TS2,TS4,TS6 4110

TS0 (non-combined),TS2,TS43100

TS0 (non-combined),TS22010

TS0 (combined)1001

TS0 (non-combined)1000

ConfigurationNumber of CCCH TimeslotsCCCH_CONF

CCCH Configuration Parameter - CCCH_CONF

BCCH contains a number of system information messages, BCCH/SYS_INFO n.

BCCH/SYS_INFO 3 carries a parameter, CCCH_CONF, which informs the mobile of the CCCH configuration to be used, including number of timeslots, combined or non-combined multiframes, reservation of AGCH blocks etc.





• In this section the following topics have been covered:

• Cell Identifier Parameters

• Cell Function Parameters

• Cell Channel Configuration Parameters

6. Network Access


6. Network Access _____________________________________________________________________ 6.1 Introduction

This section of the course looks at the functions and parameter settings required to provide and gain access to the GSM network including IMSI attach and detach and call connection.

6. Network Access



_____________________________________________________________________ 6.2 Network Access Procedures

6.2.1 NETWORK CONNECTION SEQUENCE

MS Network Connection SequenceMS Network Connection Sequence

Power on Scan RFchannels

Select highestcarrier level

Scan for FCCHfrequency correction burst

Select next highestcarrier level

FCCHdetected?

Scan for SCHsynchronisation burst

SCHdetected?

‘camp-on’ to BCCH and start decoding

Monitor PCH and adjacent carriers

YES

YES

NO

NO

When an MS powers on within network coverage, it starts by scanning all frequencies within its allocated band (e.g. 124 for standard GSM). It measures the received power on each of these frequencies and placed them in order. The MS then selects and listens out on the strongest RF level carrier for a frequency correction burst which is transmitted on the control channel of a BCCH carrier. This is to initially achieve frequency synchronisation with the transmitting BTS. Having achieved frequency synchronisation; the MS listens on the SCH for frame synchronisation information. The SCH channel provides frame timing, the current frame number and BSIC information. Once frame synchronisation is achieved, the MS starts to read and decode the additional information being transmitted on the BCCH. This includes the adjacent cell list, minimum received signal strength, the LAI and beacon frequencies from surrounding cells. The MS then continues to monitor the PCH for incoming call paging requests, sends periodic location updates and maintains a record of surround cell signal strengths. If the MS fails to detect either the FCCH or the SCH, it will reselect the next highest RF carrier level from its measured list and repeats the detection process.

6. Network Access


6.2.2 IMSI ATTACH

IMSI AttachIMSI Attach

• Mobile camps on to best serving BTS• Mobile sends IMSI to MSC• MSC/VLR is updated in HLR• Subscriber data including current location area is

added to local VLR• MSC and HLR carry out authentication check -

challenge and response using Ki

• Optionally EIR checks for status of mobile (white/grey/black)

BSC

EIRHLR

AuC

MSC

VLR

The IMSI attach procedure is used by the MS to indicate that it is has adopted the active (power-on) state within the network. The IMSI attach is also performed as part of the location updating procedure. The basic IMSI attach procedure is described below:

Stage 1 The MS sends a message to BSS on the RACH requesting a channel allocation. The BSS responds with a ‘Immediate Assignment’ message on the AGCH. This message assigns a SDCCH channel to the MS. Stage 2 On assignment of the SDCCH channel, the MS sends and IMSI attach message over the SDCCH to the MSC/VLR relayed via the BSS. This informs the MSC/VLR of the MS’s IMSI. This information may also be updated in the HLR which provides subscriber profile data to the VLR is it does not already have it. Stage 3. Security procedures are activated including authentication and (optionally) and IMEI check with the EIR. Stage 4 Assuming successful authentication, the VLR responds to the MSC with an ‘IMSI Attach Acknowledge’ message which is forwarded by the MSC, via the BSS, to the MS. Stage 5 The MSC also sends a ‘Clear Command’ message to the MS over the SDCCH in order to release the dedicated resources used to effect the IMSI attach

6. Network Access



Stage 6. The VLR assigns a Temporary Mobile Subscriber Identity (TMSI) to the MS and informs it that it is attached to the network. This function creates a ‘Mobility Management (MM) Context’. 6.2.3 IMSI ATTACH The IMSI detach procedure is invoked if the MS is deactivated either by powering down or if the SIM is removed or forced by the network. There are two causes of an IMSI detach:

• Explicit: The MS informs the network that it is detaching.

• Implicit: The VLR has not been able to contact (via the MSC) the MS for a pre-determined amount of time and forces an IMSI detach.

IMSI DetachIMSI Detach

• Explicit:• Mobile informs MSC it is switching off• HLR stores last location area for mobile• VLR records that mobile is no longer available on network• Mobile powers down

• Implicit• VLR forces IMSI Detach due to no response

BSC

HLR

AuC

MSC

VLR

The detach procedure is essentially the reverse of the IMSI attach procedure and is as follows: Stage 1 The MS sends a ‘Channel Request’ message on the RACH to the BSS. The BSS assigns a an SDCCH channel, informing the MS over the AGCH. Stage 2 The MS sends a ‘IMSI Detach Indication’ message to the BSS which identifies the MS using its TMSI. The BSS forwards this message to the MSC which in turn updates its VLR using a ‘Detach IMSI’ signalling message.

6. Network Access


Stage 3 The VLR informs the HLR of the change using a ‘Deregister Mobile Subscriber’ signalling message. The HLR responds to the VLR with a ‘Deregistration Accepted’ message. Stage 4 The VLR notifies the MSC of this acceptance with an ‘Acknowledge IMSI Detachment’ message. The MSC does not notify the MS as, by this stage, the MS may well be disconnected. Stage 5 The MSC sends a ‘Clear Command’ message to the BSS to release the assigned SDCCH resources. The BSS responds with a ‘Clear Complete’ message which completes the IMSI Detach procedure.

________________________________________________________________________________

6.3 Key Network Access Parameters

Network Access parameters refer to those parameters that can be used to modify the functions involved when an MS attempts to access and disconnect from the GSM network.

Key Access ParametersKey Access Parameters

• Minimum RXLEV necessary to access the network• Maximum allowable power level to access a cell’s control channel• If the cell is barred from access• Priority for access if contention exists• Access control class• Maximum number of Access retries• Time period between access attempts• Inactivity time period before being forced detached • Time interval before being marked for implicit detach• Time interval after lost contact before MS is deregistered

6.3.1 ACCESS PARAMETERS RXLEV_ACC_MIN (range 47 to 110) Receive Level Access Minimum. Defines the minimum dBm signal level required at the MS in order to permit access to the network 47 dBm = level 63, 110dBm = power level 0. See section relating to ‘Power Control’ for full details (default 110dBm).

6. Network Access



Access ParametersAccess Parameters

• RXLEV_ACC_MIN (range 47-110 dBm) – (default 110dBm):• Receive Level Access Minimum. Defines minimum signal level for MS to

access the network

• CCHPWR (range 13-43) – (no default):• Control Channel Power. Defines maximum power an MS can use to access a

control channel

• CB (range Y/N)– (default N):• Cell Barring. Bars the cell from being accessed by an MS

• CBQ (range High/Low)– (default Low):• Cell Bar Qualifier. Used with CB to determine access priority by applying one

of two levels

CCHPWR (range 13-43/GSM900, 4-30/GSM1800) Control Channel Power. Defines the maximum power level an MS may used to access the network on a control channel (no default). CB (range YES,NO) Cell Barring. Defines whether or not an MS is barred from network access. It is possible to use CB to bar a cell from access for cell reselection purposes. However, it is still available for handovers. Can be used in conjunction with CBQ (default NO).

YES = barred from access NO = access permitted. CBQ (range HIGH,LOW). Cell Bar Qualifier. Used in conjunction with CB to determine cell access priority. In idle mode, the MS looks for suitable cells to camp onto by checking cells in descending order of received signal strength. If a suitable cell is found, the MS camps onto it.. Cells can have 2 levels of priority. Suitable cells which are of low priority are only camped onto if there are no other suitable cells of normal priority. Interpretation of CB and CBQ are as follows:

Phase 2 MS Phase 1 MS CBQ CB Cell Sel Cell Resel Cell Sel/Resel HIGH NO Normal Normal Normal HIGH YES Barred Barred Barred LOW NO Low Priority Normal Normal LOW YES Low Priority Normal Barred

6. Network Access


6.3.2 ATTACH/CALL SETUP PARAMETERS

Attach/Call Setup ParametersAttach/Call Setup Parameters

• ACC (range 0-15, CLEAR) – (default CLEAR) • Access Control Class:

• 0-9 = Reserved for Operator Use• 10 = Emergency calls not permitted in classes 0-9• 11-15 = Specific Service uses• CLEAR = no access classes barred

• MAXRET (range 1,2,47) – (default 1)• Maximum Retries. Defines maximum number of RACH access

attempts

• T3122 (0-255) – (default 5)• Time before access retry after resource allocation rejection

ACC (0-15,CLEAR) Access Control Class. Up to 15 access classes can be defined. This parameter defines the classes that area barred (default CLEAR).

0-9 and 11-15 – Barred Access to specified Class 10 = Emergency calls not permitted to class 0-9 MSs CLEAR – NO access classes are barred Access Classes 0-9 = Reserved for Operator Use 10 = undefined 11 = PLMN use 12 = Security Services use 13 = Public Utilities 14 = Emergency Services 15 = PLMN Staff

MAXRET. (range 1,2,4,7) Maximum Retransmissions. Defines the maximum number of Access retransmission by an MS when attempting on the RACH 6.3.3 DETACH/DISCONNECTION PARAMETERS BTDM (range 6 to 150 in steps of 6, OFF) (Ericsson MSC only) Base Time Detach Mobile. This timer determines the period before an MS is forced to detach by the MSC. Must be set longer than the GSM T3212 periodic LA update timer) (default OFF). GTDM (range 0-255) (Ericsson MSC only) Guard Time Detach Mobile. Guard time before marking an MS as implicitly detached (no default).

6. Network Access



Detach/DisconnectDetach/Disconnect ParametersParameters

• BTMN (range 6-150, OFF) – (default OFF):• Base Time Detach Mobile. Defines the time before an MS is

forced to Detach

• GTMN (range 0-255) – (no default):• Guard Time Detach Mobile. Guard time before marking the MS

as implicitly detached

• TDD (range 0-255, OFF) – (default OFF):• Time Deregistration Default. Defines the time before an MS is

automatically deregistered after loss of contact

TDD (range 0-255, OFF) (Ericsson MSC only) Time Deregistration Default. Time period before loss of contact with an MS causes automatic deregistration (default OFF).


• This section has covered:

• Network access procedures• IMSI attach and detach• Access parameters• Connection setup parameters• Detach and disconnection parameters

7. BCCH Allocation (BA) Lists and Idle Mode Measurements



_____________________________________________________________________ 7.1 Introduction

This section of the notes explains the structure and purpose of Broadcast Control Channel Allocation (BA) lists and how they are used in carrying out Idle mode radio path measurements on the serving and surrounding cells.




____________________________________________________________________ 7.2 Generic Neighbour List Functionality

7.2.1 PURPOSE OF BA LISTS A BCCH allocation (BA) is a list of BCCH carriers in use within a specific geographical area of a PLMN. It indicates the RF channels that the MS is required to monitor while camped on a cell of that PLMN. 7.2.2 TRANSMISSION OF BA LIST The BA List is broadcast in the system information messages on the BCCH, and is often referred to as the BA (BCCH).

BCCH Allocation (BA) ListsBCCH Allocation (BA) Lists

• Contains a list of BCCH carriers available in a certain PLMN region

• Passed to MS and stored in the SIM during IMSI Attach procedure

• MS monitors all carriers in BA list for signal strength.• In Idle mode this is used to reselect cell whilst moving• In dedicated mode, the measured values of the six best

neighbouring cells are reported to the serving BSC for handover purposes

7.2.3 CAMPING ON WITHOUT A STORED BA LIST If an MS switches on in a PLMN where it has no knowledge of the PLMN’s BCCH carriers, it must scan the entire GSM band and prioritises the received RF signals in order of receive signal strength. It then checks each in turn for the presence of a BCCH channel to identify it as a BCCH carrier. Having detected a BCCH carrier and confirmed that it belongs to the expected PLMN, the MS reads the BCCH information to extract the BA information. It then knows which BCCH carriers to monitor for cell reselection purposes.



7.2.4 CAMPING ON WITH A STORED BA LIST Having switched off the MS off, when it is switched on again it will first refer to the existing stored BA list to scan for BCCH Carriers. This speeds up the processes of ‘camping-on’ when compared to the equivalent procedure without a BA list. However, a stored BA list is not necessarily valid when the MS is switched on again. For example, if the system operator has made a change in BA List or if the MS is switched on in a different geographical area. In these cases, the MS may not find a suitable cell for camping on using the stored BA list and reverts to the ‘no BA list’ procedure. 7.2.5 STORAGE OF BA LIST When a BA list has been received by a Mobile Station, the MS stored it in its non-volatile memory. This may or may not be the SIM depending of the form factor of the MS. When the MS switches off, it has the option of storing the last known BA(BCCH) in its SIM so that if it subsequently switches back on in the same PLMN, it does not need to search to find the BA(BCCH), and so can camp on a cell more quickly. If the BA(BCCH) is stored in the SIM, it is stored in the format specified in GSM 11.11. Any other information used by the MS in cell selection is also stored in the MS SIM. 7.2.6 THE BA(SACCH) LIST There is another BCCH carrier list, called BA(SACCH), which is sent on the SACCH when in dedicated (call connected) mode. This contains the list of BCCH carriers to be monitored by the MS for hand over purposes. The BA(BCCH) and BA(SACCH) may or may not be the same. For example, the BA(SACCH) might contain umbrella cells, or the BCCH carrier of the serving cell might be omitted. If the MS stores a BA list in the SIM, and there is a valid stored LAI, the BA list must be of the PLMN indicated by the stored LAI. 7.2.7 BA LIST INFORMATION BA list information is provide to the MS from two sources:

• The BA Range List • The BA ARFCN list

7.2.8 THE BA RANGE LIST The BA(BCCH) may or may not be the total list of BCCH carriers in use throughout the PLMN coverage area. For example there may be differences in different geographical areas, and there may be "umbrella cells" which are only used for handover traffic and hence are not to be camped on. The BA Range list message provides ranges of frequencies through which the MS can search. Multiple ranges can be transmitted, each range determined by its upper and lower ARFCN:




Parameters:

• Number of Ranges: Number of ranges to be transmitted in the TE (min = 1) • RANGE_LOWER: The ARFCN at the bottom of the range of frequencies to be used

by the MS in cell reselection • RANGE_HIGHER: The ARFCN at the top of the range of frequencies to be used by

the MS in cell reselection

BA Range ListBA Range List

Octet n

Octet 13RANGE4_HIGHER

Octet 12RANGE4_HIGHERRANGE4_LOWER

Octet 11RANGE4_LOWERRANGE3_HIGHER


Octet 9RANGE3_LOWER

Octet 8RANGE2_HIGHER


Octet 6RANGE2_LOWERRANGE1_HIGHER


Octet 4RANGE1_LOWER

Octet 3Number of Ranges

Octet 2Length of BA Range Contents

Octet 1BA Range IEI

12345678

7.2.9 THE BA ARFCN LIST The BA message lists all 124 ARFCNs but indicates which ARFCN ranges are searchable.

BA ARFCN ListBA ARFCN List

001002003004005006007008

ARFCNARFCNARFCNARFCNARFCNARFCNARFCNARFCN

CACACACACACACACA

113114115116117118119120

ARFCNARFCNARFCNARFCNARFCNARFCNARFCNARFCN

CACACACACACACACA

121122123124

ARFCNARFCNARFCNARFCNsparespareFormat ID

CACACACA0000

Cell Channel Description IEI

12345678

CA = 0 – not part of BA list CA = 1 – included in BA list



7.2.10 EFFECT OF BA LIST LOADING ON MEASUREMENTS

12-138

10-1110

6-716

3-432

Number of samples per carrier in SACCH multiframe

Number of BCCH carriers in BA List

Sample Rate Sample Rate vsvs BA List LoadingBA List Loading

_____________________________________________________________________ 7.3 Idle Mode Cell Measurements

BCCH Carrier Measurement BCCH Carrier Measurement –– Idle ModeIdle Mode

• Neighbouring Cells:• MS scans all carriers listed in the BA list and identifies the 6

strongest• Signal level averaged over at least 5 measurements• Result stored in RXLEV (n) parameter• MS must attempt to decode the BCCH channel of 6 best neighbours

at least every 30 seconds

• Serving Cell• Measurements taken during allocated paging block• Measurements averaged over 5 consecutive paging blocks or 5

seconds (whichever greater)




Measurement of channel levels must be made in both idle and dedicated mode. These measurements are critical to the following functions within a GSM Network:

Idle M ode - cell selection/reselection Dedicated Mode - handovers

- serving cell measurements - adaptive power control

This section of the course looks specifically and cell measurement parameters in Idle mode. Dedicated mode cell measurements are covered later in the course Having camped onto a cell, part of the information the MS receives on the BCCH channel is the cell’s BCCH Allocation (BA) or Neighbour list. This list identifies the BCCH carriers in the surrounding cells that are potential candidates for cell reselection. The MS then scans all BCCH carriers listed in its BA list. For each BCCH carrier detected, the received signal level is measured. These measured values must be averaged over at least 5 measurements and the averaged result is stored in the MS for each BA entry where a carrier is detected.

BCCH Carrier Measurements BCCH Carrier Measurements –– Idle ModeIdle Mode

RxLev / BSICRxLev / BSIC

RxLev / BSIC

RxLev

110dBm

85Bm

112Bm

96dBm

Upon completion of cell selection and when starting the cell reselection tasks, the MS shall synchronize to and read the BCCH information for the 6 strongest non-serving carriers in the BA list as quickly as possible. For multi- band mobile stations the strongest non-serving carriers may belong to different frequency bands. The MS must also attempt to decode the BCCH of the six best neighbouring cells at least once every 30 seconds to ensure that the BSIC values have not changed. The serving cell signal level is also measured. This measurement must take place at least once for every CCCH paging block assigned to the MS. The averaging takes place over 5 consecutive paging blocks or over a 5 second period, whichever the greater period.



These values are not communicated to the network as no uplink communication channel exists from the MS to the network in idle mode. However, they are critical to the cell reselection procedure.

____________________________________________________________________ 7.4 Key Neighbour Relation Parameters

7.4.1 NEIGHBOURING CELL RELATION PARAMETERS

Neighbour Cell Relation ParametersNeighbour Cell Relation Parameters

• Two parameters can be defined for each neighbour relation (for re-selection/handover purposes):

• Hysteresis

• Offset

• Up to 64 neighbours can be defined for each cell in up to 2 lists each of 32 entries

• As a BSC can accommodate up to 128 cells, 8192 cell relations can be defined per BSC

There are two types of parameters that can be defined for each neighbouring cell relation: Hysteresis and Offset parameters. A BA List can comprise up to 32 neighbour relations. However, it is possible to implement 2 BA lists (one Idle mode and one Dedicated mode list) giving up to 64 neighbour relations per cell. As each BSC can accommodate up to 128 cells, up to 8192 cell relations can be defined per BSC. The following Ericsson parameters are defined for neighbour relations: CELLR (range: 1 to 7 characters) This is the identity of the neighbouring cell CTYPE (range: EXT, Omitted) If the neighbouring cell belongs to a different BSC, this parameter must be set to EXT RELATION (range: SINGLE, Omitted) If the relationship with the neighbouring cell is mutual (i.e. this cell is recorded as a neighbour in the neighbouring cell using same hysteresis and offset), this is omitted. If the relationship is not mutual, or the neighbour belongs to a different BSC (i.e. CTYPE= EXT), this is set to SINGLE.




CS (range: YES, NO) If the current and neighbouring cell share the same location, this is set to YES, otherwise to NO.

BA ListBA List--Related ParametersRelated Parameters

• Examples of Ericsson BA-related parameters:

• CELLR (range: 1-7 characters) – (no default):• Neighbouring cell identifier

• CTYPE (range: EXT, omitted) – (default omitted):• Set to ‘EXT’ if neighbouring cell is in different BSC. Otherwise set to

‘omitted’

• RELATION (range: single, omitted) – (default single):• Set to ‘single’ if relationship is non-mutual or CTYPE= EXT. Otherwise set

to ‘omitted’

• CS (range Yes/No)– (default No):• Set to ‘Yes’ if neighbour cell shares the same site location. Otherwise set

to ‘No’.


• In this section the following topics have been covered:• What are BA lists?

• BA range Lists

• BA Neighbour Lists

• Effect of BA List loading on measurements

• Idle Mode BCCH carrier measurements

• BA-related Parameters

8. Cell Selection/Reselection


8. Cell Selection/Reselection _____________________________________________________________________ 8.1 Introduction

During Idle mode, a mobile terminal must be capable of moving between cells within the network. This is achieved by periodically measuring the signal strength of neighbouring cells. The mobile terminal uses these measured values to determine the point at which it moves from its current (serving) cell to a new (neighbouring) cell. This section of the notes describes the procedures used in this Idle mode decision-making process and identifies the key parameters that control these procedures.




_____________________________________________________________________ 8.2 Cell Selection Procedures

Cell Selection ProcedureCell Selection Procedure• MS powers-up

• MS starts measuring received power level of the BCCH carrier for all cells in range

• MS calculates average power level received from each cell:

• Stored in RXLEV(N) parameter

• MS calculates a C1 parameter for each measured carrier based on the RXLEV(N) values

• Mobile compares cells which give a positive value of C1 and ‘camps-on’ to the cell with the highest C1 value

Cell selection (as opposed to cell reselection) implies that the MS is switching on. There are two methods by which a suitable cell is selected for ‘camping-on: No SIM-Stored BA List On first switching on in this scenario, the MS scans all GSM frequencies for signal level (124 for P-GSM, 174 for E-GSM and 374 for DCS 1800). It prioritises those signals received in order of signal strength and starting with the strongest checks each to identify it as a BCCH carriers, through detecting a FCCH burst. It is likely that the strongest received signals will be BCCH carriers since continuous transmission is required on them. Once it detects an FCCH burst on a suitable carrier, it synchronises at TDMA frame level using the TDMA frame number and BSIC from the SCH channel. It then carries out three functions:

• Reading network information of the BCCH • Listening on its designated paging CCCH block for incoming pages • Monitors neighbouring cell BCCH carriers in preparation for cell reselection.

SIM-Stored BA List On switch-on the MS scans all BCCH carriers listed in its BA list for suitable signal strength, rather than all GSM frequencies. This is clearly a quicker procedure than scanning all GSM frequencies. Once the most suitable BCCH carrier has been identified, the MS camps-on to that cell and follows the procedure described above.



Cell Selection Cell Selection -- Parameter C1Parameter C1• Mobile uses parameter C1 (the Path Loss Criterion) to select and camp-on

to a cell when it is first switched on (idle mode)

• For a particular cell (n):C1(n) = [ A – max (B,0) ]

If A = RXLEV(n) - RXLEV_ACCESS_MIN and B = MS_TXPWR_MAX_CCH - P

Then:

C1(n) = [ RXLEV(n) - RXLEV_ACCESS_MIN - max((MS_TXPWR_MAX_CCH - P),0 ) ]

where:RXLEV(n) = average received BCCH power level from cell nRXLEV_ACCESS_MIN = minimum received power level needed by the mobile to access the systemMS_TXPWR_MAX_CCH = maximum transmit power mobile is allowed to use to access systemP = maximum possible transmit power of the mobilemax (0, x) = either x or 0 whichever is the greater

• Mobile compares cells which give a positive value of C1 and selects the highest value

The averaging is based on at least five measurement samples per RF carrier spread over 3 to 5 seconds, the measurement samples from the different RF carriers being spread evenly during this period. The averaged value is stored in the RxLev(n) parameter for each (n) cell. A multi band MS shall search all channels within its bands of operation as specified above. On switch-on, the MS scans all an MS periodically measures the received power level on each of the BCCH frequencies of all cells within range. From these periodic measurements the MS calculates the mean received level value from each cell, stored in the parameter RXLEV(n) where n=neighbouring cell number.

_____________________________________________________________________ 8.3 Cell Reselection Procedures

Having camped on to the serving cell, cell reselection is triggered by any one of the following causes:

• The path loss criterion parameter C1 indicates that the path loss to the cell has become too high

• There is a downlink signalling failure • The cell camped on (current serving cell) has become barred • There is a better cell (in terms of the path loss criterion C2) in the same LA, or a much

better cell in another LA of the selected PLMN • A random access attempt is still unsuccessful after "Max retrans" repetitions "Max

retrans" being a parameter broadcast on BCCH. The MS will then reselect a new cell based C1 (GSM Phase 1 and 2) and C2 (GSM phase 2 only) measurement parameters.




Cell Reselection CausesCell Reselection Causes

• C1 indicates that the path loss to the serving cell has become too high

• Downlink signalling failure

• Serving cell has become barred

• Better cell (in terms C1/C2 values)

• Random access attempts unsuccessful after anumber of repeated attempts

Having camped on to the serving cell, cell reselection is triggered by any one of the following causes:

• The path loss criterion parameter C1 indicates that the path loss to the cell has • become too high • There is a downlink signalling failure • The cell camped on (current serving cell) has become barred • There is a better cell (in terms of the path loss criterion C2) in the same LA, or a much

better cell in another LA of the selected PLMN • A random access attempt is still unsuccessful after "Max retrans" repetitions "Max

retrans" being a parameter broadcast on BCCH. The MS will then reselect a new cell. 8.3.1 C1 CELL RESELECTION CRITERIA Based on these calculated values, the MS selects which cell to connect to. This connection process is referred top as ‘Camping-on’ to that cell. Once camped-on, a MS in idle mode must periodically measure the received power level on each of the BCCH frequencies of neighbouring cells and stores this measurement in the parameter RXLEV(N) where n=neighbouring cell number.



Cell ReCell Re--selection selection -- Phase 1 Mobiles Phase 1 Mobiles • Once a mobile has camped on to a cell, it will continue to measure neighbouring

BCCH carriers, looking for a better cell• Phase 1 mobiles use the C1 calculation, modified as follows:

• Between cells within a location area, the criterion for selecting a new cell is:

C1 (new) > C1 (old) for more than 5 seconds

• Between cells on a location area boundary, the criterion is:

C1 (new) > C1 (old) + CELL_RESELECTION_HYSTERESIS for more than 5 seconds

• The hysteresis term prevents unnecessary re-selection on a location area boundary which would require extra signalling to perform the location update

From these periodic measurements the MS calculates the mean received level value from each cell and stores the result of the calculation in the C1 parameter for the best 6 neighbouring cells. Any C1 values of 0 or below are discarded and the best 6 of the remainder are stored. 8.3.2 C2 CELL RESELECTION CRITERIA

Cell ReCell Re--selection selection –– Phase 2 MobilesPhase 2 Mobiles

• GSM Phase 2 introduced a separate cell re-selection parameter, C2• Intended to:

• Prevent multiple handovers for fast-moving mobiles• Ensure MS camps on to cell with greatest chance of successful

communications

• The C2 calculated is:

C2 = C1 + OFFSET – (TEMPORARY_OFFSET x H(PENALTY_TIME –T)

where the function H is defined as: H(x) = 0 for x<0, H(x) = 1 for x ≥ 0




The purpose of introducing the C2 parameter was primarily to control access to microcells. The CELL_RESELECT_OFFSET can be set to make a microcell more attractive than a surrounding macrocell, while the TEMPORARY_OFFSET controls access depending on the speed of the mobile. There is an example of this in the activities at the end of this section.

C2 Cell Selection ParametersC2 Cell Selection Parameters

C2 = C1 + OFFSET – (TEMPORARY_OFFSET x H(PENALTY_TIME –T)

• Offset:• optional parameter to encourage or discourage cell selection

• H(Penalty_Time-T):• when a cell is added to list of strongest cells, a negative ‘Temporary Offset’ offset is

applied for a ‘Penalty time’:• If timer expires, offset is removed making cell more attractive• If cell is removed from list, timer is reset• Used to prevent fast-moving MSs from selecting the cell

• Temporary Offset:• Value of the negative offset applied

Cell ReCell Re--selection selection -- C2 ParameterC2 Parameter

• (CELL_RESELECT_OFFSET) effectively moves the boundary of the cell

• (TEMPORARY_OFFSET) only applies while (T < PENALTY_TIME), where T is the time since the mobile first detected the cell with C1>0

• This introduces a time hysteresis to prevent fast moving mobiles from selecting cells for very short periods

• To select a new cell using C2, either:

• C2 > 0 within a location area

or

• C2 > CELL_RESELECT_HYSTERESIS on a location area boundary



The hysteresis term prevents unnecessary re-selection on a location area boundary that require extra signalling to perform the location update. In order to optimise cell reselection, additional cell reselection parameters can be optionally broadcast on the BCCH of each cell. The cell reselection process can optionally employ a parameter C2, the value of which is determined by these parameters. The parameters used to calculate C2 are as follows: If PENALTY_TIME <> 11111 C2 = C1 + CELL_RESELECT_OFFSET - TEMPORARY OFFSET * H(PENALTY_TIME - T) If PENALTY_TIME = 11111 C2 = C1 - CELL_RESELECT_OFFSET Where: H(PENALTY_TIME-T) = 0 if x < 0 H(PENALTY_TIME-T) = 1 if x >= 0

Cell ReCell Re--selection selection -- C2 ParameterC2 Parameter

TEMPORARY_OFFSET

C1

CELL_RESELECTION_OFFSET

PENALTY_TIME

C2

Cell Reselection Offset This optional parameter is a positive or negative offset applied to each cell to encourage or discourage MSs to reselect that cell. Penalty Time When the MS places the cell on the list of the strongest carriers (Neighbour list), it starts a timer which expires after the PENALTY_TIME. This timer will be reset when the cell is taken off the list. For the duration of this timer, C2 is given a negative offset. This will tend to prevent fast moving MSs from selecting the cell. Temporary Offset This is the amount of the negative offset described in the ‘Penalty Time’ above. An infinite value can be applied, but a number of finite values are also possible.




________________________________________________________________________________

8.4 Summary of Key Cell Selection/Reselection Parameters

This section defines those configurable parameters that can be used to modify the c ell selection/reselection process.

Cell Selection/ReCell Selection/Re--selection Related Parametersselection Related Parameters

(*) Siemens DB Field Names

2dB0…63CRESOFFCELL_RESELECT_OFFSET10dB0…6TEMPOFFTEMPORARY OFFSET20sec0…30PENTIMEPENALTY_TIME

0…1CRESPARICELL_RESELECT_PARAM_IND0…1CQBCELL_BAR_QUALIFY

2dB0…7CELLRESHCELL_RESELECT_HYSTERESIS1dB0…63RXLEVAMIRXLEV_ACCESS_MIN2dB0…31MTPWRCCHMS_TXPWR_MAX_CCH

T/FCELLBARCELL_BAR_ACCESSGSMR

PCS1900GSM1800EXT900BB900

SYSIDSYS_ID

0…1023BCCHFREQBAStep SizeRangeDB Name (*)Parameter

8.4.1 CELL GSM OPERATING SYSTEM/FREQUENCY BA (range 0 to 1023) Defines the ARFCN on which the cell is operating. SYS_ID (range: system type – see above) Defines the GSM system being operated from the cell. The MS will only be able to camp-on to a cell operating on a compatible GSM system. 8.4.2 CELL ACCESS CELLBAR (range YES,NO) Cell Barring. Defines whether or not an MS is barred from network access (see ‘Network Access’ section for more details). CBQ (range HIGH,LOW). Cell Bar Qualifier. Used in conjunction with CB to determine cell access priority. (see ‘Network Access’ section for more details).



8.4.3 HYSTERESIS CELLRESH (range 0 to 14 dB in steps of 2) Cell Reselection Hysteresis. Defines the amount of hysteresis added to the nominal cell boundary threshold to prevent ping-pong effects for cell reselection on cell border areas (default 4). 8.4.4 RESELECTION THRESHOLDS CELL_RESELECT_PARAM_IND (range 0 or 1) The parameter is broadcast to the MS on the BCCH and indicates which cell reselection criterion are to be used in the cell. CELL_RESELECT_OFFSET (range 0…63 dB) This optional parameter is a positive or negative offset applied to each cell to encourage or discourage MSs to reselect that cell. PENALTY_TIME (range (0…30) x 20s) When the MS places the cell on the list of the strongest carriers (Neighbour list), it starts a timer which expires after the PENALTY_TIME. This timer will be reset when the cell is taken off the list. For the duration of this timer, C2 is given a negative offset. This will tend to prevent fast moving MSs from selecting the cell. TEMPORARY_OFFSET (range (0…6) x 10dB) This is the amount of the negative offset described in the ‘Penalty Time’ above. An infinite value can be applied, but a number of finite values are also possible.





• Cell selection procedures• Cell reselection procedures• Summary of key related parameters



Section 8 Self-Assessment Exercises Exercise 8.1

BSS parameters have been configures as follows: RXLEV_ACCESS_MIN = -90 dBm MS_TXPWR_MAX_CCH = 37 dBm Mobile Characteristics: Class 4 GSM 900 mobile RXLEV (n) measured by mobile: = -85 dBm Calculate the C1 value for the cell being measured

Exercise 8.2

When a Class 4 GSM 900 mobile is switched on, it measures the RXLEV for two cells (1 and 2) as: RXLEV(1) = -90 dBm RXLEV(2) = -93 dBm The network parameters are set as: RXLEV_ACCESS_MIN = -95 dBm MS_TXPWR_MAX_CCH = 35 dBm Decide which cell the mobile will camp on to based on C1 values.




Exercise 8.3

Macrocell

Microcell

A mobile is switched on within the coverage area of a microcell and a macrocell as shown. The set value of RXLEV_ACCESSA_MIN is –90 dBm The mobile measures the BCCH power levels for each cell as: RXLEV(macrocell) = -70 dBm RXLEV(microcell) = -80 dBm The network has set MS_TXPWR_MAX_CCH as 35 dBm. The mobile is a Class 4 GSM 900 handset with maximum power output of 33 dBm. 1. Compare C1 for the two cells and state which one the mobile will camp on to.

2. The network operator wants to attract slow moving mobiles in this location into the microcell.

Suggest a possible value for CELL_RESELECT_OFFSET in the C2 re-selection criterion of the microcell, which will achieve this. Note that values for CELL_RESELECT_OFFSET are from 0 to 126 dB in steps of 2 dB.

3. Mobiles should only re-select to the microcell if they remain in the area for more than 1 minute.

Show how the rest of the C2 calculation could be used to achieve this. Note that TEMPORARY_OFFSET values range from 0 to 60 dB in steps of 10 dB and PENALTY_TIME ranges from 20 to 620 seconds in steps of 20 seconds.




_____________________________________________________________________ 9.1 Introduction

Location management is the process by which the GSM network tracks the movement of mobile users throughout the PLMN down to Location Area (LA). Paging is process of locating the mobile user down to cell level for the purpose of establishing a Mobile-Terminated (MT) connection. This section of the course describes these tow procedures and identifies the key parameters that control their associated functions




_____________________________________________________________________ 9.2 Location Management Procedures

9.2.1 LOCATION MANAGEMENT OPTIONS

Location Management OptionsLocation Management Options

• Send location update on every cell change• No paging requirement• Excessive signalling traffic load

• Page every cell in network• No location update requirement• Excessive signalling traffic load

• Subdivide network into paging areas• Requires paging procedure with reduced traffic load• Required location updating with reduced traffic load

In order to ensure the correct routing of an incoming call to a MS, the network needs to know the current location of that MS down to cell level. This can be achieved by one of three methods:

• Location Update on Every Cell Change Every time an MS moves into a different cell area, it sends a location update to the network. This has the advantage that no paging is required to establish the cell location of an MS for each incoming call. However, it imposes a significant load on the network signalling channels.

• Paging All Cells Every time an incoming call is to be routed to an MS, all cells in the network are paged to identify the cell owning the MS. This has the advantage that no location updating is required to maintain a current MS location log. However, it imposes a significant load on the network signalling channels.

• Subdivide Network into Paging Sub-Regions Every time an MS moves in a new paging sub-region it informs the network of that sub-region identity. Every time an incoming call is to be routed to an MS, only the cells in its current paging sub-region are checked. This provides a comprise between the two above options and has been proved to reduce signalling channel loads significantly.



9.2.2 GSM LOCATION AREAS (LAs) Within GSM networks these paging sub-regions are known as a Location Areas (LAs) and comprise a number of cells. All cells within the LA must be under the control of a single MSC and within the same PLMN. Each LA within the PLMN is uniquely identified by a Location Area Identifier (LAI).

Network AreasNetwork Areas

• Cell: radio coverage area of one base station (BTS)• GSM assigns a cell global identity number to each cell

• Location Area: Group of cells served by one or more BSCs.

• When there is an incoming call, the mobile is paged throughout its location area. A unique Location Area Identity (LAI) is assigned to each LA.

• MSC Service Area: part of network covered by one MSC. • All mobiles in this area will be registered in the VLR associated

with the MSC.

• PLMN Service Area: public land mobile network area - the area served by one network operator

9.2.3 LOCATION UPDATE REQUIREMENTS

Location Update RequirementsLocation Update Requirements

• Location Area Change

• Periodic Location Update

• IMSI Attach

• Cell change during call

• TMSI update on LA change




Location Updates occur under one of the following conditions:

• On change of LA • Periodic Updates • On MS switch on (IMSI attach) • When changing cells during a call

MSC 2

Location UpdatingLocation Updating

• The PLMN is divided into a number of location areas

• Each location area consists of several cells controlled by the same MSC, but not necessarily the same BSC

• The main use of location areas is in paging a mobile

• Location area is stored in the VLR of the MSC• The HLR stores the current MSC the mobile is

registered with and is only updated if the mobile moves to new MSC

• LAI - Location Area Identity - is transmitted on BCCH

MSC 1

Location Areas

VLR

VLR

Every time a moving MS enters a new LA (identified by the information transmitted on the BCCH) it initiates a location update.

Automatic Location UpdatingAutomatic Location Updating

• Mobile receives LAI from BCCH transmission• When it detects a new LAI it automatically requests an update• Within same MSC:

Location Update Request

Acknowledgement

New Location Area stored in VLR

• Change of MSC:

MSC2

VLR

HLR

Location Update Request/ Acknowledgement

New VLR Request/ Acknowledgement

Cancel old VLR Location/ Acknowledgement

MSC1

VLR

MSC1

VLR



If an MS is not moving, LA updates will not take place. Therefore, if there has been no activity for a (operator-defined) period of time, the MS will initiate a periodic update to the network. If the parent VLR has received no updates from an MS within a certain (operator-defined) time period, it assumes it has left the network and forces an IMSI detach. Every time an IMSI attach takes place, location update information is passed to the parent VLR. If an MS has previously detached and is reattaching in the same VLR no update is required. If it is a new VLR a standard location update procedure is implemented. In this case the HLR would also be informed of the new LAI associated with the MS. If an MS changes cell during a call, a location update must be initiated to ensure traffic continues to be routed to the correct cell.

_____________________________________________________________________ 9.3 Paging Procedures

Paging is the procedure used for identifying the current cell location of an MS in order to route an incoming (mobile terminated) call.

Paging ProceduresPaging Procedures

• Paging locates MS to cell Level for call routing

• Three paging message types:

• Type 1 - 2 MSs using IMSI/TMSI

• Type 2 - 3 MSs (1xIMSI, 2xTMSI)

• Type 3 - 4 MSs using TMSI only

• Paging message requires 4 bursts (1 CCCH block)

• Paging messages may be stored at BSS

• Transmitted on PCH

• If DRX is implemented MS listens only to allocated paging group

9.3.1 PAGING MESSAGE TYPES Three paging message types have been defined:

• Type 1: can address up to 2 mobiles using either IMSI or TMSI. • Type 2: can address up to 3 mobiles, one by IMSI and the other 2 by TMSI. • Type 3: can address up to 4 mobiles using the TMSI only.




The reason different numbers of MS identities can be paged in a single message type is that the IMSI and TMSI are of different lengths. The IMSI comprises 8 octets containing the following information:

• Mobile Country Code (MCC) – 3 decimal places (e.g. 262 = Germany) • Mobile Network Code (MNC) – 2 decimal places (e.g. 01 = D1-Telekom) • Mobile Subscriber Identification Number (MSIN) – 10 decimal places

9.3.2 PAGING MESSAGE TRANSMISSION The TMSI is operator-assigned and therefore does not require the MCC or MNC. Hence it is only 4 octets in size. As a result, a paging message can store twice as many TMSIs as IMSIs. Paging requests for individual mobiles are sent from the MSC to the BSS. To reduce the signalling channel load, the BSS stores these requests temporarily until there are enough to make up a full type 1,2 or 3 message or until a configurable timer (set by the operator) expires. The contents of the paging message are then broadcast on the paging channel (PCH). 9.3.3 PAGING AND DRX To save battery power, Discontinuous Reception (DRX) functionality can be implemented. In the case, the MS is assigned to a particular CCCH paging block (paging group) and therefore is only required to listen for paging messages on that block rather than all CCCH blocks in the control channel multiframe. The designated paging group is defined in the BS_PA_MFRMS parameter. This parameter informs the mobile of the number of multiframes (ranging from 1 to 9) after which the same paging group is repeated. The mobile will only turn on its receiver to decode the paging message in its paging group, which might repeat once in 1 to 9 multiframes. This technique works by dividing the MSs within a cell into groups. The group in which an MS resides is then known locally at both the MS and the BSS. All paging requests to each group are then scheduled and sent at a particular time which is derived from the TDMA frame number in conjunction with the IMSI of the MS and some BCCH transmitted data. Thus both the BSS and the MS know when relevant page requests will be sent and the MS can power down for the period when it knows that page requests will not occur.



____________________________________________________________________

9.4 Calculations Using Paging Parameters

Paging will make more use of CCCH than the access grant messages, since paging is done across a location area. All cells in the location area are paged, whether the required mobile is in that cell or not. AGCH only takes place in the specific cell containing the mobile.

Calculating Paging CapacityCalculating Paging Capacity

X = number of mobiles paged per paging message (1 to 4)

Y = number of possible paging messages per multiframe

Duration of control channel multiframe = 0.235 seconds (235 ms)

• X depends on paging message type

• Y depends on CCCH configuration in the multiframe (e.g. 3 or 9) and the number of AGCH blocks reserved

235.0XYCapacity Paging = mobiles / second

PCH DimensioningPCH Dimensioning

Paging channel requirement in blocks per multiframe is given by:

4.25 x 3600 x PMFM x PF x MT x Calls

Calls = Number of calls predicted for the location area during busy hourMT = Fraction of calls which are mobile terminatedPF = Paging Factor = number of pages required per callM = safety marginPMF = Paging Message Factor = number of pages per messageNumber of control channel multiframes per second = 4.25 (1 / 0.235)




____________________________________________________________________

9.5 Key Paging Parameters

Paging is controlled by the MSC, so paging-related parameters are strictly related to the MSC rather than the BSS. However, as paging is a function carried out over the air interface, they have been included for completeness.

Key Paging ParametersKey Paging Parameters

• Initial Paging Request:• Number of paging blocks available• Paging message type• Paging area (one LA, multiple LAs, global)

• Repeat Paging Requests:• Type of repeat paging message• Interval between repeat pages• Maximum number of repeat paging attempts• Maximum time before paging retries cease

9.5.1 PAGING REPETITION PROCEDURE PAGREP1LA (range: 0 to 3) ) (Ericsson MSC only) Page Repeat One RA. This determines the paging repetition procedure used within a cell (default 2):

0 – paging in one LA not repeated 1 - paging in one LA repeated with either TMSI or IMSI 2 - paging in one LA repeated with IMSI only 3 – paging repeated globally

PAGREPGLOB (range: 0 to 1) (Ericsson MSC only) Page Repeat Global. This determines the global paging repetition procedure if first paging sequence was global (default 0):

0 – Global paging not repeated 1 – Global paging repeated with IMSI



Page Repetition Procedure ParametersPage Repetition Procedure Parameters

• PAGREP1LA• Page repetition in procedure in 1 LA• Range 0 – 3 (default 2)

• PAGREPGLOB• Global page repetition procedure • Range 0 – 1 (default 1)

• PAGNUMBERLA• Maximum number of LAs included in a paging request• Determines global page repetition procedure used • Range 1 – 3 (default 1)

{Ericsson MSC parameters}

PAGNUMBERLA (range: 1 to 3) (Ericsson MSC only) Paging Number LA. This indicates the maximum number of paging areas included in a single paging message (default 1). 9.5.2 PAGING REPETITION PERIOD

Paging Repetition Period ParametersPaging Repetition Period Parameters

• PAGTIMEFRST1LA• Time delay between repeat pages in 1 LA• Range 2 – 10 (default 4)

• PAGTIMEFRSTGLOB• Time delay between repeat global pages• Range 2 – 10 (default 4)





PAGTIMEFRST1LA (range: 2 to 10) (Ericsson MSC only) Paging Timer First One LA. This timer indicates the time delay between paging repetitions in one location area (default 4). PAGTIMEFRSTGLOB (range: 2 to 10) (Ericsson MSC only) Paging Timer First Global. This timer indicates the time delay between global paging repetitions (default 4). 9.5.3 PAGING CESSATION PERIOD

Paging Cessation Period ParametersPaging Cessation Period Parameters

• PAGTIMEREP1LA• Time after which paging repetitions cease in 1 LA• Range 2 – 10 (default 7)

• PAGTIMEREPGLOB• Time after which global paging repetitions cease• Range 2 – 10 (default 7)


PAGTIMEREP1LA (range: 2 to 10) (Ericsson MSC only) Paging Timer Repeat One LA. This timer indicates the time, after no response, at which no further paging is initiated in a single LA. (default 7). PAGTIMEREPGLOB (range: 2 to 10) (Ericsson MSC only) Paging Timer Repeat Global. This timer indicates the time, after no response, at which no further global paging is initiated in a single RA. (default 7).



____________________________________________________________________

Location area updates are controlled by the MSC but have been included here for completeness

9.6 Key Location Management Parameters

Location Area Change Update ParametersLocation Area Change Update Parameters

NLocation Update Timer Expires

YChange of Location Area

NIMEI Check

NAuthentication

YTMSI Allocation

YIMSI Attach

YNew Visitor

LALOCATION UPDATE

RECPARAMETER

Location Updating is controlled by the MSC and therefore is subject to MSC parameters

Periodic Location Update ParametersPeriodic Location Update Parameters

YLocation Update Timer Expires

NChange of Location Area

NIMEI Check

NAuthentication

NTMSI Allocation

NIMSI Attach

NNew Visitor

PERIODICLOCATION UPDATE

RECPARAMETER

Location Update Timer = T3212 (range 0-255 in deci-hours – default 10)




Section 9 Section 9 -- SummarySummary• In this section the following topics have been

covered:

• Location management procedures• Paging procedures and calculations• Key paging parameters• Key location management parameters



Section 9 Self-Assessment Exercises

Exercise 9.1 Calculate the paging capacity of cells with the following configurations: a) CCCH_CONF = 0

3 blocks reserved for AGCH Type 1 paging messages

b) CCCH_CONF = 1

1 block reserved for AGCH Type 3 paging messages







10. Frequency Hopping _____________________________________________________________________ 10.1 Introduction

Frequency Hopping is the process by which a cell transmits of continuously changing frequencies (each TDMA frame from each TRX) in order to reduce network interference including multi-path fading effects. This section of the course describes GSM Slow Frequency Hopping and the key parameters that control these procedures.




_____________________________________________________________________ 10.2 Frequency Hopping Procedures

10.2.1 FREQUENCY HOPPING CONCEPT Mobile radio carriers suffer from frequency-selective interferences, for example, fading due to the multipath propagation phenomena. As the carrier signal attenuates with distance, frequency-selective interference can have an increasingly significant affect on the signal quality.

Frequency Hopping ConceptFrequency Hopping Concept

TDMA Frame 1

F1 F1 F1 F1 F1 F1 F1 F1

TDMA Frame 2

F1 F1 F1 F1 F1 F1 F1 F1

TDMA Frame 3

F1 F1 F1 F1 F1 F1 F1 F1

TDMA Frame 1

F1 F1 F1 F1 F1 F1 F1 F1

TDMA Frame 2

F2 F2 F2 F2 F2 F2 F2 F2

TDMA Frame 3

F3 F3 F3 F3 F3 F3 F3 F3

TS0 TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS0 TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS0 TS1 TS2 TS3 TS4 TS5 TS6 TS7

TS0 TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS0 TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS0 TS1 TS2 TS3 TS4 TS5 TS6 TS7

Non-Frequency Hopping Carrier:

Frequency Hopping Carrier:

•

•

Frequency hopping (FH) employs a constantly changing transmission frequency on the radio carrier. Therefore the effects of frequency selective interference will be reduced by producing an averaging effect over the interference caused on each frequency employed within the FH sequence. This results in an overall improvement in S/N ratio. The GSM specification defines optional FH implementation where the frequency on a carrier changes with each new TDMA frame transmission. 10.2.2 FREQUENCY HOPPING SEQUENCE A TDMA frame has a duration of 4.617ms (8 timeslots of 0.577ms each). If the frequency changes with each TDMA frame, then it must change every 4.617ms or approximately 217 times per second. This is referred to as slow FH as the rate of frequency change is slower than the symbol rate of the data transmitted on the carrier.



Frequency Hopping SequenceFrequency Hopping Sequence

• The frequency changes follow either a sequential or pseudo-random pattern• GSM defines 1 sequential pattern and 63 pseudo-random patterns• Each pattern is defined by a Hop Sequence Number (HSN)

Hop Sequence

• One TDMA frame is 4.6 ms long• Rate of hopping = 1/ (4.6 x 10-3) = 217 hops / second

F1 F2 F3 F4 F1 F2 F3 F4 F1 F2 F3 F4Sequential:

hop sequencerepetition period

F1 F4 F3 F2 F1 F4 F3 F2 F1 F4 F3 F2Pseudo-Random:(conceptual)

TDMA Frame

The pattern of hopping used within GSM can be sequential or pseudo-random. The GSM network can assign either one sequential cyclic hopping pattern or any one of 63 pseudo-random cyclic hopping patterns. Each sequence is defined by a unique Hop Sequence Number (HSN) in the range 0 – 63. The effect of changing frequencies with every TDMA frame is that each consecutive timeslot of each channel is transmitted on a different frequency. 10.2.3 REASONS FOR IMPLEMENTING SFH Implementing SFH in GSM can have a number of benefits: Reduces Multipath Fading Interference. For a static MS, if its operating frequency suffers from multipath fading, the degree of fading interference will be constant. However, as the degree of multipath fading changes with frequency, by continually changing the operating frequency of the MS, the degree of fading can be reduced over the whole period of the frequency hopping cycle. Increases C/I Value Through Frequency Diversity. For a non-hopping GSM link, the minimum requires C/I ratio is 11-12dB. Implementing FH can reduce this margin to approximately 9dB.




10.2.4 IMPLEMENTING SFH AT THE BTS When implementing FH at the Base Station the following must be considered: The timeslot containing the BCCH must not frequency hop. This is to ensure that: • Neighbouring cells (which may not be using frequency hopping) can continue to monitor

the cell’s BCCH for signal strength measurements prior to handover. • When entering a cell implementing FH, the BCCH of that cell can pass frequency

hopping information to the MS to initiate the sequence.

Frequency Hopping at the BTSFrequency Hopping at the BTS

• BCCH carrier will not hop - mobiles must be able to access this for neighbour cell power level measurements

• Only TRXs used for traffic channels will hop through set sequences

• The set of carrier frequencies assigned to the sequence (Mobileallocation – MA) will normally be from current cell allocation

• Hopping sequence for each TRX must be different or have a different Mobile Allocation Index Offset (MAIO)

Only those carrier fully dedicated to traffic channels (TCHs) can implement frequency hopping. To avoid significantly changing the network frequency plan, the allocation of hopping frequencies is taken from the existing cell allocation. Therefore, if a cell currently has 4 TRXs, three of the four frequencies can be used to implement the hopping sequence (BCCH carrier does not hop). However, when implementing this configuration, it must be ensured that no two transmitters hop to the same frequency at the same time.



Example of 4Example of 4--Frequency HoppingFrequency Hopping

• BCCH carrier remains on single frequency

• TCH carriers must start at different points in sequence (MAIO) to avoid co-channel (C/I) interference

• Above example uses same HSN for each TRX but different MAIOs

F4F3F2F4TRX 4

F3F2F4F3TRX 3

F2F4F3F2TRX 2

F1F1F1F1TRX 1

Hop 4Hop3Hop 2Hop 1Transmitter

This can be avoided by starting the hopping sequence for each transmitter at a different time. For example, using a sequential hopping implementation: 10.2.5 HARDWARE IMPLEMENTATION AT THE BTS Two different BS hardware implementations of FH exist; Baseband Hopping and Synthesiser Hopping.

BasebandBaseband Frequency HoppingFrequency Hopping

Fixed TRX

CombinerAntenna

Switch controller

BasebandData Signal Fixed TRX

Fixed TRX

• The baseband signal is fed to one of several TRXs in turn by a switch • The TRX outputs must be combined to be fed to the antenna• The combiner must be able to handle a wide bandwidth of signals• This can be achieved using either:

• hybrid combiners - several stages causing large loss • cavity filters - one associated with each TRX - maximum loss ~ 5 dB




Synthesiser Frequency HoppingSynthesiser Frequency Hopping

• A single channel using synthesiser hopping has only one TRX output and would not require a combiner

• If several channels are to be combined and fed to one antenna, the combiner must have a wide bandwidth to deal with the range of frequencies from the synthesiser

• Hybrid combiners must be used in this case

Tuning controller

BasebandData Signal 1 TRX 1

BasebandData Signal 2 TRX 2

HybridCombiner

Load

Antenna

Baseband Hopping. Base band hopping implies switching the transmit frequency at the baseband frequency level. This can be implemented where the Base Station is equipped with a number of discreet transceivers, each operating at a fixed frequency. The data stream is switched to each transceiver in accordance with the assigned hopping sequence. Synthesiser Hopping. Implementing Synthesiser hopping requires the use of a transceiver employing frequency synthesis procedures foe frequency changes. In this case, a single synthesises transceiver is used and the transmit frequency is switched using a tuning controller set to the assigned hopping sequence.

10.2.6 IMPLEMENTING SFH AT THE MS

While Frequency Hopping (FH) is not mandatory for Base Stations (BSs), all Mobile Stations (MSs) must have this capability. This is to ensure that an MS continues to maintain contact if it is handed over to a BS currently implementing FH. When an MS implements FH it must still be capable of taking signal strength measurements from adjacent cells. This is the primary reason why Slow Frequency Hopping (SFH) has been implemented in GSM.



Frequency Hopping at the MSFrequency Hopping at the MS

• All mobiles must be capable of SFH in case it enters a cell in which it is implemented

• SFH is implemented to allow time to continue to take measurements from adjacent cells

• On connection/handover, the MS needs to know:• Frequencies used for hopping (Mobile Allocation) • Hop Sequence Number (HSN)• Start frequency (Mobile Allocation Index Offset - MAIO)

• The MS uplink HSN is the same as the TRX downlink HSN but offset by 45MHz

_____________________________________________________________________ 10.3 Key Frequency Hopping Parameters

Key Frequency Hopping ParametersKey Frequency Hopping Parameters

• If Frequency Hopping is enabled

• Hopping mode (base band / synthesised)

• Frequency range allocated to hopping

• The sequence of frequencies through which the TRX hops

• The point within the sequence where hopping is to start





• HOP {Ericsson} (range Y/N)• Hopping Enabled

• HOPMODE {Siemens} (range: BBHOP/SYNHOP)• Type of Hopping (base band / synthesiser)

• MA (range 1 to 64)• Mobile Allocation - frequencies allocated for SFH

• HSN (range 0 – 63)• Hop Sequence Number for sequence through which frequencies are to

hop

• MAIO (range 0 to N-1)• Mobile Allocation Index Offset - starting position in hop sequence



• GSM Frequency Hopping Techniques• Hardware SFH Configurations• SFH Implementation at the BS and MS• Key SFH Parameters




_____________________________________________________________________ 11.1 Introduction

When in dedicated mode, i.e. when a bi-directional communications link has been established to the network, there is a requirement to measure signal characteristics of the serving and surrounding cells for handover purposes. Through the dedicated mode periods, the MS measures and averages the signal level received from its serving and neighbouring cells and the signal quality of the serving cell. These measurements are passed up the BSC (via the BTS) in the form of measurement reports. The information contained within these reports is used to for dynamic power control and to determine when handovers take place. This section of the course describes these procedures and the parameters used to control the functions.




_____________________________________________________________________ 11.2 Dedicated Mode Cell Measurement Procedures

11.2.1 DEDICATED MODE CHANNEL MEASUREMENTS

BCCH Carrier Measurements BCCH Carrier Measurements –– Dedicated ModeDedicated Mode

• Primary Values:• Receive Signal Level• Receive Signal Quality

• MS measures neighbouring cells for:• BCCH Receive Signal Level

• MS measures serving cell for:• BCCH Receive Signal Level (no DTX) or• BCCH Receive Signal Level (with DTX)• BCCH Receive Signal Quality (no DTX)• BCCH Receive Signal Quality (with DTX)

• BSC measures MS uplink signal level and quality

Key MeasurementKey Measurement ParametersParameters

• For the Serving Cell:• BA_USED

• DTX_USED

• RXLEV_FULL_SERVING _CELL

• RXLEV_SUB_SERVING _CELL

• RXQUAL_FULL_SERVING _CELL

• RXQUAL_SUB_SERVING _CELL

• For the best 6 neighbouring cells:• RXLEV_NCELLX

• BCCH_FREQ_NCELLX where N = Cell id

• BSIC_NCELLX X = 1 – 6 best cells



FULL FULL –– SUB SUB MeasurementsMeasurements

• RXQUAL_FULL • measurements are taken over a full 104 TDMA Multiframe cycle i.e. the

time taken to transmit one full SACCH message on the uplink as ameasurement report

• RXQUAL_SUB • measurements are used when DTX is implemented.

• With DTX, only certain TDMA frames contain speech information, the remainder are filled with SID frames, providing comfort noise only.

• RXQUAL_SUB measurements are taken over 12 TDMA frame periods only and are therefore less accurate than RXQUAL_FULL measurements

• However, RXQUAL_SUB should be used when comparing power measurements with neighbouring cells that also have DTX implemented

BCCH Carrier Measurements BCCH Carrier Measurements –– Dedicated ModeDedicated Mode

RxLev / BSICRxLev / BSIC

RxLev / BSIC

RxLevRxQual

Measurement Reports




In dedicated mode, the MS carried out the same measurements on neighbouring cells as described above. In addition, as an uplink connection is established to the network, the following additional measurement functions take place:

• Measurement of the downlink RXQUAL as well as RXLEV • BSIC and BCCH Carrier identification for each neighbouring carrier signal detected. • Transmission of measurement reports to the network on the uplink

As a bi-directional traffic (TCH) or signalling (SDCCH) channel exists between the network and the MS, the MS is able to monitor received signal quality (RXQUAL) in addition to received signal level (RXLEV).

Cell MeasurementsCell Measurements• The current cell provides a list of all neighbouring BCCH carrier

frequencies - the BCCH Allocation (BA) list• Mobile measures RXLEV for these carriers in the times between its uplink

and downlink timeslots

01 2 3 4 5 6 7 0 1 2 3 4 5 6 70 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 70 1 2 3 4 5 6 7

Uplink

Downlink

1

Measurement periods

11.2.2 RXLEV AND RXQUAL MEASUREMENT LEVELS In idle mode RXLEV is measured and recorded only by the MS. In dedicated mode both the MS and the BTS measure RXLEV on the downlink and uplink respectively. Measurements are taken in the range -110dBm to -48 dBm, averaged as described above and categorised into one of 64 levels as shown in the table below:



Receive Level MeasurementsReceive Level Measurements

--48RXLEV_63

-48-49RXLEV_62

-108-109RXLEV_2

-109-110RXLEV_1

-110-RXLEV_0

To:From:

Received Signal Level (dBm)Level

RXQUAL is recorded in dedicated mode only by both the MS and BTS on the downlink and uplink respectively. Measurements are taken in the %BER range 0.2 to 12.8 and categorised into one of 8 levels as shown in the table below:

Receive Quality MeasurementsReceive Quality Measurements

-12.8RXQUAL_7

12.86.4RXQUAL_6

6.43.2RXQUAL_5

3.21.6RXQUAL_4

1.60.8RXQUAL_3

0.80.4RXQUAL_2

0.40.2RXQUAL_1

0.2-RXQUAL_0

To:From:

Bit Error Ratio (%)Level




85%95%95%> 12.8%RXQUAL_7

80%95%95%6.4% - 12.8%RXQUAL_6

70%95%95%3.2% - 6.4%RXQUAL_5

60%85%90%1.6% - 3.2%RXQUAL_4

45%85%90%0.8% - 1.6%RXQUAL_3

45%70%85%0.4% - 0.8%RXQUAL_2

35%60%75%0.2% - 0.4%RXQUAL_1

65%90%90%< 0.2%RXQUAL_0

DTXTCH/HTCH/F

Probability that correct RXQUAL band is reported by MS shall exceed:Range of actual BERQuality Band

Probability of Correct RXQUAL Level ReportingProbability of Correct RXQUAL Level Reporting

Cell MeasurementsCell Measurements• The current cell provides a list of all neighbouring BCCH carrier

frequencies - the BCCH Allocation (BA) list• Mobile measures RXLEV for these carriers in the times between its uplink

and downlink timeslots

01 2 3 4 5 6 7 0 1 2 3 4 5 6 70 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 70 1 2 3 4 5 6 7

Uplink

Downlink

1

Measurement periods



Cell MeasurementsCell Measurements• Up to 100 cell measurements are made over 480 ms period (104

frames)• In the SACCH frame of the TCH multiframe, the mobile sends a

measurement report to the BTS• In addition to BCCH carrier measurements, the mobile must also

identify the actual cell it has measured:• Mobile must synchronise with the neighbouring cell - search for the

FCCH and SCH channels and read the BSIC information• Search is done during the idle frame of the TCH multiframe• As TCH multiframe has 26 frames and BCCH has 51, the idle frame

moves relative to BCCH on each cycle of the multiframe

T T T T T T T T T T T T S T T T T IT T T T T T T T Mobile has found FCCH on this cycle of multiframe

S BCCHF CCCH S CCCHF CCCH S CCCHF CCCH S CCCHF CCCH S CCCHF CCCH I

11.2.3 CELL MEASUREMENT REPORTING MESSAGE

SACCH MessagesSACCH Messages

• SACCH is used to report measurements from neighbouring cells which have been identified

• Complete message requires 4 SACCH bursts• For TCH, this requires 4 multiframes or 480 ms

IIIIS 12 TCH12 TCH S 12 TCH12 TCH S 12 TCH12 TCH S 12 TCH12 TCH

1 SACCH message reporting measurements over the last 480 ms

4 TCH multiframes = 480 ms





• HOP {Ericsson} (range Y/N)• Hopping Enabled

• HOPMODE {Siemens} (range: BBHOP/SYNHOP)• Type of Hopping (base band / synthesiser)

• MA (range 1 to 64)• Mobile Allocation - frequencies allocated for SFH

• HSN (range 0 – 63)• Hop Sequence Number - sequence through which frequencies

are to hop

• MAIO (range 0 to N-1)• Mobile Allocation Index Offset - starting position in hop sequence

When on a TCH, the MS shall assess during the reporting period and transmit to the BSS in the next SACCH message block the following: • RXLEV: for neighbour cells in the signal level order

• RXQUAL_FULL:RXQUAL: for the full set of TCH and SACCH TDMA frames. The full

set of TDMA frames is either 100 (i.e. 104 - 4 idle) frames for a full rate TCH or 52 frames for a half-rate TCH.

• RXLEV_VAL: RXLEV measured on SACCH frames and on the 4 last time slots of each

fully received and correctly decoded data block, whether the DTX was used in downlink or not. For speech TCHs, blocks that have not been erased are considered as correctly decoded. For non-transparent data, blocks are considered to be correctly decoded according the CRC received. For transparent data, all blocks are considered as correctly decoded.

• MEAN_BEP and CV_BEP: The average over the reporting period of the Mean and

Coefficient of Variation of the Bit Error Probability.

• NBR_RCVD_BLOCKS: The number of correctly decoded data blocks, as defined for RXLEV_VAL, (excluding all SID frames, RATSCCH, SACCH and FACCH blocks) that were completed during the measurement report period.

• BSIC_SEEN: Indicates if a GSM cell with invalid BSIC and allowed NCC part of the

BSIC is one of the six strongest cells.




• This section has covered Dedicated Mode:

• Measurement Procedures• Measurement Parameters• Measurement Levels• Measurement Messages• Measurement Message Parameters





12. Power Control


12. Power Control _____________________________________________________________________ 12.1 Introduction

Power control is used in a network primarily to reduce interference levels and increase the battery life of battery-powered devices. This section deals with the methods of power control in the GSM network and the key parameters that control the power control features.

12. Power Control



_____________________________________________________________________ 12.2 Power Control Functions

12.2.1 REASONS FOR POWER CONTROL

Reasons for GSM Power ControlReasons for GSM Power Control

• Prevent unnecessary power emissions to:

• Increase life of battery-powered devices

• Reduce network interference

• Equalise MS power levels received at BTSs

• Adjustments to cell coverage

Power control within a GSM system has four main purposes:

• Reduce power outputs to the minimum required for effective communications in order to reduce interference

• Limit unnecessary power emissions in order to increase the longevity of battery-power equipments

• Prevent MSs closer to BTS de-sensitising those more distant • Enable the network controller to adjust cell coverage by adjusting BTS output

power.

12.2.2 POWER CONTROL FUNCTIONS

GSM power control is achieved by a number of methods. These include:

• Adaptive Power Control. This automatically adjusts power outputs up or down to ensure to the minimum required to meet the prescribed service quality level.

• Discontinuous Transmission (DTX). This is a procedure whereby transmissions are

only made when information is to be passed.

12. Power Control


• Discontinuous Reception (DRX). This procedure enables battery-powered MSs to

minimise power consumption by only listening out on specific control channels.

GSM Power Control FunctionsGSM Power Control Functions

• Adaptive Power Control

• Discontinuous Transmission (DTX)

• Discontinuous Reception (DRX)

12.2.3 GSM POWER CLASSES The ETSI GSM recommendations specify power classes for both MSs and BSSs. These power levels, together with the defined GSM receiver sensitivity levels are shown in the tables below.

Mobile Station Power ClassesMobile Station Power Classes

36 (4W)480DCS class 3

24 (.25W)30DCS class 2

30 (1W)120DCS class 1

29 (0.8W)96GSM class 5

33 (2W)240GSM class 4



dBmPower mW

Full RateMS Class

Power (mW) = Nominal maximum mean power output (milliwatts)GSM class 1 – deleted under GSM Phase 2 Specification

Source: ETSI GSM 02.06 (Version 4.5.2)Power (dBm) = Maximum power output in dBm (+watts)

12. Power Control



GSM 900 MSs fall into one of five (four in GSM phase 2) classes, distinguished by their power output levels. DCS1800 MSs have 3 equivalent classes. Note than the GSM 900 Class 1 MS category was dropped from the GSM Phase 2 recommendations. Typical consumer Mobile handsets fall into the Class 4 category

BTS Power ClassesBTS Power Classes

Source: ETSI GSM 05.05 (Version 4.23.1)

22.57857

106205

2.5440453803

10216022013201

MaximumO/P Power

(W)

TRX Power Class

MaximumO/P Power

(W)

TRX Power Class

DCS 1800GSM 900

Note that most GSM-900 BTSs operate in the 5-7 Class. 12.2.3 GSM REFERENCE SENSITIVITY LEVELS

Receiver Sensitivity LevelsReceiver Sensitivity Levels

Source: ETSI GSM 05.05 (Version 4.23.1)

-92dBmM3 Micro BTSGSM 1800



-102 dBmMS Class 3DCS 1800

-100 dBmMS Class 1 or 2DCS 1800




-104dBmMacro BTSGSM 900

-104dBmOther MSGSM 900

-102dBmSmall MSGSM 900

SensitivityClassSystem

12. Power Control


The reference sensitivity performance in terms of frame erasure, bit error, or residual bit error rates (whichever appropriate) is specified below, according to the type of channel and the propagation condition. The actual sensitivity level is defined as the input level for which this performance is met. The actual sensitivity level should be less than a specified limit, called the reference sensitivity level. The reference sensitivity levels are: Note that these parameters are drawn from the ETSI GSM Recommendations. Vendor-specific equipment implementations may vary. The figures shown in the tables above are maximum power levels for specific classes. Actual power levels are set according to local interference conditions and the combined losses in the base station equipment.

____________________________________________________________________ 12.3 Adaptive Power Control

12.3.1 ADAPTIVE POWER CONTROL IMPLEMENTATION

Adaptive Power ControlAdaptive Power Control• GSM power control aims to use the minimum power needed

to maintain communication• Reasons for controlling power:

• reduces interference in system• conserves energy - prolonging battery power in mobiles

• Power control is applied to:

BTS instructs MS to change power

BTS adapts power in response to measurement reports

andDownlink

Uplink

Adaptive power control is employed to minimise the transmit power required by MS or BSS whilst maintaining the quality of the radio links. By minimising the transmit power levels, interference to co-channel users is reduced. In addition, by controlling the emissions from mobile devices, the power consumption can be reduced and therefore extend battery life. Adaptive power control is not applied to the BCCH carrier from the BTS. This is continually radiated at full power. Power control on other carriers is applied independently to each timeslot.

12. Power Control



Power control can be understood by considering the case where all MSs transmit on the same power level. Mobiles far from BTS will not produce unnecessary interference because they would have to use more RF power to reach the quality target. However, if mobiles near the BTS expend the same amount of power most of this power will be wasted and the overall power level in the network increases and “excess” interference is created. This situation is known as the ‘near-far’ effect. Adaptive power control is compulsory in all MSs in order to compensate for ‘near-far’ interference effects. BTS power control is optional. However, if implemented, the BCCH carrier must still remain on constant power in order to enable neighbouring cell power measurements 12.3.2 POWER CONTROL TRIGGERS

Power Control TriggersPower Control Triggers• Decisions to increase or decrease power are triggered by:

• RXLEV - average measurements of up or downlink power• RXQUAL - average bit error rates

• Average measurements are implemented by requiring a number P of measurements out of a total N to be outside the thresholds before a power control command is triggered

• Limits on power control:

Increase power in steps of 2, 4 or 6 dB

Decrease power in steps of 2 or 4 dB

Mobile may only make one change in 60 ms

Every SACCH multiframe, the BSS shall compare each of the processed measurements with the relevant thresholds. The threshold comparison processes and the actions to be taken are as follows:

• Comparison of RXLEV_XX with L_RXLEV_XX_P (XX = DL or UL)

The algorithm is applied to the averaged RXLEV values. The comparison process is defined by the parameters P1 and N1 as follows:

- Increase XX_TXPWR if at least P1 averages out of N1 averages are lower than L_RXLEV_XX_P. (e.g. P1 = 10 and N1 = 12)

12. Power Control


• Comparison of RXLEV_XX with U_RXLEV_XX_P (XX = DL or UL)

The algorithm is applied to the averaged RXLEV values. The comparison process is defined by the parameters P2 and N2 as follows:

- Decrease XX_TXPWR if at least P2 averages out of N2 averages are greater than U_RXLEV_XX_P. (e.g. P2 = 19 and N2 = 20)

• Comparison of RXQUAL_XX with L_RXQUAL_XX_P (XX = DL or UL)

The algorithm is applied to the averaged RXQUAL values. The comparison process is defined by the parameters P3 and N3 as follows:

- Increase XX_TXPWR if at least P3 averaged values out of N3 averaged values are greater (worse quality) than L_RXQUAL_XX_P. (e.g. P3 = 5 and N3 = 7)

• Comparison of RXQUAL_XX with U_RXQUAL_XX_P (XX = DL or UL)

The algorithm is applied to the averaged RXQUAL values. The comparison process is defined by the parameters P4 and N4 as follows:

- Decrease XX_TXPWR if at least P4 averaged values out of N4 averaged values are lower (better quality) than U_RXQUAL_XX_P. (e.g. P4 = 15, N4 = 18)

Adaptive Power Control Trigger LevelsAdaptive Power Control Trigger Levels

RXQUAL

RXLEV63

7

0

U_RXLEV_XX_P

L_RXLEV_XX_P

‘dead band’Power decrease

(good level)

Power decrease(good quality)

Power Increase(bad quality)

Power increase(bad level)

L_RXQUAL_XX_P

U_RXQUAL_XX_P

12. Power Control



12.3.1 GSM/DCS MS POWER CONTROL PROCESS

Adaptive Power Control ProcessAdaptive Power Control Process

• Compulsory in MS, optional in BTS

• 32 power levels separated by 2dBm

• Power changes are commanded using:

• Reduction: POW_RED_STEP_SIZE (2, 4 dB steps)

• Increase: POW_INC_STEP_SIZE (2, 4, 6 dB steps)

• Commands issued on SACCH

• One 2dB step change every 60mS

GSM/DCS MS power output is controlled in levels, each level is separated by 2dBm as shown in the table below. However, individual adjustments can be made in 2,4 or 6dB steps. 6dB adjustments are only possible with power increases. The levels are shown in the table below:

Adaptive Power Control LevelsAdaptive Power Control Levels

015-28

214519-31

413718

612917

8111116

10101315

1291514

1481713

1671912

1862111

2052310

224259

243278

262297

281316

300335

3231354

3430373

3629390-2

NominalO/P Power (dBm)

Power Control Level

NominalO/P Power (dBm)

Power Control Level

DCS 1800GSM 900

12. Power Control


When first accessing a cell on the RACH and before receiving the first power command an MS adopts the power level defined by the M_TXPWR_MAX_CCH parameter broadcast on the BCCH of the cell. The MS then periodically measures the received power level (RXLEV) and reports this back to the BTS in the form of a measurement report which is forwarded to the BSC. It also monitors the RxLev on adjacent cells but only the BCCH carriers of these cells. The BTS commands the power level changes at the MS using the SACCH

____________________________________________________________________ 12.4 Discontinuous Transmission (DTX)

Discontinuous Transmission (DTX)Discontinuous Transmission (DTX)

• In a conversation, a person generally only speaks for about 30% to 40% of the time

• DTX makes use of this by reducing transmission when no voice signal is detected

• Uses a Voice Activity Detection (VAD) unit • Advantages:

• Reduces interference• Prolongs battery life of mobile

When a call is established, the MS remains in transmit mode for the duration of the call. However, in speech mode, it has been shown that information (encoded speech) is actually being transmitted for less than half the time. DTX is a technique that reduces emissions from the MS by only transmitting when information is to be sent. DTX is achieved by the use of a voice activation device (VAD) incorporated into the MS handset. The VAD detects speech and initiates transmission at normal speech-encoded data rates (13kbps). When no speech is detected, the data rate is reduced to approximately 500bps which is sufficient to provide comfort noise to the distant end but also significantly reduces the power output requirements.

12. Power Control



Silence Descriptor (SID) Silence Descriptor (SID)

• Silence Description Frames (SID) are sent at the end of a speech frame -prevents sudden cut off of sound

• SID frames also sent periodically during periods of silence

• Receiver produces ‘comfort noise’ for the listener

• If speech frames are lost, they can be extrapolated from previous frame to fill the gap

Voice activity SID frames Signal transmitted by mobile

Speech Processing for DTXSpeech Processing for DTX

• DTX processing functions in the mobile:

PCM voice signal

13 bit resolution

8000 samples / s

Voice Activity Detection

Speech Coder

SID Frame Generator

VAD

Voice Frame

SID Frame

DTX

Tra

nsm

issi

on

Bad Frame Replacement

BFI

Voice Frame

SID Frame

Voice Decoder

Comfort Noise Synthesiser

PCM voice signal

13 bit resolution

8000 samples / s

Transmitter Receiver

12. Power Control


____________________________________________________________________ 12.5 Discontinuous Reception (DRX)

12.5.1 DRX OUTLINE OPERATION DRX is a technique that allows the MS to power down significant amounts of its internal circuitry for a high percentage of the time when it is in the idle mode. This mode is dependant upon the MS being aware of exactly which paging block(s) will contain any valid paging DRX works by dividing the MSs within a cell into a set of groups. The group in which an MS resides is then known locally at both the MS and the BSS. All paging requests to each group are then scheduled and sent at a particular time which is derived from the TDMA frame number in conjunction with the IMSI(TMSI) of the MS and some BCCH transmitted data. Thus both the BSS and the MS know when relevant page requests will be sent and the MS can power down for the period when it knows that page requests will not occur.

Discontinuous Reception (DRX)Discontinuous Reception (DRX)

• Allows MS to power down parts of its circuitry in idle mode

• MSs within a Location Area divided into paging groups • MS only listens paging requests within its own group• Increases battery life of MS

12.5.2 MSC DRX OPERATIONS Apart from defining the Location Area to be paged, the DRX functionality is transparent to the MSC as it has no visibility of the TDMA frame numbers allocated over the air interface.

12. Power Control



12.5.3 BSS DRX OPERATIONS The BSS completely controls the scheduling of the paging requests. It does this by analysing the IMSI(TMSI) of the paging message received from the MSC in order to derive the relevant paging group identity.

Discontinuous Reception (DRX)Discontinuous Reception (DRX)• DRX is a network option to reduce mobile battery drain• The mobile is allowed to ‘sleep’ in idle mode and only listen periodically for paging

messages (PCH) and to monitor BCCH• The periods during which the mobile must be active depends on:

• CCCH configuration - set by the CCCH_CONF parameter• Reservation of CCCH blocks for AGCH (BS_AF_BLKS_RES)• Paging group allocated to mobile (BS_PA_MFRMS)

Paging group example: A mobile need only listen for PCH once every 2 multiframes

S BCCHFCCCH

A SCCCH

BFCCCH

C SCCCH

DF

CCCHE

SCCCH

FF

CCCHG S

CCCHH

FCCCH

II

S BCCHFCCCH

JS

CCCHK

FCCCH

L SCCCH

MF

CCCHN

SCCCH

OF

CCCHP

SCCCH

QF

CCCHR

I

S BCCHFCCCH

AS

CCCHB

FCCCH

C SCCCH

DFCCCH

E SCCCH

FFCCCH

G SCCCH

HF

CCCHI

I

The paging request received by the BBS from the MSC defines the cells to be paged. The BSS analyses

12. Power Control


____________________________________________________________________ 12.6 Summary of Key Power Control Parameters

Power Control ParametersPower Control Parameters

• Network Access Power Control:• Maximum initial TX power an MS is allowed to use for BCCH access• Maximum Power allowable in serving cell• Minimum Power an MS can receive to access the network • If DTX is enabled on UL/DL

• Dynamic Power Control:• If MS/BTS power control is enabled• Max/min MS BTS power level• Upper RXLEV/RXQUAL threshold for UL/DL power decrease• Lower RXLEV/RXQUAL threshold for UL/DL power increase• Step sizes for increasing/decreasing power

12.6.1 NETWORK ACCESS POWER CONTROL PARAMETERS

Network Access Power Network Access Power Control ParametersControl Parameters

• MS Transmit Power Maximum on Control ChannelMS_TXPWR_MAX_CCH (range 0-31)

• Mobile Station Transmit Power MaximumMS_TXPWR_MAX (range 0-31)

• Receive Level Access MinimumRXLEV_ACCESS_MIN (range 0-63)

• Discontinuous Transmission UsedDTX_USED (range 0/1)

12. Power Control



MS_TXPWR_MAX_CCH (range 0-31) Mobile Station Transmit Power Maximum on Control Channel. This parameter defines the maximum allowable MS power when accessing a cell’s control channel. MS_TXPWR_MAX (range 0-31) Mobile Station Transmit Power Maximum. This parameter defines the maximum allowable MS power within the serving cell. RXLEV_ACCESS_MIN (range 0-63) Receive Level Access Minimum. This parameter defines the minimum power level at the MS in order to allow access to the network. DTX_USED (range 0/1) Discontinuous Transmission Used. This parameter indicates if DTX (1) or not (0) is enabled in the cell. 12.6.2 DYNAMIC POWER CONTROL PARAMETERS

Dynamic Power Control ParametersDynamic Power Control Parameters• MS Power Control

MS_PWR_CTRL (range 0-1)

• Base Station Transmit Power MaximumBTS_TXPWR_MAX (range 0-31)BTS_TXPWR_MIN (range 0-31)

• RXLEV ThresholdsU/L_RXLEV_FULL_SERVING_CELL_UL/DL (0-63)U/L_RXLEV_SUB_SERVING_CELL_UL/DL (0-63)RXLEV_NCELL_(1-6) (0-63)

• RXQUAL ThresholdsU/L_RXQUAL_FULL_SERVING_CELL_UL/DL (0-63)U/L_RXQUAL_SUB_SERVING_CELL_UL/DL (0-63)

• Power Step SizesPOW_RED_STEP_SIZE (2,4,6 dB)POW_INC_STEP_SIZE (2,4 dB)

MS_PWR_CTRL (range 0-1) Mobile Station Power Control. This parameter enables (1) or disables power control at the MS. BTS_TXPWR_MAX/MIN (range 0-31) Mobile Station Transmit Power Maximum/Minimum. These two parameters define the maximum/minimum MS power output.

12. Power Control


RXLEV_FULL/SUB_SERVING CELL_UL/DL (range 0-63) Receive Lev el Full/Sub in the Serving Cell on the Uplink/Downlink. These parameters stores the averaged RXLEV values of the Full (without DTX) and Sub (with DTX) signal levels on the uplink (measured at the BTS) and downlink (measured at the MS). RXLEV_NCELL_(1-6) (range: 0-63) Receive Signal Level Neighbouring Cell. This parameter stores the averaged RXLEV value of one of the six best neighbouring cells (1-6). RXQUAL_FULL/SUB_SERVING CELL_UL/DL (range 0-7) Receive Level Access Minimum. This parameter defines the minimum power level at the MS in order to allow access to the network. POW_RED_STEP_SIZE (range: 2,4,6) Power Reduction Step Size. This parameter determines the size of the power reduction step. POW_INC_STEP_SIZE (range: 2,4) Power Increase Step Size. This parameter determines the size of the power increase step. 12.6.3 DISCONTINUOUS RECEPTION (DRX) CONTROL PARAMETERS

DRX Control ParametersDRX Control Parameters

• The periods during which the mobile must be active depends on:

• Maximum DRX time period• DRX_TIMER_MAX (3-bit, 000-111)

• Non-DRX time period• NON_DRX_TIMER (3-bit, 000-111)

• CCCH configuration• CCCH_CONF (00-11)

• Reservation of CCCH blocks for AGCH• BS_AF_BLKS_RES (0-6)

• Frames between presence of allocated paging group • BS_PA_MFRMS

DRX_TIMER_MAX (range: 0-7) This parameter defines the maximum value of the DRX timer in seconds as a 3-bit code. The parameter value is given as 2 to the power of the binary value minus one (2 (bv - 1) ) in units of 1 second. The binary value zero indicates the parameter value zero (i.e, the parameter takes the values: 0, 1 s, 2 s, 4 s, .. 64 s.)

12. Power Control



NON_DRX_TIMER (range: 0-7) When a paging message is received DRX is deactivated. After the paging procedure is completed, this parameter defines the time before the MS returns to DRX mode. The parameter value is given as 2 to the power of the binary value minus one (2 (bv - 1) ) in units of 1 second. The binary value zero indicates the parameter value zero (i.e, the parameter takes the values: 0, 1 s, 2 s, 4 s, .. 64 s.) CCCH_CONF (range bin 00-11) Indicates the allocation of CCCH blocks on the BCCH carrier (see Cell Parameters – Channel Configuration for more details). The number of available CCCH blocks will affect the time the DRX-enabled MS remains in sleep mode. BS_AF_BLKS_RES (range 0-6) Indicates the number of CCCH blocks on the BCCH carrier reserved for AGCH (see Cell Parameters – Channel Configuration for more details). The number of CCCH blocks reserved for AGCH reduces the number of blocks available for paging and will therefore affect the time the DRX-enabled MS remains in sleep mode. BS_PA_FRAMES Indicates the number of Control channel multiframes a DRX-enabled MS must wait between waking to listen for paging requests. The shorter this period, the less time the MS remains in sleep mode but the quicker it will respond to paging requests. Simiarly, the larger this period, the longer the MS will remain in sleep mode but the longer it will take to rerspond to paging request.



• Reasons for power control• Power control functions• GSM power classes and sensitivity levels• Adaptive power control• DTX and DRX• Key power control parameters

12. Power Control



Exercise 12.1

The following parameter values have been set:

L_RXQUAL_FULL_SERVING_CELL_UL = 5 U_RXQUAL__FULL_SERVING_CELL_UL = 3 POW_INCR_STEP_SIZE = 4 dB, POW_RED_STEP_SIZE = 2 dB The downlink power control is disabled Interference in the network has caused the averaged RXQUAL at the MS to rise to 5 1. What power control processes are likely to occur because of this change? 2. If the change in power output causes RXQUAL to fall to 3 what will be the resulting effect?

12. Power Control






13. Adaptive Frame Alignment ____________________________________________________________________ 13.1 Introduction

Adaptive Frame Alignment describes the method by which the GSM network compensates for differing propagation delays between mobile terminals at different distances from the BTS within the same cell. The method used to achieve this is by commanding a mobile terminal to begin transmission of a TDMA frame in advance of its normal transmission time. The advancing of this transmission increases with increasing distance from the BTS. The actual duration of this timing advance is derived from the Timing Advance (TA) issues periodically to each Mobile terminal in the cell. This section of the course describes this process and highlights the key parameters that control it.




____________________________________________________________________ 13.2 Timing Advance Procedures

Timing Advance ConceptTiming Advance Concept

• Signal from MS1 takes longer to arrive at BTS than that from MS2• Timeslots overlap - collision

1 2 3

MS1 - Timeslot 1

1 2 3

MS2 - Timeslot 2

1 2 3

1 2 3

time

• Timing Advance signal causes mobiles further from base station to transmit earlier - this compensates for extra propagation delay

time

time

1 2 3

MS1 - Timeslot 1

1 2 3

MS2 - Timeslot 2

1 2 3

1 2 3

time

time

time

Timing Advance

Timing Advance is needed to compensate for different time delays in the transmission of radio signals from different mobiles. The maximum value of Timing Advance sets a limit on the size of the cell. The TA value to use is found initially from the position of the received RACH burst in the guard period and is adjusted during the call in response to subsequent normal burst positions.

Timing Advance Timing Advance –– Access BurstAccess Burst

• Timing Advance is calculated from delay of data bits in the access burst received by the base station - long guard period allows space for this delay

Access burst data

delay

Guard PeriodAccess burst data

• TA signal is transmitted on SACCH as a number between 0 and 63 in units of bit periods

• TA value allows for ‘round trip’ from MS to BTS and back to MS• Each step in TA value corresponds to a MS to BTS distance of 550 metres• Maximum MS to BTS distance allowed by TA is 35 km



Timing Advance Timing Advance –– Tx / Rx DelayTx / Rx Delay

• Timing Advance value reduces the 3 timeslot offset between downlink and uplink

0 1 2 3 4 5 6 7

Delay 3 timeslots

Downlink

Uplink

TimingAdvance

Actual delay

Uplink

• The Timing Advance technique is known as adaptive frame alignment

0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7

____________________________________________________________________ 13.3 Extended Cell Range

Extending Coverage of CellsExtending Coverage of Cells

• Extending the range of a cell means overcoming two problems:• Relative timing of bursts due to path delay (Timing Advance)• Obtaining radio coverage at the extra distance

Extended range to provide coverage to offshore installations




Extended Range CellsExtended Range Cells

• The coverage limit of a cell is set by the Timing Advance maximum of 63, corresponding to a radius of 35 km

• Beyond this range, the bursts would arrive at the BTS in the next timeslot

• The limit can be extended by keeping every other timeslot free so that bursts from beyond 35 km can arrive without overlapping another transmission

• Capacity is half that of a normal cell• Coverage will also depend on having a suitable

power budget

0 1 2 3 4 5 6 7

Burst from within 35 km

Burst from beyond 35 km

Burst from about 120 km

Limit of extended range cell is about 120 km

User allocated to TS 2

____________________________________________________________________ 13.4 Key Adaptive Frame Alignment Parameters

Key Adaptive Frame Alignment ParametersKey Adaptive Frame Alignment Parameters

• Maximum cell distance• HOTMSRM (range 0-35km – default 35)

• Maximum TA value for a cell• TALIM (range 0-63 or 0-219 ext - default 63)

• Maximum extended cell distance• HOTMSRME (range 35-100km – default 100)

• If Channel is to be used in extended mode• EXTMODE (range F/ T – default F)

• Maximum TA value for a single timeslot• HOTRTGA (range 0-35)

• Maximum TA value before MS is considered lost• MAXTA (range 0-63 or 0-219 ext - default 63)



Key Timing Advance ParametersKey Timing Advance Parameters

• Maximum cell distance• HOTMSRM (range 0-35km – default 35)

• Maximum TA value for a cell• TALIM (range 0-63 or 0-219 ext - default 63)

• Maximum extended cell distance• HOTMSRME (range 35-100km – default 100)

• If Channel is to be used in extended mode• EXTMODE (range F/ T – default F)

• Maximum TA value for a single timeslot• HOTRTGA (range 0-35)

• Maximum TA value before MS is considered lost• MAXTA (range 0-63 or 0-219 ext - default 63)




Section 13 Section 13 -- SummarySummary• In this section the following topics have been

covered:

• The purpose of adaptive frame alignment

• The use of Timing Advance (TA) values

• The concept of extended range cells

• Key Adaptive Frame Alignment parameters



14. Handover Requirements ____________________________________________________________________ 14.1 Introduction

In the context of GSM, a handover is the process of moving an existing communications channel (either TCH or SDCCH) from one air interface physical channel to another. Channel. The new channel may be in the same cell or a different cell. This section of the course discuses the different types and causes of handovers and the key parameters that control the handover functions.




____________________________________________________________________ 14.2 Handover Procedures

14.2.1 HANDOVER PROCESSES In a cellular network, radio frequencies (channels) are not permanently allocated for the duration of a call. If a subscriber is mobile during the call, he may move into the coverage area of a different cell. This will require the call to be re-routed to the new cell. It may also be necessary, for traffic management purposes, to switch the call to a different channel in the same cell. This process is known as ‘Handover’ (or ‘Handoff’ in North America). The processes involved in handing over form one of basic functions of RR management.

Handover ProcessesHandover Processes

There are four different processes for handing over within a GSM system, each requiring differing procedures:

• Intra-Cell HO

• Inter-cell, Intra-BSS HO

• Inter-BSS, Intra-MSC HO

• Inter-MSC HO

GSM handovers are all ‘hard’ – i.e. mobile only communicates with one cell at a time during the process

Internal

External

BSC

MSC

VLR

BSC

MSC

VLR

BSC

Handovers within a BSC are known as ‘internal’ handovers as they involve only one Base Station Controller (BSC). To conserve signalling capacity, these handovers are managed by the BSC without involving the MSC, except to notify the MSC on completion of the handover. Handovers between BSCs (either intra- or inter-MSC) are known as ‘external’ handovers and are handled by the MSCs involved. An important aspect of GSM is that the original (or anchor) MSC, remains responsible for most call-related functions, with the exception of subsequent inter-BSC handovers under the control of the new (or relay) MSC.



Hence, there are four different types of handover in the GSM system, which involve transferring a call between:

• Between channels (time slots) in the same cell • Between cells under the control of the same BSC • Between cells under the control of different BSCs, but with a single MSC service

area • Between cells within different MSC service areas.

Handovers are generally initiated automatically as a result of exceeding certain threshold parameter values or manually (‘forced’) by command from the network (e.g. for traffic load balancing) the network can force an MS to handover.

14.2.2 HANDOVER TYPES

Handover TypesHandover Types• Handovers can be initiated by either MS or MSC• Handover decisions are based on the following parameters (in priority

order):• UL/DL Signal Quality• UL/DL Signal Level• Interference• Power Budget• Distance of MS from BTS

• Can be up- or down-link specific• Each parameter has operator-defined threshold parameters• Handover decisions can be based on one or a combination of these

parameters

There are a number of reasons for initiating handovers within the GSM network. These are known as handover ‘types’. A handover is initiated when a parameter threshold is exceeded for a specific handover type. 14.2.2.1 Handovers due to Signal Quality The MS continuously measures the signal quality on the downlink. The BTS continuously measures the signal quality on the uplink. If the signal quality in either direction falls below the operator-defined threshold, dynamic power control is used to correct the situation. If applying dynamic power control has increased the power to maximum and not resolved the problem, a handover to a new cell is initiated.




14.2.2.2 Handovers due to Signal Strength The MS continuously measures the signal strength on the downlink. The BTS continuously measures the signal strength on the uplink. If the signal strength in either direction falls below the operator-defined threshold, dynamic power control is used to correct the situation. If applying dynamic power control has increased the power to maximum and not resolved the problem, a handover to a new cell is initiated. 14.2.2.3 Handovers due to Interference The MS continuously measures the signal quality on the downlink. The BTS continuously measures the signal quality on the uplink. If the signal quality in either direction falls below the operator-defined threshold for both quality and interference a handover to a new cell is initiated.

14.2.2.4 Handovers due to Power Budget The power budget handover procedure ensures that the MS is always handed over to the cell with the minimum path loss, even though quality and level thresholds may have been exceeded. 14.2.2.5 Handovers due to Distance Each cell will set a parameter identifying the maximum Timing Advance (TA) value that can be allocated to an MS operating within that cell. The BTS will constantly update the TA value for each MS as the distance between each MS and the BTS changes. If the BTS needs to allocate a TA value to an MS which exceeds the cell maximum, a handover due to distance is initiated.

14.2.3 HANDOVER PROCESS

Measure serving and neighbouring cells’ performance

Compare measurements with enabled thresholds

Initiate handover procedure

Determine best candidate neighbouring cell

Select cell and perform handover

Handover Handover ProcessProcess



Regardless of the handover type, the same process is involved in the handover initiation: Whilst in dedicated mode (call in progress), the MS continually monitors the received signal quality (BER) and signal strength (dBm) of the allocated traffic channel on the serving BTS. It also monitors the signal strength of all neighbouring cells. It reports this information to the serving BSC, via the BTS, (traffic channel plus 6 best neighbouring cells) on a periodic basis.

Handover Handover InitiationInitiationHandover decisions are made by the network based on measurements by the mobile and the BTS:

Downlink:Mobile reports

current RXLEV and RXQUAL; RXLEV for neighbour cells

Uplink:BTS measures current RXLEV and RXQUAL; distance; interference in

unoccupied timeslots

Measurement pre-processing

Handover Decision Algorithm

MSC destination selection algorithm Required if handover involves a change of BSC

Threshold Analysis

MSC

BSC

BTS

14.2.4 HANDOVER PROCESS

Handover PrioritiesHandover Priorities• Handover algorithm prioritises the reasons for making a handover:

RXQUAL

RXLEV

Distance

Power Budget

High priority

Low priority

• Threshold parameters are defined by the operator• Handover may be triggered when a certain fraction of measurements are

outside the threshold limits

Only when Tx Power is max




The measurement results are passed to the BTS where pre-processing of the results takes place. The BTS then passes the results of this pre-processing to the BSC. Both the BSC and the MS compare the measurement taken with the threshold values set in their respective databases. If one or more of the thresholds has been exceeded, the handover procedure is initiated. The BSC identifies which of the neighbouring cells is the best candidate for handover, taking into account the neighbouring cell’s signal strength, assigned priority and traffic loading. The algorithm for when a handover decision should be taken is not specified in the GSM recommendations. There are two basic algorithms used, both closely tied in with power control. This is because the BSC usually does not know whether the poor signal quality is due to multipath fading or to the mobile having moved to another cell. This is especially true in small urban cells.

14.2.5 HANDOVER MARGIN

Handover MarginHandover Margin

Nom

inal

cel

l bou

ndar

y

BTS 1 BTS 2

Handover to BTS 2Handover to BTS 1

Mobile remains with BTS 1 or BTS 2

Hysteresis due to handover margin



Handover Procedure Handover Procedure –– Signalling ExampleSignalling ExampleSignalling for a basic Inter-BSC handover involving only one MSC (Intra - MSC):

MS MSCBSS 1 BSS 2Measurement report

Measurement report

Measurement report

Measurement report

Handover Required

Handover Request

Handover Command

Acknowledgement

Handover Command

Handover AccessHandover Detection

Physical Information

Handover CompleteHandover Complete

Clear Command

Clear Complete

Measurement report

Measurement report

____________________________________________________________________ 14.3 Key Handover Parameters

14.3.1 SIGNAL QUALITY HANDOVERS

Handover due to Signal QualityHandover due to Signal Quality

HO margin for HO due to quality -24…24dBhoMarginQual(n)

Min permissible Rx power level for cell n-110…-47dBmrxLevMinCell(n)

Max allowable transmit power for cell n0…36dBmmsTxPwrMax(n)

Threshold for initiating UL Quality HO0…7hoThresholdsQualUL

Threshold for initiating DL Quality HO0…7hoThresholdsQualUL/DL

Average measured DL RXQUAL value0…7AV_RXQUAL_DL_HO

Average measured UL RXQUAL value0…7AV_RXQUAL_UL_HO

RemarksRangeParameter

Handover Equation:

AV_RXQUAL_DL_HO < hoThresholdsQualDLAV_RXQUAL_UL_HO < hoThresholdsQualUL




14.3.2 SIGNAL STRENGTH HANDOVERS

Handover due to Signal StrengthHandover due to Signal Strength

Handover Equation:

AV_RXLEV_NCELL(n) > rxLevMinCell(n) + Max(0,A)

Where: A = msTxPwrMax(n) - PP is dependant upon MS Classmark

Min permissible Rx power level for cell n-110…-47dBmrxLevMinCell(n)

Max allowable transmit power for cell n0…36dBmmsTxPwrMax(n)

Threshold for UL/DL Handover trigger -110…-47dBmhoThresholdLevUL/DL

Average DL RXLEV for neighbour cell n -110…-47dBmAV_RXLEV_NCELL(n)

Average DL RXLEV value-110…-47dBmAV_RXLEV_DL_HO

Average UL RXLEV value-110…-47dBmAV_RXLEV_UL_HO


14.3.3 DISTANCE HANDOVERS Distance handovers are initiated as a result of a inability to compensate for propagation delays by timing advance (TA) techniques. Hence, if the maximum TA value of 63 has been assigned to a mobile and this fails to provide sufficient propagation delay compensation, a handover procedure will be initiated.

Handover due to DistanceHandover due to Distance

Enables HO through Distance Y / NenableMsDistanceProcessEquates to TA value0…63MsDistanceHoThresholdParamBSC process typesee belowmsDistanceBehaviourRemarksRangeParameter

- No release only forced handover attempt255- Release after time (1-60) secs. Try handover during that time1-60- Release immediately0

msDistanceBehaviour value:



14.3.4 POWER BUDGET HANDOVERS

Handover due to Power BudgetHandover due to Power Budget

Max allowable MS Tx power0…36dBmmsTxPwrMax

Min allowable MS Rx power-110…-47dBmrxLevMinCell

Handover power margin for cell n-24…63dBmhoMarginPBGT(n)

Period between adjacent cell measurements0-63HoPeriodPBGT

Enables power budget handoversY / NEnablePowerBudgetHO


Handover Equation:

PBGT > hoMarginPBGT(n)

Where: PBGT = (msTxPwrMax – msTxPwrMaxCell(n))- (AV_RXLEV_DL_HO - AV_RXLEV_NCELL_(n))- (BsTxPwrMax – BS_TXPWR)

14.3.5 INTERFERENCE HANDOVERS

Handover due to InterferenceHandover due to Interference

Handover Equation (downlink):

AV_RXLEV_DL_HO >= HoThresholdInterferenceDLandAV_RXQUAL_DL_HO >= HoThresholdQualDL

Sets inter/intra HP preferenceINTER/INTRAhoPreferenceOrderInterfUL/DLAllows Interference HOY / NenableIntraHoInterfUL/DLInterference HO Threshold-110…-47dBmhoThresholdInterferenceUL/DL


(replace DL with UL for UL equivalent equation)




Handover Equation:

AV_RXLEV_DL_HO >= HoThresholdInterferenceDL and AV_RXQUAL_DL_HO >= HoThresholdQualDL AV_RXLEV_UL_HO >= HoThresholdInterferenceUL and AV_RXQUAL_UL_HO >= HoThresholdQualUL

Typical Handover RXLEV ThresholdsTypical Handover RXLEV Thresholds

• Outdoor (-92 dBm)

• Good In-building (-70 dBm)

• Average in-building (-78 dBm)

• Good in-car (-85 dBm)

• Marginal in-car (-88dBm)

Section Section 1414 -- SummarySummary• In this section the following topics have been covered:

• Handover Processes and types• Handover procedure and priorities• Handover margins and signalling• Key handover parameters for:

• Signal Quality• Signal Strength• Distance• Power Budget• Interference




Exercise 14.1 The table below shows parameter values relating to a mobile’s serving cell and a neighbouring cell, n. Find the value of RXLEV_NCELL (n) which would result in a handover to the neighbour cell due to power budget.

Network settings: Mobile maximum power (P) = 33 dBm

MS_TXPWR_MAX = 35 dBm

MS_TXPWR_MAX(n) = 35 dBm Measurements:

Serving cell max power = 40 dBm RXLEV_DL = -95 dBm

Serving cell actual power = 32 dBm RXLEV_NCELL (n) = ?

HO_MARGIN(n) = 3 dBm

14. Handov

134

er Requirements

GSM BSS Functions and Parameter Optimisation


Exercise 14.2

Network settings: Mobile maximum power (P) = 33 dBm

MS_TXPWR_MAX = 38 dBm

MS_TXPWR_MAX(n) = 38 dBm Measurements:

Serving cell max power = 45 dBm RXLEV_DL = -90 dBm

Serving cell actual power = 36 dBm RXLEV_NCELL (n) = -80 dBm

HO_MARGIN(n) = 4 dBm

1. Calculate PBGT(n) and state whether a handover may occur. 2. Assuming other factors remain unchanged, what value of RXLEV_NCELL(n) would result in a handover?

Neighbour cell n

Serving cell

Appendix A – Vendor BSS Parameter Table


Appendix A Vendor BSS Parameter Table

Siemens Nokia Ericsson

Function units range default Rec ETSI NOKIA ERICSSON SIEMENS ACCESS/CH CONFIGURATION

Time taken to sieze a channel after allocation 0.5secs 0-255 6 T3101 T3101 T3101 T3101

Time between physical layer failure detection and release procedure 0.5secs 0-255 24 T3109 T3109 T3109 T3109

Time between main signalling link disconnect and channel deactivate 0.5secs 0-255 1 T3111 T3111 T3111 T3111

Time delay between repeat channel requests secs 0-255 5 T3122 T3122 T3122 T3122

indicates GSM frequency band in use system frequencyBandinUse / BAND SYSID

maximum number of RACH retransmissions unit 1,2,4,7 1 maxNumberofRetransmission / RET MAXRET MAXRETR

Controls whether IMSI attach is activated in the cell F/T F IMSIAttachDetach IMSIATDT

Number of blocks reserved for AGCH in a 51-frame multiframe unit 0-7 0 2-3 BS_AG_BLKS_RES NumberOfBlocksForAccessGrant / AG AGBLK NBLKACGR

Defines if CBCH is being used Y/N N CBCH_USED smsCBUsed / CB CBCH

Number of channels containing CCH blocks BS_CC_CHANS

Configuration of CCCH blocks CCCH_CONF

Defines number of SDCCH decode failures preceding radio link failure RADIO_LINK_TIMEOUT

PAGING FUNCTIONALITY

Defines number of paging groups (or period of transmission) between paging requests)

CCCH multiframes 2-9 2 BS_PA_MFRMS noOfMultframesBetweenPaging / MFR MFRMS

Number of times a paging message is repeated in one LA unit 0-3 2 PAGREP1LA

Number of times a global paging message is repeated unit 0-1 0 PAGREPGLOB

Time between repeat of paging message within 1 LA if no response secs 2-10 4 noOfMultiframesBetweenPaging PAGTIMEREPT1LA

Time between repeat of global paging messages if no response secs 2-10 4 PAGTIMEREPGLOB

Identity of a CCCH block containing a specifc paging group CCCH_GROUP

Identity of a specific paging group PAGING_GROUP

LOCATION MANAGEMENT

Time interval between period location updates deci hr 0-255 10 40-50 T3212 timerPeriodicUpdateMS / PER T3212 T3212

Identity of Location Area unit 0 - 65535 LAC locationAreaId / LAC

© AIRCOM International 2002 A-1



Function units range default Rec ETSI NOKIA ERICSSON SIEMENS POWER CONTROL

Indicates if the MS has power control enabled F/T F powerCtrlEnabled / PENA DMPSTATE EMSPWRC

Indicates if the BTS has power control enabled F/T F PowerCtrlEnabled DBPSTATE EBSPWRC

Number of 2dB steps for reducing BTS power output 2dB Steps 0-6 6 PWRRED

Step size when increasing MS power output dB dB2,dB4,dB6 dB2 Pwr_Inc_Step_Size powIncrStepSize / INC PWRINCSS

Step size when reducing MS power output dB dB2,dB4 dB4 Pwr_Red_Step_Size powRedStepSize / RED PWRINCSS

Maximum Tx power used by an MS when accessing the BCCH of a cell unit 0-31 2 MS_TXPWR_MAX_CCH msTxPwrMacCCH / TXP CCHPWR MSTXPMAXCH

Maximum power an MS can use in the serving cell unit 0-15 2 MS_TXPWR_MAX MsTxPwrMax / PMAX MSTXPWR MSTXPMAX

Lower UL RXQUAL threshold for power increase unit 0-7 5 L_RXQUAL_UL_P pcLowerThresholdsQualUL LOWTQUAU

Upper UL RXQUAL threshold for power increase unit 0-7 5 U_RXQUAL_UL_P pcUpperThresholdsQualUL HIGHTQUAU

Lower DL RXQUAL threshold for power increase unit 0-7 5 L_RXQUAL_DL_P pcLowerThresholdsQualDL LOWTQUAD

Lower DL RXQUAL threshold for power increase unit 0-7 5 U_RXQUAL_DL_P pcUpperThresholdsQualDL HIGHTQUAD

Lower UL RXLEV threshold for power increase dBr 0-63 -103 to-73 L_RXLEV_UL_P pcLowerThresholdsLevUL LOWTLEV

Upper UL RXQUAL threshold for power increase dBr 0-63 U_RXLEV_UL_P pcUpperThresholdsLevUL HIGHTLEV

Upper UL RXLEV threshold for power decrease dBr 0-63 L_RXLEV_DL_P pcLowerThresholdsLevDL LOWTLEV

Upper DL RXLEV threshold for power decrease dBr 0-63 U_RXLEV_DL_P pcUpperThresholdsLevDL HIGHTLEV

Indicates if DTX is enabled in theUL inclusion of parameter DTX_USED dtxMode / DTX DTXU DTXUL

Indicates if Full-rate DTX is activated in the DL F/T F dtxMode / DTX DTXD DTXDLFR

Minimum MS power required to access system dBm -110 to -47 -105 RXLEV_ACCESS_MIN rxLevAccessMin / RXP ACCMIN RXLEVAMI

BTS BCCH power output dBm 0-63 none BSPWRB

BTS TCH power output dBm 0-63 none BSPWRT

Minimum power level setting at the BTS dBm -20 -to+50 -20 bsTxPwrMin / PMIN BSPWRMIN

Minimum power an MS is permitted to use on a TCH channel in a cell MS_TXPWR_MIN MsTxPwrMin

Maximum allowable BTS Transmit Power BS_TXPWR_MAX BsTxPwrMax / PMAX

RESELECTION

applies negative offset to C2 for duration of 'Penaltytme' 10dB 0-6 1 TEMPORARY_OFFSET temoraryOffset / TEO TO TEMPOFF

Duration for which C2 Penatly offset is applied 20s 0-30 0 PENALTY_TIME penaltyTime/ PT PT PENTIME

Applies an offset to the C2 parameter 2dB steps 0-63 1 CELL_RESELECT_OFFSET cellReselectOffset / REO CRO CRESOFF

Value of RXLEV hysteresis required for cell reselection 2dB steps 0-7 2 4 CELL_RESELECT_HYSTERESIS cellReselectHysteresis / HYS CRH CELLRESH

calculated RF signal level for each neighbouring cell RLA_C

A-2 © AIRCOM International 2002



Function units range default Rec ETSI NOKIA ERICSSON SIEMENS HANDOVER

Maximum number of repeats of physical information during handover unit 1-254 20 NOOFPHYSINFOMSG NY1

If HO due to bad UL/DL RXQUAL is enabled F/T F RXQUAL_HO_ENABLED RXQUALHO

If HO due to bad UL/DL RXLEV is enabled F/T F RXLEV_HO_ENABLED RXLEVHO

If HO due to distance is enabled F/T F DIST_HO_ENABLED enableMSDistanceProcess / EMS

Minimum Signal received by MS in Cell to accept handover dBr 0-63 20 RXLEV_MIN(n) rxLevMinCell / SL MSRXMIN RXLEVMIN

If HO due to power budget enabled F/T F PBGT_HO_ENABLED enablePowerBudgetHO / EPB PBGTHO

Defines UL RXQUAL threshold for intercell handover unit 0-7 6 hoThresholdQualUL HOLTHQUUL

Defines DL RXQUAL threshold for intercell handover unit 0-7 6 hoThresholdQualDL HOLTHQUDL

Defines UL RXLEV threshold for intercell handover dBr 0-63 5 hoThresholdLevUL HOLTHLVUL

Defines DL RXLEV threshold for intercell handover dBr 0-63 10 hoThresholdLevDL HOLTHLVDL

Defines TA averaging window size for HO decison 1 SACCH multiframe 1 -20 8 TAAVELEN HOAVDIST

Lower UL RXQUAL threshold for handover unit 0-7 5 L_RXQUAL_UL_H hoLowerThresholdsQualUL

Upper UL RXQUAL threshold for handover unit 0-7 5 U_RXQUAL_UL_H hoUpperThresholdsQualUL

Lower DL RXQUAL threshold for handover unit 0-7 5 L_RXQUAL_DL_H hoLowerThresholdsQualDL

Lower DL RXQUAL threshold for handover unit 0-7 5 U_RXQUAL_DL_H hoUpperThresholdsQualDL

Lower UL RXLEV threshold for handover dBr 0-63 L_RXLEV_UL_H hoLowerThresholdsLevUL

Upper UL RXQUAL threshold for handover dBr 0-63 U_RXLEV_UL_H hoUpperThresholdsLevUL

Upper UL RXLEV threshold for handover dBr 0-63 L_RXLEV_DL_H hoLowerThresholdsLevDL

Upper DL RXLEV threshold for handover dBr 0-63 U_RXLEV_DL_H hoUpperThresholdsLevDL

CELL/SITE SPECIFIC

Inidcates if SMSCB is in use T/F F SMSCBUSE

Indicates if the BSC has HSCSD enabled T/F F ENHSCSD

Indicates if the BTS has HSCSD enabled T/F F BTSHSCSD

Defines standard or extended cell STDCELL/ EXTCELL STDCELL CELLTYPE

Unique Cell identifier CI + LAI CGI CELLGID

Cell name string 37438 none CELL

Indicates if the cell bars an MS from camping-on T/F F CELL_BAR_ACCESS BAR CB CELLBARR

Uniquely identifies a carrier within a cell NCC+ BCC BSIC BSIC BSIC

Defines the ARFCN of the BCCH channel 0-1023 BCCHNO BCCHFREQ

Site Identity string 3-15 none RSITE

© AIRCOM International 2002 A-3


A-4 GSM BSS Functions and Parameter Optimisation


n units range default Rec ETSI NOKIA ERICSSON SIEMENS

Defines Combined/non-combined BCCH configuration text comb, combc ncomb ncomb BS_CCCH_SDCCH_COMB BCCH TYPE

FREQUENCY HOPPING

Number of the list of absolute frequencies used in hopping sequence unit 0-1023 none MA usedMobileAllocation / MAL MOBALLOC

Offset of trhe mobile allocation index in generating a SFH sequence unit 0-63 0 MAIO maioOffset / MO MAIO

Determines the hopping sequence unit 0-63 none HSN hoppingSequenceNumber / HSN HSN HSN

Specifies if SFH is enabled F/T F HOP HOPP

Specifies BB or Synth SFH BBHOP/ SYNHOP BBHOP HOP FHOP HOPMODE

FRAME ALIGNMENT

Specifiies the maximum allowed MS-BTS distance for the standard cell 1km 0-35 35 HOTMSRM

Specifiies the maximum allowed MS-BTS distance for the extended cell 1km 35-100 100 HOTMSRME

Defines maximum TA value in a single timeslot 1km 0-35 4 HOMRGTA

For extended cells, defines if the channel will be used in extended mode F/T F XRANGE EXTMODE

Maximum TA value in a specific cell unit 0-63 (0-219 Ext) 62 maxMSDistanceHOThreshold / MAX TALIM

Maximum TA value assigned before MS is considered lost unit 0-63 (0-219 Ext) 63 MAXTA

NEIGHBOUR RELATIONS

If BCCH Allocation used BA_USED

Related Cell Designation string 1-7 none CELLR CELLR

Defines if a neighbouring cell belongs to a different BSC string EXT, Omitted Omitted CTYPE CTYPE

Defines a one-way neighbour relationship string SGL, Omitted Omitted RELATION RELATION

Defines if a neighbour is co-located string YES/NO NO Cell Sitecolocation

Functio

Appendix B – Answers to Self-Assessment Exercises

GSM BSS Functions and Parameter Optimisation © AIRCOM International 2002 B-1

Appendix B Answers to Self-Assessment Questions SECTION 8 – CELL SELECTION/RESELECTION Exercise 8.1

C1(n) = [RXLEV(n) – RXLEV_ACCESS_MIN – max(0, (MS_TXPWR_MAX_CCH – P))] A Class 4 GSM900 mobile has a maximum power output of 33dBm. Therefore, the value of P in the C1 calculation is 33. C1 = -85 – (-90) – max(0, 37 – 33) = 5 – max (0,4) = 5 – 4 = +1

Exercise 8.2

C1(n) = [RXLEV(n) – RXLEV_ACCESS_MIN – max(0, (MS_TXPWR_MAX_CCH – P))] A Class 4 GSM900 mobile has a maximum power output of 33dBm. Therefore, the value of P in the C1 calculation is 33. C1(1) = -90 – (-95) – max(0 , 35-33) = 5 – 2 = 3 C1(2) = -93 – (-95) – max(0 , 35-33) = 2 – 2 = 0 Cell 1 has the highest positive C1 value so the MS will camp on to this cell.

Exercise 8.3

1. C1(macrocell) = -70 – (-90) – max(0, (35-33)) = 20 – 2 = 18 C1(microcell) = -80 – (-90) – max(0, (35-33)) = 10 – 2 = 8 The macrocell will be selected.


B-2 GSM BSS Functions and Parameter Optimisation


2. Set CELL_RESELECT_OFFSET as 12 dB for the microcell and 0dB for the macrocell. Then: C2 (macrocell) = 18 C2 (microcell) = 8 + 12 = 20 The mobile will re-select the microcell. 3. C2 (macrocell) should remain higher than C2 (microcell) for the first 60 seconds.

Use: TEMPORARY_OFFSET = 10 dB PENALTY_TIME = 60 seconds Then: C2 (microcell) = 20 – 10 x H(60 – T) While T ≤ 60 seconds, C2 (microcell) = 20 – 10 = 10 When T > 60 seconds, C2 (microcell) = 20 – 0 = 20 After 60 seconds, C2 will be higher in the microcell than the macrocell and the mobile will re-select to the microcell.



SECTION 9 - PAGING Exercise 9.1

(a) CCCH_CONF = 0 means TS0 is used in a non-combined multiframe, providing 9 CCCH blocks. 3 blocks reserved for AGCH, so 6 are available for PCH. Type 1 messages can page 2 mobiles per message. Paging capacity = 6 x 2 / 0.235 = 51 mobiles / second (b) CCCH_CONF = 1 means TS0 is used in a combined multiframe, providing 3 CCCH blocks. 1 block reserved for AGCH, so 2 available for PCH. Type 3 messages can page up to 4 mobiles per message. Paging capacity = 2 x 4 / 0.235 = 34 mobiles / second




SECTION 12 – POWER CONTROL

Exercise 12.1

The following parameter values have been set:

L_RXQUAL_FULL_SERVING_CELL_UL = 5 U_RXQUAL__FULL_SERVING_CELL_UL = 3 POW_INCR_STEP_SIZE = 4 dB, POW_RED_STEP_SIZE = 2 dB The downlink power control is disabled Interference in the network has caused the averaged RXQUAL at the MS to rise to 5 What power control processes are likely to occur because of this change?

1. The increase in RXQUAL will match the L_RXQUAL_FULL_SERVING_CELL_UL value of 5.

This will trigger a BTS command to the MS (on the SACCH) to increase the TX power by one step, i.e., 4dB (POW_INCR_STEP_SIZE = 4dB,)

2. The C/I value increases by 4 dB causing the RXQUAL to fall to 3.

This has now reached the upper threshold (U_RXQUAL__FULL_SERVING_CELL_UL = 3) and should trigger the BTS to command the MS to lower its TX power by one step, i.e., 2 dB (POW_RED_STEP_SIZE = 2 dB). Now RXQUAL falls to the “deadband” region between the two thresholds and no further power control commands are issued until another change in RXQUAL is detected.



SECTION 14 - HANDOVERS Exercise 14.1

PBGT(n) = [ min (35,33) – (-95) – (40 – 32)] – [ min(35, 33) – RXLEV_NCELL(n)] PBGT(n) = 33 +95 – 6 – 33 + RXLEV_NCELL(n) PBGT(n) = 89 + RXLEV_NCELL(n) For handover, PBGT(n) >0 AND PBGT(n) >HO_MARGIN i.e. 89 + RXLEV_NCELL(n) > 3 RXLEV_NCELL(n) > 3 – 89 RXLEV_NCELL(n) > - 86 dBm Handover will occur if the measured level RXLEV_NCELL(n) becomes –85 dBm or higher.

Exercise 14.2

1. PBGT(n) = [min(38, 33) – (-90) – (45-36)] - [min(38, 33) – (-80)] = [33 + 90 – 9] - [33 + 80] = 1 dB PBGT(n) > 0 but PBGT < HO_MARGIN Handover will not occur. 2. For a handover to occur, PBGT(n) must be at least 5 dB, i.e. an increase of 4 dB. RXLEV_NCELL(n) must therefore increase by 4 dB to (–80 + 4) = -76 dBm.




Appendix C – Glossary of Terms

GSM BSS Functions and Parameter Optimisation © AIRCOM International 2002 C-1

Appendix C - Glossary of Terms

ABBR MEANING 2G Second Generation 3G Third Generation 3GPP Third Generation Partnership Project 4G Fourth Generation APN Access Point Name ARQ Automatic Request for Retransmission ATM Asynchronous Transfer Mode AuC Authentication Centre BCCH Broadcast Control CHannel BCS Block Check Sequence BEC Backward Error Correction BG Border Gateway BH Block Header BLER BLock Error Rate BS Base Station BS Billing System BSC Base Station Controller BSN Block Sequence Number BSS Base Station Subsystem BSSGP BSS GPRS Protocol BTS Base Transceiver Station BVC BSSGP Virtual Circuit BVCI BSSGP Virtual Circuit Identifier CCCH Common Control CHannel CDMA Code Division Multiple Access CDR Charging Detail Record CG Charging Gateway CH CHannel ? C/I Carrier/Interference Ratio CNLS Connectionless CONS Connection-Oriented CRC Cyclic Redundancy Check CS Circuit Switched CS-x Coding Scheme-x {x = 1-4} CSD Circuit Switched Data DHCP Dynamic Host Control Protocol DNS Domain Name Server ECSD Enhanced Circuit Switched Data ED&C Error Detection and Correction EDGE Enhanced Data rate for GSM {Global} Evolution


C-2 GSM BSS Functions and Parameter Optimisation


ABBR MEANING EGPRS Enhanced General Packet Radio Service EIR Equipment Identity Register ETSI European Telecommunications Standards Institute FCS Frame Check Sequence FEC Forward Error Correction FH Frame Header FR Frame Relay GAA GPRS Application Alliance GGSN Gateway GPRS Support Node GMM GPRS Mobility Management GMSK Gaussian Minimum Shift Keying GPRS General Packet Radio Service GSM Global System for Mobile Communications GSN GPRS Support Node GTP GPRS Tunnelling Protocol GTP-U GPRS Tunnelling Protocol – Uplink HLR Home Location Register HPLMN Home PLMN HSCSD High Speed Circuit Switched Data HTML Hypertext Markup Language HTTP Hypertext Transfer Protocol IMEI International Mobile Equipment Identity IMSI International Mobile Subscriber Identity IP Internet Protocol ISDN Integrated Services Digital Network ISO International Standards Organisation ISP Internet Service Provider LA Location Area LAC Location Area Code LAI Location Area Identity LIG Legal Intercept Gateway LLC Local Link Control MAC Medium Access Control MAI Mobile Applications Initiative MAP Mobile Applications Part MCC Mobile Country Code MM Mobility Management MNC Mobile Network Code MS Mobile Station MSC Mobile Services Switching Centre MSIN Mobile Subscriber Identification Number MT Mobile Terminal NMS Network Management System N-PDU Network Packet Data Unit


GSM BSS Functions and Parameter Optimisation © AIRCOM International 2002 C-3

ABBR MEANING NSAPI Network Service Access Point Identifier NS-VC Network Services Virtual Services OMC Operations and Maintenance Centre OSI Open Systems Interconnection PACCH Packet Associated Control CHannel PAD Packet Assembler-Disassembler PAGCH Packet Access Grant CHannel PBCCH Packet Broadcast Control CHannel PCCCH Packet Common Control CHannel PCM Pulse Code Modulation PCU Packet Control Unit PDA Personal Data Assistant PDCH Packet Data CHannel PDN Packet Data Network PDP Packet Data Protocol PDTCH Packet Data Traffic CHannel PDTCH-D Packet Data Traffic CHannel – Downlink PDTCH-U Packet Data Traffic CHannel – Uplink PDU Packet Data Unit PH Packet Header PIM Packet Idle Mode PLMN Public Land Mobile Network PNCH Packet Notification Channel PPCH Packet Paging Channel PPM Packet Paging Message PRACH Packet Random Access Channel PS Packet Switched PSI Packet data specific System Information PSK Phase Shift Keying PSN Packet Switched Network PSPDN Packet Switched Public Data Network PSTN Packet Switched Telephone Network PTCCH Packet Timing Advance Control CHannel PTCCH-D Packet Timing Advance Control CHannel – Downlink PTCCH-U Packet Timing Advance Control CHannel – Uplink PTCH Packet Traffic CHannel PTM Packet Transfer Mode PTM Point to Multipoint PTM-G Point to Multipoint-Group PTM-M Point to Multipoint-Multicast P-TMSI Packet Temporary Mobile Subscriber Identity PTP Point To Point PVC Permanent Virtual Circuit QoS Quality of Service


C-4 GSM BSS Functions and Parameter Optimisation


ABBR MEANING RA Routing Area RAC Routing Area Code RAI Routing Area Identity RAND Random Number RBS Radio Block Structure RLC Radio Link Control RR Radio Resource SAP Service Access Point SAPI Service Access Point Identifier SDU Service Data Unit SGSN Serving GPRS Support Node SIM Subscriber Identity Module SM Session Management SMS Short Message Service SNDCP SubNetwork Dependent Convergence Protocol SNN SNDCP Network PDU Number SRES Signature Response SVC Switched Virtual Circuit TA Timing Advance TBF Temporary Block Flow TCP/IP Transmission Control Protocol/Internet Protocol TDMA Time Division Multiple Access TE Terminal Equipment TFI Temporary Flow Identity TFT Traffic Flow Template TI Transaction Identifier TID Tunnel IDentifier TLLI Temporary Logical Link Identifier TMSI Temporary Mobile Subscriber Identity TOS Type Of Service TRX Transmitter-Receiver TS Time Slot UDP User Datagram Protocol UMTS Universal Mobile Telecommunications System URL Universal Resource Locator USF Uplink State Flag VC Virtual Circuit VLR Visitor Location Register V-PLMN Visitor PLMN VPN Virtual Private Network WAP Wireless Access Protocol

Technology

Bss functions and paramaters