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© Childerley Solutions 2002 1

GSM Radio Network Optimisation v1.4Page 1© Telecom network Consultants Ltd 2002

GSM Radio Network GSM Radio Network OptimisationOptimisation

February 2006February 2006

Trainer:Trainer: Mr Neville Hawkins Mr Neville Hawkins



•• IntroductionIntroduction–– Definition Definition –– ObjectivesObjectives–– Types of optimisationTypes of optimisation–– Network expansionNetwork expansion–– Interfacing groupsInterfacing groups–– Optimisation strategyOptimisation strategy

•• System basicsSystem basics–– GSM air interface GSM air interface –– Measurements Measurements

•• BSS ParametersBSS Parameters–– Idle modeIdle mode–– Measurement filteringMeasurement filtering–– Power ControlPower Control–– Locating (Handover)Locating (Handover)

Contents

••Quality assessmentQuality assessment––Network performance Network performance measurementsmeasurements––Field measurementsField measurements

••Optimisation measuresOptimisation measures––Antenna adjustmentsAntenna adjustments––Frequency and interference planningFrequency and interference planning––Neighbour list planningNeighbour list planning––Common problems Common problems ––Advanced techniquesAdvanced techniques

••OrganisationOrganisation––TimetablesTimetables––TeamsTeams––PreparationPreparation––DatabasesDatabases––Implementation proceduresImplementation procedures



Contents

� Introduction• System Basics• BSS Parameters • Quality Assessment• Optimisation Measures• Organisation



Introduction

• Definition • Objectives• Types of optimisation• Network expansion• Interfacing groups• Optimisation strategy



Introduction

• Definition– “the process of fine tuning the radio network cost effectively, to improve the air interface performance to achieve the desired performance quality targets”

• Objectives– Minimise interference– Achieve specified GOS – Achieve other network quality targets

• Call success rate > 99%

Radio optimisation is an essential process of fine tuning the network in the most cost-effective manner in order to improve the air interface performance so that it meets the required network performance quality targets. Radio network optimisation is a process which is continuous throughout the lifetime of the network but can be subdivided into categories namely, initial (or pre-launch) and ongoing optimisation. The main objectives of optimisation are to minimise interference, achieve the required network quality target (GOS better than 1%), achieve high call success rate (99% or better), in a cost effective manner.The results of achieving this include increased revenue and maximum customer satisfaction.In order to achieve these objectives, it is necessary to define the key network performance metrics and the thresholds to be used in the analysis of the network statistics. Generally two thresholds are defined, the first is an optimisation threshold which enables worst performing cells to be identified for scheduled remedial work, while the second is a fault threshold which identifies cells with problems requiring immediate solution.



Introduction

• Types of optimisation

– Initial optimisation• A good radio network planning process may reduce level of optimisation at this stage

– Ongoing optimisation• Output from this stage should be fed back into the radio network planning process

– Augments/improves knowledge of radio network planners

– Improves the radio network planning

Initial Optimisation is carried out prior to and immediately following system launch and aims to maximise the ability of the network to deliver service at a predefined and acceptable level of network performance quality at commercial launch. It is also carried out immediately following the turn on of new cells for network expansion.

Ongoing Optimisation is a continuous program that aims to find and cure problems, and enhance the performance of the network during its operational lifetime.



Introduction

• Initial optimisation– Takes place prior to and immediately after network launch.

– Aims to maximise the ability of the network to deliver service at a predefined and acceptablelevel of network performance quality at commercial launch

– Also takes place after new cell additions

For a network roll-out, initial optimisation can sometimes be hampered by the fact that the network is under loaded. For example, capacity bottlenecks and increased capacity effects on interference can only be properly evaluated when the network is fully loaded. Therefore optimisation will continue after commercial launch, and further adjustments made as traffic grows. At the initial stage, there is a rapid improvement in network quality due to the fact that the network quality at that time is heavily influenced by simple problems (such as neighbour definitions) which are more easily solved. However, when the network is operational, the problems become more localised and are perhaps not as easy to solve. In addition, the introduction of major changes or features in the network may result in reduced quality, but rapid improvements should be realised following the resolution of such problems.When new cells are integrated into the live commercial network, initial optimisation is required to ensure that the parameter settings and handovers to neighbouring sites are correct and that no new problems are introduced. In this case, the network is loaded and therefore the optimisation is carried out in such a way as to minimise negative customer impact.



Introduction

• Ongoing optimisation

– Continuous program during operational life of network

– Find and cure problems

– Enhance network performance to meet performance quality targets

Ongoing optimisation takes place continuously on a network in order to improve quality performance with increased traffic loading, provide additional capacity (new channel additions or network-wide frequency re-tunes) and resolve specific problems which arise. Both these optimisation functions need a disciplined approach to network implementation, operation and quality and require well controlled and documented procedures.



Introduction

• Ongoing optimisation

– Network Expansion• Increasing the network capacity • Extending coverage to new areas

– Implemented in stages or at regular intervals• Addition of extra TRXs on existing cells• Addition of new sites

Expansion is an integral part of the operation of a mobile network. It is driven primarily by the actual growth of the subscriber base, which in turn is driven by the marketing strategy and the actual performance of the network as perceived by the user. It is essential to ensure that there is always enough capacity in the network to satisfy demand, and therefore, a strategy for network expansion planning is generally established at the early stages of the life of the network. The additional capacity must be introduced whilst maintaining and/or improving the quality of the network.

The growth of the radio network is therefore an ongoing process of refinements and adjustments based on a number of input parameters, most of which are not under the control of Radio Planning. They include: · The projected subscriber growth· The projected Usage in milli Erlangs (mE) per subscriber· Special Value-added-services· Special promotion plans· Types of subscriber equipment used· The projected number of mobile data users· Areas in the network requiring coverage improvements as identified by Marketing, Sales, Operations, Customer Care



Introduction

• Sources of information

– Network statistics• Daily/weekly – from tool such as Metrica

– Regular drive testing• Using test equipment (TEMS)

– Customer complaints• Via customer service

– Internal problem reports• Generated within the operating organisation

Network stats: is a very good source of information given that the amount of traffic in the network is high enough to provide reliable statistics. The frequency and level of detail of the report should also be set to ensure that there is sufficient information for the groups involved in the optimisation activities, and for management. Drive testing: while the traffic in the network is still in the early growing stages and not statistically reliable, it is useful to perform regular drive tests along standard defined routes. Calls of 2 minute duration should be made to generate data which can be analysed to obtain relevant stats. This practice should be continued throughout lifetime of network.Customer complaints: Although this is a good source of information, the details such as location and type of problem are sometimes imprecise. It is preferable not to have customer complaints because by the time the complaint is received, the problem has already caused inconvenience to a customer. It is better to find the problem before the customer does. Internal problem reports: staff in the organisation are encouraged to use the network and call to a service desk or answering machine (set up for the purpose) to lodge any faults they may find with the network (friendly customers!). All problems can then be forwarded to the optimisation team for investigation (after flitering by O&M).



Introduction

• Radio network optimisation– Network Expansion

Traffic

Quality

For a given quality target, a certain traffic level is achieved. As network traffic increases, the quality degrades as shown by the blue curve. To get the quality back to target,

Generally, network capacity can only be increased at regular intervals, not gradually. To provide additional capacity on existing sites as the number of subscribers to the service grows, extra radio channels have to be provided within each base station. When base stations have their full complement of channels, then existing cells have to be reduced in size by adding new sites. Coverage is provided to new areas by the integration of new sites. Therefore, site activation and frequency re-tunes are part of the ongoing system improvement, and all or parts of the network will need to be optimised after each site integration or frequency retune process. The network therefore requires ongoing optimisation



Introduction

• Interfacing groups

Operations Dept

NMC

Field Engineers

OMCCustomerServiceCenter

Sales &Marketing

Radio PlanningDept

‘Umbrella View’Statistics;Performance;Reporting

ProblemAreas &Cells

Statistics,Reports & ActualCoverage Maps

Network

Site Acceptance

Status &Clears

CustomerComplaints

CustomerComplaints

ChangeRequests

Fault Clears

NetworkStatus

New Plans

Suggestions/Requirements for Cell-selection and Acquisition

Production and update of Predicted Coverage Maps and Problem Areas

Quality Dept

OptimisationTeam

Trouble Reports Statistics, Reports

NPC

The figure above is an idea of the relationships between the various groups in relation to the Network and to the Customer-facing groups. It may be that Operations also have direct contact with the customers but in most cases this should not be necessary.



Introduction

• Optimisation strategyPhase1: Preparation

Project plan, databases,Team/interfaces, test equipment, performance targets/thresholds

Phase2: Cluster definitionDefine clusters, generate input data (site data, maps, plots, neighbour lists, BSS parameters )

Phase3: Initial optimisationBasic site checks, cluster verification, network tuning

Phase4: Ongoing optimisationMeasurements, data analysis, solution proposal, solution implementation, verification of solution

Phase5: Database maintenance

Update all databasesFeedback results

As required for any successful project, and in particular for network optimisation, good planning and preparation are essential requirements. The optimisation campaign may be sub divided into the following stages: Phase 1: Preparation: definition of project plan, creation of database s, definition of

project team and interfaces, provision of measurement equipment/tools, generation of performance targets/thresholds, creation of optimisation guidelinesPhase 2: Cluster definition: identification and definition of BS clusters for optimisation, generation and/or collation of input data for the cluster (site data, maps, plots, neighbour lists, BSS parameters) Phase 3: Initial optimisation: site validation (basic site checks), clu ster verification, network tuning Phase 4: Ongoing optimisation: diagnostic measurements (to include test data, metrica statistics, customer complaints), identification of problems and proposal of solutions, implementation of solutions, verification of improvement in network performancePhase 5: Database maintenance: update of optimisation and other plannin g databases.



Introduction -review

• Definition • Objectives• Types of optimisation• Network expansion• Interfacing groups• Optimisation strategy



Contents

• Introduction �System Basics• BSS Parameters • Quality Assessment• Optimisation Measures• Organisation



GSM basics

Mast & antennas

MSC

Point ofInterconnection

BaseTransceiverStation

BTS

Base StationController

BSC

VLR

HLR

AUC

Home Location Register

AuthenticationCentre

MobileSwitchingCentre

EIR Equipment IdentityRegister

OMC/NMC Operations & Maintenance Centre/Network Management Centre

POI

Mobile Station

MS

VisitorLocationRegister

BSS

OSS

NSS

GSM System Architecture

A GSM network is a Public Land Mobile cellular Network (PLMN). It uses a network of radio transmitters to transmit radio signals over the designated service area. The radio signals are digitally encoded. This allows more services and greater security than analogue systems. The Base Station Subsystem provides the distribution function of the network. The base transceiver stations provide the actual radio link with the mobiles used by the subscribers. The BSS has a standard interface so that it is possible to connect to different types of switching centresThe Network and Switching Subsystem is responsible for handling all the switching and routing functions. The MSC does the actual switching, whilst the HLR/VLR store the subscriber data. The AUC and the EIR provide security of access to the network.The Operations Sub System is the operating nerve centre that monitors the various BSS in the network, whilst the NMC is able to monitor the NSS as well as the BSSs.



GSM basics

• GSM Interfaces

TO PSTN

BSC

Um Radio

Interface

BSS

TRAUNSS

Abis

InterfaceA-InterfaceAter

InterfacePSTN

Interface

The various components in the PLMN are linked either via the air interface or terrestrial interfaces. The main interfaces are:1. Um: radio interface connects the mobile station to the BTSs.2. Abis interface provides communication between the BTS and BSC.3. Ater interface connects the BSC to the TRAU.4. A interface provides communication between the BSS and the NSS, in particular from the TRAU to the MSC.



Contents

• System Basics�GSM channels

�Spectrum allocation�Access scheme�Frame structures�Physical channel�Logical channels�Channel mapping (logical onto physical)

– Measurements



GSM Air interface

• GSM standards – 05.01: Physical layer on the radio path: general description

– 05.02: Multiplexing and multiple access on the radio path

– 05.03: Channel coding – 05.04: Modulation – 05.05: Radio transmission and reception – 05.08: Radio subsystem link control – 05.10: Radio subsystem synchronisation

The GSM standards are available from the Internet. If they were printed out they would use and enormous a mount of paper. Many are to do with fixed networking and with detailed protocols. The ones mainly relevant to the radio interface are the “05 series”. It is thoroughly recommended that radio planners and optimisation engineers read the 05 series specifications entirely.



GSM Air interface

• Spectrum Allocation

– 900 MHz band

– 1800 MHz band

890 MHz

915MHz

935 MHz

960 MHz

MS Transmit BS Transmit


1710 MHz

1785MHz

1805 MHz

1880 MHz

The spectrum allocation for Standard GSM 900 Band is890 - 915 MHz: mobile transmit, base receive;935 - 960 MHz: base transmit, mobile receive.

The Extended GSM 900 Band, E-GSM (includes Standard GSM 900 band) is:880 - 915 MHz: mobile transmit, base receive;925 - 960 MHz: base transmit, mobile receive.

The allocation in the GSM 1800 Band is 1710 - 1785 MHz: mobile transmit, base receive;1805 - 1880 MHz: base transmit, mobile receive.



GSM Air interface

• The ARFCN– Channel bandwidth is 200kHz

GSM 900 F-DL(n) = 890 + 0.2*n 1 ≤ ≤ ≤ ≤ n ≤ ≤ ≤ ≤ 124 F-UL(n) = F-DL(n) + 45

E-GSM 900 F-DL(n) = 890 + 0.2*n 0 ≤≤≤≤ n ≤ ≤ ≤ ≤ 124 F-UL(n) = F-DL(n) + 45

F-DL(n) = 890 + 0.2*(n - 1024) 975 ≤≤≤≤ n ≤≤≤≤ 1023GSM 1800 F-DL(n) = 1710.2 + 0.2*(n - 512) 512 ≤≤≤≤ n ≤≤≤≤ 885 F-UL(n) = F-DL(n) + 95

935.2 MHz (n=1)

200 KHz 200 KHz

890.2 MHz (n=1)


45 MHz

Each frequency carrier or channel has a bandwidth of 200kHz. The carrier frequency is designated by the Absolute Radio Frequency Channel Number (ARFCN).There are 124 channels in the standard 900 MHz band, and 374 in the 1800 MHz band. (although there are 125 channels in the 25 MHz at 900MHz band and 375 in the 1800MHz band, the lowest channel is not used to prevent interference with nearby non-GSM systems). The Mobile to Base Station path is referred to as the Uplink (UL), and the Base Station to Mobile path is the Downlink (DL).Therefore, one ARFCN comprises one Uplink frequency and a corresponding Downlink frequency.



GSM Air interface

• Access scheme – TDMA with FDMA

200 kHz

TS0 TS1 TS3 TS4 TS5 TS6 TS7TS2

577µµµµs




Time

Frequency

f1

f2

f3

f4

TDMA Frame (4.615 ms)

The 200 KHz spectrum is divided in time into 8 slots. Each of the 8 slots is called a Timeslot, and its duration is 0.577ms.



GSM Air interface

• TDMA frame structures – Timeslot (15/26 ms)– Frame:

• 8 timeslots (TS0 - TS7)– Multiframe

• 26 frames (FN0 - FN25)• 51 frames (FN0 - FN50)

– Superframe• 51 * 26-frame multiframes• 26 * 51-frame multiframes

– Hyperframe• 2048 superframes

The 200 KHz spectrum or frame is divided in time into 8 slots. Each of the 8 slots is called a Timeslot, and its duration is (15/26ms) 0.577ms. The duration of the frame is 8*0.577=4.615ms.

Each frame has a unique number called the Frame Number (FN), starting from 0. A frame structure/hierarchy is important in order to give the BTS an internal clock system. This clocking system is used for other functions such as network access, logical channel configuration etc.

A 26-frame multiframe is used to carry Traffic channels (TCH) and associated control channels (SACCH). The 51-frame multiframe is used for control channels exclusively.



GSM Air interface

• TDMA frame structures

0 1 3 4 5 6 72FN0

0 1 3 4 5 6 72 0 1 3 4 5 6 72FN1 FN50

0 1 3 4 5 6 72FN25

0 1 3 4 232 24 25 0 1 3 42 48 49 50

26-frame MF 51-frame MF

0 1 3 4 232 24 25

0 1 3 42 48 49 50 51*26-Multiframe Superframe

25*51-Multiframe Superframe

0 1 3 42 2045 2046 2047

Hyperframe: 2048 Superframes



Exercise!

• Given• TDMA frame period = 4.615ms

– Calculate the periods for each• Multiframe• Superframe• Hyperframe



GSM Channels

• Channel types– Defined in GSM 05.02

– Physical channel• Frequency and timeslot• HSN and MA and MAIO

– Logical channels• Speech (e.g. TCH/FS, TCH/HS)• Data (e.g. TCH/F9.6)• Control (e.g. BCCH, SDCCH, SACCH etc)

GSM Specification 05.02 defines all the channel types. There are two categories: Logical and Physical. Physical channels are defined by the frequency or frequency sequence and the timeslot number, while logical channels by the kind of information they carry.

There are various kinds of logical channel, broadly speaking traffic and control. Traffic may be data or voice traffic. It is not possible to carry data over a voice channel (unlike with an analogue line).



GSM Channels

• Physical channel - Bursts– Information carried on physical channels is transmitted in bursts

– The modulation scheme is GMSK• Gaussian Minimum Shift Keying with BT=0.3• Modulation rate is 270.83 kb/s (=1625/6 kb/s)

– Corresponds to 156.25 bits in the timeslot• No amplitude modulation• Gives minimum spectrum requirements• Enables constant output power to be used

Timeslots transmit bursts of data. Five types are defined, four full ones and one short burst.

A burst is the information or physical content (speech or data) transmitted during one timeslot - it is a period of the RF carrier that is modulated by a data stream. Bursts have very precise timing characteristics, so that all network components know exactly when to transmit and when to receive. The size of the burst depends on the type of data that is transmitted. One burst contains a maximum of 156.25 bits, the odd 0.25 bit being due to a guard period of 8.25 bits duration (30µs).

Where no data is required to be conveyed, no burst is transmitted and the timeslot is empty.Reduction of BTS or MS power will result in bursts of reduced amplitude filling a timeslot.



GSM Channels

• Physical channel - the GSM burst

» Ref: GSM 05.05

dB

t

- 6

- 30

+ 4

8 µs 10 µs 10 µs 8 µs

(147 bits)

7056/13 (542.8) µs 10 µs(*)

10 µs

- 1+ 1

(***)

(**)

156.25 bits

A timeslot is divided into 156.25 bit periods. A particular bit period within a timeslot is referenced by a bit number (BN), with the first bit period being numbered 0, and the last (1/4) bit period being numbered 156. The bit with the lowest bit number is transmitted first.

A burst consists of sections as follows:•A guard period (approx 30µs) to prevent overlapping with adjacent bursts•A useful part containing information (147 bits)•A mid amble or training sequence, used by equaliser to calculate multipath delay and compensate.

Ramp-up and ramp-down takes place in the guard period.This is mandatory for MS transmission, but the BTS is not required to ramp up and down between adjacent bursts.



GSM Channels

• Physical channel - Bursts

– Five types• Normal burst (NB)• Frequency correction burst (FB) • Synchronisation burst (SB)• Access burst (AB)• Dummy burst (DB)

Timeslots transmit bursts of data. There are different kinds of burst associated with different channel types.



GSM Channels

• Physical channel - bursts

Normal Burst

3 142 3 81/4

3 39 3964 3 81/4

8 41 36 3 681/4

Frequency Correction Burst

Synchronisation Burst

Dummy Burst

Access Burst

1 1

Tail Guard

Period

Extended Training Sequence

3 58 5826 3 81/4Encrypted Data Encrypted DataTraining

Sequence

Tail

Fixed Sequence

Encrypted Data Encrypted Data

Encrypted DataSynchronisation

Sequence

Extended Guard Period

3 58 5826 3 81/4Encrypted Data Encrypted DataTraining

Sequence

Tail

Normal Burst (NB): full burst used for carrying user encrypted data or control signalling on uplink and downlink. 1 bit on either side of the training sequence are given the function of “stealing flags” to denote if the burst carries data or has been “stolen” to provide urgent signalling channel FACCH.Frequency Correction Burst (FB): full burst, used in downlink only and is the simplest burst. All data and training periods are combined into one long period of 142 bits all set to ‘0’. It is used by a mobile to correct its frequency and demodulate the synchronisation burst.Synchronisation Burst (SB): full burst, used in downlink only on the SCH which transmits frame number and initial identification information (BSIC) of the cell. The extended training sequence provides sufficient information for the mobile to attain frame synchronisation with the BTS and obtain the Timeslot Number (TN) in the Hyperframe.Dummy Burst (DB): full burst, used in downlink direction only and has same structure as normal burst except it does not carry any useful information. The encrypted data is a known pre-defined series. It is used on the BCCH carrier which has to transmit all the time to enable mobiles to synchronise and carry out signal measurements for handover purposes.Access Burst (AB): the only short burst in GSM, used by the mobile in the uplink to access the network. The extended guard period of 68.25 bits makes allowance for burst transmissions from other mobiles.



GSM Channels

• Physical Channel

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

Timeslot156.25 bits

0.577 ms

Physical Channel

TDMA Frame

TDMA FrameDuration: 4.615msNo.of timeslots: 8Numbering: 0 – 2 715 647

(25 x 51 x 2048 –1)

TimeslotDuration: 577usNo.of bits: 156.25Numbering: 0 - 7

A TDMA Frame consists of the 8 consecutive timeslots [0,1,2,3,4,5,6,7]. The TDMA frames are numbered rigidly, because different frames carry different channels, for example a TCH and a SACCH share the same timeslot number and frequency, but are differentiated through the TDMA frame number sequence that they use.

The Physical channel is the repetition of a particular timeslot - in this example, TS 1. The repetition of TS 2 would be another physical channel, etc. etc.Therefore one RF carrier can carry up to 8 simultaneous conversations, in other words it carries transmissions from 8 different subscribers simultaneously. The Mobile or base station must transmit the information related to one call in the same timeslot until the call is terminated.

Each physical channel carries a varying number of logical channels.



GSM Channels

• Physical channels– Frequencies, channel allocation

• CA: the list of frequencies allocated to a cell• MA: the list of frequencies allocated to a mobile

– When frequency hopping• MAI: indexes the list of mobile frequencies

– For each TDMA frame• MAIO: offset to the MA Index to avoid two TRX in one cell using the same frequency

• HSN: Hopping sequence number

Each cell is allocated a set of frequencies. The allocation is stored in the CA (Cell Allocation). The frequencies may be hopping or not. When frequency hopping, a mobile will be allocated a set of frequencies called the MA (Mobile Allocation). The MA will be a subset of the CA.The hopping sequence generation algorithm is carefully defined in GSM 05.02. The algorithm itself generates an index (MAI) for each TDMA frame, which is used to look up from the MA list the actual frequency used in each TDMA frame. Transceivers in one cell using the same MA are each given an offset (MAIO) to the index number for each frame. This makes it impossible for two TRX in the same cell to use the same frequency in the same TDMA frame.The sequence generation algorithm uses the Hopping Sequence Number (HSN) and the TDMA Frame Number (FN) to generate the MAI. FN is effectively random for non synchronised BSs, but is the same for the cells on the same site.



GSM Channels

• Logical Channels– Traffic CHannels (TCH)

• Speech channels– Full rate traffic channel for speech (TCH/FS)– Half rate traffic channel for speech (TCH/HS)

• Data channels– Full rate traffic for 9.6 kbit/s data (TCH/F9.6)– Full rate traffic for 4.8 kbit/s data (TCH/F4.8)– Full rate traffic for ≤≤≤≤ 2.4 kbit/s data (TCH/F2.4)– Half rate traffic for 4.8 kbit/s data (TCH/H4.8)– Half rate traffic for ≤≤≤≤ 2.4 kbit/s data (TCH/H2.4)

GSM requires a great variety of information (data and control) to be transmitted in both uplink and downlink. The concept of logical channels is used to convey the different types of data. Therefore, to use a given channel is to transmit and receive specific bursts at specific instants in time and on specific frequencies.

Speech traffic channels may be Full Rate or Half Rate or Enhanced Full Rate. Half Rate channels only occupy half of each time slot.



GSM Channels

• Logical Channels– Traffic CHannels (TCH)

• Data channels

TCH

TCH/F TCH/H

TCH/H 4.8 TCH/H 2.4TCH/F 9.6

TCH/F 4.8

TCH/F 1.2

TCH/F 2.4

The Traffic channels carries either speech or data.

The Full Rate channel carries encoded information at a gross rate of 22.8 kb/s. The net rate for speech is 13 kb/s, whilst for data, the net rates are 9.6 kb/s, 4.8 kb/s, 2.4 kb/s. •TCH/F9.6: 9.6 kb/s full rate data•TCH/F4.8: 4.8 kb/s full rate data•TCH/F2.4: 2.4 kb/s full rate dataThe Half Rate channel have less coding overhead and carry encoded information at a gross rate of 11.4 kb/s, and net rates of 4.8 kb/s, 2.4 kb/s. •TCH/H4.8: 4.8 kb/s half rate data•TCH/H2.4: 2.4 kb/s half rate data

Since 9.6 kbit/s is already slow enough, few people use the 4.8k or 2.4k channels.



GSM Channels

• Logical Channels– Control channels

• Broadcast Channels (BCH)

• Common control channels (CCCH)

• Dedicated Control Channels (DCCH)

There are a large number of control channels defined for different purposes. The Control channels (CCH) carry signalling or synchronisation information. There are three main types of control channels:BCCH: Broadcast Control Channel: downlink only and are transmitted to all mobilesCCCH: Common Control Channel: used for a temporary period to make connections and set up other channelsDCCH: Dedicated Control Channel: used for a temporary period to make connections and set up other channels



GSM Channels

• Logical Channels– Control CHannels (CCH)

CCH

DCCH

SDCCH

BCCH

SCH FCCH

BCCH

FACCH

ACCH

SACCH

CCCH

RACH

PCH AGCH

(DL)

(UL)

(DL) (DL)CBCH

(DL)

(UL&DL)

BCCH: Point to multipoint, unidirectional (Downlink) channel, transmitted at constant power all the time from the BS. It carries information such as List of frequencies used in cell, cell identity, location area identity, list of neighbour cells, access control (emergency calls etc.), power control & DTX information. It includesCCCH: Point to multipoint, bi-directional (Up & Downlink) channel, used for carrying signalling data for access management functions. It includesDCCH: Point to point, directional (Up & Downlink) channel, used for carrying signalling data for call setup or for measurement and handover purposes. It includes•SDCCH: Stand Alone Dedicated Control Channel, used for data transfer to/from mobile during call setup, and for transmission of SMS•ACCH: Associated Control channel, can be associated with either a TCH or an SDCCH, and are used for the processes associated with those two channels

•SACCH: Slow Associated Control Channel, carries timing and power control information downlink to the mobile, and quality and signal strength measurements uplink to the BS.•FACCH: Fast Associated Control channel is used to implement user authentication and handovers. It is transmitted instead of a TCH, and is referred to as burst stealing - the FACCH steals the TCH burst and replaces it with its own information.



GSM Channels

• Logical Channels: Control channels

– Broadcast CHannels (BCH)• Frequency correction channel (FCCH)• Synchronisation channel (SCH)• Broadcast control channel (BCCH)

– Common Control CHannels (CCCH)• Paging channel (PCH)• Random access channel (RACH)• Access grant channel (AGCH)• Cell Broadcast Channel (CBCH)

BCCH: Point to multipoint, unidirectional (Downlink) channel, transmitted at constant power all the time from the BS. It carries information such as List of frequencies used in cell, cell identity, location area identity, list of neighbour cells, access control (emergency calls etc.), power control & DTX information. It includesFCCH, Frequency Correction Channel, consists of bursts which have 142 fixed bits and enables the Mobile to synchronise to the right frequency for the BS. It is transmitted in frames immediately before the SCH.SCH, Synchronisation Channel (DL) consists of regular sequence of bits and enables the mobile to synchronise on first registration to the right TDMA frame using the frame number and BSIC. A timeslot containing the SCH is transmitted once every tenth TDMA frame. There is an extended training sequence to help identify the cell to which the mobile is registering.

CCCH: Point to multipoint, bi-directional (Up & Downlink) channel, used for carrying signalling data for access management functions. It includesPCH: Paging Channel, downlink channel for paging mobilesAGCH: Access Grant channel , downlink channel used to assign dedicated channel to a mobile station for setting up calls.RACH: Random Access channel, an uplink channel used by the Mobile for requesting for a dedicated control channel when initiating a call.CBCH: Cell Broadcast Channel, a downlink channel used to transmit broadcast messages to all mobiles. It is transmitted in the place of an SDCCH - steals SDCCH.



GSM Channels

• Control channels– Dedicated Control CHannels

• Slow associated control channel (SACCH/TF)• Fast associated control channel (FACCH/TF)• Stand alone dedicated control channel (SDCCH/8)• Slow associated control channel (SACCH/C8)• Stand alone dedicated control channel, combined with CCCH (SDCCH/4)

DCCH: Point to point, directional (Up & Downlink) channel, used for carrying signalling data for call setup or for measurement and handover purposes. Dedicated channels are so called because they are dedicated to one mobile in dedicated mode (as opposed to idle mode). Dedicated control channels fall into two categories: There are “stand alone” channels and “associated” channels. The stand alone channels can be set up in their own right. SDCCH: Stand Alone Dedicated Control Channel, used for data transfer to/from BS/MS during call setup, and for transmission of SMS. Messages inc. “Layer 3” messages and indicate commands such as “Assign Channel”, “Update Location Area”, etc. The SDCCH can be combined on the same physical channel as the BCCH and CCCHs, and is time division multiplexed, or can be allocated an entire physical channel itself, depending on the traffic requirements.ACCH: Associated Control channel, can only be associated with either a TCH or an SDCCH, and are used for the processes associated with those two channels

SACCH: Slow Associated Control Channel uses a small number of timeslots occasionally to carry timing and power control information downlink to the mobile, and quality and signal strength measurements uplink to the BS.FACCH: Fast Associated Control channel is used to implement user authentication and handovers. It is transmitted instead of a TCH, and is referred to as burst stealing - the FACCH steals the TCH burst and replaces it with its own information. That is, a FACCH exists when a TCH is temporarily used for SDCCH purposes.



GSM Channels

• Logical Channels

Normal Burst

SDCCH

BCCH

CBCHPCH

AGCH

FACCH

SACCH

Access Burst

RACH

Dummy Burst

BCCH FCH SCH

Frequency Burst

SynchronisationBurst



GSM Channels

• Mapping Logical to Physical channels– Physical channel has several logical channels

• TCH/F + FACCH/F + SACCH/TF

• FCCH + SCH + BCCH + CCCH• SDCCH/8 + SACCH/C8

– “Non-combined”

• FCCH + SCH + BCCH + CCCH + SDCCH/4 + SACCH/C4

– “Combined”

• where CCCH = PCH + RACH + AGCH



GSM Channels

• Channel Mapping: Logical to Physical– TCH carrier

• TCH/F + SACCH/TF + FACCH/F

• 24 slots for TCH/F• 1 slot for SACCH• 1 idle slot

TCH

TCH

TCH

TCH

TCH

TCH

TCH

TCH

TCH

TCH

TCH

TCH

SACC

H

TCH

TCH

TCH

TCH

TCH

TCH

TCH

TCH

TCH

TCH

TCH

TCH

IDLE

0 1 3 4 5 6 72FN0

0 1 3 4 5 6 72FN1

0 1 3 4 5 6 72FN25

The TCH configuration comprises 24 TS where TCH/F (speech or user data) is transmitted. 1 TS for its SACCH (each TCH has an associated SACCH to convey signalling between MS and BTS in active mode), and 1 TS is idle. The TCH/F period is 120ms, chosen as a multiple of 20ms in order to obtain some synchronisation with fixed networks, especially ISDN.

If the network sets the “stealing flags” in the normal burst, a timeslot can be stolen and replaced with a FACCH to send urgent signalling data



GSM Channels

• Channel Mapping: Logical to Physical– BCCH carrier (non combined)

• FCH + SCH + BCCH + CCCH

– 5 TS for FCH– 5 TS for SCH– 4 TS for BCCH– 36 TS for CCCH– 1 TS is idle

FCC

HS

CH

BCC

HBC

CH

BCC

HBC

CH

CCC

HCC

CH

CCC

HCC

CH

FCC

CH

SC

HCC

CH

CCC

HCC

CH

CCC

HCC

CH

CCC

HCC

CH

CCC

HFC

CH

SC

HCC

CH

CCC

HCC

CH

CCC

HCC

CH

CCC

HCC

CH

CCC

HFC

CH

SC

HCC

CH

CCC

HCC

CH

CCC

HCC

CH

CCC

HCC

CH

CCC

HFC

CH

SC

HCC

CH

CCC

HCC

CH

CCC

HCC

CH

CCC

HCC

CH

CCC

HID

LE

0 1 3 4 5 6 72FN0

0 1 3 4 5 6 72FN1

0 1 3 4 5 6 72FN25

0 1 3 4 5 6 72FN50

With non-combined, a separate timeslot is used for eight SDCCH channels and their SACCHs.

©Childerley Solutions

200243

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Radio N

etwork O

ptimisation v1.4

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onsultants Ltd 2002

GSM

Channels

•Channel M

apping: Logical to Physical–SD

CCH non com

bined (SDCCH/8 + SA

CCH/C8)

Cycle repeated after 102 TD

MA fram

es

SDCCH/4(0)

SDCCH/4(0)

SDCCH/4(0)

SDCCH/4(0)

SDCCH/4(1)

SDCCH/4(1)

SDCCH/4(1)

SDCCH/4(1)

SDCCH/4(2)

SDCCH/4(2)

SDCCH/4(2)

SDCCH/4(2)

SDCCH/4(3)

SDCCH/4(3)

SDCCH/4(3)

SDCCH/4(3)

SDCCH/4(4)

SDCCH/4(4)

SDCCH/4(4)

SDCCH/4(4)

SDCCH/4(5)

SDCCH/4(5)

SDCCH/4(5)

SDCCH/4(5)

SDCCH/4(6)

SDCCH/4(6)

SDCCH/4(6)

SDCCH/4(6)

SDCCH/4(7)

SDCCH/4(7)

SDCCH/4(7)

SDCCH/4(7)

SACCH/C4/(0)

SACCH/C4/(0)

SACCH/C4/(0)

SACCH/C4/(0)

SACCH/C4/(1)

SACCH/C4/(1)

SACCH/C4/(1)

SACCH/C4/(1)

SACCH/C4/(3)

SACCH/C4/(3)

SACCH/C4/(3)

SACCH/C4/(3)

SACCH/C4/(3)

SACCH/C4/(3)

SACCH/C4/(3)

SACCH/C4/(3)

IDLE

IDLE

IDLE

01

34

56

72 FN

00

13

45

67

2 FN1

01

34

56

72 FN

250

13

45

67

2FN

50

01

34

56

72FN

101

SDCCH/4(0)

SDCCH/4(0)

SDCCH/4(0)

SDCCH/4(0)

SDCCH/4(1)

SDCCH/4(1)

SDCCH/4(1)

SDCCH/4(1)

SDCCH/4(2)

SDCCH/4(2)

SDCCH/4(2)

SDCCH/4(2)

SDCCH/4(3)

SDCCH/4(3)

SDCCH/4(3)

SDCCH/4(3)

SDCCH/4(4)

SDCCH/4(4)

SDCCH/4(4)

SDCCH/4(4)

SDCCH/4(5)

SDCCH/4(5)

SDCCH/4(5)

SDCCH/4(5)

SDCCH/4(6)

SDCCH/4(6)

SDCCH/4(6)

SDCCH/4(6)

SDCCH/4(7)

SDCCH/4(7)

SDCCH/4(7)

SDCCH/4(7)

SACCH/C4/(4)

SACCH/C4/(4)

SACCH/C4/(4)

SACCH/C4/(4)

SACCH/C4/(5)

SACCH/C4/(5)

SACCH/C4/(5)

SACCH/C4/(5)

SACCH/C4/(6)

SACCH/C4/(6)

SACCH/C4/(6)

SACCH/C4/(6)

SACCH/C4/(7)

SACCH/C4/(7)

SACCH/C4/(7)

SACCH/C4/(7)

IDLE

IDLE

IDLE

TS1 is used for SD

CC

H in the non com

bined configuration. Each SDC

CH

has an associated SA

CC

H. For every eight S

DC

CH

TDM

A fram

es there are four S

AC

CH

frames.

The idle frames are an opportunity for the m

obile to synchroniseto neighbouring

cells and to decode their BS

IC.

©Childerley Solutions

200244

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Radio N

etwork O

ptimisation v1.4

Page 44©Telecom

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onsultants Ltd 2002

GSM

Channels

•Channel M

apping: Logical to Physical–BCCH carrier (com

bined)•FC

CH + SC

H + B

CCH + C

CCH + SD

CCH/4 + SA

CCH/C4

Cycle repeated after 102 TD

MA fram

es

FCCH

SCH

BCCH

BCCH

BCCH

BCCH

CCCH

CCCH

CCCH

CCCH

FCCCH

SCH

CCCH

CCCH

CCCH

CCCH

CCCH

CCCH

CCCH

CCCH

FCCH

SCH

SDCCH/4(0)

SDCCH/4(0)

SDCCH/4(0)

SDCCH/4(0)

SDCCH/4(1)

SDCCH/4(1)

SDCCH/4(1)

SDCCH/4(1)

FCCH

SCH

SDCCH/4(2)

SDCCH/4(2)

SDCCH/4(2)

SDCCH/4(2)

SDCCH/4(3)

SDCCH/4(3)

SDCCH/4(3)

SDCCH/4(3)

FCCH

SCH

SACCH/C4/(0)

SACCH/C4/(0)

SACCH/C4/(0)

SACCH/C4/(0)

SACCH/C4/(1)

SACCH/C4/(1)

SACCH/C4/(1)

SACCH/C4/(1)

IDLE

FCCH

SCH

BCCH

BCCH

BCCH

BCCH

CCCH

CCCH

CCCH

CCCH

FCCCH

SCH

CCCH

CCCH

CCCH

CCCH

CCCH

CCCH

CCCH

CCCH

FCCH

SCH

SDCCH/4(0)

SDCCH/4(0)

SDCCH/4(0)

SDCCH/4(0)

SDCCH/4(1)

SDCCH/4(1)

SDCCH/4(1)

SDCCH/4(1)

FCCH

SCH

SDCCH/4(2)

SDCCH/4(2)

SDCCH/4(2)

SDCCH/4(2)

SDCCH/4(3)

SDCCH/4(3)

SDCCH/4(3)

SDCCH/4(3)

FCCH

SCH

SACCH/C4/(2)

SACCH/C4/(2)

SACCH/C4/(2)

SACCH/C4/(2)

SACCH/C4/(3)

SACCH/C4/(3)

SACCH/C4/(3)

SACCH/C4/(3)

IDLE

01

34

56

72 FN

00

13

45

67

2 FN1

01

34

56

72 FN

250

13

45

67

2FN

50

01

34

56

72FN

101

Synchronisation and frequency correction happens every tenth TD

MA

frame.

Each S

DC

CH

has an associated SAC

CH

. For every eight SD

CC

H TD

MA

frames

there are four SAC

CH

frames.



GSM Channels

• Call set-up– Mobile terminated

• PCH used to transmit page to mobile in all cells within the Location Area in which it was last registered in the VLR

PCH



GSM Channels


• Mobile “hears” page and requests communication on the RACH

PCH

RACH



GSM Channels


• Base station responds on the Access Grant Channel (AGCH), with details of a Dedicated Control Channel (SDCCH)

RACH

AGCH



GSM Channels


• The SDCCH is used to transfer all call set-up information, e.g. authentication details, callers number (if enabled), etc.

SDCCH



GSM Channels


• On the SDCCH, the mobile is told which traffic channel to use (frequency, hopping sequence, timeslot)

SDCCH

TCH



GSM Channels

• Call set-up– Mobile originated

• Rather than starting with a “downlink” page, the mobile initiates proceedings on the RACH

RACH

AGCH



GSM Channels

• Call set-up– Summary

Paging (PCH) -mobile

terminated onlyRandom Access Request (RACH)

Access Grant (AGCH)

Call setup (SDCCH)

Call in progress (TCH)



GSM Channels - Review

•• GSM channelsGSM channels–– Spectrum allocationSpectrum allocation–– Access schemeAccess scheme–– Frame structuresFrame structures–– Physical channelPhysical channel–– Logical channelsLogical channels–– Channel Mapping: Logical onto physicalChannel Mapping: Logical onto physical



Contents

• System Basics– GSM Channels�Measurements

• Idle mode• Dedicated mode• RxLev• RxQual• Radio Link Timer• Timing Advance



GSM Measurements




GSM Measurements

• Downlink, idle mode– Signal level of BCCH carrier frequency– Signal level of BCCH carrier from 6 neighbours

• Uplink, idle mode– No measurements

In idle mode it is not possible to measure the Bit error rate. Also, it is not possible to measure the bit error rate of neighbours in dedicated mode.



GSM Measurements

• Downlink, dedicated mode– Signal level of serving carrier– Signal level of BCCH carrier from 6 neighbours– Bit error rate of serving channel

• Uplink, dedicated mode– Signal level of serving carrier– Bit error rate of serving channel



GSM Measurements

• Signal level, RxLevRxLev Signal0 < -110dBm1 -110 to -109dBm2 -109 to -108dBm: :: :61 - 49 to - 48dBm62 - 48 to - 47dBm63 > - 47 dBm

Signal level is represented as RxLev for transmission back to the BSC. The RxLev actually represents a signal level range, usually 1 dB. Therefore Signal levels lower than –110dBm are reported as RxLev 0, and levels higher than –47 dBm are represented as RxLev 63. Even if a test mobile can measure higher, it is still reported to the BSC as 63. Signal level higher than –110dBm but lower than –109dBm is reported as RxLev1 etc. etc.



GSM Measurements

• Bit Error Rate (BER(), RxQualRxQual BER range BER mean0 < 0.2% 0.14%1 0.2 to 0.4% 0.28%2 0.4 to 0.8% 0.57%3 0.8 to 1.6% 1.13%4 1.6 to 3.2% 2.26%5 3.2 to 6.4% 4.53%6 6.4 to 12.8% 9.05%7 > 12.8% 18.1%

RxQual of 4, about 2% BER, is about the limit of acceptable voice quality when not hopping. 5 is unacceptable. In a hopping system RxQual of 6 may still give acceptable speech quality. The error correction coding will restore the original data to a lower BER.



GSM Measurements

• Measurement reporting– Reported once every (SACCH/TCH-F multiframe)

• Every 104 TDMA frames = 480ms for TCH• Every 102 TDMA frames = 471ms for SDCCH

– 4 TDMA frames carry SACCH channel• Measurements reported on uplink• Messages sent on downlink• 2 idle frames

Measurements made by the MS on the neighbour cells are sent to the BSC on the SACCH channel.



GSM Measurements

• RxLev SUB and RxQual SUB

– Full measurements based on all timeslots– With DTX not all Timeslots transmit– SUB Measurements based on 12 timeslots which always transmit



GSM Measurements

• Radio Link Timer (RLT)– Radio link timer counts down from a maximum value whenever synchronisation is lost

– Timer at BS and MS– When synch is returned counts up in 2’s– Maximum value is a settable parameter– Call disconnected when timer expires

• Long timer, fewer dropped calls, more wasted capacity

• Shorter timer, calls disconnected unnecessarily



GSM Measurements

• Measurements– Timing advance

BS Tx

MS Rx ττττ1111

t = range / c

MS Tx3 TS

ττττ1111BS Rx

ττττ2222

ττττ2222

Different mobiles at different ranges have different propagation times from and to the BS. Without timing advance the second (dotted) burstbelonging to a closer mobile would interfere with the first. The MS with the shortest delay should then wait longer to transmit, so that its received at the MS at the appropriate slot.

Mobiles closer to the BS have their transmission delayed up to 63 bit periods (232ms), so that all incoming bursts arrive in the correct timeslots at the BS. The 232ms allows for a round trip delay corresponding to 69.6km, or a range differential of 34.8km. Since there is a guard time between timeslots, the maximum range for GSM is generally considered as 35km.



GSM Measurements - review




Contents

• System Basics�BSS Parameters• Quality Assessment• Optimisation Measures• Organisation



Contents

• BSS Parameters� Idle Mode Behaviour– Measurement Filtering– Power Control– Handover (locating)



Idle mode behaviour

• PLMN selection• Cell selection• Cell reselection• Location Updating



Idle Mode Behaviour

• PLMN Selection– At power on, MS first tries to select last registered PLMN

– If no previous registered PLMN, selection is made in

• Automatic mode: uses PLMN list in order of priority• Manual mode: selection is made by user based on list made available by MS

Automatic mode: selection done in following order if available/allowed:1. Home PLMN2. Stored list in SIM in order of priority3. Other PLMNs with signal strength> -85 dBm4. All other PLMNs in order of decreasing signal strength

Manual Mode:MS first tries to select registered or home PLMN. Otherwise, MS will indicate a list of all available PLMNs from which user selects. User can reselect any other PLMN at any time.



Idle Mode Behaviour

• PLMN Selection: National Roaming– If roaming permitted, another PLMN in the home country can be selected

– MS will periodically try to obtain service on its home PLMN.

• Time period stored in SIM: – 6 mins to 8 hours in steps of 6 mins– No time period indicates no attempts



Idle Mode Behaviour

• Cell Selection - Where do I camp on ?

• Two strategies– Normal cell selection– Stored list cell selection/double BA list

?



Idle Mode Behaviour

• Normal Cell Selection– A cell is suitable if

• it belongs to selected PLMN• is not barred• does not belong to list of “forbidden LA areas for roaming”

• Cell selection criterion is met– Cells have normal or low priority– Priority controlled by CBQ (Ph2) and CBparameters

If no normal cells available, cells of low priority will be camped on.CBQ: Cell Bar Qualify CB: Cell Bar Access

Behaviour of MS for various combinations of CBQ & CB

CBQ CB At Cell Selection At Cell ReselectionHigh No Normal NormalHigh Yes Barred BarredLow No Low NormalLow Yes Low Normal



Idle Mode Behaviour

• Cell Selection – Cell selection parameter C1

• Enables MS to camp on cell with which high probability of communications is possible

• Based on signal strength only• C1 calculated for several cells

– Mobile selects cell with highest C1• C1=(Received Signal Level-ACCMIN) -MAX[(CCHPWR-P),0]

• Only cells with positive C1 are considered

CCHPWR: maximum transmitting power that a MS is allowed to use when accessing the networkP: maximum output power of the MS according to its class.

C1 Criterion is based only on signal strength. It is satisfied if C1>0



Idle Mode Behaviour

• Cell Selection: ACCMIN– Minimum level for access to the network in idle mode

• One for each cell• Usually around the same level as the mobile sensitivity

• Attract roamers by setting to -110dBm at airports and borders

– But phase 2+ picks roaming network at random provided RxLev > -85 dBm



Idle Mode Behaviour

• Stored List Cell Selection– MS may have optional BA list stored in the SIM– Same measurements carried out as for normal cell selection, but BCCH carriers in stored list are scanned, not neighbours

– Speeds up cell selection– List updated if MS receives new data– If not successful, normal selection done



Idle mode behaviour

• Cell selection

Monitor BCCH carrier of “Camped Cell”

Monitor BCCH of Neighbours

The mobile is in idle mode except when making a call or switched off!

When in idle mode, the MS is camped on one cell, there is no speech or data traffic being carried. However, the MS is “listening” to neighbour cells (contained in neighbour list), and sending measurements back to the BSC via the BS.



Idle Mode Behaviour

• Cell Reselection– MS monitors all neighbour BCCH carriers and selects cell best cell

– Cell reselection parameter C2• C2=C1+CRO – TO * H(PT-T) for PT ≠≠≠≠ 31• C2=C1- CRO for PT = 31

– H(x) = 0 for x<0– H(x) = 1 for x≥≥≥≥0

• CRO: Cell Reselect Offset• TO : temporary negative offset applied for duration PTPenaltyTime

• T : Timer starts from zero when cell placed on nbr list

The MS always aims to camp on the best server. Cell reselection takes place when the MS moves from one serving cell to another, or if the propagation characteristics change to make the current cell not the best server.C2 also used in Phase 2 for selection of microcells.TO (dB), negative offset prevents fast moving MSs from selecting cell.PT (secs), duration for which TO is applied. The value of 31 indicates that CRO is negated and TO is ignored.T (secs), timer is reset to zero when cell falls out of list of best six nbrs.CRO, TO, PT are broadcast on the BCCH of each cell



Idle Mode Behaviour

• Location Updating– Service area divided into Location Areas

• Location Area Identity, LAIs– Process of informing network of the location of MS

– LU performed at pre defined intervals– Three types of Locating

• Normal• Periodic registration• IMSI attach/detach

LAI1

LAI4

LAI3

LAI2

Location Areas are essential for routing incoming calls efficiently. If all area was one LA, then a page would have to be sent to all MSs in the network, which would be inefficient. If each cell were one location area, then the mobile would have to update its location each time it left the cell area.

Normal locating: initiated by MS when it enters a new LA. If LAI in new cell is different to that stored in MS, then LU takes place. If LU fails (e.g by entering a forbidden LA), then MS will try to select another cell or return to PLMN selection state.

Periodic Registration: MS informs network regularly if it is still ‘attached’, even if a change in LA does not occur.

IMSI (International Mobile Subscriber Identity) attach/detach: MS notifies network if it is powered on or off.



Idle Mode Behaviour

• Normal Locating– Incoming calls result in paging for mobile in all cells within one location area

– When mobile moves location area, it updates the network

• Large LAs: Much paging traffic (PCH)• Small LAs : Much update traffic (SDCCH)



Idle Mode Behaviour

• LAI Periodic Registration– Updates LAI even if mobile has not changed LA

• In case of HLR crash• In case of long periods out of coverage• In case MS runs out of battery power

– Controlled by parameter T3212– Set from 0.1 hr to 25.5 hrs in 0.1 hr steps

• Shorter for networks with patchy coverage?• Longer for mature networks?

Periodic Registration: Parameter T3212, a timeout value, determines how regularly the MS informs network if it is still ‘attached’. Ranges from T3212=1 (6 mins) to T3212=255 (25.5 hrs), in steps of 6 minutes. It is reinitiated when MS returns to idle mode after being in dedicated mode.



Idle Mode Behaviour

• Location Areas

River?

Major road?

LA planning:Do not put major roads across two location areas, because otherwise every MS crossing the boundary would have to do an LA update, using up SDCCH resources.Do not use rivers or non propagation boundary type features to demarcate Las.



Idle Mode Behaviour

• IMSI Attach/Detach– MS powers on – IMSI attach– MS powers off – IMSI detach– Prevents unnecessary paging of MS– MS can be implicitly detached if no updates received within a supervision period

• Supervision period must be longer than periodic update timer

• Borders between LAs• CRH cell reselect hysteresis• LU takes place only if

– C2(new cell) > C2(old cell) + CRH

When MS is powered on, IMSI attach is sent to MSC/VLR. When MS is powered off, IMSI detach message is sent. Prevents unnecessary paging of MS.If no contact between MS and network for a specified supervision period, then the MSC will mark the MS as implicitly detached. The supervision period = Base Time duration BTDM + Guard Time duration GTDM. The BTDM must be coordinated with T3212 so that the MS is not unexpectedly removed from network before LU is performed.

For Ph1 mobiles, C1 is used instead of C2 for updates in LA borders.CRH may be different for each cell, and the one broadcast by the serving cell is used for calculations.



Idle Mode Behaviour

• BSIC– Base Station Identity Code– MS decodes BSIC from the BCCH– Enables mobile to differentiate between cells with the same BCCH frequency

– Made up of NCC (0-7) and BCC (0-7)• NCC: normally one per network - for differentiating networks at international borders

• BCC: all values available

NCC = Network Colour CodeBCC = Base Station Colour Code

BSIC coding takes place as part of frequency planning process



Contents

• BSS Parameters– Idle Mode Behaviour�Measurement Filtering– Power Control– Handover (locating)



Measurement Filtering

• Measurement preparation• Filtering




• Measurement Preparation– Radio parameters, signal strength, quality and timing advance

– Downlink measurements by MS are basis for Locating

– Uplink measurements by BS are used for• MS power control• Basic ranking for Ericsson3• Triggering urgency and intra-cell handover

– Every SACCH multiframe (480 ms)




• Missing measurements– Neighbour not eligible for handover if consecutive reports missing

– MISSNM maximum number of missing measurements permitted

– Missing measurements interpolated if reporting resumes before MISSNM report periods

– Measurements on neighbour terminated if MISSNM exceeded.




• Filtering– Applied to signal strength and quality measurements

• Smoothes out measurement noise• Filters out fading components of duration about same as filter response time

– Five filter types• General FIR• Recursive straight average• Recursive exponential• Recursive 1st order Butterworth• Median

General FIR filter Implemented as straight average filters

n = filter length in SACCH periods, wi are weight coefficients, cn are normalisation coefficients

Recursive Straight Average Filter

t is time of arrival of latest measurement reportMaximum computational efficiency (min load on BSC)

Recursive Exponential filter Quick step and impulse response

β = 1- α, α is the filter coefficientRecursive 1st order Butterworth filter

β = (1- α)/2

∑=

=n

iiin strengthsignalwcrxlev

1

)_(

−

+=−

−n

strengthsignalstrengthsignalrxlevrxlev ntttt

)_()_(1

ttt strengthsignalrxlevrxlev )_(1 ×+×= − βα

[ ]11 )_()_( −− +×+×= tttt strengthsignalstrengthsignalrxlevrxlev βα




• Median Filter– Selects median value from the last set of n measurements

– Less sensitive to measurement errors

• Timing Advance Filter– One type available– Straight average filter with length specified by TAAVELEN




• Selection of Signal strength filtersFilter selection parameter SSEVALSI, SSEVALSD

Filter Type Filter length, SACCH periods

1 General FIR 22 General FIR 63 General FIR 104 General FIR 145 General FIR 186 Recursive straight

averageSSLENSI, SSLENSD

7 Recursive exponential

SSLENSI, SSLENSD

8 Recursive 1storder Butterworth

SSLENSI, SSLENSD

9 median SSLENSI, SSLENSD

SSEVALSI : selects filter type during signalling phase (SDCCH).SSEVALSD: selects filter type during speech/data phase (TCH).SSLENSI: specifies length of SSEVALSI filter.SSLENSD: specifies length of SSEVALSD filter.

Filter parameter settings can be specified separately for serving and neighbour cells.




• Selection of Quality filtersFilter selection parameter QEVALSI, QEVALSD

Filter Type Filter length, SACCH periods

1 General FIR 42 General FIR 83 General FIR 124 General FIR 165 General FIR 206 Recursive

straight averageQLENSI, QLENSD

7 Recursive exponential

QLENSI, QLENSD

8 Recursive 1storder

Butterworth

QLENSI, QLENSD

9 median QLENSI, QLENSD

QEVALSI : selects filter type during signalling phase (SDCCH).QEVALSD: selects filter type during speech/data phase (TCH).QLENSI: specifies length of QEVALSI filter.QLENSD: specifies length of QEVALSD filter.

Filter parameter settings can be specified separately for serving and neighbour cells.




• Initiation of filters– When filter is not filled, it is modified– Filter operates as straight average

• All except median• Filter length equal to number of available measurements



Contents

• BSS Parameters– Idle Mode Behaviour– Measurement Filtering�Power Control– Handover (locating)



Power Control

• Aim is to reduce transmit power to minimum necessary for good reception

Tone it down!



Power Control

• Benefits– Reduces interference

• Closer frequency reuse, hence capacity increase

– Minimises battery consumption• Improves talk time of mobiles

– Maximise battery backup consumption• Improves standby time for BTS power supply

– Minimises receiver saturation



Power Control

��MS Power controlMS Power control•• BTS Power controlBTS Power control



MS Power Control

• Possible on TCH & SDCCH– PC on SDCCH enabled by SDCCHREG

– Measured UL signal strength and quality values sent to BSC in Measurement Result message

– Minimum regulation interval between two power control instructions is REGINT

SDCCHREG parameter enables power control

PC command is given every REGINT SACCH period. A new command is sent only if different from previous one.

REGINT cannot be less than one SACCH period (480ms). MS can change power output 8 times in one SACCH period (i.e. every 13th TDMA frame). Power is changed in 2dB steps, giving a total of 16dB change in one SACCH period.

Data Description SourceSignal Strength UL Full set (no DTX) BTSSignal Strength UL Subset (DTX enabled) BTSQuality UL Full set (no DTX) BTSQuality UL Subset (DTX enabled) BTSPower level used by MS MSDTX used by MS or not MS



MS Power Control

• Two modes of operation– Initial regulation: on assignment of new channel and at handover

• MS power reduction only, done very quickly• Short initial signal strength measurement filter

– INILEN measurements needed• No quality input

– Stationary regulation: normal mode• Filter length SSLEN longer than INILEN• Measurements start at same time as initial filter

Initial Regulation: prevents receiver saturation, especially if MS close to BS. Initial regulation performed only after initial filter is filled – and INILEN measurement reports available. Stationary Regulation: will only take place after an initial regulation has been performed.



MS Power Control

• Three process stages– Measurement preparation

• Missing measurements estimated• Selection of full or sub set

– Measurement filtering• Filtering of measurements to remove temporary variations

– Power change calculation• Power step change value calculated, based on received quality. First unconstrained value, then constraints applied.

Measurement filtering: determines if minimum signal strength is received. Quality filtering is average of predetermined number of samples.Power change calculation: two stages, unconstrained, constrained with power step size and MS power range.



MS Power Control

• Measurement preparation– Estimation of some missing measurement

• missing signal value = lowest(value before loss, value after loss).

• missing quality value = worst (value before loss, value after loss).

– Selection of measurement set • Full set used if DTX not enabled• Subset used if DTX enabled

If DTX is not enabled, full set is used, but if DTX is enabled, then subset measurements used. Full set always used for SDCCHMS will continue to use DTX in a new cell when HO occurs, even if new cell does not use DTX. The period of use in new cell is set by DTXFUL.If measurement result missing at next pc command, no extrapolation done for missing signal level and quality measurements, until next set of measurement result received. Then missing signal value = lowest( value before loss, value after loss). missing quality value = worst (value before loss, value after loss).

Estimation of missing MS power level is always done – set to highest known value



MS Power Control

• Measurement Filtering– Signal strength:

• INIDES, target UL value is calculated first

• SScomp=(1/SSLEN)ΣΣΣΣ[SS +MSTXPWR-PWRused)]

– Quality: • QDESUL is the target UL quality• Q_Ave, the filtered rxqual value is average of QLEN samples

• QDESUL and Q_Ave can be transformed into C/I values QDES_dB and Q_Ave_dB

Signal StrengthSScomp: signal strength that would have been received by BTS if no power control is enabled, ie compensated for power reduction regulation. Really is path loss estimation!!SS = actual signal strength received by BTSPWRused = MS output power during measurement periodMSTXPWR = maximum MS output powerSSLEN = filter length (number of samples) for stationary filter.

QualityQuality is measured in rxqual dtqu units (deci-transformed quality units).dtqu = rxqual*10, ranging from dtqu=10 to 100.

Q_Ave_dB and QDES_dB are estimated C/I values, transformed asQ_Ave_dB = 32 – 10*Q_Ave/25Q_DES_dB = 32 – 10*QDESUL/25

Each rxqual = 4 dB



MS Power Control

• Power Order Calculation– Initial phase: unconstrained power order pu

• pu = MSTXPWR – αααα(SScomp –SSDES)– SSDES is target UL signal strength

• “One-shot” stage for achieving the correct power after channel assignment

• No quality parameter involved

LCOMPUL : path loss compensation factor (0-100%), 0=no regulationQCOMPUL: quality deviation compensation factor (0-60%)Normally, PC is a function of signal strength or quality. However, in the Ericsson case, PC function is made to be a combination of both.



MS Power Control

• Power Order Calculation– Stationary phase

• For tracking propagation variations– Includes signal strength and quality parameters

• pu is the absolute power levelpu = MSTXPWR – αααα(SScomp –SSDES) –

ββββ(QDES_dB – Q_Ave_dB)– αααα = LCOMPUL/100 – ββββ = QCOMPUL/100

• dpu is the Power regulation reduction, dpu = LCOMPUL/100*(SScomp –SSDES) –QCOMPUL/100*4/10*(Q_Ave – QDESUL)

LCOMPUL : path loss compensation factor (0-100%), 0=no regulationQCOMPUL: quality deviation compensation factor (0-60%)Normally, PC is a function of signal strength or quality. However, in the Ericsson case, PC function is made to be a combination of both.



MS Power Control

• Example, power order calculation• Let SSDES = -90dBm, SScomp= -64dBm, LCOMPUL=50, QDESUL=10 (rxqual=1) , Q_Ave=40, QCOMPUL=60

Then • Pt1 = 50/100(-64 + 90) = 13 dB • Pt2 = 60/100*4/10*(40-10) = 7.2• dpu = 13 – 7.2 = 5.8 dB power reduction

–– Exercise: How to prevent power reduction Exercise: How to prevent power reduction with poor quality?with poor quality?



MS Power Control

• Power order constraints– constraints are applied if unconstrained power order exceeds dynamic range

• Power step size limitation: 16dB maximum allowable in one SACCH period

• MS Power range: depends on MS power class. Regulation interval ranges from MSTXPWR down to minimum power level of MS



Power Control

•• MS Power controlMS Power control��BTS Power controlBTS Power control



BTS Power Control

• Power order constraints

– Not possible on downlink BCCH carrier– Possible on TCH & SDCCHs

• PC on SDCCH enabled by SDCCHREG• Measured DL signal strength and quality values sent to BSC in Measurement Result message

– Minimum interval between two power control commands is REGINTDL

– Maximum power change is 30dB



BTS Power Control

• Measurement preparation– Output power level conversion– Selection of full or sub data set– Signal strength and quality compensated for use of frequency hopping

• Measurement filtering– Exponential non-linear filters used to eliminate temporary variations



BTS Power Control

• Power Order Calculation: three steps– Calculate two basic power orders pu1, pu2

• BSTXPWR, SSDESDL, SSbstxpwr, QDESDL, Qbstxpwr, αααα1, αααα2, ββββ1, ββββ2, LCOMPDL, QCOMPDL

• pu = max (pu1, pu2) – Apply power order constraints– Convert constrained power order from dBm scale to PLused

• PLused = 0, full power• PLused = 15, 30dB power down

SSDESDL: target value for DL signal strengthQDESDL: target value for DL qualityBSTXPWR:BTS output power on all non BCCH frequencies.BSPWRMIN: minimum allowed BTS output power for non BCCH freqs.SS/Qbstxpwr: signal strength/quality that would be received without use of power control.

If unconstrained power is outside dynamic range, then Power order constraints applied. There are two possible casesIf unconstrained power > BSTXPWR, then pu=BSTXPWRThe lowest pu = max(min BTS output power, BSTXPWR-30, BSPWRMIN)



BTS Power Control

• Power Order Calculation: three steps– Calculate two basic power orders pu1, pu2

• BSTXPWR, • SSDESDL, SSbstxpwr, • QDESDL, Qbstxpwr, • αααα1 = LCOMPDL/100, αααα2 = 0.3• ββββ1 = QCOMPDL/100, ββββ2 = 0.4• pui = ααααi *(SSDESDL - SSbstxpwr) – ββββi *4/10*(Q_Ave –Qbstxpwr)

• pu = max (pu1, pu2) –– Exercise: settings to avoid power reduction on Exercise: settings to avoid power reduction on bad qualitybad quality

SSDESDL: target value for DL signal strengthQDESDL: target value for DL qualityBSTXPWR:BTS output power on all non BCCH frequencies.BSPWRMIN: minimum allowed BTS output power for non BCCH freqs.SS/Qbstxpwr: signal strength/quality that would be received without use of power control.

If unconstrained power is outside dynamic range, then Power order constraints applied. There are two possible casesIf unconstrained power > BSTXPWR, then pu=BSTXPWRThe lowest pu = max(min BTS output power, BSTXPWR-30, BSPWRMIN)



Contents

• BSS Parameters– Idle Mode Behaviour– Measurement Filtering– Power Control– Handover (Locating)



Locating

• Introduction• Ericsson 1• Ericsson 3• Urgency conditions

– Quality– Timing Advance

• Auxiliary functions– Intra-cell handover– Hierarchical cell structures



Locating

• Locating Algorithm– Works out conditions for handover decisions for MS in active mode

– Inputs to algorithm are• Signal strength measurements• Quality measurements

– Output is list of candidate cells for handover• Cells are ranked and sorted in descending order of preference for handover



Locating

• Basic Cell Ranking– Two algorithms

• Ericsson 1: signal strength & path loss• Ericsson 3: signal strength only

– Common process stages• Correction for base station output power

– different levels possible on BCCH/TCH carriers• Calculation of minimum signal strength

– Thresholds MSRXMIN (DL) and BSRXMIN (UL)– SSmin = min (MSRXMIN, BSRXMIN)

• Application of signal strength penalties

What happened to Ericsson 2 ???Algorithms aim to let TCH carriers control cell borders.Corrected signal strength SS_DLn in neighbour cell n: for different output powers between BCCH (BSPWR) and other carriers BSTXPWR:

SS_DLn = rxlevn + BSTXPWRn – BSPWRnMinimum signal strength conditions:

SS_DLn >= MSRXMINnSS_ULn >= BSRXMINn

Where SS_DL is estimated by calculating DL path loss and subtracting from maximum MS output power.

SS_ULn = min(P,MSTXPWRn) – (BSTXPWRn – SS_DLn)Penalties are added to make it more difficult to handover to unsuitable cells. This is done by subtracting a signal value from the signal strength estimate for the unwanted cell, making it look worse than it really is. Penalties are applied for handover failure, bad quality urgency handover and excessive timing advance. A penalty is removed after the penalty duration has expired.



Locating

• Sufficient Level Condition• Threshold separating low signal strength cells from high signal strength cells

high signal strength

low signal strength

DL min levelUL min level

DL effective sufficient level

UL effective sufficient level

B

A

Cells satisfying minimum condition are processed for sufficient condition.

Calculation of sufficient level: s=serving cell, n=neighbour cellSS_DLn >= MSRXSUFFn – TROFFSETn,s + TRHYSTn,sSS_ULn >= BSRXSUFFn – TROFFSETn,s + TRHYSTn,s

Solid lines in diagram represent final combined UL and DL condition. Sufficient level for a serving cell may be different in relation to each different neighbour cell. Setup shown in diagram is valid only for BS pair A,B. It would be different for BS pair A,C.



Locating

• Ranking – signal strength (K) criterion– Signal strength relative to sufficient level

• K-cells = Low signal strength cells, – K values are

– K_DLn,s = SS_DLn,s – MSRXMINn,s– K_ULn,s = SS_ULn,s – BSRXMINn,s

• Effective K value is minimum of UL and DL K values modified by KHYST and KOFFSET

– K ranking• K_RANKn= min(K_DLn, K_ULn) – KOFFSETn,s -KHYSTn,s

• Cells are ranked with the highest K_RANK first

To rank the serving cell as K or L, the sufficient level is evaluated with respect to the best neighbour n1. If K-cell, then it is ranked with the other K-cells. Otherwise, it is ranked with the L-cells.

KHYST is used to decrease ranking values to underrate neighbour cells –to prevent ping pong handovers. Defined for a pair of cells and is always symmetrical KHYSTa,b = KHYSTb,aKOFFSET if positive decreases ranking value and if negative increases ranking value. The cell border is displaced AWAY from cell with positive value, and moved TOWARD the cell with a negative value. It is defined anti-symmetrical for a pair of cells: KOFFSETa,b = -KOFFSETb,a



Locating

• Ranking – path loss (L) criterion– Path loss is assumed symmetrical

• Applied to high signal strength cells – Path Loss values

• p_Ln,s = BSTXPWRn,s – SS_DLn,s

– L ranking values• L_RANKs = p_Ls• L_RANKn = p_Ln + LOFFSETn,s + LHYSTn,s• Cells are ranked with the lowest L_RANK first

LHYST and LOFFSET have the same properties as the K counterparts.

Path Loss criterion is independent of BS and MS power ratings. It facilitates transfer of calls from big cell (strong interference) to small cells (less interference). L-criterion should lower overall statistical interference in network



Locating

• Basic Ranking Candidate List

L-cells list

K-cells list

Best cell

Worst cell

Highest L-Rank (lowest path loss)

Lowest L-Rank

Highest K-Rank (highest signal level)

Lowest K-Rank



Locating

• Ericsson 3– Considers only signal strength– Ranking values

• RANKs = SS_DLs• RANKn = SS_DLn – OFFSETn,s – HYSTn,swhere• HYST = LOHYST if rxlevDLS < HYSTEP• HYST = HIHYST if rxlevDLS ≥≥≥≥ HYSTEP

• HYSTEP indicates Low or High signal strength for serving cell

The effects of OFFSET and HYST are similar to those described for Ericsson1. HYSTEP specifies when signal strength is high or low for serving cell. When high, a larger hysteresis value can be allowed than when it is low, in order to reduce the number of handovers. LOHYST and HIHYST are symmetrical and OFFSET is anti-symmetrical, defined for a pair of cells. HYSTEP is a cell parameter.



Locating

• Urgency Condition: Bad Quality– Handover is initiated when rxqual exceeds specified thresholds, even if the level is good

• rxqualUL > QLIMUL or • rxqualDL > QLIMDL

– Handover is allowed to cell of lower ranking, but not to cell with worse quality.

• BQOFFSET, applied to K-rank and L-rank values, defines how far from nominal border MS can be to qualify for the quality handover.

When BQ urgency exists, unsuitable neighbours are removed from candidate list. Signal strength of serving cell is compared with signal strength of candidates, and those cells with large differences are removed from the list.Ericsson1If K_RANKn – K_RANKs < -KHYSTn,s – BQOFFSETn,s remove n.If L_RANKn – L_RANKs > LHYSTn,s – BQOFFSETn,s remove n.Ericsson3If RANKn – RANKs < -HYSTn,s – BQOFFSETn,s remove n.

If BQ urgency handover performed, a penalty value PSSBQ and penalty duration PTIMBQ are applied to prevent immediate handover back to the old cell.

AB

Hysteresis corridor BQ urgency HO prohibited

BQ urgency region

BQOFFSETb,aNominal cell border



Locating

• Urgency Condition: Timing Advance– Timing advance (TA) can be used as a soft cell limiter, to force small cells

– TALIM is the defined cell limit, maximum (63 bits or 35 km).

– TA urgency occurs if TAs ≥≥≥≥ TALIM – Urgent handover is performed to neighbour cells where TAn < TALIMs

– If no suitable candidate found, call remains on serving cell

If TA urgency handover performed, a penalty value PSSTA and penalty duration PTIMTA is applied to prevent immediate handover back to the old cell.



Locating

• Auxiliary network functions – Assignment to another cell– Hierarchical cell structures– Dynamic overlaid/underlaid subcells– Intra-cell handover– Extended range– Cell load sharing

Assignment to another cell: performed only a certain period after immediate assignment.where a better cell other than the serving cell is found, this cell is first in

the locating candidate list, and setup is “assignment to better cell”.where congestion exists on serving or better cell, “assignment to worse

cell” can be made.Hierachical cells: Up to three layers, used for directing traffic from higher to lower layers. Higher layers to pick up traffic when congestion or coverage problems occur.Overlaid/Underlaid: for increasing traffic capacity. Overlaid cell serves smaller area, smaller re-use distance possible.Extended Range: allows cells with radius up to 72 km.Cell Load Sharing: enables traffic load sharing during peak traffic when traffic load exceeds a defined threshold. All calls close to border to cells with low load (below defined threshold) become load sharing candidates. The ranking values for candidate neighbour cells are recalculated using reduced hysteresis values.



Locating

• Intra-cell handover– Try to find another frequency and/or timeslot in the same cell with better quality

– Only if RxQual is bad AND RxLev is good• RxQual_UL/DL > QOFFSETUL/DL +FQSS(RXLEV_UL/DL +SSOFSETUL/DL)

– RxLev_DL/UL = actual measured signal strengths, no pc compensation

– FQSS = quality vs signal strength function– Does not work for:

• BCCH downlink• Random frequency hopping

QOFFSETUL/DL: quality offset parameters uplink/downlinkSSOFSETUL/DL: signal strength offset parameters uplink/downlinkFQSS table

RXLEV rxqual<=30 infinity31 6032-35 5936-38 5839-41 5742-45 5646-48 5549-52 5453-55 5356-58 5259-62 51>=63 50



Locating

• Hierarchical cell structures– Up to three cell layers

• Can be configured as an umbrella layer over a microcell layer

• Dual band network can be configured as different layers

– Aim to carry most traffic on the smaller/lower layer cells.

– Handover to a higher layer if lower layer congested or coverage problems exist

– Cells in different layers ranked separately



BSS Parameters - review

• Idle mode behaviour• Measurement filtering• Power Control• Handover (Locating)



Contents

• System Basics• BSS Parameters�Quality Assessment• Optimisation Measures• Organisation



Contents

• Quality Assessment�Network Performance Measurements

• Use of statistics• Traffic• Blocking• Dropped calls• Noisy calls• Call success rate• Handover causes

– Field Measurements



Network performance stats




Network Performance Stats

• Introduction– Counters are available from the OMC, eg:

• Traffic volume• Blocking rates• RxQual• RxLev• Handover success• Dropped calls… etc etc….

– Evaluated by cell, BSC, MSC etc– Software is available to process counters

This is a very good source of information given that the amount of traffic in the network is high enough to provide reliable statistics. In order to facilitate the identification and resolution of problems, it is important to determine the key system metrics to monitor. The frequency and level of detail of the report should also be set to ensure that there is sufficient information for the groups involved in the optimisation activities, and for management. Important key metrics which should be considered include call success rate, blocking (TCH and SDCCH), call setup and handover success. The performance monitoring tool will produce regular statistics reports for each cell for the previous 24 hours. The metrics will be calculated for the busy hour for each cell. Different operators offer different counters. E.g. some count number of RxQual=5, others count noisy calls, or noisy call minutes.




• Types of thresholds

– Target• Desired/specified threhold

– Optimisation• Level at which improvement is required

– Fault• Level indicating serious problem requiring immediate rectification

The key performance parameters are monitored against a set of thresholds: Target, optimisation and fault thresholdsThe Target threshold is defined as the level that enables the customer to initiate and complete a call successfully with good quality. The Optimisation threshold is defined as the level for a performance indicator which requires some improvement. This threshold will focus attention on the worst performing cells and optimisation activities are scheduled along with any others and implemented as necessary. The Fault threshold is defined as the level for a performance indicator which represents a serious problem and is considered to be a fault condition. It therefore requires an immediate solution and the necessary optimisation activities should be scheduled with greater priority.

The thresholds may change depending on the maturity of the network, and should be periodically reviewed.



Network Performance StatsMetric Definition Target

thresholdOptimisati

on threshold

Fault threshold

Comments

Call attempts Number attempts to start a speech, dat or fax call.

400 for signifi canc

e

N/A N/A Used to evaluate the significance of other metrics

Setup success rate Number o f successful TCH call setups out of call attempts.

96% 92% 80%

Call completion suc cess rate

Calls which, once set upare successfully con cluded

98% 92% 80%

Dropped call rate 1 - Call completion suc cess rate

2% 8% 20%

TCH RF- loss rate % Calls dropped only due to interference or lack of signal (Radio Link Timeout and handover timeout)

2% 8% 20% Pointer to coverage holes, or to interference caused by a bad frequency plan, or to an RxLe vAccessMin which is too low, or RTL too short.

SDCCH RF- loss rate %SD CCH channels dropped only due to inter ference or lack of signal

2% 8% 20% Pointer to coverage holes, or to interference caused by a bad frequency plan or to an RxLe vAccessMin which is too low. Also includes failed LAC up dates.

TCH blocking rate Failed TC H assignments because all TCHs are in use.

1% 2% 20% An indication of whether there are sufficient transceivers on the cell. Normally the network should have been extended to cope with traffic growth before blocking is experi enced.

SDCCH blocking rate Fa iled SDCCH assignmentsbecause all TCHs are in use.

0.5% 1% 5%

Intra cell HO success rate Handovers between timeslots on the same cell

96% 90% 80%

Inter cell HO success rate 96% 90% 80%

TCH traffic Busy hour traffic in Er langs, average of the 5 daily busiest hours in the last week.

N/A N/A N/A Used to weight the metrics and to plan growth. (See traffic planning

guidelines).

Metr ic Definition Target thres h old

Optimis a tion

threshold

Fault thres h old

Comments

Call attempts Number attempts to start a speech, dat or fax call.

400 for signif i canc

e

N/A N/A Used to evaluate the significance of other metrics

Setup success rate Number o f successful TCH call setups out of call

attempts.

96% 92% 80%

Call completion su c cess rate

Calls which, once set upare successfully co n cluded

98% 92% 80%

Dropped call rate 1 - Call completion su c cess rate

2% 8% 20%

TCH RF - loss rate % Calls dropped only due to interference or lack of signal (Radio Link Timeout

and handover tim e out)

2% 8% 20% Pointer to coverage holes, or to interference caused by a bad frequency plan, or to an

RxLe vAccessMin which is too low, or RTL too short.

SDCCH RF - loss rate %SD CCH channels dropped only due to

inte r ference or lack of signal

2% 8% 20% Pointer to coverage holes, or to interference caused by a bad frequency plan or to an

RxLe vAccessMin which is too low. Also includes failed LAC u p dates.

TCH blocking rate Failed TC H assignments because all TCHs are in use.

1% 2% 20% An indication of whether there are sufficient transceivers on the cell. Normally the network should have been extended to cope with traffic growth before blocking is

exper i enced.

SDCCH blocking rate Fa iled SDCCH assig n mentsbecause all TCHs are in use.

0.5% 1% 5%

Intra cell HO success rate Handovers between timeslots on the same cell

96% 90% 80%

Inter cell HO success rate 96% 90% 80%

TCH traffic Busy hour traffic in E r langs, average of the 5 dail y busiest hours in the last

week.

N/A N/A N/A Used to weight the metrics and to plan growth. (See traffic planning

guidelines).




• Significance of statistics– Binominal distribution

• Ask 10 people if they are married• 5 say yes• Are 50% of all people married?• 45% to 55%?• Chance that 40% or 60% are married.

To have a resolution of 1% in the call success rate would require 100 samples. However, there is still a distribution of the measured results around the true probability.




• Significance of statistics– Binominal distribution

Confidence of 1% accuracy for given number of calls

0.0%

10.0%

20.0%

30.0%

40.0%

50.0%

60.0%

70.0%

80.0%

90.0%

100.0%

0 100 200 300 400 500 600 700 800 900 1000 1100 1200Number of Calls

Con

fidence Probability

2%

5%

10%

20%

Dropped call rate

Confidence of 1% accuracy for given number of calls

0.0%

10.0%

20.0%

30.0%

40.0%

50.0%

60.0%

70.0%

80.0%

90.0%

100.0%

0 100 200 300 400 500 600 700 800 900 1000 1100 1200Number of Calls

Confid

ence Probability

2%

5%

10%

20%

Dropped call rate




• Significance of statistics

– Hundreds of samples must be taken to be 90% confident of only a ±1% tolerance

– Combine Busy hour statistics for the whole week




• Traffic– Traffic volume must include time period

– Busy hour normally• eg 3 busiest hrs of the week

– First work out when is the busy hour• Requires all-day measurements

– TCH traffic and SDCCH traffic

– Busy hour important for ALL statistics

The determination of the busy hour is important for all statistics. Many problems only manifest when load is high. Exception: downlink BCCH interference.




• Traffic– Forecasting– Weekly busy hour traffic extrapolated

Traffic

Time

Individual cells can have forecast traffic growth estimated before the traffic is combined into a traffic map.




• Traffic– Forecasting– Local growth or national growth?

Traffic

Time

Individual cells might have a significantly different prognosis than the overall growth forecast. For example a high traffic cell might cover the operator’s headquarters. Fast early growth, but now saturated.




• Traffic– Forecast 3 months ahead for TRX count

• Procurement• Frequency planning

– Forecast 12 months ahead for site count• Planning • Acquisition• Build

The frequency planning of the next turn-on-cycle will require as an input the amount of traffic in each cell. The cell capacity will need to last until the turn-on-cycle after that. A margin for error must be included.




• Blocking rate– Must be measured in the BH

• Traffic measurements required first• TCH blocking and SDCCH blocking

– Need to know:• Number of Call Attempts• Number of Successful TCH (or SDCCH) seizures

– Utilisation• % of TCH in use

In a frequency hopping system it may be that hard blocking does not occur, only soft blocking.




• Dropped calls– Various causes for this:

• Poor BER (Radio Link Timeout – RF Loss)• Deliberate disconnection (eg maximum range)• Hardware problems• Fixed network problems

• Lots of obscure counters!




• Noisy calls– RxQual measurements

• What is the definition of a noisy call?– e.g. 10% of RxQual ≥≥≥≥ 4

• Classify individual calls within the cell to identify problem cells

• Alternatively, determine by using all RxQual measurements taken over a measurement period (uplink and downlink)




• Call success rate– Service (coverage)– No blocking– No RF Loss or other drop– Not defined as noisy

– From the network it is not possible to see call attempts which fail due to no coverage.




• Call success rate– Target for a new (or newly expanded) network:

90% for each cell95% for each BSC

– Target for a mature network:96% for each cell98% for each BSC

The target performance of course needs to be met in the busy hour. Averaging over the whole day is cheating!




• Call success rate– Report to the responsible engineer on a weekly basis:

• Any cells in engineer’s area not meeting the target • Or the 10 worst cells in engineer’s area

• (First remove cells whose poor performance is due to a known hardware problem)




• Handover causes– Power Budget (L-criterion) should be dominant (90%)

– Signal level (K-criterion) only for indoors

– Quality cause should be rare

– Distance cause only in rural areas

– Uplink and Downlink causes




• Link balance– Imbalance in statistics (eg noisier uplink than downlink) can be caused by link imbalance

• Can carry out detailed measurements of cables, combiners, output powers, sensitivities, diversity gains, etc

• Can analyse NPC data or A-bis traces.

The A-bis interface is between the BS and the BSC. Possible to record all RxQual measurements for the cell in uplink and downlink. Imprt these into Excel and perform regression analysis.



Network performance review




Contents

• Quality Assessment– Network Performance Measurements �Field Measurements

�Measurement Equipment�Statistics�Analysis�Call Logging Equipment



Field measurements

• Measurement kit• Statistics• Analysis• Call logging equipment



Field Measurements

• Measurement kit

Rooftop antenna



Field Measurements

• Measurement kit– Engineering enabled mobile

• Records downlink measurements every 480 ms in dedicated mode

• Serving cell: – BCCH, BSIC, RxLev, RxQual, TA– Layer three messages

• Neighbour cells– BCCH, BSIC, RxLev_N

– GPS receiver• Location of every measurement• Enables display on a map

Engineering mobiles manufactured by SAGEM, Ericsson, Nokia etc. These mobiles have special engineering software (not available to Joe Bloggs on the street) that is used for measuring the relevant data. They do not have storage capabilities, therefore, data collected must be stored elsewhere. Known test mobiles include:• Nokia: 8148, PT11• Ericsson: TEMS pocket• SAGEM: OT35• Nortel: 1822



Field Measurements

• Statistics– Call success rate– Probability of coverage

• Signal above required threshold, NOT above median planning level

• Check “indoor coverage” with a 20 dB attenuator– post processing RxLevs would have to take into account DL power control



Field Measurements

• Data analysis– Dropped calls– In-building Coverage

RxLev > -90 dBm– (= -102 + 18 – 6 = -90dBm)



Field Measurements

• RxQual– Acceptable <= 4– Unacceptable >= 5



Field Measurements

• Outdoor coverage– RxLev ≥≥≥≥ -108 dBm– (-102 - 6 dB = -108 dBm)



Field Measurements



Field Measurements

• Dropped call - interference

In this example the signal level is reasonably good, while the RxQual is bad, indicating an area of interference led to the call dropping.



Field Measurements

• Dropped call - coverage

The serving signal drops very low, and the signals from neighbouring cells are also low, so there is no opportunity for a handover. In the low signal, the BER becomes high and the call drops.



Field Measurements

• Dropped Call - Unexpected release

In this example the signal level is adequate, and the BER remains low. Nevertheless the call is terminated by a network command.



Field Measurements

The Layer 3 messages indicate that the call dropped because there were no channels available on the target cell during a handover. The mobile fell back to the original cell, which eventually became unusable

.



Field Measurements

• Call logging equipment

– Test mobile (eg TEMS) in taxis, buses and employees cars, making repeated calls

• 2 minute call every 2.5 minutes• Data deleted if call is successful• If call drops within two minutes, call into computer via modem and download data for analysis

• Statistical results including no service areas

This method of data collection is sometimes used to collect data, in addition to regular drive testing, or when the network needs to be “ loaded”for specific investigation. It requires finding friendly customers that will agree to having the equipment installed in their vehicles for long periods of time. It is quite subjective in that the measurement routes are defined by the daily routine of the vehicle in which the kit is installed. However, it is highly likely that the calls will be made where there is potential “people traffic”.



Field measurements - review

• Measurement kit• Analysis• Statistics• Call logging equipment



Contents

• System Basics• BSS Parameters• Quality Assessment�Optimisation Measures• Organisation



Contents

• Optimisation Measures�Antenna Adjustments– Frequency & Interference Planning– Neighbour List Planning– Common Problems– Advanced Techniques



Antenna adjustments

• Tilt• Electrical and mechanical tilt• Side-lobes and nulls



Antenna adjustments

• Tilt - LL003:C and LL001:B are co-channelPlots from Quantum, courtesy of Quotient

A problem with automatic frequency planning tools is that they strictly apply the input thresholds given by the user, or at least take them into account. However, in certain circumstances the thresholds may not be appropriate.

In this example, cell LL001:B is co-channel with LL003:B, but they appear very close together. The size of LL001:B however, makes even a relatively large interference area only a small percentage of the area, or possibly a small percentage of the traffic.



Antenna adjustments

• Tilt -AFP tolerates interference (<10% of traffic?)Plots from Quantum, courtesy of Quotient

In this case a relatively large area of interference only affects a small number of Erlangs. However the area affected is a short stretch of very important road. In addition, the prediction radius for LL003 does not appear to be large enough. Other interference exists, which is not shown on the plot.

The network needs to be optimised to remove this interference in the BCCH layer.



Antenna adjustments

• Tilt (4 degrees electrical)Plots from Quantum, courtesy of Quotient

Replacing the antenna with one that has 4 degrees of electrical tilt reduces the interference to LL001 so that the important road is no longer affected.

Now it is important to predict the side effects.



Antenna adjustments

• Tilt (4 degrees electrical)– Check side effects

Coverage compromised?

Plots from Quantum, courtesy of Quotient

Tilting the beam has reduced the interference, but has also reduced the signal level closer to the site and a couple of coverage holes have appeared.Can the other road tolerate a lower signal in order to give the first road interference free coverage?Maybe a 2 degree tilt would have been sufficient?Perhaps a combination of tilt and a change in azimuth a few degrees to the south would give both roads good quality.A better solution might have been to substitute a new BCCH frequency in either of the two cells. However this might just move the interference to somewhere else.

It is the cell planner / optimiser who must make the decisions regarding the trade offs. This is why it is better that optimisers and cell planners are the same people.



Antenna adjustments

• Sidelobes– In the vertical pattern of most antennas are sidelobes

• Too much tilt can start to increase interference again

• Nulls– The null in the vertical pattern is best pointed towards the horizon

– Nulls below the horizontal can cause coverage holes close to the site



Antenna adjustments - review

• Tilt• Electrical and mechanical tilt• Side-lobes and nulls



Contents

• Optimisation Measures– Antenna Adjustments�Frequency & Interference Planning– Neighbour List Planning– Common Problems– Advanced Techniques



Frequency planning

• Cell planning practice• BCCH carrier planning and optimisation• Non-BCCH carriers• Frequency hopping• Interference reduction



Frequency planning

• Cell planning practice– Many “optimisation” problems are in fact due to poor cell planning

– Optimisation is a question on fine tuning the capacity / quality tradeoff

Q

T

Expansion

Optimisation / better planning



Frequency planning

• Cell planning practice– Problems when

• Interference not contained• One cell carries too much traffic• Inappropriate position of cell boundaries• Multiple servers• Imprecise service area

– All the above will affect the quality for a given traffic load (or the traffic load for a given quality)

• by making frequency planning harder



Frequency planning

• BCCH carrier planning– For BCCH carriers downlink interference always present

– Frequency plan must be interference free– Interference can be removed by changing the frequency plan



Frequency planning

• Non-BCCH carriers– Interference affected by DTX, PC and load

– PC more effective if most traffic is near the site

– Frequency planning relatively easy (1/3 or 1/1)

– Main issue is traffic planning



Frequency planning

• Frequency hopping– With 1/3 or 1/1, and fractional load: swapping frequencies does not remove interference

– Important to limit interference for all cells– New site? Surrounding cells should all have down-tilts reviewed.



Frequency planning

• Interference reduction– Antenna tilt– Reduced height – Reduced power– Terrain or clutter containment



Frequency planning - review

• Cell planning practice• BCCH carrier planning and optimisation• Non-BCCH carriers• Frequency hopping• Interference reduction



Contents

• Optimisation Measures– Antenna Adjustments– Frequency & Interference Planning�Neighbour List Planning– Common Problems– Advanced Techniques



Neighbour list planning

• Too many neighbours• Too few neighbours• Automatic neighbour planning• Undefined neighbour reporting• Double BA lists



Neighbour lists

• Too many neighbours– Impossible adjacent channel planning– Co-channel planning made difficult– Inappropriate handovers to distant cells– Less accurate neighbour RxLev measurements

Update neighbour lists in cells surrounding a new site!

The time for neighbour measurements is fixed within the SACCH multiframe. More neighbours means fewer samples are taken of each neighbour’s signal level. There is an opportunity for measurement once every TDMA frame, so 104 measurements every 480 ms.

For example, 6 neighbours : 17 samples per neighbour per measurement report. 26 neighbours is only 4 samples per neighbour per measurement report.



Neighbour lists

• Too few neighbours– No handover– Idle mode problems when returning to coverage

The problems of missing neighbours are obvious. Perhaps for this reason most networks seem to have too many neighbour relationships.



Neighbour lists

• Automatic neighbour planning– Measure length of common boundary– Determine area of overlap

• Overlap defined as where 2nd (or nth) server is less than X dB below the best server

– Second method preferred

– Manual fine tuning normally necessary: not too bad in a mature network



Neighbour lists

• Undefined neighbour reporting– Vendor feature– Heavy processing load– Mobile reports ALL cells measured, not just neighbours

– Post processing statistically identifies neighbours which were missed in planning



Neighbour lists

• Double BA lists– Problem:

• When coverage is “lost” mobile looks for last used BCCH

• In a vehicle coverage might be recovered some distance away

• “Old” cell still gives sufficient signal• “New”, local cells are not neighbours of the old cell• If a call is started it will soon drop



Neighbour lists

• Double BA lists– Solution:

• Long neighbour lists• Bad idea!• Two neighbour lists

– Idle mode– Dedicated mode



Neighbour list plan - review

• Too many neighbours• Too few neighbours• Automatic neighbour planning• Undefined neighbour reporting• Double BA lists



Contents

• Optimisation Measures– Antenna Adjustments– Frequency & Interference Planning– Neighbour List Planning�Common Problems– Advanced Techniques



Common problems

• Interference• Missing neighbours• Multiple servers• Blocking• Failed handovers



Common problems

• Interference– Specific cells:

• Tilt• Height• Re-plan

– General, limits capacity for given quality• Need to identify “jamming” frequencies and cells• Change CA lists so that “jamming” cells do not always interfere with the same other cells



Common problems

• Missing neighbours– Normally not an “obvious” neighbour– A terrain effect makes a distant cell the only server

– Since the distant cell is not a neighbour, the call drops, or is noisy



Common problems

• Multiple servers– No dominant server

• Mobile is likely to choose a cell which is not planned for use at that location

– Interference likely (especially BCCH) • Frequency plan assumed a different cell

– Many “ping pong” handovers• Measurements etc take time to settle after a handover



Common problems

• Blocking– Solution, extra TRX

• BUT, what about frequency plan?– Not relevant in a soft-blocking network

• In a FH network interference happens first• UNLESS many fewer TRX than frequencies



Common problems

• Blocking– Plan capacity so that number of Erlangs < 40% of Number of Frequencies x 8

• Exceeding this causes interference to OTHER cells

• One or two cells might exceed limit, if others are less than limit

• Well contained cells may carry more traffic

In a hopping network, the consequence of too much traffic in a single cell will be interference in other cells. This is directly opposite to what happens in a non-hopping network, where extra traffic leads to blocking in the high traffic cell.



Common problems

• Failed handovers– Target cell congestion

• Relieve congestion in target cell• Stretch source cell to overlap more

– Mobiles moving faster than handover timing• Speed up handovers• Design more overlap

– Rapid field drop• Speed up handovers• Design more overlap



Common problems

• Trouble shooting – Quality related

Poor Quality

RxLev RxQual Other

Coverage Hole

Antenna System

BTS/RadioProblem

Co/AdjInterference

OtherInterference

Time Dispersion

BTS/Radio Problem

BTS/Radio Problem

System Problem

Bad Handset



Common problems

• Trouble shooting

– Handover problems

Handover Problem

Cell Dragging

Handover Failure

Ping-Pong Handovers

Neighbour List

Hysteresis

Interference

BTS/Radio Problem

Neighbour List

BTS/Radio Problem

System Problem

No Best Server

Neighbour Cell Data

Hysteresis

BTS/Radio Problem

Congestion

BadRxLev/RxQual



Common problems

• Trouble shooting– Call setup Dropped

Calls

RxLev RxQual Other

Coverage Hole

Handover Problem

Antenna System

BTS/Radio Problem

Co/AdjInterference

Other Interference

Time Dispersion

BTS/Radio Problem

BTS/Radio Problem

System Problem

BSS Parameters

Bad Handset



Common problems - review

• Interference• Missing neighbours• Multiple servers• Blocking• Failed handovers



Contents

• Optimisation Measures– Antenna Adjustments– Frequency & Interference Planning– Neighbour List Planning– Common Problems�Advanced Techniques



Advanced techniques

• Dynamic frequency planning• Smart antennas• Underlay/Overlay• Dual band networks• National roaming



Advanced techniques

• Dynamic frequency planning– Use OMC data to auto-optimise a frequency plan

– BCCH neighbour measurements– On hopping frequencies these neighbours are also interferers

– Don’t necessarily use 1/3 pattern with groups• Could have more of an ad-hoc plan

Some advanced frequency planning ideas with application particularly to hopping networks are in the “research” phases. Many different ideas are being put forward, as can be established by visiting the conferences.



Advanced techniques

• Smart antennas– Electrically steerable beam patterns– Steer a null towards an interferer– Antennas themselves expensive– Control a nightmare

• Each mobile link has a different interferer• With FH each TDMA frame is a different interferer• More potential for CDMA systems



Advanced techniques

• Underlay / overlay– Handover from inner to outer cells using special algorithm (interference triggered)

– Estimated 30% extra traffic• IF traffic density is highest close to the sites

D

R



Advanced techniques

• Dual band networks– 1800 MHz for capacity in cities– 900 MHz for coverage in rural areas– Coverage footprints different– Cell selection and handover should favour 1800MHz cells where possible

– Issue: one or two BCCHs per cell?



Advanced techniques

• National roaming– 1800MHz mobile selects 900MHz network when home network not available

• Exactly like international roaming• Need to reselect back to home network when possible

– Handover to 900MHz cell when 1800MHz handover not possible

• Only level triggered handover• Use priority handovers to favour 1800MHz cells



Advanced techniques - review

• Dynamic frequency planning• Smart antennas• Underlay/Overlay• Dual band networks• National roaming



Contents

• System Basics• BSS Parameters• Quality Assessment• Optimisation Measures�Organisation



Organisation

• Timetable• Teams• Preparation• Databases



Organisation

• Timetable– Coverage / capacity planning– Frequency planning– Neighbour planning– Parameter planning– “On-air”– Intensive optimisation– Ongoing optimisation

Networks undergoing regular expansion normally mature from the chaotic early days into a regular cycle of “long term planning” – “short term planning” – “optimisation”.

New sites are integrated into the network at regular, or at least pre-agreed intervals, followed by a short period of very intensive optimisation work to convert the planned network into one which meets the quality targets while carrying the planned amount of traffic.



Organisation

• Timetable

Turn-on-date

Frequencies and parameters

Drop-dead-date

Intensive optim

isation

3 month Traffic forecast

and TRX count

12 month Traffic forecast

and BS

count

New BS Planning

Ongoing optimisation

After a new turn on cycle a new frequency plan, neighbour plan and BSS parameter plan will be loaded into the network. To avoid negative impact on customers this is often done on a Friday night. Immediately following this is a period of intensive optimisation. Often it will involve working the whole weekend,, inn an attempt to ensure that on the Monday morning the initial call success rate target is met. (90% worst cell, 95% average)Ongoing optimisation will continue after this intensive optimisation period in order to raise the CSR to 95% in the worst cell and averaging better than 98%. However, the attention of the radio engineers will shift to longer and medium term expansion planning until the time comes to prepare for the next turn on cycle.The “drop dead date” is the final date at which sites must be listed for inclusion in the next ToC. After this the traffic and frequency planning activity will depend on having a stable network plan.



Organisation

• Teams– Quality

• Independent assessment of network quality• Drive tests• Network performance data

– Radio planning / Optimisation• Ideally within the same department• One person/small team responsible for an area of 50 to 100 sites

NB these functions are often organised differently within different operating companies (also at different times), but the basic functions remain.The quality department will monitor the network and report areas requiring attention to RF. Independent monitoring encourages RF to chase targets.Radio planning and optimisation ought to be within the same department, since all decisions in this area require trade-offs between quality (traditionally optimisation) and capacity (traditionally planning).



Organisation

• Teams– Drive testing

• Drivers and technicians/navigators• Resource available for Quality and Radio dept.

– Operations• Implementation of BSS parameters• Maintenance issues• Delivery of statistics

– Implementation• Build of new sites• Installation of TRX upgrades• Changes to antenna configurations

Drive test resource might be independent or in the quality department or in the RF department.

Operations, often have responsibility for the OMC. Their function is maintenance of the network, but this will often overlap with optimisation. The obvious area is where parameter changes are necessary.

Implementation will be making changes to antennas where necessary.



Organisation

• Preparation

– Cluster definition• Optimise manageable bits of the network• Edge of cluster should be an unchanged area

– BS testing• New sites should be tested for faults BEFORE optimisation

– Antennas connected correctly– Parameters set correctly – neighbours / BCCHs

An optimisation area, or cluster must be defined, so that a team can manage its work well. Ideally the network expansion and rollout will be organised so that the surrounding area will be not require optimising at the same time.

Many so called “optimisation problems” turn out to be hardware and software faults, incorrectly connected antennas or simple typos. Soon after the integration of new sites, they should be tested for functionality and correct configuration.



Organisation

• Preparation– Quality assessment

• Identify and locate problems

– Sources of data• Network performance statistics• Drive tests• Customer complaints

The first step in both the intensive optimisation stage and in the ongoing optimisation will be to identify the locations of network problems. Different methods of doing this each have their advantages and disadvantages. Network Performance Stats take time to collect and optimisation is usually scheduled for low traffic periodsDrive tests only measure downlink, unless linked to A-bis traces, which can be tedious.Customer complaints normally come after the end of the weekend, rather than early in the optimisation campaign, where it is desired to find all the problems.



Organisation

• Databases– Planning tool

• Current network situation• History• Plans

– Network• Live database of parameters• Antenna tilts and site locations

Database integrity is often difficult to maintain during an optimisation event. The problem is that settings and parameters are changing so quickly that it is sometimes difficult for the databases to keep up.

A direct link from planning tool to OMC can help. In the absence of this, and certainly for antenna changes, a disciplined change request procedure is required.



Organisation

• Databases– Measurements

• Large amounts of data• Catalogue to match with correct history database in planning tool

– Optimisation database• History of all optimisation problems and solutions• “Trouble ticket” system• Problems should be formally closed• Library of common problems for future help



Organisation

• Databases

– Optimisation database example

Problem Input- Operations- Qual. measurements- Custumer Complains- EmployeeProblemreports

DCS-Measurement

datas

-Logical Connection ofthe Measurement data tothe OptimisationProblem- Measurement data

DCS-Measurement

Request

- Optimisation Problem- Opt. Project Managment- Measurement Requests- Para.Change request forms- Optimisationproblem Solutions

Optimisation-database

Problemerfassung

ChangeRequestform

OptimisationReports

ToMeasurementteam

- To Fieldengineers- To OMC- To Radioplanning

Internal inOptimisation

Projekt Reports

Internal inOptimisation forProplemmanagement

DB Output

DB-Management

Map InfoGeographicalProblemdisplay

The optimisation database should be multi-user with a number of functions including:· Storage of information on problem originator· Prioritisation of problems· Logical connection of problems to Optimisation areas· Grouping of problems to a master/main problem· Storage of problem resolution measures· Printing of Change Requests and Measurement Requests· Historical record of Problems· Attachment of Win-files (pictures, documents) to a problem

The database could be configured as required, local to each region, which means that access will not be possible from another region or from a different location within the region. Each optimisation problem would still have a unique problem number, each new number being automatically assigned by the database. All measurement and change requests, optimisation and project reports will be generated in paper form. An administrator should be appointed to maintain the database, thereby ensuring the integrity over the lifetime of the network.



Organisation

• Implementation procedure– Identification of problems– Allocation of drive routes– Analysis of data– Solution of problems

• Check out side effects!!• Use planning tool• Liaise with other RF teams

– Implementation of solution– Verify solution



Organisation

Optimisation

Optimisation Guidelines Optimisation Database

Input Data collection:Metrica Statistics,Drive Test MeasurementsCustomer Complaints

Cluster Definition

Initial Site Validation

Data Analysis/Problem Identification

Solution Recommendationand Implementation

Validation of Solution

In a nutshell, the organisation that is established for optimisation is required to carry out these processes



Finally

• Take action ………

• Go optimise with confidence!



Contact details

Telecom Network ConsultantsHighfield House90 West DriveHighfields CaldecoteCambridge CB3 7NYTel: +44 1954 210841Fax: +44 1954 210840Email: [email protected]: www.tnc-ltd.com

Documents

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