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FINAL REPORT OF
6 MONTH INDUSTRIAL TRAININGIN
IDEA CELLULAR LTD.
Engineering RO, Feroze Gandhi market, Ludhiana.
BACHELOR OF TECHNOLOGY
IN
ELECTRONICS AND COMMUNICATION
SUBMITTED TO: SUBMITTED BY:Prof.BHUPINDER VERMA (H.O.D) Hanul Vig
7080405585 ECE-8A, G-2
LOVELY INSTITUTE OF TECHNOLOGY, PHAGWARA
Department of Electronics and Communication Engineering
ACKNOWLEDGEMENT
It is a pleasure of mine to find myself penning down these lines to express my sincere thanks to our Principal & Training & Placement officer of Lovely Institute of Technology, Jalandhar who gave us an opportunity of industrial training for 6 months to enhance our professional practice & to get preliminary industrial exposure in the concerned discipline.
It gives me immense pleasure & honor to express my heartiest thanks to management & staff of IDEA CELLULAR Ltd specifically to Mr. Jaspreet Singh (Senior Engineer) for giving me opportunity for the training in their reputed industry.
I express my deep sense of gratitude to Mr. Amandeep Gill (Engineer), BSS Team for giving me knowledge about cellular communication and concepts related Project department and other departmental services explaining the theoretical as well as practical concepts.
Hanul VigRoll No. 7080405585
INTRODUCTION
Necessity:
Learning comes from doing. To learn something one has to go through Practical conditions.
Recognizing this fact, the University has made it compulsory for the students to undergo
Industrial training for one whole semester. During this period, the student learns about the
functioning of the organization and the actual business environment.
This project report was prepared during the training period in IDEA Cellular Pvt. Ltd.
Mohali. During this period, an effort is made to understand the various operations in the
Engineering Department at IDEA and to finish the project assigned to me. This report lays
special emphasis on the operation work, tasks and projects carried out during training
period.
Objective:
Technology has rapidly grown in past two-three decades. An engineer without practical
knowledge and skills cannot survive in this technical era. Theoretical knowledge does matter but
it is the practical knowledge that is the difference between the best and the better. Organizations
also prefer experienced engineers than fresher ones due to practical knowledge and industrial
exposure of the former. So it can be said the industrial exposure has to be very much mandatory
for engineers now a days. The practical training is highly conductive for:-
1. Solid foundation of knowledge and personality
2. Exposure to industrial environment.
3. Confidence building.
4. Enhancement of creativity.
Introduction to Company:
IDEA Cellular is a GSM network provider in the region of Delhi, Andhra Pradesh, Gujarat,
Maharashtra, Haryana, Kerala, Madhya Pradesh Uttar Pradesh (West), Uttar Pradesh (East),
Rajasthan, Himachal Pradesh, Bihar, Mumbai, Karnataka, Punjab and Orissa. It was established
in the year 1995 and since then its network accessibility and coverage has increased by leaps and
bounds and shows no signs of slowing down. The secret behind the success is its availability in
the remotest corners of the state. The spearhead of success is the flexibility in the schemes
offered by the company and the customer satisfaction.
All the departments work in close harmony with one another and problems relating to the
network are solved immediately by the adept and experienced engineers and non-technical staff,
working in the various departments of the company. The company is an icon and stands out of all
the other network providers in the state.
History and Evolution of Idea Cellular Ltd:
Idea Cellular is a wireless telephony company operating in various states in India. It initially
started in 1995 as a joint venture among the Tatas, Aditya Birla Group and AT&T by merging
"'Wings Cellular'" operating in Madhya Pradesh, Uttar Pradesh (UP) West, Rajasthan and Tata
Cellular as well as Birla AT&T Communications.
Initially having a very limited footprint in the GSM arena, the acquisition of Escotel in 2004
gave Idea a truly pan-India presence covering Maharashtra, Goa, Gujarat, Andhra Pradesh,
Madhya Pradesh, Chhattisgarh, Uttar Pradesh (East and West), Haryana, Kerala, Rajasthan and
Delhi (inclusive of NCR).
The company has its retail outlets under the "Idea n' U" banner. The company has also been the
first to offer flexible tariff plans for prepaid customers. It also offers GPRS services in urban
areas.
Idea Cellular won the GSM Association Award for "Best Billing and Customer Care Solution"
for 2 consecutive years.
IDEA Innovative, Stimulate, Liberate:
IDEA Cellular is a publicly listed company, having listed on the Bombay Stock Exchange (BSE)
and the National Stock Exchange (NSE) in March 2007.
IDEA Cellular is a leading GSM mobile service operator with pan India licenses. With a
customer base of over 43 million as on end March ’09, in 16 service areas, operations are soon
expected to start in Tamil Nadu including Chennai; Kolkata & West Bengal, North East &
Assam, and J&K.
A frontrunner in introducing revolutionary tariff plans, IDEA Cellular has the distinction of
offering the most customer friendly and competitive Pre Paid offerings, for the first time in India,
in an increasingly segmented market. From basic voice & Short Message Service (SMS) services
to high-end value added services such as Mobile TV, Games etc – IDEA is seen as an
innovative, customer focused brand.
IDEA ‘Women’s Card’ caters to the special needs of women on the move, and ‘Youth Card’
covers the emerging youth segment. IDEA ‘My Gang’ – the widely popular community user
group product recently bagged the prestigious ‘Golden Peacock Award 2008’ under the Most
Innovative Product category at the “19thWorld Congress on Total Quality”.
A brand known for many firsts, IDEA was the first to launch GPRS and EDGE in India. IDEA
has partnered with Research in Motion (RIM) to offer Blackberry services on its network. IDEA
‘Net Setter’– Plug & Play, EDGE enabled USB Data Card offers affordable data connectivity
with faster speed and consistency.
IDEA offers seamless coverage to roaming customers traveling to any part of the country, as
well as to international travelling customers across over 200 countries. IDEA Cellular has
Partnership with over 400 operators worldwide to ensure that customers are always connected
while on the move, across the globe.
IDEA has received several national and international recognitions for its path-breaking
innovations in mobile telephony products & services. It won the GSM Association Award for
"Best Billing and Customer Care Solution" for 2 consecutive years. It was awarded “Mobile
Operator of the Year Award – India” for 2007 and 2008 at the Annual Asian Mobile News
Awards.
IDEA Cellular is part of the Aditya Birla Group, India's first truly multinational corporation.
The group operates in 25 countries, and is anchored by over 1,25,000 employees belonging to 25
nationalities. The Group has been adjudged 'The Best Employer in India and among the Top 20
in Asia' by the Hewitt-Economic Times and Wall Street Journal Study 2007.
Our Service Areas:
The Indian telecommunications market for mobile services is divided into 22 "Service Areas"
classified into "Metro", Category "A", Category "B" and Category "C" service areas by the
Government of India. These classifications are based principally on a Service Area's revenue
generating potential.
Our 16 operational Service Areas are broken up into Established and New Service Areas.
Established Service Areas:
The established service areas are Delhi, Andhra Pradesh, Gujarat, Maharashtra, Haryana, Kerala,
Madhya Pradesh and Uttar Pradesh (West).
Licenses for the Maharashtra and Gujarat Service Areas were awarded in December 1995, with
network rollout and commercial launch achieved in 1997. In January 2001 the mobile operations
in Andhra Pradesh Service Area were integrated with IDEA through a merger with Tata Cellular
Limited.
In June 2001, the mobile operations in Madhya Pradesh Service Area were fully integrated with
IDEA through an acquisition of RPG Cellcom Limited. In October 2001, the license for Delhi
Service Area was acquired during the fourth mobile license auction, with network rollout and
commercial launch in November 2002.
In January 2004, Escotel Mobile Communications Private Limited ("Escotel"), was acquired
with its original licenses in the Service Areas of Haryana, Uttar Pradesh (West) and Kerala. All
these Service Areas were re-branded and integrated with IDEA in June 2004.
New Service Areas:
The New Service Areas are Uttar Pradesh (East), Rajasthan, Himachal Pradesh, Bihar, Mumbai,
Karnataka, Punjab and Orissa.
Licenses for Uttar Pradesh (East), Rajasthan and Himachal Pradesh were acquired through the
acquisition of Escotel (Escorts Telecommunications Limited).
Brand Idea was launched in Karnataka and Punjab, through the acquisition of
Spice Communications.
Idea launched its services in Mumbai and Bihar in 2008. The Mumbai launch was the largest
Idea Cellular Punjab:
IDEA comes to Punjab (Chandigarh, December 19, 2008)
IDEA Cellular Ltd., a leading telecom services provider, made its entry into Punjab by formally
unveiling its logo and brand identity at a function here today.
As part of its growth strategy, IDEA Cellular Ltd. had recently acquired Spice Communications
paving its entry into Punjab. IDEA will build on the 23 lakh strong subscriber base of Punjab's
oldest mobile network, and will introduce its complete range of mobile telephony products and
services for existing subscribers, and other mobile users and intenders in the state.
The IDEA logo in yellow, which symbolizes strength, vibrancy and vitality, will be seen across
the rural and urban landscape of Punjab, starting today. With this launch, IDEA now covers over
80% of the telephony potential of the country, and is the 3rd largest private GSM player with
over 36 million subscribers. IDEA Cellular is part of the Aditya Birla Group and is India's fastest
growing mobile service provider.
Speaking on the occasion of launch of services in Punjab, Mr. Sanjeev Aga, Managing
Director, IDEA Cellular Ltd., said, "We are happy to announce our entry into Punjab, and
welcome the people to join IDEA's pan-India network. IDEA's commitment to offer the best
telephony experience for our customers will usher in a new dimension in mobile telephony
experience for the people of the state."
The IDEA network in Punjab covers over 10,000 towns and villages, operating on the highly
efficient 900 MHz GSM frequency, riding on a next generation switching network, with 2.75G
capabilities and EDGE services. IDEA aims to provide superior connectivity to mobile users,
with a network of over 2500 cell sites in rural and urban Punjab.
IDEA is the leader in introducing value added services in the Indian mobile telephony market.
With the launch of IDEA in Punjab, mobile users in the state will now have a richer experience
while watching movie previews on IDEA TV, Voice chats, Instant Messenger, multimedia
messages with video attachments, web-infotainment, high-speed video downloads, Java game
downloads and other Internet-based multi-media experiences on their EDGE-enabled mobile
phones.
With the launch of IDEA in Punjab, the brand identity will now permeate all forms of external
and internal communication synergistically across its various telecom functions.
Mission and Values :
Idea Cellular Punjab, we have set ourselves the goal of being market leaders in all we do.
Achieving this is far harder than saying it. To succeed, we need to focus on two main
thrust areas- Total Quality Management & Professionalism. By recognizing and
committing to these areas, our mission will be achieved.
Mission:
Mission of IDEA CELLULAR is to:
To have satisfied customers, employees and shareholders.
Focus Areas:
The above said mission will be achieved through / by :
_ Setting and implementing the budget and Business Plan.
_ Benchmarking best practices to constantly monitor quality of service
delivered to internal and external customers.
_ Motivating employees to optimize productivity.
_ Facilitating employees work through well defined processes.
Core Values
• Team Work.
• Trust
• Strive for Excellence.
• Integrity.
• Commitment and Ownership.
• Recognition of performance.
The Idea Culture
The Idea Culture is an expression of our corporate community, guided by the Mission of Idea
Telecom i.e. to have satisfied customers, employees and share holders. Every Person reflects the
core values of team work, trust, strive for excellence, integrity, commitment, ownership and
discipline on which we have castled our success. People of Punjab have recognized and
rewarded us by adding Idea to their lives!!
The openness, the positive approach and assertiveness of every Person is reflected in the service
extended and the style of conducting each other (there are very few doors at Idea offices!).
We welcome opinions, recommendations, new ideas and constructive criticisms on how we all
might more effectively reach our goals, from everyone through open lines of communication.
Our responsibilities at Idea, very simply, are to adhere to our unshakable belief in honesty,
integrity and ethical conduct in all we do. Our dedication to these values and goals has enabled
us to continue to serve our customers better.
Company Achievements
1995
_ Incorporated as Birla Communications Limited.
_ Obtained licenses for providing GSM-based services in the Gujarat and Maharashtra
Circles following the original GSM license bidding process.
1996
_ Changed name to Birla AT&T Communications Limited following joint venture between
Grasim Industries and AT&T Corporation
1997
_ Commenced operations in the Gujarat and Maharashtra Circles
7
1999
_ Migrated to revenues share license fee regime under New Telecommunications Policy
("NTP")
2000
_ Merged with Tata Cellular Limited, thereby acquiring original license for the Andhra
Pradesh Circle
2001
_ Acquired RPG Cellular Limited and consequently the license for the Madhya Pradesh
(including Chhattisgarh) Circle
_ Changed name to Birla Tata AT&T Limited
_ Obtained license for providing GSM-based services in the Delhi Circle following the fourth
operator GSM license bidding process
2002
_ Changed name to Idea Cellular Limited and launched "Idea" brand name
_ Commenced commercial operations in Delhi Circle
_ Reached the one million subscriber mark
2003
_ Reached the two million subscriber mark
2004
_ Completed debt restructuring for the then existing debt facilities and additional funding
for the Delhi Circle.
_ Acquired Escotel Mobile Communications Limited (subsequently renamed as Idea
Mobile Communications Limited)
_ Reached the four million subscriber mark
_ First operator in India to commercially launch EDGE services 2005
2005
_ Reached the five million subscriber mark
_ Turned Profit Positive
_ Won an Award for the "Bill Flash" service at GSM Association Awards in Barcelona,
Spain
_ Sponsored the International Indian Film Academy Awards
2006
_ Became part of the Aditya Birla Group subsequent to the TATA Group transferring its
entire shareholding in the Company to the Aditya Birla Group
_ Reached the 10 million subscriber mark
_ Received Letter of Intent from the DOT for a new UAS License for the Mumbai Circle.
_ Received Letter of Intent from the DOT for a new UAS License for the Bihar Circle
through Aditya Birla Telecom Limited. ABNL, the parent of Aditya Birla Telecom
Limited, pursuant to a letter dated November 22, 2006, agreed to transfer its entire
shareholding in Aditya Birla Telecom Limited to the Company for the consideration of
Rs. 100 million.
2007
_ Won an award for the "CARE" service in the "Best Billing or Customer Care Solution" at
the GSM Association Awards in Barcelona, Spain
_ Initial Public Offering aggregating to Rs. 28,187 million and Listing of Equity Shares on
the Bombay Stock Exchange and the National Stock Exchange
ENGINEERING DEPARTMENT
NETWORK OPERATION AND MAINTAINANCE
(NOM)
NETWORK DESIGN AND DEVELOPMENT (NDD)
OPERATIONS AND
MAINTAINANCE RADIO (OMC-R)
NETWORK SWITCHING SUB-SYSTEM (NSS)
PLANNING
ENGINEERING AND FRONT DESK (EFD)
PERF.
BASE STATION SYSYTEM (BSS)
2008
_ Idea acquired 9 licenses for Punjab, Karnataka, Tamil Nadu & Chennai, West Bengal,
Orissa, Kolkata, Assam, North East and Jammu & Kashmir
_ Acquired Spice Communications with the operating circles of Punjab and Karnataka
_ Launched services in Mumbai metro in the largest single metro city launch, ever
ENGINEERING DEPARTMENTS IN IDEA
The engineering department at IDEA ensures round the clock availability of the network and the
services associated with it. The various departments under it function hand in hand for the
smooth operation of the network, its optimization and removal of snags and technical faults. The
engineering department can be divided into 2 broad categories. They further have many
departments under them. The tree below shows the various departments and their sub
departments.
1. BSS (Base Station System)
2. OMC-R (Operations and Maintenance for Radio)
3. EFD (Engineering Front Desk)
4. NSS (Network Switching Centre)
5. Planning
6. Performance
BSS: It is involved in the maintenance of the GSM Network. It involves daily routines like
Preventive Maintenance, Weather proofing, Site Expenditures, Fuel availability, Power
availability, etc. These people if required also do any reconfiguration.
OMC: Operation Maintenance & Control is there for the daily/weekly/monthly maintenance and
operations of the radio. It consolidates the network outages/changes. It handles alarms and
notifications for the same are sent to the concerned regions. It escalate faults and monitors the
overall network to ensure maximum network availability. It keeps the updated information of
sites, cells, carriers and PSTNs in the network.
EFD: Engineering Front Desk is the front desk for the Engineering department. Any customer
complaints or queries from any other department have to go through this for evaluation. EFD has
to give feedback on customer related problems to the customer care on daily basis.
NSS: Network Switching System is involved in the maintenance of the Switch, over which all
the calls of the IDEA customers are routed in the Network. Operation & Maintenance of NSS
equipment comprising of MSC, OMCs, VMS, SMSC & ACD.
It also performs IREG testing for both national and international roaming partners and to assist
IT & NRMG in post commercial scenario. It provides support to Billing and reconciliation,
Performance Team and EFD in solving customer problems. It also ensures provisioning of
statistics.
RF PLANNING AND PERFORMANCE: Planning and Implementation Department is
involved in planning and implementation of sites in the most cost effective way and handing
over to field maintenance staff as per procedures. It also conducts propagation tests for new
planned sites and carries out advanced planning and ordering of BTS, Microwave and other
associated equipment according to site planning and business plan. It also carries out the Drive
tests of new sites
Performance department is there to keep a check on the Network performance and to enhance the
performance when required from time to time. It collects GSM statistics viz. Call statistics,
interface statistics, processor utilization statistics from GSM network entities and displays them
for analysis. It monitors network traffic and equipment loading and provides necessary
information for network management and planning. It is involved in RF planning and
optimization.
Departments and Their Functions
Planning And Implementation:
• Overall responsibility of network planning and rollout as per business plans.
• Planning and implementation of sites in the most cost effective way and handing over to
field maintenance staff as per procedures.
• To conduct propagation test for new planned sites.
• Drive testing of new sites and submission of its report to planning group.
• Advance planning and ordering of BTS, Microwave and other associated equipment
according to site planning and business plan.
• Co-ordination with sales, marketing, customer services and site acquisition & build group
for smooth process of delivering new sites.
• To work on network traffic statistics for trending, identification of in-fill sites and
prediction of future requirements.
• Co-ordination of TEC evaluation of coverage and POI.
• Co-ordination with sales and marketing group for presenting customized solutions & new
features to corporate customers.
• Interaction with vendors for new products/features to enhance QOS and value addition to
network.
• Implementation of special projects for new revenue opportunities.
Engineering Front Desk:
• To interact with customer care and solve customer problems.
• To give feedback on customer related problems to the customer care on daily basis.
• To escalate any kind of problems/faults occurring in the network to the customer care.
• To analyze the problems from customer view.
• To escalate faults to the concerned person and track the faults.
NSS:
Operation & Maintenance of NSS equipment comprising of MSC, OMC-S, VMS, SMSC
& ACD.
To Perform IREG testing for both national and international roaming partners and to
assist IT & NRMG in post commercial scenario.
Support to Marketing in planning and implementation of new features in the network.
Billing and reconciliation support.
Managing POI related issues.
Planning and executing system H/W & S/W upgrades.
Liaison with BSNL and TEC.
Providing support to Performance Team.
To ensure provisioning of statistics.
To support EFD in solving customer problems.
OMC-R:
To handle alarms, escalate faults and overall monitoring of network to ensure maximum
network availability.
Basic level co-ordination of OMC, BSS outages planned/unplanned and to ensure service
availability at all the time.
To perform operation and maintenance of OMC, DXX, EMOS & other systems.
To perform daily/weekly/monthly routines of OMC-R.
To consolidate the network outages/changes into weekly and monthly reports.
Ensuring documentation, database integrity and backup management of all NMS systems.
To keep the updated information of sites, cells, carriers and PSTNs in the network.
To maintain the updated copy of DDF and microwave diagram for the whole network.
To create database for BSCs, XCDRS, BTSs and their devices.
BSS Maintenance:
To ensure the maximum Network Availability & reduce downtime to minimum.
To perform routine Maintenance activities on the BSC, BTS, Microwave and Backbone
Sites.
To handle all alarms which are generated at any site in the area of responsibility.
To handle all Power related problems in all sites.
To maintain all intercity and intra city links.
To implement all upgrades in the network (BSS site specific)
Asset management (Tools, testers, manuals etc)
To suggest any changes in the network required to enhance the coverage and
performance.
To assist in any implementation activities as the case may b.
Network Performance and Optimization
System Dimensioning and Optimization
To collect GSM statistics viz. Call statistics, interface statistics, processor them for
analysis.
To monitor network traffic and utilization statistics from GSM network entities and
archiving them in a database and displaying equipment loading.
To provide necessary information for network management and planning.
To introduce new features and control network up gradation.
To forecast on network growth and capacity planning.
To send reports to network operations manager.
To interact with EFD in solving customer problems.
CELLULAR NETWORK COMPONENTS
The following network components are required to connect a cellular phone into the Public
Switched Telephone Network (PSTN).
Cell Site ( Base Station Equipment)
Mobile Switching Centre (MSC)
The “CELL” Cellular radio involves dividing a large service area into regions called “cells”.
Each cell has the equipment to switch, transmit and receive calls from any subscriber located
within the borders of its radio coverage area.
If cells were not used the transmitter would need to use very high power to cover a large area.
Using cells, means that the area covered by a single transmitter is reduced, thereby reducing the
need for high powered transmission.
Cells are conventionally regarded as being hexagonal, but in reality they are irregularly shaped.
The cell shape is determined by the nature of the surrounding area e.g. hills, tall buildings etc.
The cells also overlap one another. The cell pattern becomes more complex as the number of
cells in the system increases. The hexagonal regions are known as cells and represent the
geographic area covered by one RF Carrier.
The Frequency Spectrum
The frequency spectrum is very congested with only a narrow bandwidth allocated for cellular
telecommunications. This means that the bandwidth we have must be used very efficiently. Each
cell in the Cellular Network requires a RF carrier.
A RF carrier is a pair of radio frequencies, one is used in each direction (transmit and receive) so
that information may be passed I both directions simultaneously. The transmit and receive
frequencies are separated by 45MHz (GSM) OR 75 MHz (DCS 1800) to avoid interference.
There are not enough frequencies available for every cell to have a different RF carrier. There
are 124 RF carriers in the GSM frequency band, therefore if each carrier can carry seven phone
calls a maximum of 868 (124x7) calls may be made. This is clearly not enough and therefore the
frequencies must be reused.
The GSM 900 standard has been adopted for PCN operation in the 1.8GHz band. In the UK, the
1710-1880MHz band has been allocated for DCS 1800 providing two bands of 75MHz with a
20MHz separation for split duplex operation. DCS1800 therefore has three times the allocation
of GSM 900 which is consistent with the peak traffic densities anticipated for PCN.
The network planner designs the cellular network around the available carriers or frequency
channels. The frequency channels are allocated to the network provider from the GSM band:
Receive (uplink) 890-915 MHz
Transmit (downlink) 935-960 MHz
Frequency channels = 124 (200 kHz B/W)
Frequency Re-Use:
By reusing frequencies many more phone calls may be made. The same RF carrier frequency can
be used for many conversations in several different cells at the same time.
The radio frequencies available are allocated according to a regular pattern which repeats over
the whole coverage area. In this way, each carrier is used repeatedly throughout the coverage
area according to a frequency re-use pattern. The diagram next page illustrates a 7-cell pattern,
each number represents a different RF carrier.
Frequencies are commonly reused every 2, 4 or 7 cells, these patterns combine adequate
coverage density with efficient usage of the available RF spectrum. The pattern that is chosen
depends very much on the nature of the area to be covered. This may range from a densely
populated inner city to a sparsely populated rural expanse.
Co-Channel Interference
Co-channel interference occurs when RF carriers of the same frequency are transmitting in
nearby cells. The transmission from one interferes with the other.
Adjacent Channel Interference
Adjacent Channel Interference occurs when a RF source of a different frequency interferes with
the carrier.
Cell Size:
The number of cells in any geographic area is determined by the number of mobile subscribers
who will be operating in that area and the geographic layout of the area (hills, lakes, buildings)
Large Cells
The maximum cell size is mainly determined by the distance radio waves can travel and still be
of practical use. Maximum cell radius is about 32kms. Large cells are generally used in remote
areas where there are very few subscribers.
Remote Areas
High Transmission Power
Few Subscriber
Small Cells
The minimum cell size is determined by the number of mobile subscribers who will be using the
cell. In an urban area where a large number of people are located, very small cells will be used
which are about 0.8 Km. Small cells have the advantage of being able to use a low transmit
power this means that small lightweight h and portable phones may be used.
_ Urban Areas
_ Low Transmission Power
Omni-Directional Cells
All the cells which have their own Cell Site are known as OMNI cells. When traffic density is
very high cells can be reduced in size by “sectorising”.
120 Degree Sectors
The diagram here shows a cell with 120 degree sectorisation. The original cell is divided into
three smaller cells, these cells share the same cell site but each has its own allocation of radio
carriers.
60 Degree Sectors
This diagram shows a cell with 60 degree sectorisation. With current analogue systems, this
arrangement is common in the centres of large cities where peak subscriber demand is very
heavy. GSM will also use 60 degree sectorised cells, with only a two site repeat pattern.
ARCHITECTURE OF THE GSM NETWORK
The GSM technical specifications define the different entities that form the GSM network by
defining their functions and interface requirements.
The GSM network can be divided into four main parts:
1. The Mobile Station (MS).
2. The Base Station Subsystem (BSS).
3. The Network and Switching Subsystem (NSS).
4. The Operation and Support Subsystem (OSS).
The architecture of the GSM network is presented in figure.
SS7BTS
BSC MSCVLR
HLR AuC
GMSC
BSS
PSTN
NSS
AE
CD
PSTNAbis
B
H
MS
Mobile Station (MS)
A Mobile Station consists of two main elements:
The Mobile Equipment or Terminal.
The Subscriber Identity Module (SIM).
a) The Terminal or Mobile Equipment
There are different types of terminals distinguished principally by their power and
application:
The `fixed' terminals are the ones installed in cars. Their maximum allowed output power
is 20 W.
The GSM portable terminals can also be installed in vehicles. Their maximum allowed
output power is 8W.
The handheld terminals have experienced the biggest success thanks to their weight and
volume, which are continuously decreasing. These terminals can emit up to 2 W. The
evolution of technologies allows decreasing the maximum allowed power to 0.8 W.
b) The SIM
A SIM card is a stamp or credit card size card, containing a microprocessor & a small
amount of memory, which is used when the subscriber wants to use the mobile system or
mobile equipment. To use a SIM card, the subscriber must insert the SIM into his MS. The
SIM is a card, which plugs into the Mobile Equipment. This card identifies the mobile
subscriber and also provides other information regarding the service that subscriber should
receive. The subscriber is identified by an identity number called the International Mobile
Subscriber Identity (IMSI). While this card is in the phone, it becomes subscriber’s personal
phone. All his personal data: short-code dialing, services subscribed to, authentication key,
IMSI, etc. are stored in the smart card.
The Base Station Subsystem (BSS)
The BSS connects the Mobile Station and the NSS. It is in charge of the transmission and
reception. The BSS can be divided into two parts:
The Base Transceiver Station (BTS) or Base Station.
The Base Station Controller (BSC).
a) The Base Station Controller (BSC)
The BSC controls a group of BTS and manages their radio resources. A BSC is principally in
charge of handovers, frequency hopping, exchange functions and control of the radio
frequency power levels of the BTS’s.
b) Base Transceiver Station (BTS)
The BTS provides the air interface connection with the Mobile, it also has a limited amount
of control functionality this reduces the amount of traffic which needs to pass between the
BTS and the BSC and so makes it faster. Each BTS cabinet will provide between 1 and 6
RTF carriers which, in turn, will provide between 7 and 48 simultaneous telephone calls.
The Daisy Chain
Another BSS configuration is the Daisy Chain. A BTS need not communicate directly with the
BSC which controls it, it can be connected to the BSC via a chain of BTSs.
Daisy chaining reduces the amount of cabling required to set up a network as a BTS can be
connected to its nearest BTS rather than all the way to the BSC.
Problems may arise when chaining BTSs due to the transmission delay through the chain. The
length of the chain must therefore be kept sufficiently short to prevent the round trip speech
delay becoming too long.
Other topologies are also permitted including stars and loops. Loops are used to introduce
redundancy into the network, for example if a BTS connection was lost the BTS may still be able
to communicate with the BSC if a second connection was available.
BSS Configurations
A BSC may control several BTSs; the maximum number of BTSs which may be controlled by
one BSC is not specified by GSM.
The BTSs and BSC may either be located at the same cell site “Collocated” or located at
different sites “Remote”.
Transcoder
The Transcoder (XCDR) is required to convert the speech or data output from the MSC (64Kb/s
PCM) into the form specified by SMG specifications for transmission over the air interface, that
is, between the BSS and MS (i.e. 64 Kbps to 16 Kbps and vice versa)
The 64 Kbps Pulse Code Modulation (PCM) circuits from the MSC, if transmitted on the air
interface without modification, would occupy an excessive amount of radio bandwidth. This
would use the available radio spectrum inefficiently. The required bandwidth is therefore
reduced by processing the 64 Kb/s circuits so that the amount of information required to transmit
digitized voice falls to 13 Kbps.
The Transcoder may be located with the MSC, BSC or BTS. If it is located at the MSC, the
13Kb/s channels are transmitted to the BSS by “bit stuffing” them to a data transfer rate of
16Kb/s and then fitting four of them into each 64 Kbps terrestrial circuit. Thus each 30 channel
2Mbps PCM link can carry 120 GSM specified voice channels, with obvious cost savings for the
system operator
Network Switching System(NSS)
The Network Switching System includes the main switching functions of the GSM network. It
also contains the databases required for subscriber data and mobility management. Its main
function is to manage communications between the GSM network and other telecommunications
networks.
The components of the Network Switching System are listed below:
Mobile Services Switching Centre – MSC
Home Location Register – HLR
Visitor Location Register – VLR
Equipment Identity Register – EIR
Authentication Centre – AUC
Interworking Function – IWF Echo Canceller – EC
GSM has Location Register network entities. These entities are:
Home Location Register (HLR)
Visitor Location Register (VLR)
Equipment Identity Register (EIR)
The location registers are database-oriented processing nodes which address the problems of
managing subscriber data and keeping track of a mobile subscriber’s location as it roams around
the network.
Functionally, the Interworking Function and the Echo Cancellers may be considered as parts of
the MSC since their activities are inextricably linked with those of the switch as it connects
speech and data calls to and from the MS
NETWORK SWITCHING SYSTEM
Mobile Services Switching Centre – MSC
The MSC is included in the GSM system for call-switching and its overall purpose, is the same
as that of any telephone exchange.
The MSC will carry out several different functions depending upon its position in the network.
When the MSC provides the interface between the PSTN and the BSSs in the GSM network it
will be known as the Gateway MSC. In this position it will provide the switching required for all
mobile originated or terminated traffic.
Each MSC provides service to mobiles located within a defined geographic coverage area, the
network typically contains more than one MSC. One MSC is capable of supporting a regional
capital with approximately one million inhabitants. The functions carried out by the MSC are
listed below:
Call Processing – Includes control of data/voice call setup, Inter-BSS and Inter-MSC Handovers
and control of mobility management (subscriber validation and location).
Operations and Maintenance Support – Includes database management, traffic metering and
measurement and a man machine interface.
Internetwork Interworking – Manages the interface between the GSM network and the PSTN.
Billing – Collects call billing data
Home Location Register – HLR
The HLR is the reference database for subscriber parameters. Various identification numbers and
addresses are stored as well as authentication parameters. This information is entered into the
database by the network operator when a new subscriber is added to the system.
The HLR is a centralized network database that stores and manages all mobile subscriptions
belonging to a specific operator. It acts as a permanent store for a person's subscription
information until that subscription is cancelled. The information stored includes:
Subscriber identity
Subscriber supplementary services_
Subscriber location information
Subscriber authentication information
The HLR can be implemented in the same network node as the, MSC or as a stand-alone
database. If the capacity of a HLR is exceeded by the number of subscribers, additional HLRs
may be added
Visitor location register – VLR
The VLR contains a copy of most of the data stored at the HLR. It is, however, temporary data
which exists for only as long as the subscriber is “active” in the particular area covered by the
VLR. The VLR database will therefore contain some duplicate data as well as more precise data
relevant to the subscriber remaining within the VLR coverage.
The VLR provides a local database for the subscriber wherever he is physically located within a
PLMN, this may or may not be the “home” system. This function eliminates the need for
excessive and time-consuming references to the “home” HLR database.
The additional data stored in the VLR is listed below:
Mobile status (busy/free/no answer etc.)
Location Area Identity (LAI)
Temporary Mobile Subscriber Identity
Mobile Station Roaming Number
VLR Location Area Identity
Cells within the Private Land Mobile Network (PLMN) are grouped together into geographical
areas and each area is assigned a Location Area Identity (LAI), a location area may be typically
containing 30 cells. Each VLR controls several LAIs and as a subscriber moves from on LAI to
another, the LAI is updated in the VLR. As the subscriber moves from on to another, the VLR
address is updated at the HLR.
Temporary Mobile Subscriber Identity
The VLR control the allocation of new Temporary Mobile Subscriber Identity (TMSI) numbers
and notifies them to the HLR. The TMSI will be updated frequently, this makes it very difficult
for the call to be traced and therefore provides a high degree of security for the subscriber. The
TMSI may be updated in any of the following situations:
Call setup
On entry to a new LAI
On entry to a new VLR
Mobile Subscriber Roaming Number As a subscriber may wish to operate outside its “home”
system at some time, the VLR can also allocate a Mobile Station Roaming Number (MSRN).
This number is assigned from a list of numbers held at the VLR (MSC). The MSRN is then used
to route the call to the MSC which controls the base station in the MSs Current location.
The database in the VLR can be accessed by the IMSI, the TMSI or the MSRN. Typically there
will be one VLR per MSC.
Equipment identity register – EIR
The EIR contains a centralized database for validating the International Mobile Equipment
Identity (IMEI). This database is concerned solely with the MS equipment and not with the
subscriber who is using is to make or receive a call. The EIR database consists of lists of IMEIs
(or ranges of IMEIs) organized as follows:
The EIR database is remotely accessed by the MSCs in the network and can also be accessed by
a MSC in a different PLMN.
As in the case of the HLR, a network may well contain more than one EIR with each EIR
controlling certain blocks of IMEI numbers. The MSC contains a translation facility, which
when given an IMEI, returns the addresses of the EIR controlling the appropriate section of the
equipment database.
Authentication centre – AUC
The AUC is a processor system; it performs the “authentication” function.
It will normally be co-located with the Home Location Register (HLR) as it will be required to
continuously access and update, as necessary, the system subscriber records. The AUC/HLR
centre can be co-located with the MSC or remotely from the MSC. The authentication process
will usually take place each time the subscriber “initializes” on the system. In the authentication
process secure data stored on the SIM card is manipulated and compared with data held in the
HLR database. This data is entered into the SIM and the system database (HLR) at the time the
SIM card is issued.
Authentication process
The MSC/VLR transmits the RAND to the MS.
The MS computes the signature SRES using RAND and the subscriber authentication
key(Ki) through the A3 algorithm.
The MS computes the Kc by using Ki and RAND through A8 algorithm. Kc will
thereafter be used for ciphering and deciphering in MS.
The signature SRES is sent back to MSC/VLR, which performs authentication, by
checking whether, the SRES from the MS and the SRES from the AUC match. If so, the
subscriber is permitted to use the network. If not, the subscriber is barred from network
access.
Operations and management centre – OMC
The OMC provides a central point from which to control and monitor the other network entities
(i.e. Base Stations, switches, database, etc) as well as monitor the quality of service being
provided by the network as a whole.
Equipment manufacturers have their own OMCs which are not compatible in every aspect with
those of other manufacturers. This is particularly the case between Radio Base Station equipment
suppliers, where in some cases the OMC is a separate item and Digital Switching equipment
suppliers, where the OMC is an integral, but functionally separate, part of the hardware.
There are two types of OMCs. These are:
OMC(R)- OMC controls specifically the Base Station System
OMC(S) – OMC controls specifically the Network Switching System
The OMC should support the following functions:
Event/Alarm Management
Fault Management
Performance Management
Configuration Management
Security Management
PHYSICAL AND LOGICAL CHANNELS
Physical Channels
Each timeslot on a TDMA frame is called a physical channel. Therefore, there are 8 physical
channels per carrier frequency in GSM.
Physical channels can be used to transmit speech, data or signalling information. A physical
channel may carry different messages, depending on the information that is to be sent. These
messages are called logical channels. For example, on one of the physical channels used for
traffic, the traffic itself is transmitted using a Traffic Channel (TCH) message, while a handover
instruction is transmitted using a Fast Associated Control Channel (FACCH) message
Logical channels
There are two main groups of logical channels:
1. Traffic channels
2. Control channels
The traffic channel carries speech or data information. The different types of traffic channel are
listed below:
Full rate: TCH/FS: Speech (13 Kb/s net, 22.8 Kb/s gross)
TCH/F9.6: 9.6 Kb/s – data
TCH/F4.8: 4.8 Kb/s – data
TCH/F2.4: 2.4 Kb/s – data
Half rate: TCH/HS: Speech (6.5 Kb/s net, 11.4Kb/s gross))
TCH/H4.8 4.8Kb/s – data
TCH/H2.4 2.4Kb/s – data
BCCH Group
The Broadcast Control Channels are downlink only (base station to mobile) and comprise the
following:
1. BCCH carries info about the network, a mobiles present cell and the surrounding cells.
It is transmitted continuously as its signal strength is measured by all mobiles on
surrounding cells.
2. The Synchronizing Channel (SCH) carries information for frame synchronization.
3. The Frequency Correction Channel (FCCH) provides information for carrier
synchronization.
CCCH Group
The Common Control Channel Group is bi-directional i.e. it works in both uplink and downlink
directions.
1. Random Access Channel (RACH) is the “uplink” used by mobiles to gain access to the
system.
2. Paging Channel (PCH) and Access Granted Channel (AGCH) operate in the “downlink”
direction. The AGCH is used to assign resources to the M.S., such as a Standalone
Dedicated Control Channel (SDCCH). The PCH is used by the system to call a mobile.
The PCH and AGCH are never used at the same time.
Cell Broadcast Channel (CBCH) is used to transmit messages to be broadcast to all mobiles
within a cell e.g. traffic information.
DCCH Group
Dedicated Control Channels are assigned to a single mobile for call setup and subscriber
validation. DCCH comprises:
Standalone Dedicated Control Channel (SDCCH) which supports the transfer of Data to and
from the mobile during call setup and validation.
Associated Control Channel which consists of Slow ACCH which is used for radio link
measurement and power control messages. Fast ACCH is used to pass “event” type messages
e.g. handover messages. Both FACCH and SACCH operate in uplink and downlink directions.
Burst Structure
As it has been stated before, the burst is the unit in time of a TDMA system. Four different
types of bursts can be distinguished in GSM:
• The frequency-correction burst is used on the FCCH. It has the same length as the normal
burst but a different structure.
• The synchronization burst is used on the SCH. It has the same length as the normal burst
but a different structure.
• The random access burst is used on the RACH and is shorter than the normal burst.
• The normal burst is used to carry speech or data information. It lasts approximately 0.577
ms and has a length of 156.25 bits.
The tail bits (T) are a group of three bits set to zero and placed at the beginning and the end of a
burst. They are used to cover the periods of ramping up and down of the mobile's power. The
coded data bits correspond to two groups, of 57 bits each, containing signalling or user data. The
stealing flags (S) indicate, to the receiver, whether the information carried by a burst corresponds
to traffic or signalling data. The training sequence has a length of 26 bits. It is used to
synchronize
the receiver with the incoming information, avoiding then the negative effects produced by a
multipath propagation.
The guard period (GP), with a length of 8.25 bits, is used to avoid a possible overlap of two
mobiles during the ramping time.
Channel Coding On Air Interface
GSM BURSTS
The diagram illustrates a GSM burst. It consists of several different elements. These elements are
described below:
Info – This is the area in which the speech, data or control information is held.
Guard Period – The receiver can only receive the burst and decode it if it is received within the
timeslot designated for it. The timing, therefore, must be extremely accurate but the structure
does allow for a small margin of error by incorporating a ‘guard period’ as shown in the diagram.
To be precise, the timeslot is 0.577ms long, whereas the burst only 0.546ms long, therefore there
is a time difference of 0.031ms to enable the burst to hit the timeslot.
Stealing Flags – These two bits are set when a traffic channel burst has been “stolen” by a
FACCH (the Fast Associated Control Channel). One bit set indicates that half of the block has
been stolen.
Training Sequence – This is used by the receiver’s equaliser as it estimates the transfer
characteristic of the physical path between the BTS and the mobile. The training sequence is 26
bits long.
Tail Bits – These are used to indicate the beginning and end of the burst.
Multipath Fading
Multipath Fading results from a signal travelling from a transmitter to a receiver by a number of
routes. This is caused by the signal being reflected from objects, or being influenced by
atmospheric effects as it passes, for example, through layers of air of varying temperatures and
humidity.
Received signals will therefore arrive at different times and not be in phase with
each other, they will have experienced time dispersion. On arrival at the receiver, the signals
combine either The constructively or destructively, the overall effect being to add together or to
cancel each other out. If the latter applies, there may be hardly any usable signal at all. The
frequency band used for GSM transmission means that a ‘‘good” location may be only 15 cm
from a ‘‘bad” location! When the receive antenna is moving, the exact phase of each path
changes and consequently the combined signal-strength is also continually changing. When the
antenna is moving rapidly, this loss is recovered by interleaving and channel coding. When it is
slow moving or stationary however, the receiver may be in a “null” (point of minimum signal)
for several consecutive frames.
A typical urban profile would cause dispersion of up to 5 microseconds, whereas, a hilly terrain
would cause dispersion of up to 20 microseconds.GSM offers five techniques which combat
multipath fading effects:
Equalization.
Diversity.
Frequency hopping.
Interleaving.
Channel coding.
The equalizer must be able to cope with a dispersion of up to 17 microseconds.
Frequency Hopping
Frequency hopping allows the RF channel used for carrying signaling channel timeslots or traffic
channel (TCH) timeslots to change frequency every frame (or 4.615 msec).This capability
provides a high degree of immunity to interference, due to the effect of interference averaging, as
well as providing protection against signal fading. The effective “radio channel interference
averaging” assumes that radio channel interference does not exist on every allocated channel and
the RF channel carrying TCH timeslots changes to a new allocated RF channel every frame.
Therefore, the overall received data communication experiences interference only part of the
time.
All mobile subscribers are capable of frequency hopping under the control of the BSS. To
implement this feature, the BSS software must include the frequency hopping option. Cyclic or
pseudo random frequency hopping patterns are possible, by network provider selection.
GSM Services
Enhanced Range of Series:
GSM has the potential to offer a greatly enhanced range of services compared with existing
analogue cellular systems. As well as a full range of data transmission options and fax, there will
be a wide range of supplementary services.
The services available to a subscriber will be determined by four factors:
• The level of service provided by the network operator.
• The level of service purchased by the subscriber.
• The capabilities of the subscriber’s mobile equipment.
• The capabilities of the terrestrial network to which we are connected (ISDN, PSTN).
Teleservices:
• Telephony
• Emergency calls
• Short Message Services (E1, E2, A Fax mail. Thanks to this service, the subscriber can
receive fax messages at any fax machine.
• Voice mail. This service corresponds to an answering machine.
Number Identification:
• Receiving party requests calling number to be shown.
• Calling party requests calling number not to be shown.
Call Barring:
• Bar all incoming or all outgoing calls.
• Bar specific incoming or outgoing calls.
Call forwarding:
• Forward all calls.
• Forward calls when subscriber is busy.
• Forward calls if subscriber does not answer.
• Forward calls if subscriber cannot be located
Call completion:
Enable incoming call to wait until subscriber completes current call. Enable subscriber to place
incoming calls on hold.
Features of GSM
Compatibility:
Due to the rapid development of cellular in Europe, there are now many different cellular
systems, which are incompatible with one another.
They need for a common standard for mobile telecommunications is therefore obvious. An
executive body was set up to co-ordinate the complicated task of specifying the new standardized
network.
GSM has been specified and developed by many European countries working in co-operation
with each other. The result is a cellular system which will be implemented throughout Europe.
Noise Robust:
In the current cellular telephone systems the mobile unit communicates with the cell site by
means of analogue radio signals. Although this technique can provide an excellent audio quality
(it is widely used for stereo radio broadcasting, for example), it is vulnerable to noise as anyone
who has tried to receive broadcast stereo with a poor aerial will testify.
The noise which interferes with the current system may be produced by any of the following
sources:
1. A powerful or nearby external source (a vehicle ignition system or a lightening bolt,
perhaps);
2. Another transmission on the same frequency (“co-channel” interference);
3. Another transmission “breaking through” from a nearby frequency (“adjacent channel”
interference);
4. Background radio noise intruding because the wanted signal is too weak to exclude it.
Flexibility and Increased Capacity:
The success of the current analogue cellular systems means that there is a requirement for not
only increased cellular phone capacity in Europe, but ease of expansion as well. The current UK
cellular networks have to some extent become the victims of their own success. So many
subscribers have registered on these systems so quickly that it has been difficult to expand their
capacity fast enough to satisfy call demand .With the current analogue air interface, every
connection between a mobile subscriber and a cell site requires a separate RF carrier and that, in
turn, requires a separate set of RF hardware at the cell site. Therefore, to expand the capacity of a
cell site by a given number of channels, an equivalent quantity of RF hardware must be checked
to the cell site equipment. System expansion, therefore, is time-consuming, expensive and labour
intensive. Such operations also involve very intricate RF planning.
To operate legally, both networks must use a closely-defined range of RF frequencies. This
frequency “spectrum” (872-960 MHz) is obviously limited and, as only a finite number of
conversations can be squeezed onto a given number of radio carriers, there is frequent localized
overloading at time of peak demand. This results in “call blocking” (the subscriber hears a tone
indicating that no system capacity is available) and consequent subscriber dissatisfaction.
Once again, the digital air interface used by GSM comes to the rescue. It uses the available radio
spectrum more efficiently. Eight simultaneous conversations can now be carried out on one RF
carrier. This means that separate RF hardware is only required for every eight subscribers, and as
the system expands, hardware changes are required less frequently than for the old system.
Subscriber Identification:
With the current analogue systems a mobile subscriber is identified by a telephone number which
is associated with their mobile equipment. This number is held in the mobile equipment of that
subscriber, therefore if the subscriber wishes to make or receive calls he must take the mobile
equipment with him.
With the GSM system the subscriber and the mobile equipment are identified separately.
The subscriber is identified by means of “Smart Card” known as a SIM (Subscriber
Identification Module). This means that a subscriber needs to have only one subscription to
the cellular system but may use several different types of mobile equipment (e.g. FAX,
computer and telephone). This also means that when a subscriber is travelling abroad he
needs only to take the SIM card with him. On arrival the SIM may be placed into any GSM
mobile equipment and the subscriber may then make or receive calls or messages. In
addition because the SIM identifies the user, wherever the call is made the bill will always
be sent to the subscribers Home Location Register (HLR).
ISDN Compatibility
ISDN (Integrated Services Digital Network) is a standard that most developed countries are
committed to implement. This is a new and advanced telecommunications network designed to
carry voice and user data over standard telephone lines. The GSM network has been designed to
operate with the ISDN system and provides features which are compatible with it. GSM can
provide a maximum data rate of 9.6Kb/s while ISDN provides much higher data rates than this
(standard rate 64 Kb/s, primary rate 2.048 Mb/s).
CALL PROCESSING:
MS originated call (MOC)
The following highlights the actions required as well as the actions being performed by the BSS
as part the MS originated call. The events required for an MS originated call are shown in a
diagram in this section.
MS CHANNEL REQUEST: After the dialled digits are entered, the MS transmits a Channel
Request on the RACH. After receiving this request, the BTS decodes the message. The BSS
software immediately assigns the MS to a SDCCH with an Immediate Assignment message
sent on the AGCH channel.
MS RESPONSE: The MS responds to the immediate assignment message and switches to
the assigned SDCCH. Once on the SDCCH, the MS transmits the Set Asynchronous
Balanced Mode (SABM). The network responds to SABM with UA to establish the Layer 2
radio link. Within the SABM the MS transmits a Service Request indicating to the BSS what
type of service, for example, a call or location update is required. This service request is
processed by the BSS then passed to the MSC via the A interface signalling link.
AUTHENTICATION REQUEST: After receiving the service request, the MSC sends an
Authentication Request to the MS. This service request is passed through the BSS via the
signalling link. The BTS transmits the request to the MS on the SDCCH. Since no action is
required by the BSS on the authentication request, it is passed through the BSS and is
considered transparent to the BSS.
MS AUTHENTICATION RESPONSE: The MS responds to the authentication request with
an Authentication Response. The authentication response from the MS is received by the
BTS and is passed through the BSS on the signalling link, as with the authentication request
no action is required by the BSS and as such is transparent to the BSS.
CIPHER MODE COMMAND: After receiving the correct authentication response, the
MSC sends a Cipher Mode Command. The network must start the cipher mode because the
set up message contains sensitive information such as dialled digits. The use of
encryption is optional and is controlled by the MSC on a call-by-call basis.
MS CIPHER MODE COMPLETE: The MS responds to the set cipher command by
transmitting a Ciphering Mode Complete message indicating to the BSS that the MS
is now communicating encrypted with the previously assigned cipher key.
MS SET UP: The MS sends a set up message on the SDCCH, which indicates to the
MSC the bearer service, called party or both. After the MSC receives and processes
the set up message, the MSC transmits an Assignment Request. The assignment
request is used by the MSC to indicate what type of traffic channel is required, that is,
half or full-rate speech, or data. The BTS then allocates and assigns the MS to a free
TCH by sending an Assignment Command via the SDCCH.
MS ASSIGNMENT COMPLETE: In response to the assignment command, the MS
switches to the assigned TCH and transmits an Assignment Complete message on a FACCH
(the main signaling channel on a TCH).
ALERT MESSAGE: The MSC sends an Alerting message to the MS. The alert message
informs the MS the called phone is ringing, which initiates the MS generated ring-back tone.
This message is transparent to the BSS. When the called party answers the phone (goes offhook),
a Connect message is sent to the MS. This signal is transparent to the BSS and is
switched through in the same manner as the alerting message. The connect message is
transmitted via the FACCH. In response to the connect signal, the MS opens the audio path
and transmits, via the FACCH, a Connect Acknowledge message to the MSC. Conversation
can now take place.
MS IDLE TIME REPORTING: During the conversation, the MS only transmits and
receives for one eighth of the time that is during one timeslot in each frame. During its idle
time (the remaining seven timeslots), the MS switches to the BCCH of the surrounding cells
and measures its signal strength. The signal strength measurements of the surrounding cells,
and the signal strength and quality measurements of the serving cell, are reported back to the
serving cell via the SACCH once in every SACCH Multiframe. This information is evaluated
by the BSS for use in deciding when the MS should be handed over to another traffic
channel. This reporting is the basis for MS assisted handovers.
UPLINK TRAFFIC: This is the conversation from an MS to a landline telephone.
BTS UPLINK PATH: The MS converts speech to digital voice information (traffic), which
is transmitted by the MS in bursts on its assigned timeslot and carrier. This traffic is received
by the BTS, which converts the traffic down to base band and passes it to the channel coders,
which decode the traffic. The TDM interface converts the traffic to a TDM format for output
onto a timeslot on the switch-bound TDM bus. The BTS switches the traffic to another
outbound TDM timeslot. The BTS converts the traffic from TDM format and outputs the
traffic data in a traffic channel timeslot on the E1/T1 line going to the MSC via the BSC.
BSC UPLINK PATH: Traffic data from the BTS on an E1/T1 timeslot is converted to a
TDM format by an MSI for output on to a timeslot on the switch-bound TDM bus. The KSW
switches the traffic to another outbound TDM timeslot for input to the MSI. Within the MSI
the traffic is converted from TDM format to traffic data in a traffic channel timeslot on the
E1/T1 line to the MSC.
MS Terminated Call (MTC)
The following highlights the events required to terminate (receive) a call as well as the actions
being performed by the BSS to set up the MS terminated call. The events required for an MS
terminated call are shown in a diagram in this section.
PAGING REQUEST: After dialled digits are received from the PSTN/ISDN, the MSC
sends a Paging Request to the BSS via the E1/T1 line. The BSS processes the paging request
and schedules it for transmission on the PCH at the appropriate time.
MS RESPONSE: Upon receiving the paging request, the MS responds by transmitting a
Channel Request on the RACH.
SDCCH ASSIGNMENT: After receiving the channel request, the BSS processes it and
immediately assigns the MS a SDCCH. This assignment is encoded as an Immediate
Assignment and transmitted on the AGCH.
MS PAGING RESPONSE: After receiving the immediate assignment command, the MS
switches to the assigned SDCCH and transmits within SABM a Paging Response. The
network responds to SABM with UA to establish the Layer 2 radio link. This paging
response is received by the BSS for processing.
The paging response is then sent to the MSC via the E1/T1 line.
AUTHENTICATION REQUEST: After receiving the paging response, the MSC sends an
Authentication Request to the MS. This request is sent on the E1/T1 line to the BSS. The
authentication request is routed through the BSS on the signalling link. The authentication
request requires no processing by the BSS and is considered transparent to the BSS.
MS AUTHENTICATION RESPONSE: In response to the authentication request, the MS
transmits its Authentication Response on the SDCCH. The authentication response is
transparent to the BSS and is passed through the BSS to the MSC.
CIPHER MODE COMMAND: After receiving the correct authentication response from
the MS, the MSC sends a Ciphering Mode Command message. The BSS processes the
ciphering mode command and transmits the command to the MS.
MS CIPHER MODE COMPLETE: In response to the ciphering mode command, the MS
transmits a Ciphering Mode Complete message to the BSS. From this point onwards all radio
transmissions by the BSS and the MS are encrypted using the appropriate algorithm.
SET UP MESSAGE: The MSC sends a Set up message to the MS that indicates to the MS
the bearer service and or called party. The BSS sends the set up message via the SDCCH.
This set up message is transparent to the BSS.
MS CALL CONFIRMATION: After receiving the set up information, the MS transmits a
Call Confirmation message. This message confirms that the MS is capable of receiving the
call type identified in the set up message. The MS transmits this message on the SDCCH.
The BSS receives the call confirmation and passes to the MSC via the A interface.
ASSIGNMENT COMMAND MESSAGE: After receiving the call confirmation, the MSC
sends an Assignment Command message. The BSS takes the assignment command and
allocates and assigns the MS to a free TCH and transmits the assignment command to the MS
via the SDCCH.
MS ASSIGNMENT COMPLETE: The MS then switches to the assigned TCH and
transmits an Assignment Complete message on FACCH (which is a logical channel on a
TCH). This assignment complete is received and sent to the MSC.
ALERT MESSAGE: The MS sends an Alert message to the MSC on the FACCH, which
informs the MSC that the called MS is ringing and causes the MSC to send a ring-back tone
to the calling phone. This message is transparent to the BSS.
MS CONNECT ACKNOWLEDGE: When the MS subscriber answers, the MS transmits a
Connect message on the FACCH, and opens the audio path to the user. The connect message
is transparent to the BSS and is passed to the MSC via the signalling link. The Connect
Acknowledge message is passed from the MSC to the PSTN/ISTN, which in turn stops the
ring-back tone and opens the audio path.
SET UP COMPLETE: The connection is now established and a conversation can now take
place.
PROJECT
INTRODUCTION TO ASSIGNED DUTIES
In the Idea Telecom we all trainees were assigned the duty in the Engineering Department. This
is the main department of the company which provides 24 hours Network availability, with
optimized performance, to all the customers of Idea telecom. Our main work was in BSS
department. In this department there are various interconnected duties to be performed. We were
given training in different duties and our duties changed from time to time. The various duties
performed in BSS department are:
To ensure the maximum Network Availability & reduce downtime to minimum.
To perform routine Maintenance activities on the BSC, BTS, Microwave and Backbone
Sites.
To handle all alarms which are generated at any site in the area of responsibility.
To handle all Power related problems in all sites.
To maintain all intercity and intracity links.
To implement all upgrades in the network (BSS site specific)
Asset management (Tools, Testers ,manuals etc)
NETWORK AVAILABILITY:
Network availability is the main duty which ensures that full signal is available at all the sites at
each hour of the day. It also takes care to reduce the downtime to the minimum so that if full
network is not available at any particular time, at any particular site or station then due care is
taken to find out and rectify the problem. This helps to provide maximum network within the
minimum possible time.
Necessity:
Maximum network availability is one of the prime functions of BSS. If maximum network
availability is not ensured then mobiles will not be able to function properly bringing the
communication to a standstill.
Risk Factors:
The major risk factor involved is the failure of proper functioning of the mobiles as well as the
congestion occurring due to downlink of the particular network.
ROUTINE MAINTENANCE:
Routine maintenance of the BTS sites is another essential activity. Routine checkup of the BTS
sites is done by the engineers even if there is no detectable error in the performance of various
machines and instruments.
Necessity:
Routine checkup of BTS and backbone sites is necessary to ensure proper and optimum working
of various machineries and equipments. It also helps to keep under check any error which may
creep in unknowingly.
Risk Factors:
If routine checkup is not done then some small malfunctioning, not rectified in time, can lead to
a major internal problem bringing the process of communication to a standstill.
So it’s very necessary to have routine checkup of BTS sites.
BTS SITE ARCHITECTURE
A site mainly consists of following:
Shelter
DG
Tower (including antenna)
H GSM Course
Base Station Cell Site Architecture
MainsPowerPanel
DCPowerSupplyUnit Battery
BackupAbis
BTSDMR
GSM Antenna System
BTS Cabin/Shelter/Room
AirCon
GSM ANTENNA
MW ANTENNA
TOWER
SITES (BTS)
Shelter
For the shelter we use four cemented base which are raised from ground to a height approx. 1-2
feet two metal rails run over this base the shelter is mounted over this by metal nails the Back
side of the shelter has an AC exhaust fan mounted over by two metal nails. As the shelter is at a
height of 1-2 feet so we use 3 to 4 stairs for getting into the shelter conveniently.
Diesel Generator
It is one of the important components used in a site. It is used in case of power breakdown, in
that case it starts automatically and when the mains are ok, it stops automatically. The
specifications of the DG are:
AC generator:- 50 Hz, 1500 RPM, 240 V, 15 KVA
Tower
For constructing the tower we firstly construct a concrete square wall of 3-4 feet. The thickness
is such that it can withhold the weight of the antenna. It is painted by orange and white colour as
it is the standard for any antenna using microwave frequency. The two antennas i.e. the GSM
and the Microwave antenna is installed on the top of the tower using moulds. The jumper cables
are connected from top of the BTS and then connected to the feeder cables which is routed
through the cable tray on to the top of the tower then further connected by the jumper to the
antenna.
The BTS is installed in a cabin/shelter or a room. There is an AC Mains Panel to which the AC
mains enters and is properly through fuse panels is distributed to the DC Power Supply unit,
which rectifies this AC and provides DC power Supply to the Base Station. Typical Operating
Voltage Levels of Macro BTS is 48V. There is also a Battery Backup to provide power to the
BTS in the event of the Main Power Failure. The switching from Mains to Batteries is also done
through the Power Supply Unit. All the elements inside the cabinet generate failure alarms and
are connected to an Alarm Interface Panel which is then connected to the BTS.
The BTS on the other side is connected to the Antenna
System, which comprises of Transmit and Receive Antennas. The number of Antennas depends
on the loading on the Base Station , basically the number of sectors it controls. The BTS is also
connected on a Abis Interface (E1/T1) to the BSC. The transport media for this could be coaxial,
fiber or most commonly used Digital Microwave Radio.
We will now further understand the architecture inside the BTS cabinet and also the differenet
variations in the Antenna System. Then we will also see the Abis configurations.
BTS has Transceivers to communicate with the mobile in its area.
One BTS covers one or more then one cell.
The capacity of the cell depends upon no of transceivers in the cell.
BTS is connected to BSC via Abis interface which is 2Mbps
BTS transmit and receive voice at 13kbps over air interface to mobiles
BTS commands mobiles to set transmission power, timing advance and handovers.
Each Antenna will receive two signals, so four signals come to the Splitter. Each transceiver
needs inputs from both antennas, the splitter will split this energy coming at input to both the
TRX's.
ZTE BTS hardware configuration
BTS are of following three types:
1. Indoor BTS
2. Outdoor BTS
3. Mobile BTS
Main Modules of BTS
CMM:Controller & Maintenance Module
TRM:Transceiver Module
AEM:Antenna Equipment Module
FCM:Fan Control Module
PDM:Power Distribute Module
CMM module functions
BS interface functions
Providing various clocks needed by BS
Remote operation & maintenance function of BTS
Local operation & maintenance functions of BTS
Equipment alarm collection
Active/standby hot backup
Hardware of CMM
TRM module function
TRM module is also called as “CARRIER”
TRM module has 8 or 16 TDMA time slots.
Each time slot supports only 1 call at full rate
In every TRM 2 to 3 time slots are reserved for DATA and calls can be made on these
time slots if they are free.
TRM is connected to CDU module and CMM module.
TRM gets two inputs MAINS and DEVERSITY signals for distortion less received
signal.
Hardware of TRM
CDU module function
CDU stand for combiner and distributor unit (also called as AEM).
CDU is connected directly to GSM antennas through feeders.
It contains combiner which combines inputs from all TRM’s.
It also distributes all the signals b/w all TRM’s.
CDU Hardware Module
FCM module functions
Temperature monitoring
Fan control and inspection
Power Distribute Module
It distribute DC power too all the modules
It contains switches to on/off power of module.
ODU (Out Door Unit)
ODU (Out Door Unit) is weather proofed sealed assembly designed to be latched onto an
antenna. Within the tuning range, any frequency plan can be established & implemented from the
IDU. Capacity & transmit power are also selected from the IDU.
ODU Features:
1) Dual data rate.
2) Fully tunable over entire RF band from IDU.
3) Output power controllable from IDU over at least 30db of range.
4) ODU’s are software configurable so that capacity upgrades can be made without
climbing towers.
5) Low power consumption.
6) Adjustable Tx output power.
ODU can be installed either directly to the antenna (Co-located ODU) or can be installed
remotely (Remote or Separated ODU). For attaching remotely a remote ODU mounting kit is
necessary.
Polarization:
ODU can be configured in 2 types of polarization:
1) Horizontal Polarization
2) Vertical Polarization
To indicate the type of polarization, a polarization indicator arrow is there on ODU. For
Horizontal polarization, the polarization indicator arrow should be horizontal & vice versa.
IDU (In Door Unit)
IDU (In Door Unit) or a Microwave is a indispensible part of a BTS site which performs
functions like multiplexing/data interface, reference frequency generation, error correction,
alarm/status monitoring, & site to site communications. All these functions are integrated into a
single PCB inside. A memory backup holds all the relevant data so that if IDU loses power, the
unit is operational when power is restored. IDU’s are frequency independent so that they can be
used with any ODU. There is only a single coaxial cable connection between ODU & IDU. The
single cable feeds DC power from the IDU to ODU and supports bidirectional traffic, alarm and
control signals.
Other features of IDU are:
1) Adjustable Tx output power.
2) Frequency/channel setting with keyboard or laptop PC.
3) Selectable data rates.
4) Low power consumption.
An IDU also contains a IF frequency cable connector through which IF cable is connected to
it, which is connected to ODU from the other end. The display screen generally shows a
receiving field in dBm, which shows the alignment of microwave antennas with respect to one
another, and hence the amount of field received is displayed. Generally, a field between 35 to 50
dBm is acceptable. In case any problem arises, changing the angle of the microwave antenna can
change the receiving field.
IDU-ODU Interconnection:
The interconnection between IDU & ODU is carried out & consists of an only bi-directional line
carrying a composite signal comprising the radio signal (Tx & Rx) and an IDU/ODU auxiliary
service channel.
The IDU-ODU connection, as far as transmission/reception of radio signal is concerned, consists
of two IF signal:
- 320 MHz TFM Modulated signal from IDU to ODU, for transmission of signal to be
transmitted through the radio equipment.
- 70 MHz TFM modulated signal from ODU to IDU, for transmission of signal received
through radio equipment.
The use of these two frequencies allows minimizing the interference between TX & Rx signal.
IDU RACK
IDU LOGIN PAGE
PROJECTS
1. OPERATIONS AND MAINTENANCE OF BTS SITES
Work involved in project
1. Changing faulty hardware from sites.2. Increasing and decreasing BTS capacity.3. Preventive maintenance (PM).4. Checking ALARMS.5. Customer complaints (Technical).
1. Changing faulty hardware from sites
In this I changed the faulty hardware from site. When Modules in BTS gets faulty, OMCR used to inform us on phone about the faulty hardware and problem with the hardware. Then I used to take ok hardware with me and replace it with the faulty one. This was a routine work and also it was important as faulty hardware hinders the quality of telecom services to subscribers.
Hardware included
ETRM (Edge transmission and reception unit)DTRU (Dual transmission and reception unit)CDUCMM
Various alarms that requires change of hardware:
ETRM, DTRU:
LAP D/HDLC: This alarm tells that particular TRM has lost its communication link with BSC. This alarm requires change of module. HDLC is same as LAP D it occurs in DTRU.
PA o/p power alarm: This alarm tells that OPAMP of TRM module is faulty. It also requires change of hardware.
TPU power alarm: This alarm tells that power supply to TRM is faulty. It’s because of some error in power card of module. It requires a replace.
CDU:
AEM power alarm: This alarm is similar to power alarm of TRM. This alarm arrives because of faulty power card of CDU. It requires a replace.
AEM absent alarm: This occurs when BTS is unable to pick CDU. It’s generally because of faulty backplane or faulty CDU.
CMM:
SYN/CLCK failure: This alarm occurs because of faulty clock pulse provided to TRM. It require a replace.
Flash memory failure: This alarm occurs because of the flash memory failure. It requires replacement.
2. Increasing and decreasing BTS capacity
Whenever we get a mail from NOC for addition and deletion of TRM modules from particular site and particular sector, we add or remove the module for same. Addition an deletion is necessary for efficient network.
Addition: Addition is done when we need to increase the call capacity of a particular site and particular sector. Each addition of ETRM increases the capacity of sector by 8 calls. Each addition of DTRU increases the capacity of sector by 16 calls. Addition is done when there is call congestion in a sector.
Deletion: Deletion is done when we need to decrease the call capacity of a particular site and particular sector. Each deletion of ETRM decreases the capacity of sector by 8 calls. Each deletion of DTRU decreases the capacity of sector by 16 calls.
3. Preventive maintenance (PM)
Preventive maintenance in IDEA is done once in a year for all sites.
It comprises of following things:
Check shelter conditions i.e. check cleanliness and leakages. Check DG automation. Check if AC works. Check battery backup. Noting down data of link i.e. RX level, TX power, Modulation scheme, No. of E1 used,
TX and RX frequency. Check weather proofing of connectors of GSM and microwave antennas.
Ensuring that cables are tied on tower and they are not loose.
4. Checking ALARMS
We have to ensure that all the external alarms are correctly punched on krone. If there is any problem with alarms i.e. alarms are not reaching at OMCR end then we have to rectify it. Problem is rectified by one of the following:
Check weather wires are punched ok. Check weather problem is from our end or technician’s end. Changing the KRONE. Changing CMM on BTS. Changing alarm cable from BTS to KRONE.
KRONE
5. Customer complaints (Technical)
If there is any technical complaint of customer, it is forwarded to us. First step is to verify the problem that is done by call testing. Then we contact the concerned persons ensuring him that his problem will be rectified soon. We then visit the site which serves the problem area. We check for any alarms on the BTS. If there is any alarm we rectify the alarm and again do call testing (at BTS as well as BSC level). If all the things from our side are ok and still fault is not rectified then we forward the complaint to RF department.
2. INDUSTRIAL AREA EXTN. A SITE ON AIR
During this project I along with an engineer did INDUSTRIAL AREA EXTN. A site ON AIR. This means Industrial area extn. A was a new site of IDEA in Ludhiana and we have to make the site operational. All the hardware was installed by PROJECTS team of idea. We as a BSS department have to provide media for the site and to put alarms of site. We took the following procedure for it:
1. Firstly we went to Gill Rd BSC. TIC ports were assigned to us by OMC for the new site.TIC port assigned was 2-6-11-3.
2. 2 stands for 2nd BSC rack. 6 stand for 6th shelf of 2nd rack.
11 Stands for 11th TIC card of 6th shelf.3 stand for 3rd E1 of 11th card.
3. We then found the KRONE of 11th card and then jumped the 3rd E1 of that KRONE to 11TH E1 of Dabba rd. Link.E1 is jumped by using a wire and connecting it to both KRONES.
4. Then we visited Dabba rd. site. We then back looped the 11th E1 of Dabba rd.-Gill rd. BSC link. Each E1 comprises of a pair of trans and a pair of receive wires. Back loop means connecting trans and receive.
5. We then confirmed the Back loop from OMCR. The back loop confirmed us that the media has reached to Dabba rd. site from BSC.
6. We then jumped the 11th E1 of Dabba rd. to the link of Dabba lohara rd. site.E1 we jumped to was 4th E1. We can choose any E1 which is free.
7. Now we visited Dabba lohara rd. site which was a far end of our new site. We confirmed the back loop on 4th E1 of link to Dabba rd. Now the media had reached far end of our new site. Far end means the site to which the particular link is connected with.
8. We punched the 4th E1 with 1st E1 of link to INDUSTRIAL AREA EXTN. A site.9. We now visited the new site which was to be on aired. We now inserted one end of E1
cable to E1 port of BTS and punched the other end on KRONE.10. We punched only 1st E1 of E1 cable to the 1st E1 of link.11. Now we switched on the BTS and waited the BTS for loading. It took about 20 minutes
for BTS to load and it was good to know that BTS started picking calls. That meant that media was successfully brought to that site i.e. now BTS was successfully connected to BSC.
12. Now we have to put alarms. For putting alarms we have to coordinate with technician of the site.
13. He took the alarms from different sensors on site and handed over the wires to us.14. We took the alarm cable and inserted its one end on alarm port of BTS and we punched
the other end on KRONE.15. Alarms punched were according to color coding which was as follows:
WHITE BLUE RECTIFIER 1BLACK BLUE RECTIFIER 2WHITE ORANGE LOW FUELBLACK ORANGE FIREWHITE GREEN ENGINE FAULTBLACK GREEN AC FAILWHITE BROWN MAINS FAILBLACK BROWN HIGH TEMPERATUREBLUE RED DG RUNNING
16. These are the standard color coding for all IDEA sites. Corresponding alarms were punched according to color coding.
17. At last we did call testing for each sector of site and confirmed that site was perfectly running.
BTS of new site
REFERENCES/BIBLIOGRAPHY
MOTOROLA cp02 file. Google Wikipedia Training diary. www.gsm.org
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