BASICS OF GSM by KATHIRESAN.M , IWS

GSM Fundamentals

By,M.KATHIRESAN

[email protected]

What you will learn here?

Basic Telecom concepts Various Wireless Technologies Cellular concepts & Principal of cellular Comm. GSM Network Architecture GSM channel Architecture Call Flows in GSM GSM Planning steps (Nominal Plan & RF surveys) GSM Optimization Steps ( Performance, Drive testing &

Benchmarking)

BASIC Telephony

•Off Hook

•Dial Tone

•Dialing Digits

•RBT

•Conversation

•Ring

•Off Hook & Conversation

•Signaling•Traffic SWITCH / EXCHANGE

Wireless Communication

Alternative means of wireless communication Walkie - Talkie Pagers Trunked private radios

Mobile Phone - the magic technology that enables everyone to communicate anywhere with anybody.

Wireless Telephony

BSCBTS BTS

Mobile Subscriber...

MSC

Different Standards Worldwide

Till 1982 Cellular Systems were exclusively Analog Radio Technology.

Advanced Mobile Phone Service (AMPS)

U.S. standard on the 800 MHz Band

Total Access Communication System (TACS)

U.K. standard on 900 MHz band

Nordic Mobile Telephone System (NMT)

Scandinavian standard on the 450 & 900 MHz band

Different Standards Worldwide

GSM - 900GSM - 900

The term GSM-900 is used for any GSM system which operates in any 900 MHz band.

P-GSM - 900

P-GSM-900 band is the primary band for GSM-900 Frequency band for primary GSM-900 (P-GSM-900) : 2 x 25 MHz

890 – 915 MHz for MS to BTS (uplink)

935 – 960 MHz for BTS to MS (downlink)

E-GSM - 900

In some countries, GSM-900 is allowed to operate in part or in all of the following extension band. E-GSM-900 (Extended GSM-900) band includes the primary band (P-GSM-900) and the extension band :

880 – 890 MHz for MS to BTS (uplink)

925 – 935 MHz for BTS to MS (downlink)R-GSM-900R-GSM-900R-GSM-900 (Railway GSM-900) band includes the primary band (P-GSM-900) and the following extension band:

876 – 890 MHz for MS to BTS (uplink)921 – 935 MHz for BTS to MS (downlink)

GSM-1800GSM-1800Frequency band: 2 x 75 MHz

1710 – 1785 MHz for MS to BTs (uplink)1805 – 1880 MHz for BTS to MS (downlink)

Different Standards Worldwide

Industry Vs Technology Spread

Telecom Service Providers/Operators GSM CDMA Basic-WLL Internet Services Long Distance

Vendor Telecom Consultancy

Analog Mobile Telephony

End of 1980’s Analog Systems unable to meet continuing

demands

Severely confined spectrum allocations

Interference in multipath fading environment

Incompatibility among various analog systems

Inability to substantially reduce the cost of mobile

terminals and infrastructure required

Digital Mobile Telephony

Spectrum space - most limited and precious resource

Solution - further multiplex traffic (time domain)

Can be realized with Digital Techniques only

GSM History and Organization 1979 Europe wide frequency band reserved for

Cellular 1982 “Groupe Speciale Mobile” created within

CEPT 1986 GSM had full time in Paris 1988 ETSI takes over GSM Committee 1990 The phase 1 GSM Recommendations

frozen 1991 GSM Committee renamed “Special Mobile

Group” and GSM renamed as “Global System for Mobile

Communication” 1992 GSM launched for commercial

operations

Service Industry Service Provider is not a Equipment Manufacturer.

The Service Provider has a license to operate in a

geographical boundary (state/circle/ country).

It buys equipment from OEM Suppliers (Vendors).

Installs & commissions the equipment thus making it’s own

Network.

Provides the desired service to it’s subscribers.

Vendor

Vendor is a Equipment Manufacturer.

It supplies Product, Consultancy and Trainings

Service provider has the option of taking the Consultancy

and Training

Cellular Communication

A cellular system links Mobile subscribers to Public

Telephone System or to another Mobile subscribers.

It removes the fixed wiring used in a traditional telephone

installation.

Mobile subscriber is able to move around, perhaps can travel

in a vehicle or on foot & still make & receive call.

Advantage of Cellular Communication

Mobility

Flexibility

Convergence

Greater QOS

Network Expansion

Revenue/Profit

WHAT IS CELLULAR TELEPHONY ?CONSIDERATIONS -

FREQUENCY

SUBSCRIBER DENSITY

COVERAGE

Base Station

Base Station

Base Station

Base StationBase Station

Base Station

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. Cells - Reduce the need of High powered transmission Cells - Conventionally regarded as being hexagonal, but in reality

they are irregularly shaped. Cell shape is determined by the nature of the surrounding

area e.g. Hills , tall building etc.

Cell Size

Large Cells

35 Km Remote Areas High Transmission

Power Few subscribers

Small Cells

Near about 1 KM Urban Areas Low Transmission

Power Many Subscribers

Coverage & Capacity

Coverage Percentage of the geographical area covered by

cellular service where mobile telephony is available

Capacity - Number of calls that can be handled in a certain

area within a certain period of time. Capacity can also refer to the probability that

users will be denied access to a system due to the simple unavailability of radio channels.

Frequency Spectrum

Designation Abbreviation Frequencies Free-space WavelengthsVery Low Frequency VLF 9 kHz - 30 kHz 33 km - 10 km

Low Frequency LF 30 kHz - 300 kHz 10 km - 1 kmMedium Frequency MF 300 kHz - 3 MHz 1 km - 100 m

High Frequency HF 3 MHz - 30 MHz 100 m - 10 mVery High Frequency VHF 30 MHz - 300 MHz 10 m - 1 mUltra High Frequency UHF 300 MHz - 3 GHz 1 m - 100 mmSuper High Frequency SHF 3 GHz - 30 GHz 100 mm - 10 mm

Extremely High Frequency EHF 30 GHz - 300 GHz 10 mm - 1 mm

GSM - IN CELLULAR TELEPHONY Each Cell in the Cellular Network consists of one or more RF

carriers. An RF carrier is a pair of radio frequencies

One used in upward direction by MS - Uplink Other used in downward direction by BTS - Downlink The transmit and receive frequencies are separated by a

gap of 45 MHz in GSM of 75 MHz in DCS. There are 124 carries in GSM Band. With each carrier carrying 7

timeslots, only 124 x 7 = 868 calls can be made! Frequency Reuse is the solution

Frequency & ARFCNul

= 89

0 t o

91 5

MH

z

dl=

935

t o 9

60 M

Hz

Ful(n) = 890.0 + (0.2) *n MHz

Fdl(n) = Ful + 45 MHz

where n =ARFCN ; 1 n 124

Power

Frequency

Time

FDMA

Frequency

Power Time

TDMA

FrequencyCDMA

PowerTime

Multiple Access Methods

FrequencyTime

Power

TDMA

FrequencyTime

Power

FDMA

FrequencyTime

Power

CDMACODE

FDMA: AMPS & NAMPS•Each user occupies a private Frequency, protected from interference through physical separation from other users on the same frequency •TDMA: IS-136, GSM•Each user occupies a specific frequency but only during an assigned time slot. The frequency is used by other users during other time slots. •CDMA•Each user occupies a signal on a particular frequency simultaneously with many other users, but is uniquely distinguishable by correlation with a special code used only by this user

Multiple Access Methods

Frequency Reuse Pattern

Three types of frequency reuse patterns

7 Cell reuse pattern

4 cell reuse pattern

3 cell reuse pattern

3 Site Reuse Pattern

c2

c1c3

a1a2

a3

b1

b2

b3

c1c2

c3Cell Re-use

Cell Dia = R

FREQUENCY RE - USE

Frequency Re-use

7/21 cell cluster

1

23

45

6

7D D=R (3N)

where N is Cluster size

Principal Of Sectorization

Omni Directional Cells

120 degree Sectors

60 Degree sectors

Each Sector in a Site has its own allocation of Radio Carriers

Advantage

By frequent reuse of frequency more capacity can be achieved

Multipath Fading results in variations in signal strength which is known as Rayleigh Fading.

Rayleigh Fading phenomenon is dependent on path difference and hence frequency of reception.

A fast moving mobile may not experience severe effect of this fading since the path difference is continuously changing.

A slow moving mobile ( or a halted mobile ) may experience severe deterioration in quality.

But, if the frequency of reception is changed when this problem occurs ,could solve it.

The fading phenomenon is fast and almost continuos, this means the frequency change should also be continuos.

This process of continuously changing frequency is known as Frequency Hopping.

Frequency Hopping

Frequency Hopping is done in both Uplink and Downlink . Frequency is changed in every TDMA Frame Mobile can Hop on maximum 64 frequencies The sequence of Hopping can be Cyclic or Non-Cyclic There are 63 Non-Cyclic Hopping sequences possible Different Hopping sequence can be used in the same cell.

BCH Timeslot can never HOP, but the remaining Timelsots can very well hop.

Frequency Hopping

Reduction in Average Interference With Frequency Hopping consistent interference will become bursty. So even though, both the co-channel cells will be using the same set of ARFCN's for

Hopping, interference will not be continuos. This is because, GSM cells are not Frame synchronized, and change in frequency is

related to Frame nos. If same HSN is used in two cells, then either the interference will be nil , or if a phase

correlation exists then it will be continuos. So the two cells should preferably use different HSN's . Sectorial cells ( controlled by the same BTS) can use same HSN, since the sectors don't

come up at the same time. Cells if they are synchronized, can use same HSN, if each cell has an offset of some

TDMA frames. Offset of TDMA frames is also required to avoid SACCH occurring at the same time in all

synchronized cells, as they kills away the objective of DTX.

Frequency Hopping

a1a2

a3a3

a4a6a5

Cell Sectorisation

OMNI CELL1 ANTENNA

b1

b2

b3

120O CELLS3 ANTENNAS

60O CELLS6 ANTENNAS

Features of GSM

Compatibility Noise Robust Increased Capacity & Flexibility Use of Standard Open Interfaces Improved Security & Confidentiality Cleaner Handovers Subscriber Identification ISDN Compatibility Enhanced Range of Services

HandoversHard Handoff

Analog, TDMA and GSMSoft Handoff

CDMA

Break before Make Make before Break

120

181

198

200

132

41

44

24

69

75

113

28

71

73

70

80

7

8

11 12

13 1617

18

19

20

22

25

32

40

171

173

175

182

187

197

199

201

213

214

215

216

218

219220

221

222

225

Handovers

Cleaner Handovers

The mobile measures up to 32 adjacent cells for Signal Strength (RxLevel) Signal Quality (RxQual) updated every 480 mS and sends to BTS

Sophisticated Handover based on RxLevel Interference RxQual Timing Advance Power Budget

BTS

BTS

BTS

BTS

BTS

BTS

BTS

BTS

BSC

VLR

HLR EI

R

OMC

SMSCB

C

AUC

VMSC

MSC

Abis

A

MS

BTS

BTS

BTS

BTS BTS

BTS

BTS

BTS

BSC

BSC

PSTN

VLR

TRAU HLREIR

OMC

SMSC

BC

AUC

VMSC

MSC

Abis

A

OML

GSM NETWORK ELEMENTS

Mobile Station Identities

MSISDN : Human Identity used to call a Mobile Station

IMEI: Serial number unique to every Mobile Station

IMSI : Network Identity unique to a SIM3 digits

2 digits

10 digits TMSI : Identity unique in a LAI

MSRN : Mobile Station Roaming NoCC NDC SN

98 XXX 12345

MCC MNC MSIN404 XX 12345

TAC FAC SNR S

6 digits 2 digits 6 digits 1 digit

GSM Network Components

Mobile Station consists of two parts- Mobile Equipment (ME) Subscriber Identity Module (SIM)

ME Hardware e.g. Telephone, Fax Machine, Computer.

SIM Smart Card which plugs into the ME.

ME (Classmark Information)

Revision Level Phase of the GSM specs ME comply with.

RF Power Capability Max power ME is able to Transmit.

Ciphering Algorithm Used Presently A5 Phase 2 specifies Algorithms A5/0 to A5/7.

Frequency Capability

SMS Capability

Typical Settings

Mobile Equipment

Class Power O/p 1 20 W

2 8 W

3 5 W

4 2 W

5 0.8 W

SIM(IMSI)

IMSI(International Mobile Subscriber Identity) Transmitted over Air Interface on initialization

Permanently stored on SIM card

15 digit Decimal

SIM (TMSI)

Temporary Mobile Subscriber Identity Periodically changed by the System Management on

instances like location update etc.

Reason for use of TMSI To prevent a possible intruder from identifying GSM users,

TMSI is used

Management Assignment, Administration & Updating is performed by

VLR.

Transcoder

Converts 64 Kbps PCM circuits from MSC to 16 Kbps BSS circuits.

Each 30 channel 2 Mbps PCM link can carry 120 GSM - specified voice channels.

Base Station System (BSS)

BSS (Base Station System) BSC (Base Site Controller) BTS (Base Transceiver Station) XCDR (Transcoder)

Network Switching System (NSS)

XCDR

BSC

BTS

Base Station System (BSS)

BSC Controls upto 40 BTS Conveys information to/from BTS Connects terrestrial circuits & Air Interface Channels Controls handovers between BTSs under itself

BTS Contains RF Hardware Limited control functionality 1 - 6 carriers in a BTS Cabinet 7 - 48 simultaneous calls per BTS

BSS Configuration

Collocated BTS

Remote BTS

Star Configuration

Daisy Chain BTS Loop Configuration

BSC

BTS

BTS

BTSA

ll BTS on 1 E1

BSC

BTS

BTS

BTS

BTS

Network Switching System(NSS) NSS (Network Switching System)

MSC (Mobile Switching Centre)

HLR (Home Location Register)

VLR (Visitor Location Register)

EIR (Equipment Identity Register)

AUC (Authentication Centre)

IWF (Interworking Function)

EC (Echo Canceller)

GSM Network Component MSC

Call Switching Operation & Management Support Internetwork Interworking Collects call billing data

Gateway MSC MSC which provides interface between PSTN & BSS’s in

the GSM Network.

Home Location Register (HLR)

Reference database for the Subscriber profiles- Subscriber ID (IMSI & MSISDN) Current VLR Address Supplementary Services subscribed Supplementary Service Information Subscriber Status (Registered/deregistered) Authentication Key and AUC functionality TMSI MSRN

Visitor Location Register (VLR)

Temporary Data, which exists as long as the subscriber is active in a particular Coverage area.

Contains the following- Mobile Status (Busy/ Free/ No Answer/etc.) Location Area Identity (LAI) TMSI MSRN (Mobile Station Roaming Number)

Equipment Identity Register (EIR)

Contains Database for validating IMEI

White List (valid ME)

Black List (Stolen ME)

Grey List (Faulty ME)

Provides function to enable the GSM System to interface with Public/Private Data Networks.

The basic feature of the IWF are Rate Conversion Protocol adaptation

IWF incorporates Modem Bank.

e.g. GSM DTE PSTN DTE IWF Analogue Modem

Inter Working Function

Echo Canceller

Echo is apparent only in Mobile - Land conversation & is generated at the 2 wire to 4 wire interface.

To avoid it, Echo Canceller (EC) is used. Echo is irritating to MS Subscriber

Total Round Trip delay of 180 ms in the GSM system

EC is placed on the PSTN side of the Switch

Cancellation up to 68 ms with EC

Operation & Maintenance Centre Event & Alarm Management

Fault Management

Performance Management

Configuration Management

Security Management

GSM Terrestrial Interfaces

Broadly classified into two types of interfaces-

Standard Interfaces

2 Mbps Trunks (E1)

Signalling System No. 7 SS7 ( CCS7)

X.25 (Packet Switched Mode)

GSM Interfaces

GSM Interfaces

Um MS - BTS Abis BTS - BSC A BSC - MSC B MSC - VLR C MSC - HLR D VLR - HLR E MSC - MSC F MSC - EIR G VLR - VLR H HLR - AUC

GSM protocols are basically divided into three layers:Layer 1: Physical layer± Enables physical transmission (TDMA, FDMA, etc.)± Assessment of channel quality± Except on the air interface (GSM Rec. 04.04), PCM 30 or ISDNlinks are used (GSM Rec. 08.54 on Abis interface and 08.04 onA to F interfaces).Layer 2: Data link layer± Multiplexing of one or more layer 2 connectionson control/signaling channels± Error detection (based on HDLC)± Flow control± Transmission quality assurance± RoutingLayer 3: Network layer± Connection management (air interface)± Management of location data± Subscriber identification± Management of added services (SMS, call forwarding, conferencecalls, etc.)

GSM Protocol Layers

Basic Processes

AUTHENTICATION

CIPHERING

REGISTRATION

CALL ESTABLISHMENT

HANDOVER / HANDOFF

ROAMING

AUTHENTICATION ALGORITHM

NSS

MS

HLR

AUC

AUTH.ALGORITHMS

A3

SIM

MS

AUTH.ALGORITHMS

A3

Ki

RAND

RAND

COMPARE

SRES

SRES

Ki

AIR INTERFACE

Ciphering

Data protection is required on air interface. A specific key called Ciphering Key (Kc), is

generated from RAND and A8 algorithm. A8 is on the SIM.

A8RANDKi

Kc

Ciphering

A5Data

Kc

CipheredData A5

Kc

Data

Transmission Media

Access Network

Microwave 15 /23 GHz Backbone Network

Microwave 7 GHz Optical Fibers Leased Line( From Dot or any other service provider on

any media)

Optical Fiber

Different Possible Combinations Mono Mode Step Index 10 / 125 m Mono Mode Graded index Multi Mode Step Index 100 / 300 m Multi Mode Graded Index 75 / 130 m

Mono Mode Graded Index would have been the best but fabrication not possible

140 Mbps OLTE , Mono Mode Step Index in our case

Channels On Air Interface Physical Channel Logical Channel

Physical Channel Physical channel is the medium over which the information

is carried.

Logical Channel Logical channels consists of the information carried over

the Physical Channel.

LOGICAL CHANNELS

0 1 2 3 4 5 6 7

3

57 encrypted

57 encrypted

26 training

1S

1S

3T

8.25GP

3T

577S

577S x 8 = 4.615mS

TDMA Frame

Normal Burst

26 Frame Multi-frame

GSM Channels

Traffic Channel

TCH carries payload data - speech, fax, data

• Connection may be:

- Circuit Switched - voice or data or - Packet Switched – data

• TCH may be:

• Full Rate (TCH/F)

- one channel per user

- 13 kb/s voice, 9.6 kb/s data or

• Half Rate (TCH/H)

- one channel shared between two users

- 6.5 kb/s voice, 4.8 kb/s data

Traffic Channels

TCH/FFull rate 22.8kbits/s

TCH/HHalf rate 11.4 kbits/s

Time is divided into discrete periods called “Timeslots”

Control Channel

DCCH(Dedicated Channels)Downlink & Uplink

CCCH(Common Control Chan)Downlink & Uplink

Synch.Channels

RACHRandom

Access ChannelCBCH

Cell Broadcast Channel

SDCCHStandalone dedicated

control channel

ACCHAssociated

Control Channels

SACCHSlow associated Control Channel

FACCHFast Associated

Control Channel

PCH/AGCH

Paging/Access grant

FCCHFrequency

Correction channel

Control Channels

BCH ( Broadcast channels )Downlink only

BCCHBroadcast

control channel

SCHSynchronization

channel

Broadcast Channels (BCH)

BCH channels are all downlink and are allocated to timeslot zero.

Channels are:

• FCCH: Frequency control channel sends the mobile a burst of all ‘0’ bits which allows it to fine tune to the downlink frequency

• SCH: Synchronization channel sends the absolute value of the frame number (FN), which is the internal clock of the BTS, together with the Base Station Identity Code (BSIC)

• BCCH: Broadcast Control Channel sends radio resource management and control messages, Location Area Code and so on.

Some messages go to all mobiles, others just to those that are in the idle state

Common Control Channels (CCCH)

CCCH contains all point to multi-point downlink channels (BTS to

several MSs) and the uplink Random Access Channel:

• CBCH: Cell Broadcast Channel is an optional channel for general information such as road traffic reports sent in the form of SMS

• PCH: Paging Channel sends paging signal to inform mobile of a call

• RACH: Random Access Channel is sent by the MS to request a channel from the BTS or accept a handover to another BTS.

A channel request is sent in response to a PCH message.

• AGCH: Access Grant Channel allocates a dedicated channel (SDCCH) to the mobile

• NCH: Notification Channel informs MS about incoming group or

broadcast calls

Dedicated Control Channels (DCCH)

SDCCH( Standalone Dedicated Control Channel )

Uplink and Downlink

Used for call setup, location update and SMS.

SACCH( Slow Associated Control Channel )

Used on Uplink and Downlink only in dedicated mode.

Uplink SACCH messages - Measurement reports.

Downlink SACCH messages - control info.

FACCH( Fast Associated Control Channel )

Uplink and Downlink.

Associated with TCH only.

BURST

The Time Slots are arranged in a sequence , conventionally numbered 0 to 7.

Each repetition of this sequence is called a TDMA Frame.

The information content carried in one time slot is called a “burst”.

BURST Information

Main Area where the Speech, Data or Control info is held Guard Period

To enable the burst to hit the time slot (0.031ms) Stealing Flags

2 bits are set when TCH is to stolen by a FACCH Training Sequence

For estimation of transfer characteristics of physical media Tail Bits

Used to indicate beginning and end of the burst.

GSM Burst & TDMA Frame

0 1 2 3 4 5 6 7 2 4 5 6 730 1

FRAME 1 FRAME 2

Training Sequence

Information Information

GUARD PERIOD

GUARD PERIOD

TAIL BITS TAIL BITS

Five Types of Burst

Normal BurstTraffic & Control Channels Bi-directional

Frequency Correction Burst

FCCH Downlink Synchronization Burst

SCH Downlink Dummy Burst

BCCH Carrier Downlink Access Burst

RACH Uplink

Call Scenarios

Mobile to Mobile Intra-city Inter-city

Mobile to Land Intra-city Inter-city

Land to Mobile Intra-city Inter-city

Mobile To Land Sequence

1

3

CHANNEL REQUEST

DCCH ASSIGN

SIGNALLING LINKESTABLISHED

REQUEST FOR SERVICE

SET CIPHER MODE

SET-UP

EQUIPMENT ID REQUEST

AUTHENTICATION

MS BSS MSC VLR HLR PSTNEIR

RACH

AGCH

SDCCH

SDCCH

Call Info7

4

6

5

2CR

CC

8 COMPLELTE CALLCALL PROCEEDING

9 ASSIGNMENT COMMAND

INITIAL & FINALADDRESS (IFAM)

ASSIGNMENT COMPLETE (ACM)

10

ANSWER(ANS)

11

CONNECT ACKNOWLEDGE

SDCCH

SDCCH

ASSIGNMENT COMPLELTE

MS HEARS RINGTONEFROM LAND PHONE

ALTERING

RING TONESTOPS

CONNECT

(channel)

(TCH)

FACCH

FACCH

FACCH

TCH

(circuit)

FAACH

BILLING STARTS

Hello!

MS BSS MSC

VLR HLR PSTN EIR

Call Contt.

Supplementary Services

• Calling Line Identification– Present– Absent

• Connect Line Identification– Present– Absent

• Closed User Group - CUG– Only incoming– Only outgoing

• Operator Controlled Barring

Data Services

Data rates supported as of today areData rates supported as of today are2.4 Kbps2.4 Kbps

4.8 Kbps4.8 Kbps

9.6 Kbps9.6 Kbps

GPRS & EDGE implementation takes the data GPRS & EDGE implementation takes the data capability to higher level of the order of 184 capability to higher level of the order of 184 kbps and morekbps and more

Customer..Expectation

• Good coverage – where ever he goes• Good quality• No blocking• Value added services

– SMS– Voice mail– MMS– Call forward/call waiting– Data/internet at high data rates– prepaid

Basic Network Design Objectives

The basic objectives of a wireless system are:– COVERAGE: provide sufficient cell sites to deliver RF coverage

of the entire desired area.– BUILDING/VEHICLE PENETRATION: deliver sufficient signal

levels to adequately penetrate buildings and vehicles where appropriate.

– TRAFFIC: ensure that no cell captures more traffic than it can handle at the desired grade of service (i.e., blocking percentage)

– PERFORMANCE: design, construct, and adjust the network to deliver reliable service free from excessive origination and call delivery failures, dropped calls, quality impairments, and service outages.

– ECONOMICS: provide return on investment sufficient to support operating and capital expenses, expand the network to take advantage of growth opportunities, and retire costs of construction prior to depreciation of the network equipment.

High Level DesignInputs

– Coverage objectives• Area coverage objectives• Coverage penetration objectives

– Morphology data/clutter information– Terrain data and Vector maps– Traffic objectives

• Number of subscribers defined• Traffic per subscriber defined• Desired grade of service defined

– City regulations– BTS Hardware specifications– Link Budget– Business and Logistical objectives

• Capital budget• Timing: launch data• Operating revenue Vs. total costs

• Output– Cell database and traffic model– Composite coverage plot– Equal power handoff boundaries plot

“Background” Issues Impacting System Design

• Site acquisition– Availability of suitable candidate (building or land) – Owner interest– Cost of leasing– Frequency clearance (SACFA)– Government authority approval– Space constraints and other construction issues

• Candidate Location – line of sight to the objective• Clutter type• Terrain variations• Physical Blocking – buildings, hoardings• Water• Mumbai – High end, high traffic areas are very close to

water…. Makes RF design much more challenging

• Deviation from desired location impacts surrounding site locations

Design considerations of Network (GSM/CDMA)

• Understand geographical area as per license agreement• Define coverage expectations in terms

– On road coverage– In-building coverage (different penetration margins)

• Capacity considerations – busy hour per subscriber call attempts and minutes of use (Erlangs)

• 1 Erlang is 1 call of 1 hour duration• Decide number of sites based on coverage capacity requirement• Propagation tools used for this analysis• Finalize exact site locations after field survey• Initiate candidate identification process• Site acquisition/antenna positioning• Modify existing design if site location changes

Traffic & Growth Analysis

System Optimisation

Site Coverage Confirmation

Site Search & Selection

Propagation model

verification

System/Site Dimensioning

RF &Network Planning

Market Requirement

Site Acquisition

Site Build

Operational Network

Site Search Plan

Performance Monitoring

Flow Chart for Network Deployment

GSM Planning Steps

Various steps are listed below CW survey Model Tuning Nominal Planning RF site Surveys Realized Planning Frequency Planning

Implementation Optimization

Drive Testing Performance Analysis

Nominal Planning

It consists of planning a set of sites on planning tool so as to predict the coverage of the target area

Tool needs to be made intelligent so as to predict the coverage as close as possible to actual coverage

Coverage plots are based on customer intension of providing indoor and outdoor coverage

Mumbai – Coverage Expectation Boundary

Coverage Maps – Reverse Link.

Colaba

Malabar Hill

Mazgaon

>=30dB:: 3-4 wall coverage

25-30dB : 3 Wall Coverage

23-25 dB : 2-3 Wall Coverage

18-23dB: 2-3 Wall Coverage

16-18 dB : 2 Wall Coverage

8-16dB : 1-2wall Coverage

08 dB : On Road-1 Wall Coverage

00 dB : On Road/No Coverage

Indoor Coverage: Penetration Margin Legend

Composite Coverage Plot

• Propagation models are used to predict coverage from a particular site

• A composite coverage plot shows the overall coverage produced by each sector in the field of view

• The color of each pixel corresponds to the signal level of the strongest server at that point

• Such plots are useful for identifying coverage holes and overall coverage extent

Clutter Types

Clutter types Dense Urban Urban Sub Urban Rural Water Vegetation Industrial Forest

RF surveys

Each nominal has a search ring defined by the RF Planner

Candidates needs to be identified as close as possible to the nominal within the search ring

Height, orientations & antenna placement at site are the key RF parameter which are based upon the coverage requirement in the area

Major obstructions and clutter type in various directions to be observed on RF survey

RF surveys

Equipment required for RF Survey GPS Digital Camera Binoculars Magnetic Compass

There might be 3 or more candidates surveys for one site

Each candidate would have an RF survey form and panoramic associated with it

Drive Testing• Drive testing is an important activity to get statistics & graphs on coverage, quality & capacity in the downlink direction

• Drive test setup – DT tool, Engineering Handset, GPS, accessories

• Call in 2 modes

•Dedicated – while the mobile is on call

•Idle – while the mobile is idle

Important parameters observed during drive testing

•Coverage – Rx level (Full & Sub)

•Quality – RxQual & SQI

•Handover, Dropped call, Neighbor list, TA

Selecting and Tuning Propagation Models• Parameters of propagation

models must be adjusted for best fit to actual drive-test measured data in the area where the model is applied

• The figure at right shows drive-test signal strengths obtained using a test transmitter at an actual test site

• Tools automate the process of comparing the measured data with its own predictions, and deriving error statistics

• Prediction model parameters then can be “tuned” to minimize observed error

Drive Test Screen

What is Performance Optimization?

• The words “performance optimization” mean different things to different people, viewed from the perspective of their own jobs

• System Performance Optimization includes many different smaller processes at many points during a system’s life– recognizing and resolving system-design-related issues (can’t

build a crucial site, too much overlap/soft handoff, coverage holes, etc.)

– “cluster testing” and “cell integration” to ensure that new base station hardware works and that call processing is normal

– “fine-tuning” system parameters to wring out the best possible call performance

– identifying causes of specific problems and customer complaints, and fixing them

– carefully watching system traffic growth and the problems it causes - implementing short-term fixes to ease “hot spots”, and recognizing problems before they become critical

Optimization

• Optimisation is an ongoing process of analysing network performanceagainst Quality of Service targets:

Performance

•Measurements of network performance cover:

• Traffic in erlangs

• TCH and SDCCH Grade of Service (Congestion)

• Call success rate

• Handover failure

• Coverage area

• Coverage quality

• Subscriber base and growth

• Key Performance Indicators (KPI) are measurable dynamic

parameters that help to target areas of concern

KPI’s

• Appropriate KPIs to use depend on:• The nature of the network• Data sources available• Measurement tools available• Ability of engineering team• Cost of network infrastructure

• Sources of data include:• Surveyed data - from drive tests• Network statistics - from OMC • Field engineer reports

Radio Interface Optimization

Transmission Timing Power Control VAD Voice Activity Detector and DTX Multipath Fading Equalization Diversity Frequency Hopping Antenna Parameters ( Height, Azimuth, Tilts )

Antenna Tilts

Antenna Tilts

Benchmarking•Surveyed data from test-mobile measurements can be used to

benchmark system performance against that of a competitor

• Problems that may be identified from surveyed data:

• Poor coverage

• Unexpected interference

• Missing handover definitions

• Installation problems at BTS

• Test-mobile measurements should include:

• continuous calls to test coverage

• repetitive short calls to test call-success

Overview

RF Planning Tool

Drive Test Tool

Optimization Tool

MapInfo