GSM Fundamentals

By,M.KATHIRESANkathiresanece@gmail.com

What you will learn here?Basic Telecom conceptsVarious Wireless TechnologiesCellular concepts & Principal of cellular Comm.GSM Network ArchitectureGSM channel ArchitectureCall Flows in GSMGSM Planning steps (Nominal Plan & RF surveys)GSM Optimization Steps ( Performance, Drive testing & Benchmarking)

BASIC TelephonyOff HookDial ToneDialing DigitsRBTConversation RingOff Hook & ConversationSignalingTrafficSWITCH / EXCHANGE

Wireless Communication Alternative means of wireless communicationWalkie - TalkiePagersTrunked private radios

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

Wireless Telephony

BSCBTSBTSMobile Subscriber...MSC

Different Standards WorldwideTill 1982 Cellular Systems were exclusively Analog Radio Technology.Advanced Mobile Phone Service (AMPS)U.S. standard on the 800 MHz BandTotal Access Communication System (TACS)U.K. standard on 900 MHz bandNordic Mobile Telephone System (NMT) Scandinavian standard on the 450 & 900 MHz band

Different Standards Worldwide

GSM - 900The term GSM-900 is used for any GSM system which operates in any 900 MHz band.P-GSM - 900P-GSM-900 band is the primary band for GSM-900 Frequency band for primary GSM-900 (P-GSM-900) : 2 x 25 MHz890 915 MHz for MS to BTS (uplink)935 960 MHz for BTS to MS (downlink)E-GSM - 900In 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-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-1800Frequency band: 2 x 75 MHz1710 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/OperatorsGSMCDMABasic-WLL Internet ServicesLong DistanceVendorTelecom Consultancy

Analog Mobile TelephonyEnd of 1980s Analog Systems unable to meet continuing demandsSeverely confined spectrum allocationsInterference in multipath fading environmentIncompatibility among various analog systems Inability to substantially reduce the cost of mobile terminals and infrastructure required

Digital Mobile TelephonySpectrum space - most limited and precious resource Solution - further multiplex traffic (time domain)Can be realized with Digital Techniques only

GSM History and Organization

1979Europe wide frequency band reserved for Cellular1982Groupe Speciale Mobile created within CEPT1986GSM had full time in Paris1988ETSI takes over GSM Committee 1990The phase 1 GSM Recommendations frozen1991GSM Committee renamed Special Mobile Group and GSM renamed as Global System for Mobile Communication1992GSM launched for commercial operations

Service IndustryService 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 its own Network. Provides the desired service to its subscribers.

VendorVendor is a Equipment Manufacturer. It supplies Product, Consultancy and TrainingsService provider has the option of taking the Consultancy and Training

Cellular CommunicationA 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 CommunicationMobilityFlexibilityConvergenceGreater QOSNetwork ExpansionRevenue/Profit

WHAT IS CELLULAR TELEPHONY ?CONSIDERATIONS -

FREQUENCY

SUBSCRIBER DENSITY

COVERAGEBase StationBase StationBase StationBase StationBase StationBase Station

The CellCellular 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 transmissionCells - 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 SizeLarge Cells

35 Km Remote AreasHigh Transmission PowerFew subscribers

Small Cells

Near about 1 KMUrban AreasLow Transmission PowerMany Subscribers

Coverage & CapacityCoveragePercentage 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

PRIVATEDesignation

Abbreviation

Frequencies

Free-space Wavelengths

Very Low Frequency

VLF

9 kHz - 30 kHz

33 km - 10 km

Low Frequency

LF

30 kHz - 300 kHz

10 km - 1 km

Medium Frequency

MF

300 kHz - 3 MHz

1 km - 100 m

High Frequency

HF

3 MHz - 30 MHz

100 m - 10 m

Very High Frequency

VHF

30 MHz - 300 MHz

10 m - 1 m

Ultra High Frequency

UHF

300 MHz - 3 GHz

1 m - 100 mm

Super 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 TELEPHONYEach Cell in the Cellular Network consists of one or more RF carriers.An RF carrier is a pair of radio frequenciesOne used in upward direction by MS - UplinkOther used in downward direction by BTS - DownlinkThe 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= 890 to 915 MHzdl= 935 to 960 MHzFul(n) = 890.0 + (0.2) *n MHz

Fdl(n) = Ful + 45 MHz

where n =ARFCN ; 1 n 124

PowerFrequencyTimeFDMAFrequencyPowerTimeTDMAFrequencyCDMAPowerTimeMultiple Access Methods

FDMA: AMPS & NAMPSEach user occupies a private Frequency, protected from interference through physical separation from other users on the same frequency TDMA: IS-136, GSMEach user occupies a specific frequency but only during an assigned time slot. The frequency is used by other users during other time slots. CDMAEach 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 PatternThree types of frequency reuse patterns7 Cell reuse pattern4 cell reuse pattern3 cell reuse pattern

3 Site Reuse Patternc2c1c3a1a2a3b1b2b3c1c2c3Cell Re-use

FREQUENCY RE - USEFrequency Re-useCell Dia = R7/21 cell cluster1234567DD=R (3N)where N is Cluster size

Principal Of SectorizationOmni Directional Cells120 degree Sectors 60 Degree sectorsEach Sector in a Site has its own allocation of Radio CarriersAdvantageBy 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 FrameMobile can Hop on maximum 64 frequenciesThe sequence of Hopping can be Cyclic or Non-CyclicThere are 63 Non-Cyclic Hopping sequences possibleDifferent 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 InterferenceWith 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

Cell Sectorisationa1a2a3a3a4a6a560O CELLS6 ANTENNAS

Features of GSMCompatibilityNoise RobustIncreased Capacity & FlexibilityUse of Standard Open InterfacesImproved Security & ConfidentialityCleaner HandoversSubscriber IdentificationISDN CompatibilityEnhanced Range of Services

HandoversHard HandoffAnalog, TDMA and GSMSoft HandoffCDMABreak before MakeMake before Break

Handovers

Cleaner HandoversThe mobile measures up to 32 adjacent cells forSignal Strength (RxLevel)Signal Quality (RxQual)updated every 480 mS and sends to BTSSophisticated Handover based onRxLevelInterferenceRxQualTiming AdvancePower Budget

GSM NETWORK ELEMENTS

Mobile Station Identities

GSM Network ComponentsMobile Station consists of two parts-Mobile Equipment (ME)Subscriber Identity Module (SIM) ME Hardware e.g. Telephone, Fax Machine, Computer.SIMSmart Card which plugs into the ME.

ME (Classmark Information)Revision LevelPhase of the GSM specs ME comply with.RF Power CapabilityMax power ME is able to Transmit.Ciphering Algorithm UsedPresently A5Phase 2 specifies Algorithms A5/0 to A5/7. Frequency CapabilitySMS Capability

Mobile EquipmentClassPower O/p 120 W 28 W 35 W 42 W 50.8 W

Typical Settings

SIM(IMSI)IMSI(International Mobile Subscriber Identity)Transmitted over Air Interface on initializationPermanently stored on SIM card15 digit Decimal

SIM (TMSI)Temporary Mobile Subscriber IdentityPeriodically changed by the System Management on instances like location update etc.Reason for use of TMSITo prevent a possible intruder from identifying GSM users, TMSI is usedManagementAssignment, Administration & Updating is performed by VLR.

TranscoderConverts 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)

Base Station System (BSS)BSCControls upto 40 BTSConveys information to/from BTSConnects terrestrial circuits & Air Interface ChannelsControls handovers between BTSs under itselfBTSContains RF HardwareLimited control functionality1 - 6 carriers in a BTS Cabinet7 - 48 simultaneous calls per BTS

BSS ConfigurationCollocated BTSRemote BTSStar ConfigurationDaisy Chain BTSLoop Configuration

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 ComponentMSC Call SwitchingOperation & Management SupportInternetwork InterworkingCollects call billing dataGateway MSCMSC which provides interface between PSTN & BSSs in the GSM Network.

Home Location Register (HLR)Reference database for the Subscriber profiles-Subscriber ID (IMSI & MSISDN)Current VLR AddressSupplementary Services subscribedSupplementary Service InformationSubscriber Status (Registered/deregistered)Authentication Key and AUC functionalityTMSIMSRN

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)TMSIMSRN (Mobile Station Roaming Number)

Equipment Identity Register (EIR)Contains Database for validating IMEIWhite List (valid ME)Black List (Stolen ME)Grey List (Faulty ME)

Inter Working FunctionProvides function to enable the GSM System to interface with Public/Private Data Networks.

The basic feature of the IWF are Rate ConversionProtocol adaptationIWF incorporates Modem Bank. e.g. GSM DTE PSTN DTE IWFAnalogue Modem

Echo CancellerEcho 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 SubscriberTotal Round Trip delay of 180 ms in the GSM systemEC is placed on the PSTN side of the Switch Cancellation up to 68 ms with EC

Operation & Maintenance CentreEvent & Alarm ManagementFault ManagementPerformance ManagementConfiguration ManagementSecurity Management

GSM Terrestrial InterfacesBroadly classified into two types of interfaces-Standard Interfaces2 Mbps Trunks (E1)Signalling System No. 7 SS7 ( CCS7)X.25 (Packet Switched Mode)GSM Interfaces

GSM InterfacesUmMS- BTSAbisBTS- BSCABSC- MSCBMSC- VLRCMSC- HLRDVLR- HLREMSC- MSCFMSC- EIRGVLR- VLRHHLR- 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 ProcessesAUTHENTICATIONCIPHERINGREGISTRATIONCALL ESTABLISHMENTHANDOVER / HANDOFFROAMING

AUTHENTICATION ALGORITHMNSSMSHLRAUCAUTH.ALGORITHMSA3SIMMSAUTH.ALGORITHMSA3KiRANDRANDCOMPARESRESSRESKiAIR INTERFACE

CipheringData 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.

CipheringA5DataKcCipheredDataA5KcData

Transmission MediaAccess NetworkMicrowave 15 /23 GHzBackbone NetworkMicrowave 7 GHzOptical FibersLeased Line( From Dot or any other service provider on any media)

Optical FiberDifferent Possible Combinations Mono Mode Step Index 10 / 125 mMono Mode Graded indexMulti Mode Step Index 100 / 300 mMulti Mode Graded Index 75 / 130 mMono 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 InterfacePhysical Channel Logical Channel

Physical ChannelPhysical channel is the medium over which the information is carried.

Logical ChannelLogical channels consists of the information carried over the Physical Channel.

LOGICAL CHANNELS3577S577S x 8 = 4.615mSTDMA FrameNormal Burst26 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/sTime is divided into discrete periods called Timeslots

Control Channel DCCH(Dedicated Channels)Downlink & Uplink CCCH(Common Control Chan)Downlink & Uplink

Synch.Channels

RACHRandom Access Channel

CBCHCell Broadcast Channel

SDCCHStandalone dedicated control channel

ACCHAssociated Control Channels

SACCHSlow associated Control Channel

FACCHFast Associated Control Channel

PCH/AGCHPaging/Access grant

FCCHFrequency Correction channelControl Channels BCH ( Broadcast channels )Downlink onlyBCCHBroadcast control channelSCHSynchronization 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 toseveral 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 orbroadcast calls

Dedicated Control Channels (DCCH)

SDCCH( Standalone Dedicated Control Channel )Uplink and DownlinkUsed 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.

BURSTThe 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.

BURSTInformationMain Area where the Speech, Data or Control info is held Guard PeriodTo enable the burst to hit the time slot (0.031ms)Stealing Flags2 bits are set when TCH is to stolen by a FACCHTraining SequenceFor estimation of transfer characteristics of physical mediaTail BitsUsed to indicate beginning and end of the burst.

GSM Burst & TDMA Frame

Five Types of BurstNormal BurstTraffic & Control ChannelsBi-directionalFrequency Correction Burst FCCHDownlinkSynchronization Burst SCHDownlinkDummy Burst BCCH CarrierDownlinkAccess Burst RACHUplink

Call ScenariosMobile to MobileIntra-city Inter-cityMobile to LandIntra-city Inter-cityLand to MobileIntra-city Inter-city

Mobile To Land Sequence

Call Contt. 8COMPLELTE CALLCALL PROCEEDING9ASSIGNMENT COMMAND

INITIAL & FINALADDRESS (IFAM)

ASSIGNMENT COMPLETE (ACM)10ANSWER(ANS)11CONNECT ACKNOWLEDGESDCCHSDCCHASSIGNMENT COMPLELTEMS HEARS RINGTONEFROM LAND PHONEALTERINGRING TONESTOPSCONNECT(channel)(TCH)FACCHFACCHFACCHTCH(circuit)FAACHBILLING STARTSHello!MSBSSMSCVLRHLRPSTNEIR

Supplementary ServicesCalling Line IdentificationPresentAbsentConnect Line IdentificationPresentAbsentClosed User Group - CUGOnly incomingOnly outgoingOperator Controlled Barring

Data ServicesData rates supported as of today are2.4 Kbps4.8 Kbps 9.6 KbpsGPRS & EDGE implementation takes the data capability to higher level of the order of 184 kbps and more

Customer..ExpectationGood coverage where ever he goesGood qualityNo blockingValue added services SMSVoice mailMMSCall forward/call waitingData/internet at high data ratesprepaid

Basic Network Design ObjectivesThe 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 DesignInputsCoverage objectivesArea coverage objectivesCoverage penetration objectivesMorphology data/clutter informationTerrain data and Vector mapsTraffic objectivesNumber of subscribers definedTraffic per subscriber definedDesired grade of service definedCity regulationsBTS Hardware specificationsLink BudgetBusiness and Logistical objectivesCapital budgetTiming: launch dataOperating revenue Vs. total costsOutputCell database and traffic modelComposite coverage plotEqual power handoff boundaries plot

Background Issues Impacting System DesignSite acquisitionAvailability of suitable candidate (building or land) Owner interestCost of leasingFrequency clearance (SACFA)Government authority approvalSpace constraints and other construction issuesCandidate Location line of sight to the objectiveClutter typeTerrain variationsPhysical Blocking buildings, hoardingsWaterMumbai High end, high traffic areas are very close to water. Makes RF design much more challengingDeviation from desired location impacts surrounding site locations

Design considerations of Network (GSM/CDMA)Understand geographical area as per license agreementDefine coverage expectations in termsOn road coverageIn-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 durationDecide number of sites based on coverage capacity requirementPropagation tools used for this analysisFinalize exact site locations after field surveyInitiate candidate identification processSite acquisition/antenna positioningModify existing design if site location changes

Flow Chart for Network Deployment

GSM Planning StepsVarious steps are listed belowCW surveyModel TuningNominal PlanningRF site SurveysRealized PlanningFrequency PlanningImplementationOptimizationDrive TestingPerformance Analysis

Nominal PlanningIt consists of planning a set of sites on planning tool so as to predict the coverage of the target areaTool needs to be made intelligent so as to predict the coverage as close as possible to actual coverageCoverage plots are based on customer intension of providing indoor and outdoor coverage

Mumbai Coverage Expectation Boundary

Coverage Maps Reverse Link.ColabaMalabar HillMazgaon

Composite Coverage PlotPropagation models are used to predict coverage from a particular siteA 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 pointSuch plots are useful for identifying coverage holes and overall coverage extent

Clutter TypesClutter typesDense UrbanUrbanSub UrbanRuralWaterVegetationIndustrialForest

RF surveysEach nominal has a search ring defined by the RF PlannerCandidates needs to be identified as close as possible to the nominal within the search ringHeight, orientations & antenna placement at site are the key RF parameter which are based upon the coverage requirement in the areaMajor obstructions and clutter type in various directions to be observed on RF survey

RF surveysEquipment required for RF SurveyGPSDigital CameraBinocularsMagnetic CompassThere might be 3 or more candidates surveys for one siteEach 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 modesDedicated while the mobile is on callIdle while the mobile is idleImportant parameters observed during drive testingCoverage Rx level (Full & Sub)Quality RxQual & SQIHandover, Dropped call, Neighbor list, TA

Selecting and Tuning Propagation ModelsParameters of propagation models must be adjusted for best fit to actual drive-test measured data in the area where the model is appliedThe 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 statisticsPrediction 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 jobsSystem Performance Optimization includes many different smaller processes at many points during a systems liferecognizing and resolving system-design-related issues (cant 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 normalfine-tuning system parameters to wring out the best possible call performanceidentifying causes of specific problems and customer complaints, and fixing themcarefully 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:

PerformanceMeasurements 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 dynamicparameters that help to target areas of concern

KPIs 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 OptimizationTransmission TimingPower ControlVAD Voice Activity Detector and DTXMultipath FadingEqualizationDiversityFrequency HoppingAntenna Parameters ( Height, Azimuth, Tilts )

Antenna Tilts

Antenna Tilts

BenchmarkingSurveyed data from test-mobile measurements can be used tobenchmark 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

OverviewRF Planning Tool

Drive Test Tool

Optimization Tool

MapInfo

Since radio spectrum is a limited resource shared by all users, a method must be devised to divide up the bandwidth among as many users as possible. The method chosen by GSM is a combination of Time and FrequencyDivision Multiple Access (TDMA/FDMA). The FDMA part involves the division by frequency of the total 25 MHz bandwidth into 124 carrier frequencies of 200 kHz bandwidth. One or more carrier frequencies are then assigned to each base station. Each of these carrier frequencies is then divided in time, using a TDMA scheme, into eight time slots. One time slot is used for transmission by the mobile and one for reception. They are separated in time so that the mobile unit does not receive and transmit at the same time, a fact that simplifies the electronics