GSM Capacity PlanningZTE university

ContentsGeneral introductionCapacity planning flowPlanning site configurationChannel planningLAC planningCommon problem about capacity planning

Purpose of capacity planningClassifciationWhat is Erlang Busy hour and BHCATraffic model of speech serviceWhat is GOSTraffic of each subscriber on busy hourErlang B Table

I General introduction

1. Purpose of capacity planningPrinciple of network planning and optimization: To construct a piece of wireless network with as much capacity and coverage as possible under a certain amount of cost, and make it adapt to capacity expansion and network development in the future, that is, CCCQ principle of optimality (C-Cost, C-Coverage, C-Capacity, Q-Quality) GSM capacity planning aims to plan the network scale and configuration according to the predicted capacity requirements under certain cost and satifactory QoS.Network capacityQuality of serviceSuggestions for Network scale and configurationCost

2. Classification

3. What is Erlang ?Erlang is an index to measure traffic. It indicates the traffic volume of a channel within the test time; To put it simply, traffic refers to the occupation time of a speech channel. If it has being occupied for an hour, then the traffic is 1 Erlang; If it has being occupied for half an hour, then the traffic is 0.5 Erlang; (Erlang is used as the unit to measure the traffic to honor the scientist Elang)

4. Busy hour and BHCABusy hour: Traffic in the period of busy hour are the most heavy of a day; BHCA is an abbreviation for Busy Hour Call Attempt;Busy hour in the morning: It refers to the time with the most heavy traffic in the morning; For example: 10: 0011: 00; Busy hour at night: It refers to the time with the most heavy traffic in the morning; For example: 20: 0021: 00; Busy hour of the system: It refers to the time with the most heavy traffic according to the system statistics;

5. Traffic model of speech service Traffic model of speech service is embodied by GOS and Traffic of each subscriber on busy hourGOS Traffic of each subscriber on busy hourTraffic models of speech service

6. What is GOSGOS is the abbreviation for Grade of Service, which can also be called call loss rate;GOS: when all of channels in the system are occupied, if there are more calls coming in, those calls will be blocked due to connection failure.Call loss rate is the probability of blocked calls, that is GOS.Generally, GOS of TCH is planned as 2% or 5% in GSM system.Call cannot be connectedNormal

7. Traffic of each subscriber on busy hour Traffic of each subscriber on busy hour: is traffic per subscriber on busy hour is calls of each subscriber in a day is call duration is coefficient of busy hours (traffic on busy hour to total traffic in a day)

Generally, traffic of each subscriber on busy hour is planned as 0.0150.03Erl/userActually, traffic of each subscriber on busy hour is calculated based on the fomula of (total traffic/number of VLR subscribers)Example: Suppose each subscriber makes 10 calls averagely a day, and the call duration is 60S (1/60Erlang), and the coefficient of busy hours is 1/8: Traffic of each subscriber on busy hour: =[10 X (1/8) X 60]/3600=0.0208Erl/user

8. Erlang B TableErlang-B Table gives relationship of number of TCHs, GOS and available Erlang. If any two of them are known, the third can also be figured out.

Capacity planning procedureStep 1: Capacity forecastStep 2: Analyze traffic distributionStep 3: Site configurationStep 4: Decide quantity of BTSsIs final network scale determined by coverage or capacity

II Capacity Planning Flow

1. Capacity planning procedureCapacity planning

2. Step 1: capacity forecastCapacity planningTraffic modelArea divisionCapacity forecastTraffic model of speech/data service in each areaDivide areas to be plannedCapacity forecast for speech/data service in each area12345Determine site distributionCapacity forecastAscertain quantity of BTSsAnalyze traffic distributionSite configuration

3. Step 2: Analyze traffic distributionCapacity planningTraffic distributionTraffic distribution forecast for each areaArea divisionDivide areas to be plannedPopulation distributionIncome levelVehiclesTelephones Traffic statistics of OMC12345Determine site distributionCapacity forecastAscertain quantity of BTSsAnalyze traffic distributionSite configuration

4. Step 3: Site configurationCapacity planningSubscriber distributionMax. siteconfigurationEquipment capacityDecide site configuration based on wireless environment and subscriber distributionFigure out max. configuration of the site based on selected multiplexing mode and available frequency resourcesConfiguration capacity of wireless products12345Determine site distributionCapacity forecastAscertain quantity of BTSsAnalyze traffic distributionSite configuration2

5. Decide quantity of BTSs Figure out quantity of BTSs based on capacity:

6. Is final network scale determined by coverage or capacityCapacity planning is the preliminary stage to decide quantity of BTSs and site configuration based on coverage planning.Network planning is a process to determine quantity of BTSs and site configuration after constant improvements based on coverage and capacity.For example:

Coverage planning shows 120 sets of BTSs are needed, but capacity planning shows 100 sets are needed. Then, it can be concluded the final number is 120.

Frequency resources available for GSM systemFrequency multiplexing methods of GSM system Max. site configuration Load of frequency hoppingMax. site configuration under different ways of frequency multiplexing

III Planning site Configuration

1. Frequency resources available for GSM systemFrequency resources for GSM system:

GSM systemUplink/ MHzDownlink/ MHzBandwidth/ MHzDuplex internal/ MHzNumber of duplex channelsGSM900890 ~ 915935 ~ 9602 2545124EGSM900880 ~ 915925 ~ 9602 3545174GSM18001710 ~ 17851805 ~ 18802 7595374GSM19001850~19101930~19902 6080299

2. Frequency multiplexing methods of GSM systemGSMFrequency multiplexingFrequency hoppingCommon multiplexing3*34*35*32*3Commonly usedRF hoppingBaseband FH1*11*3Commonly usedSite HoppingSector Hopping

3. Max. site configurationMax. site configuration of GSM system is determined by frequency resources and frequency multiplexing. Frequency resourcesFrequency multiplexing Max. site configuration of GSMCase: With 7.2MHz GSM900 frequency resources available, the operator asks to use 4*3 multiplexing for BCCH, and use 1*1 RF hopping for TCH. What is the maximum site configuration in this case7.2MHz frequency resource provides 36 frequency points. For BCCH using 4*3 multiplexing, it needs 12 frequency points. Excluding 1 frequency point reserved for isolation, the rest 23 (36-12-1) frequency points are for TCH, which uses 1*1 RF hopping. The load of frequency hopping is no bigger than 50%.MAlist={1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23}; MAIO planning is as follows: Cell 1 MAIO = { 1, 7, 13, 19 }; Cell 2 MAIO = { 3, 9, 15, 21 }; Cell 3 MAIO = { 5, 11, 17, 23 }; Hence, max. site configuration of TCH is S444, and it is S555 if taking BCCHS111 into consideration.

4. Load of frequency hoppingLoad of frequency hopping: number of TRXs for frequency hopping/number of FH points configured for the siteIf load of frequency hopping is

5. Max. site configuration under different ways of frequency multiplexingCase:With 7.2MHz GSM900 frequency resources available, what is the maximum site configuration under different ways of frequency multiplexing

I No frequency hopping, use 4*3 multiplexing for BCCH, and 3*3 multiplexing for TCH12 (4*3) frequency points for BCCH;24 (36-12) frequency points for TCH; For multiplexing of 3*3, 24/9=2, remaining 6; In this case, max. site configuration for TCH is S332The max. site configuration is S443, taking BCCH into consideration.

II Use 4*3 multiplexing for BCCH, and 1*1 FH hopping for TCH; reserve one frequency point for isolation between BCCH and TCH; load of frequency hopping is 50%12 (4*3) frequency points for BCCH;Number of available TCH frequency points is 23 (36-12-1), int(23*50%) =11; in this case, the max. site configuration of TCH is S443.The max. site configuration is S554, taking BCCH into consideration.

Configuring BCCH/CCCH (Combined)Configuring BCCH/CCCH (Non Combined)Planning SDCCH Planning PDCHHow to figure out number of TCHsPoints of attention in HR planning

IV Channel Planning

1. Configuring BCCH/CCCH (Combined)BCCH is broadcast control channel. Each cell must be configured with 1 BCCH, which can be at TS0, TS2, TS4 or TS6 of C0. Generally, it is configured over the first TS0 of the first C0.CCCH is common control channel, including AGCH, PCH and RACH. Those channels are for all mobile stations in a cell. Each cell must be configured with 1 CCCH, which can be over at TS0, TS2, TS4, TS6 of C0. Generally, it is configured over the first TS0 of the first C0.Combined:

2. Configuring BCCH/CCCH (Non Combined)Non Combined: BCCH/CCCH needs 1 physical chanel

3. Planning SDCCHLocation updateIMSI attached/detachedCall setupSMSFax/supplementary serviceServices over SDCCHTraffic per subscriber for different service: Configuration without HR enabled

TRXConfiguring SDCCH when there is CBCHGeneral cellsIntra-cellsBoundary cells1SDCCH/8SDCCH/8SDCCH/82SDCCH/8SDCCH/82*SDCCH/832*SDCCH/82*SDCCH/82*SDCCH/842*SDCCH/82*SDCCH/82*SDCCH/852*SDCCH/82*SDCCH/83*SDCCH/863*SDCCH/83*SDCCH/83*SDCCH/873*SDCCH/83*SDCCH/83*SDCCH/883*SDCCH/83*SDCCH/84*SDCCH/8

TRXConfiguring SDCCH when there is no CBCHGeneral cellsIntra-cellsBoundary cells1SDCCH/8SDCCH/8SDCCH/82SDCCH/8SDCCH/8SDCCH/832*SDCCH/82*SDCCH/82*SDCCH/842*SDCCH/82*SDCCH/82*SDCCH/852*SDCCH/82*SDCCH/82*SDCCH/863*SDCCH/82*SDCCH/83*SDCCH/873*SDCCH/83*SDCCH/83*SDCCH/883*SDCCH/83*SDCCH/83*SDCCH/8

4. Planning PDCHPDCH must be planned based on traffic model of data services (GPRS/EDGE). The traffic model includes such factors as subscribers of data services, average subscriber rate on busy hour and coding method. Based on the model, figure out the average bearing rate in the IP layer of each PDCH channel, and thus number of PDCH channels in a cell.

ParameterOptionUnitNumber of speech subscriber in each cellASubscriber penetration rate of data serviceBProbability of subscribers activating data service at the same timeCNumber of data service subscribers on busy hour in each cellD=A*B*CAverage data service rate per subscriber on busy hourEbpsAverage data service rate per cell on busy hourF=D*E/1000kbpsEffective rate of i-coding in the IP layerGkbpsProportion of i-codingHAverage bearing rate over each PDCH in the IP layerI=SUMi(G*H) i=CS1CS4, MCS1MCS9kbpsNumber of PDCHs requrired for each cellJ=F/I

5. How to figure out number of TCHsTCH Calculation formula : Number of TCHs= number of TRXs * 8 - BCCH/CCCH SDCCH - PDCHFor a swap project, if the existent network capacity can be obtained through the OMCR, number of TCHs can be figured out by checking the ErlangB table according to subscribers of speech service, subscriber distribution and traffic model.

Number of TRXsNumber of channelsBCCH/CCCHNumber of SDCCHsNumber of PDCHsNumber of TCHsCapacity GOS=2% (Erlang) 1811151.66216111137.43241212013.184321222719.275401223526.436481334131.927561334939.338641345645.87

6. Points of attention in HR planningProportion of HR can be understood in two angles of views : Proportion of HR =Number of FRs converted into HR/total number of FRs before conversion to HRProportion of HR =Number of HRs after conversion/number of HRs and FRs (this meaning is generally accepted) Points of attention in HR planning: Keeping a certain proportion (60%) of HR to meet the increasing signaling load, but it is also necessary to increase number of SDCCHs accordingly.

What is LACWhat is BS-AG-BLK-RESDifference between TMSI paging and IMSI paging LAC planning procedure from the angle of Um Impact of too small/big LAC divisions Principles of selecting boundaries of LA

V LAC Planning

1. What is LACLAC (Location Area Code) is a unit for paging scope. The paging message of MS is sent to all of the cells in the LAC where the MS is .The GSM network is divided into many different LACs.An LAC may has one set of BSC or more, and all of them belong to one MSC; while one set BSC/MSC may cover multiple LACs.Principle of LAC planning: to minimize location updates while controlling paging load.

2. What is BS-AG-BLK-RESThis parameter defines number of message blocks specially reserved for AGCH in each BCCH multi-frame. For cells where CCCH and SDCCH are shared, value span of BS-AG-BLK-RES is 0~2; For cells where CCCH and SDCCH are shared, value span of BS-AG-BLK-RES is 0~7; if there is CBCH, then the value span is 1~7.

CCCH_CONFBS_AG_BLK_RESBlocks reserved for AGCH in each BCCH in each BCCH multi-frameBlocks reserved for PCH in each BCCH multi-frame

1003112221Others009118227336445554663772

3. Difference between TMSI paging and IMSI pagingThree configurations of BTS paging blocks : a) 2 IMSI pagingb) 2 TMSI and 1 IMSI pagingc) 4 TMSI pagingCompared to IMSI paging, TMSI paging can help to improve paging capacity of the system;For large-capacity paging network, using TMSI paging can increase connection-through rate, and the connecting time can also be shortened.

Three configuration of paging blocks

4. LAC planning procedure from the angle of UmPaging blocks per secondPaging messages in each paging blockPaging times sent per secondPaging times supported per hourTraffic in each location areaTRX quantity supported by each location areaX(1 frame =4.615ms, 1 multi-frame =51 frame =0.2354s) For non-combined BCCH: number of paging blocks per second=(9-AGB) /0.2354For combined BCCH: number of paging blocks per second =(3-AGB) /0.2354For non-combined BCCH, ZTEs configuration is AGB=2, number of paging blocks per second29.7 paging blocks/secondIf using IMSI paging: X2 paging times/paging blockIf using TMSI paging : X = 4 paging times/paging blockFor non-combined BCCH, in case of AGB =2: If using IMSI paging: P= 59.47 paging times/second; If using TMSI paging: P=118.95 paging times/second; Conversion from second to hourFor existent network: collect paging messages sent by BSC;For new network: calculate the traffic based on the traffic model; For example: T*30%/(1/60) *1.25 = P*50%(T is traffic , P means paging times) If using IMSI paging and non-BCCH, AGB=2, P= 59.47, -T=4757.6 ErlProcessing ability of BTS: V3: at most 39 paging blocks in the BTS, that is 39*3600=140400 paging messages/hour, which is about140, 000/hour; SDR: no limitation as above; From the angle of the Abis interface, LAPD can support up to 400, 000 paging messages per hour; so processing ability of BSC to 400, 000 paging messages per hou, which shows the limitation is generally over the Um interface.

5. Impact of too small/big LAC divisionsWaste channel resources, and also increase load of MSC and HLRIt will take an MS about 10s to update LAFrequent location updatesCause the secondary callPaging messages get lost, and thus impact paging success rateIncrease paging load of the system, thus impact paging success rate Big paging scopeTry to lessen location updates with paging load under control

6. Principles of selecting boundaries of LAPrinciples of selecting boundaries of LA Boundaries of LA should not be at the areas where the traffic is heavy, eg. downtown of a city.Boundaries should be skew crossing instead of overlapping with roads;Boundaries of several neighbor LAs cannot can cross each othe at a small place It is necessary to take future capacity expansion into consideration when design paging capacity and traffic capacity.

Problems if lack of network capacityWays to increase network capacity

VI Common problems about capacity planning

1.Problems if lack of network capacityA call cannot be connected ~Sorry, network is busySubscribers change an operator, which is not good for brand image and operating profitDeteriorate KPI indicesShort messages cannot be sent successfullyFailed to sent the messageCannot access Internet by GPRS/EDGELack of network capacityDecrease perceptibility of subscribers

2. Ways to increase network capacityBreak of cellular cellsAdd TRXs/sitesAdd cellular equipmentExtend frequency bandMore compact multiplexing of frequencyHR......

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