CNCELLULARNETWORKThe geographical area to be covered by the Radio Network is divided into cells. A cell is the area covered by a set of frequencies (transceivers). Each cell has at least one control channel (for BCCH, PCH, SDCCH, etc)1. Type of CellsThere are two main types of cells: omni-cell and sector-cellAn omni cell is served by a BTS placed in its center. The antenna system transmits equally in all directions (360) and can be constituted of an omni-antenna or an array of sector antennas.A sector cell is served by a BTS placed on its edge and uses a sector antenna (e.g. 120 or 180).One BTS site can serve one, two or three sector cells.Typically, omni directional cells are used to gain coverage, whereas sector cells are used to gain capacity. Each cell requires two RX antennas (for RX diversity) and a number of TX antennas (depending on the type of TX combiner). It is possible to reduce the number of antennas by using duplex filters and X-polarised antennas, see below.Example of a 32 sector site RBS2000 CDU ABTS ConfigurationAntenna Configuration top view (with duplex filter)2. Frequency AllocationSince an operator only has access to a limited number of frequency carriers, the frequencies have to bereused in the network. In order to prevent co-channel interference (C/I), the frequencies are reused in an organised way, according to certain re-use pattern. Example: a reuse-factor 3.The distance D between two cells using the same frequencies must be long enough to ensure that C/I issuperior to a certain threshold. With a reuse factor 9, C/I will be superior to 9 dB; with reuse factor 12, C/I > 12 dB and with reuse factor 21, C/I > 18 dB. If we use 3-sector sites, the corresponding cell patterns are called 3/9 (3 sites/9 cells), 4/12 and 7/21. The figure below shows 4/12 and 3/9.Ericsson recommends (C/I)min = 18 dB for analog systems (NMT, TACS) and 12 dB for GSM. But 9 dB is acceptable if interference-reducing features are used (such as frequency hopping, DTX, MS/BTS power control). This means that a 4/12 pattern must be used for BCCH carriers (which cannot use features such as fhop, DTX, pwr ctrl). However, the other carriers can have tighter reuse factor such as 9 or less. This is called Multiple Reuse Pattern (MRP).Example MRP :The operator has 37 frequencies. BCCH carriers have a frequency reuse factor 12. The second TRX in each cell have a frequency reuse-factor 8, the third have a reuse-factor 6 and the fourth have a reuse-factor 4.3. Cell CapacityCell planning begins with traffic and coverage analysis. The analysis should produce information about thegeographical area and the expected capacity (traffic load). The types of data collected are:CostCapacityCoverageGrade of Service (GoS)Available frequenciesSpeech qualitySystem growth capabilityThe basis for all cell planning is the traffic channel demand, i.e. how many subscribers use the network and how much traffic they generate. The Erlang (E) is a unit of measurement of traffic intensity. It can be calculated with the following formula.A = n x T/3600 ErlangWhere, A = offered traffic from one or more users in the system n = numbers of calls per hour T = average call time in secondsThe geographical distribution of traffic demand can be calculated by the use of demographic data such as:Population distributionCar usage distributionIncome level distributionLand usage dataTelephone usage statisticsOther factors like subscription/call charge and price of MSs.Calculation of required number of BTSs. To determine the number and layout of BTSs the number of subscribers and the Grade of Service (GoS)have to be known. The GoS is the percentage of allowed congested calls and defines the quality of the service.If n = 1 and T = 90 seconds the traffic per subscriber is: A = 1 x 90/3600 = 25 mEIf the following data exist for a network:Number of subscribers = 10000Available frequencies = 24Cell pattern = 4/12 Gos = 2% Traffic per subscriber 25 mEThis lead to the following calculations:Frequencies per cell = 24/12 = 2Traffic channels per cell = 2 x 8 2 (control ch.) = 14 TCHTraffic per cell = 14 TCH with a 2% GoS implies 8.2 Erlangs per cell (use erlang table)The number of subscribers per cell = 8.2 E / 25 mE = 328 subscribers per cellIf there are 10000 subscribers then the number of cells needed is 10000 / 328 = 30 cellsTherefore the number of three sector sites needed is 30 / 3 = 10

HOSRHandover AnalysisHandover is an important function, which shows the integrity of the GSM network. If the handover performance is poor, the subscriber will perceive the quality of the network as bad.Probable Reason of Bad Handover PerformanceBad locating parameter settingsBad setting might cause the locating will not rank the best cell as a candidateUplink interferenceIncoming handover failed as the target cell could not decode the handover burst message from the mobileMissing measurement frequency in BA-listPrevent any handover to affected neighbor cellsExtra measurement frequencyCan provide inaccuracy of measurement for handover decisionsCo-Channel and Co-BSICMeasurement result from neighbors can not be distinguished and MS may perform a handover to the wrong cell.Unnecessary neighbor relationNone or few handover might indicate a unsuitable neighbor relation.HW faultsCan cause bad neighbor relation.Permitted NCC (network color code)Missing NCC of the neighbors will not allow any handover.Wrong use of HCS parametersCause unnecessary handoverCongestionHigh congestion might lead to dragged calls (handover performed at a not intended location) a lot of unsuccessful handover.Handover Analysis Flowchart.The following procedure should be performed for handover analysis:- Check the successful handover per cell- Check for the handover success rate below certain criteria for example X%. If it doesnt meet the criteria and change the X% to a higher value and check for the next cell.- Check the handover activity from the number of handover performed. If the number is above certain value for example Y and then take into consideration.- Check the site location, whether the site to site distance or co-sited. (Good map is needed here).- Check whether the cell is isolated or not, if already known problem of no dominant serving cell and take other cell.- Check the handover flow whether is balance between incoming and outgoing.- Check the difference performance of incoming and outgoing handover. This is to ensure the priority for more problem direction.- Focus on the bad direction.- Check the worst relation and pick one cell.- Check the cell whether it is external or internal. If external, start inter-BSC analysis.- If the cell is internal, check the high ratio of lost handover, urgency handover and reversion.- If one of them is yes, check the uplink & downlink interference problem.- Check the frequency plan. There might be problem on co-channel or adjacent channel.- Check the handover related parameters such as relation, BA-list, BSIC, hysteresis, offsets etc.- Check if many Ping-Pong handover.- Check if assignment handover are used.- Check if cell has HW problem. If problem found, swap or repair hardware.- Check if congested target cell. If the target cell is congested and then solve the congestion by adding TRU.- Perform measures to improve HO performance. This is the assumption comes from the above analysis.No or Few Handover AttemptsNo or Few Handover Attempt Flowchart.The following procedure should be performed for no or few handover attempts:- Check the neighbor relation with low traffics (less than 10% of average number of handover per relation) and unbalance relations.- Check from the unbalance relation whether the target cell is congested, if congested, solves the congestion problem.- Check the missing measurement frequency (MBCCHNO) in Double BA-list in active list (if yes, add the measurement frequency in the BA-list.- Check unnecessary neighbor cell relations and if found, remove unnecessary relations.- Check NCCPERM, if NCC of the neighbor is missing, add the NCC of the neighbor list into the NCCPERM list.- Check the setting of the cells whether they are set in different layer of HCS. (Layer 1 is the highest priority)- Check if the cell is at the inter BSC border, if so , check the inter BSC HO performance (SIEMENS System).- Check locating parameters and list out.- Check the poor setting of parameter and if so, correct the parameter setting- Check BTS definition (RX commands especially RXMOP).- Check if BTS is defined but might not be in service. If yes, correct parameter setting or deblock it.Diposkan oleh waveice di 00:05 0 komentarLabel: Handover Analysis

Label: Handover Analysis

TCHTCH Assignment analysisSuccessful assignments show the number of successful TCH allocations at call setup.At unsuccessful assignment, the Assignment Complete message, sent by the MS, was never received by the BTS.The formula is defined as:% TCH ASSIGNMENT SUCCESS RATE=TFCASSALLX 100 %TASSATTProbable ReasonNo dominant serving cellThe serving cell cannot cope with the TCH traffic.Severe congestion on TCHFailing TCH allocation for assignment or handover due to congestionLow signal strength for call accessThe signal strength might be higher on the BCCH than on the TCH.InterferenceDisturbance on SDCCH or target TCHFaulty transceiverFaulty equipmentThe following procedure should be performed for TCH Assignment analysis:For TCH assignment success rate, the first thing, check the TCH Time Congestion.If there is congestion on TCH, it is recommend doing the dimensioning and adding TRU based on carried TCH traffic demand.If there is no congestion on TCH, check the output power of the BTS. If the output power is low, increase the output power.If the output power is ok, check the faulty BTS by extracting BTS error log.If hardware fault found, swap or repair HW.Perform drivetests to check the coverage and received RxLEV.If no dominant cell or similar signal strengths of a few cells found during drivetests, it is recommended to add BTS.If there is no problem on the dominant cell, check the interference whether co-channel or adjacent channel.Check the disturbance whether it is on SDCCH or target TCH. If disturbance found, improve the frequency plan.Mostly, the problems of low TCH assignment are TCH availability and interference.Diposkan oleh waveice di 00:21 0 komentarLabel: TCH Assignment analysisCongestion AnalysisTraffic congestion is one of the major network problems in a mobile system. A high congestion deteriorates the overall performance of the network and should be minimized.Short term growthIf the high traffic related to an occasional event, like sports event, fairs, conference, a temporary solution might be considered.Long term growthIf there is a long-term growth the network capacity has to grow according to the demand.Type of CongestionThe congestion analysis begins by identifying if there is only SDCCH or TCH congestion or both. Congestion on both SDCCH and TCH may mean that the only way to get rid of the congestion is to add more physical capacity in terms of transceivers or sites.Consider how many channels that are allocated in the cell. If possible, expand the capacity with new transceivers, otherwise a new site must be implemented. Frequency planning schemes such as MRP and FLP could be used to relieve congestion. Microcells couSDCCH CongestionIn R8, the time congestion should be used instead of congestion based on access attempts as there is no way to estimate the number of access attempts a single mobile does.Ericsson recommends using the SDCCH Time congestion as a KPI in R8. The formula is defined as:SDCCH TIME CONGESTION OF TOTAL MEASUREMENT INTERVAL=CTCONGSX 100 %PERLEN * 60where PERLEN is the measurement period in minutes.SDCCH Congestion Analysis FlowchartThe flowchart below, Figure 51, explains a general approach to investigate SDCCH Congestion. The next section describes the action points in this flowchart. The reference to each action point is indicated on the flow chart as well.Diposkan oleh waveice di 00:20 0 komentarLabel: Congestion AnalysisSDCCH Congestion Analysis.Low AvailabilityWhat should I check?SDCCH Availability.Where do I look for it?STS Counters on SDCCH availability. The formula is:Available SDCCHs of Total Number of Defined SDCCHs=CAVAACCX 100 %CAVASCAN * CNUCHCNTRun BSC commands to see if the channels are manual, control or automatic blocked.Why do I need to check this?We need to check this area to make sure that there is no hardware problem as faulty equipment can affect SDCCH availability. If needed, the O&M procedures need to be reviewed.Location Area Border Cell & CRHWhat should I check?Check site position and location area border, Location Update Performance and parameter CRH.Where do I look for it?Refer to site database for site info.Location Update performance should come from the MSC.You can run BSC command RLSSP to check CRH value.Why do I need to check this?If the cell is situated on a misplaced Location Area border, this means that unnecessary many normal Location Updating are performed. If the site is located close to major road or railway, consider moving the Location Area border.The CRH is the hysteresis value used when the MS in idle mode crosses a LA border. The default value for this parameter is 4. If a high number of Location Updating occurs in a Location Area border cell, a higher CRH can be set in order to reduce the numbeTCH CongestionWhat should I check?Check if TCH congestion exists and if the SDCCH mean holding time is high. Check CLS and Assignment to Worse cell parameter settings.Where do I look for it?Use STS Counters and look into time congestion to see how severe is the TCH Congestion. The formula is:Note that if the feature Adaptive configuration of logical channels is active the formulahave no meaning. Then S_AV_NR is recommended to be used instead.Diposkan oleh waveice di 00:18 0 komentarLabel: SDCCH Congestion Analysis.TCH Congestion AnalysisWhat should I check?Check if TCH congestion exists and if the SDCCH mean holding time is high. Check CLS and Assignment to Worse cell parameter settings.Where do I look for it?Use STS Counters and look into time congestion to see how severe is the TCH Congestion. The formula is:TCH TIME CONGESTION OF TOTAL MEASUREMENT INTERVAL=TFTCONGSX 100 %PERLEN * 60If activated, check CLS and Assignment to worse cells parameters from CNA.Why do I need to check this?TCH congestion causes the mobiles to stay extra long time on the SDCCH. Increase TCH capacity if required. Utilize the features for traffic distribution such as CLS and Assignment to Worse Cell.SMS UsageWhat should I check?Check SMS activity.Where do I look for it?Check STS counters for SMS on SDCCH. Counters are CSMSDWN and CSMSUP.Why do I need to check this?Extensive SMS usage increases the SDCCH traffic and could cause congestion if badly dimensioned SDCCH channels. Re-dimension the SDCCH channels with consideration taken to SMS usage.Too Frequent Periodic RegistrationWhat should I check?Check Random Access Distribution. Check the timer T3212 in the BSC.Where do I look for it?STS Object Type RANDOMACC for Random Access and look into CNA for T3212 setting.Why do I need to check this?To prevent intervals of Location Updating which is too short that it affects Random Access Performance to deteriorate.Increasing Traffic DemandWhat should I check?Check if its short-term traffic growth and whether combined SDCCH is used.Where do I look for it?Compare the traffic trends and refer to planning on how SDCCH is dimensioned.Why do I need to check this?The high traffic could be related to an occasional event or due to a long-term growth. If its a special one-time event of surge in traffic, then it shouldnt cause too much concerned. But if the trends continue, then SDCCH might need to be re-dimensionedCell Broadcast UsedWhat should I check?Check if Cell Broadcast is active.Where do I look for it?Run BSC command RLCCP.Why do I need to check this?CBCH is the cell broadcast channel and indicates whether or not a CBCH shall be included in one of the SDCCH/8 sub-channels for the cell or channel group. It is defined per cell or per channel group. If it is active, check if the network uses it. If it isLong Mean Holding timeWhat should I check?Check SDCCH Mean Holding Time.Where do I look for it?STS counter for SDCCH Mean Holding time. The formula is:SDCCH MEAN HOLDING TIME=CTRALACC*PERLEN*60X 100 %CNSCAN*CMSESTABWhy do I need to check this?If the mean holding time is too long, this can possibly generates a higher traffic load.SDCCH DimensioningWhat should I check?Check how SDCCH is dimensioned.Where do I look for it?Check the SDCCH settings from CNA parameters.Why do I need to check this?As no of subscribers steadily increase, previous SDCCH dimensioning plan might be insufficient. Review SDCCH dimensioning requirement to existing demands.Bad use of Adaptive Configuration of Logical ChannelsWhat should I check?Check if ACSTATE is on or off. If its on, check the parameter settings.Where do I look for it?Run RLACP in BSC for ACSTATE status and use CNA to check these feature parameter settings.Why do I need to check this?By using the Adaptive Configuration of Logical Channels feature, the basic SDCCH configuration in a cell will be under-dimensioned. If this feature is not used correctly, it will cause SDCCH congestion.

Label: TCH Assignment analysisCongestion AnalysisLabel: Congestion AnalysisSDCCH Congestion Analysis.Available SDCCHs of Total Number of Defined SDCCHsNote that if the feature Adaptive configuration of logical channels is active the formulahave no meaning. Then S_AV_NR is recommended to be used instead.Label: SDCCH Congestion Analysis.TCH Congestion Analysis

frequency planningFrequency Planning(GSM)CELLDefinition: Area Coverage of Radio Base of Station.Type :Sectored Cell, Omni Cell, etcCoverage measure:MacroCell (>5 km), MicroCell (3 ====>* TDMA (GSM) : C/I > 12 dB ===>====>* CDMA :Quality evaluated from Eb/IoCluster (K) = Frequency grouping* Measure of Cluster depended from C/I system condition.N ( Total Frequency Spare)Example : Frequency Reuse pattern with N = 6so that:K = 4SIGNAL TO INTERFERENCE RATIO :1. Consider closest co-channel cells (SIRmin)2. Measure of Cluster (N)3. Co-Channel reuse distance ratioCELL SPILTTINGIs needed at the time of :1. Overload traffic on cell mount.2. TCH CongestionTo increase the capacity, the operator performs cell splittings:Strategy Frequency Reuse pattern for cell splittingPosted in 2G RF PLANNING | Leave a Comment InterferencePosted by goengineer on October 5, 2009Type of Interference :Co Channel InterferenceAdjacent Channel InterferenceReasons is:Poor frequency planNo dominant cell > low C/I > increased RxqualFrequency Hopping is offExternal interference e.g. jammerAnalysis :Identify areas with Rxqual > 5=>> Identify source using Map and STS=>> New drive test around problem area?Solution:Enable Frequency Hopping or add frequencies to Hopping group.Enable BTS Power Control, MS power control and make it less aggressive.Change frequency of interferer or interfered cell (Possible to find new frequency by using TEMS Scanning).Down tilt or change antenna of interferer.Redo frequency plan.

* FDMA (AMPS) : C/I > 18 dB ===>* TDMA (GSM) : C/I > 12 dB ===>====>InterferencePosted by goengineer on October 5, 2009

InterferanceInterferenceType of Interference :Co Channel InterferenceAdjacent Channel InterferenceReasons is:Poor frequency planNo dominant cell > low C/I > increased RxqualFrequency Hopping is offExternal interference e.g. jammerAnalysis :Identify areas with Rxqual > 5=>> Identify source using Map and STS=>> New drive test around problem area?Solution:Enable Frequency Hopping or add frequencies to Hopping group.Enable BTS Power Control, MS power control and make it less aggressive.Change frequency of interferer or interfered cell (Possible to find new frequency by using TEMS Scanning).Down tilt or change antenna of interferer.Redo frequency plan.Add new site.

Ping pongHandover Ping Pong(Repeated)Handover case :1. Repeated handover (Ping Pong)2. Repeated Intra-cell handover3. Handover failure4. Unrealistic handoverReasons :1. Repeated HandOver (Ping pong)No dominant serverLocating penalty settings e.g. PSSBQ, PTIMBQToo small hysterisis settingSolution :a. Change physical AntennaAntenna directionAntenna TiltsPlan for new site ChangeLocating Parameter e.g. KHYST or LHYSTb. Change Parameter, KHYST or LHYST2. Repeated Intra-Cell HandOverRepeated Intra-Cell HandOver the following reasons is:Wrong intra-cell handover settingsExternal Uplink InterferenceSolution :Consider to change parameters:SSOFFSETUL, SSOFFSETDLQOFFSETUL, QOFFSETDLA wrong setting of parameters will cause unnecessary IHOTurn off Intra-cell Handover?3. HandOver ReversionCheck layer 3 messageHandover command BSC correct?Check reason for handover SS, RXQUALTarget cell?Handover Reversion the following reasons is :Duplicates of BSIC BCCH combinations in neighboring listSolution:Change one of the BSIC between BTS with same BSIC or Rotation Cell Parameters.Other Reasons:Uplink interference in target cellDownlink interference at MSSolution:Interference InvestigationStatisticsScaning4. Unrealistic HandOverReasons :Wrong locating settings, in Serving or Target cellNote : Could be on purpose e.g. Dual Band network with HCSSolution:Fix locating settings e.g. MSRXSUFF, BSRXSUFF

CSFACall Setup FailureAnalysisCall Setup Failure the following reasons is :1. Low Signal Strength2. Interference3. High Congestion on SDCCH4. High Congestion on TCH5. Transmission Fault6. Faulty TRU/Hardware7. Central Processor Overload8. Software File Congestion9. Cell is not defined in MSCPossible Solutions:Low signal strength=> Signal strength analysis.Interference=> Interference analysis.High Congestion on SDCCH:==> Define more SDCCHs.==> Activate adaptive configuration of logical channel feature and immediate assignment to TCH.High Congestion on TCH:==> Add capacity/Tune coverage array.==> Activate assignment to worse cell.Analysis :SDCCH BlockingMultiple Channel Requests.Successful Random Access after the third try.==> Congestion in SDCCH.From plot, identify which & where in logfile the dropped call occurs.In the log file, Jump the drop call event.Check if there is a disrupt in the recording. If yes ==> could be a false drop due to TEMS mobile disconnection during recording!!!Check the Radio environment just before drop:If High Rxqual for a longer period of time and RLINKT expire==> Interference problem.If Low SS DL, SS DL < MS SENS ( -104dBm)==> low signal strength problem.If TA > 63==> too far from the cell.If DL radio is good, check the TX power. If there is MS power down regulation when the MS is close to the cell. If full power==> suspect uplink interference or antenna, TMA problem.Verify or isolate the problem using STS (Drop call and reasons).Possibly related posts: (automatically generated)SDCCH Success Rate (SD-SUC)

SDCCH Success Rate (SD-SUC)

SignallingSignalling protocols are decomposed into layers, each layer having a specific function.Example :The protocols used in BSS are :On Layer 1 :G.703. This protocol is used in the Transmission Network ( A, A-bis)Signalling processing and Radio. This used in the Radio Network ( Um)On Layer 2 :LAPD (Link Access Procedure on D-Channel). This protocol is used on A-bis, for safe transport of BTS O&M and Traffic Management messages. BTS O&M use the OML Link, Traffic Management use the RSL Link.LAPDm. This protocol is use on Um, for safe transport of Traffic management messages between Mobile and BTS.On layer 3 :BTS O&M. This protocol is only used on A-bis (between BTS and BSC), for operation and maintenance of the BTSs.Traffic Management. This protocol is used on all interfaces ( between Mobile, BTS, BSC and MSC) to handle the phone calls.Signalling used layer 1, 2 and 3 while speech and data only layer 1.

DPDAILYPERFORMANCEThe following metrics can be used to measure the performance of the network. these counters should be monitoried daily on per cell basis.

TCH BlockTCH Blocking maybe due to the following reasons1. Handover and Power budget margins2. Cells too large3. Capacity Limitations (Congestion)4. Incorrector Inapproriate TimerOptimization for tips :1. Handover and Power budget MarginsHandover Margins shouldbe properly optimised to move the traffic to neighbouring cell. Strict handover margins can results in lower handovers and ultimatelly congestion in cell.TIPS :6 dB handover margin is considered to be an approriate margin for handover. A strict handover margin results in the strict criteria for Power Budget Handovers also. Setting a lower value of handover margin will initiate ping pongs handovers, which are not considered good for network health. (handover margin have already been discussed).2. Cells too LargeIf cell are too large meaning antenna too high or antenna too shallow, it will pull in out of area traffic again causing congestion in the cell.TIPS :Consider reducing antenna height to reduce the footprint of the site. Also increase the antenna tilt (the max tilt is 12)

SDCCHSDCCHBlockingSDCCH Blocking is probably due to one or more reasons1. No Access to SDCCH2. Failure before Assignment of TCH.3. High Paging Load4. Incorrect or Inapproriate timer valuesOptimization for tips :1. No Access to SDCCHThis cases before has already been discussed2. Failure before Assignment of TCHThis cases before has already been discussed3. High Paging LoadIrreguler paging distribution in location areas results in SDCCH Blocking. Higher paging load in certain location area mean higher location updates on SDCCH resulting in SDCCH Blocking.TIPS :A location area with a high paging load needs to be reduced in size to relieve SDCCH Blocking. A location area with low paging load need to be enlarged in size to reduced the overal number of location ares.4. Incorrect or Inapproriate timer valuesTimer rr_t3 111 sets the amount of time allowed to delay the deactivation of a traffic channel (TCH) after the disconnection of the main signaling link.TIPS :The suitable value for this timer is 1200 ms (max being 1500 ms). The timer will cause the BSS to wait before the channel in question is allocated another connection. A lower value of timer will result in higher capacity since the channel is held for less time before being released.

HOSR-FHigh Handover FailureRateHigh handover failures rate will probably be due to one or more of the following reason.1. High Neighbour Interference2. No Dominant Server3. Database ParametersOptimization for tips :1. High Neighbour InterferenceWhile handling off to the best neighbour the interference on the target cell frequency may result in the hand off failure.TIPS:When designing the cell frequencies care should be taken that there is proper frequency spacing between the cells to avoid neighbour interference. In most of the cases Ping Pong Handover starts i.e the mobile hand off to a cell for better level and due to interference (Quality issues) hand off again to original cell. A through drive test can determine the interfering frequencies which should be eliminated from the frequencies plan.2. No Dominant ServerIf cell sites are designed poorly there might be areas where neighbour being received at the same level and some neighbour randomly look good for hand off for a certain amount of time. Such situation is disastrous because handoff decision will be hard and mostly it will end up unsuccessful handovers.TIPS :Antenna tilts provide the good way to reduce the footprint of the sites. Efforts should be made that asingle dominant server should serve the specific area. Timing advance limitation is applied to cell areas where there is multiple servers.3. Database ParametersReceived level, receive quality and power budget algorithm are set in the system information to define the criteria for handover. Improper values for these criteria may result in poor handoff.TIPS:Enable the per neighbour feature which dispalys the successful and unsuccessful handovers on a per cell basis. In optimization, monitor the following stats, which comes under cell statistic category.All those cells can be identified which are problematics in terms of hand off so one can focus only specific cell causing the major contribution towards poor HSSR. Ensure that handover margins are optimised. Rule of thumb is a 4 dB for adjecent frequencies and 6 dB per cell without adjecent frequencies. The following parameters can be played for defining the threshold for imperative and non-imperative handovers.a. Defines the lower threshold for uplink quality handovers.ex : Range 0to 1800 Step size = 0.01a value of 500 defines the lower threshold value of 5 (BER) for a quality handover to be triggered for uplink. The optimum for thisthreshold is 500.b. Defines the lower threshold fordownlink quality handovers.c. Defines the lower threshold for received level uplink handovers.Ex :A valueof 20 defines the threshold value of -90 dBm for a level handover to be triggered for uplink.Range 0 to 63Where 0 = -110 dBm1 = -109 dBm63 = -47 dBmThe optimum value for this threshold is 15 ( 95 dBm). If the signal level goes below that, a level handover is initiated.d. Defines the lower threshold for received level downlink handovers.e. Defines theupper threshold for uplink interference handoversf. Defines theupper threshold for downlink interference handoversPossibly related posts: (automatically generated)Handover Ping Pong (Repeated)Call Setup Failure AnalysisHandover Failure due to same BCCH-BSIC

Handover Ping Pong (Repeated)Call Setup Failure AnalysisHandover Failure due to same BCCH-BSIC

HCDRHigh Call Drop Rate (HCR)GuidelinesFor healthy network the drop call rate should be less than 1%. There are again number of reasons, which could contribute towards higher dropped call rate is :1. Drop on Handover2. Low signal Level3. Adjacent channel Interference4. Co-channel Interference5. Extraneous Interference6. Link ImbalanceOptimization for Tips :1. Drop on HandoverThe call may drop on handover. Its mostly high neighbor interference on the target cell, which causes the main problem. Sometime the mobile is on the wrong source cell (not planed for that area but serves due to the antenna overshoot) which may the result in the drop call.TIPS :Within optima, monitor the following statistic. Theses statistics are defined under the category of BSC level statistics.a. total and successfulhandover on UL/DL qualityb. total and successful handover on UL/DL signal strength.c. total and successful power budget handovers.From the above statistics, quality or level mustbe estimated.2. Low signal LevelSignal level below -95 dBm is considered to be poor. If the mobile is unable to handoff to a better cell on level basis, the call will possiblybe dropped. Topology or Morpology issues may also be there like if Mobile enters into a tunnel or a building , higher RF losses will be develoved.TIPS:First of all path balances should be checked. If path balances are deviating fro the standard value then check the BTS transmited power with the help of wattmeter. BTS may transmitlow power because of the malfunctioning of radio or higher combiner losses. Also check the feeder losses, antenna connectors. Enable Downlink power control. Power control is be directional. The lower and Upper recieve level downlink power control values should be properly defined.a. I_Rx Lev_DL_pDefined the lower value for receive level for the power control to be triggered.Range 0 to 63Where 0 = -110 dBm1 = -109 dBm 63 = -47 dBmExample : If the value of 20 is set it means that the BTS will start transmitting more if it senses that downlink receive level is below -90 dBm.b. U_RxLev_DL_pDefines the upper threshold value for receive level for the power control to be triggered (Range is same as described above).Example : On setting the value of 50 (equivalent to -60 dBm) BTS will lower down the power.3. Adjacent and Co-channel InterferenceFrequency planning playsa major role to combat adjecent channel and Co-channel Interference. Co channel is observed mostly when mobile is elevated and receives signals from cell far away but using the same frequencies.TIPS :An Optimization tools like Neptune could be helpful in identifying the interference on the particular area. Such frequencies can be cleaned from existing frequency plan. The following statistic can also be monitored to confirm that there interferences issues in the cell. These stats are defined in optima under the category of BSC stats.a. TCH Interference level 1b TCH Interference level 2c. TCH Interference level 3d. TCH Interference level 4When a TCH timeslot is idle it is constantly monitored for an uplink ambient noise. During a SACCH Multiframe an idle timeslot is monitered 104 times. These samples are the processed to procedure a noise level average per 480 ms. An interference band is allocated to an idle slot depending upon the interference level. The threshold for these levels can be set in the system parameters. Interference level 1 being the least ambient and interference level 4 being the most ambient. While planning the Network care should be taken that the cell do have the proper frequency spacing.4. Extraneous InterferenceExtraneous Interference might be from :a. Others mobile networkb. Military communicationc. Cordless Telephonesd. Illegal radio communition equipment.TIPS :External interference is always measured through spectrum analyser which can scan the whole band. Some spectrum analyser can even decode voice from AMPS circuits or Cordless Phones.5. Link ImbalanceSometime the multifunctionality of vendor hardware becomes responsible for high Call Drop Rate. One of the possible scanarios could be :a. Transmited and receiving antenna facing different directionb. Transmited and receiving antennas withdifferent tilts.c. Antenna feeder demage, crossion or water ingress.d. Physical obstruction.

SDCCH -SRSDCCH Success Rate is percentace of MS Call Setup success due to TimeSlot at the first call.Where :SDCCH success rate = [(Call Setup Success - Call Setup Failure )/ Call setup success] x 100%The call setup rate should be above 90% for a healthy network. However a cssr of 85% 90% is satisfactory.There could be so many reasons for a poor cssr. Some are described as follows :1. No access to SDCCH2. CM Service Reject3. TCH Failure Assignment4. Hardware ProblemOptimization Tips for :1. No Access to SDCCH.BSS detacts channel request (in the form of RACH) from a source, requesting resources for networks transactions. After validation of the RACH, BSS will attempt to allocate a dedicated channel (SDCCH) for the source. One the availability of SDCCH channel is confirmed, the BSS will send immediate assignment to MS indicating the dedicated SDCCH sub-channel (via AGCH), wherby subsequent message exchange will be preformed over the dedicated SDCCH.Case :a. Valid RACH ( SDCCH Congestion)Due to unavailability of SDCCH, BSS will response to MS with immediate assignment reject, terminating the transactions. In which case, call setup is termed as unsuccessful due to SDCCH congestion.Invalid RACH (Invalid established cause detected in the received RACH)b. Phantom RACHsThe received RACH is in fact genereted from an unknown source, wherby it fails to continue the transaction after SDCCH has been allocated by the BSS. For instances, case of channel request detected by overshooting cells, handover access burst from distanced MS, hardware deficiency, UL/DL imbalance path, MS moving out of range would carry the Phantom RACHs symptoms.TIPS:Within the optima there are certain stats which can be monitored before coming to conclusion that there is SDDCH problem :a. SDCCH Blockingb. SDDCH Congestion (Valid RACH)If the SDCCH blocking greater than 1% or SDCCH Congestion greater than 2% than that mean that it is a capacity related issue and more slots should be assigned for SDCCH.A TCH can be allocated by passing SDCCH. A parameter namely Immediate Assign Mode when enabled allocates TCH by passing SDCCH.2.CM Service RejectCM Service Request (MOC) or Paging Response (MTC) to BSC/MSC. Inside the CM service request message (MS initiated service request), MS informs the network the types of service it requires (i.e. Mobile Originationl, Emergency Call, Short Message transfer or Suplementary services activity), wherby Pagingresponse is specific to MTC. Subsequently, BSS embraces the information with its own initiated connection request BSSMAP message, send to MSC to approval. MSC will response with either connection confirmed, confirming the success in link establishment between MS-BSC-MSC, or connection Refused, Indicating the termination of the specific network transaction.3. TCH Failure AssignmentUpon completion of MS/BSC/MSC link established, MS issues Assignment Request to BSC, Requesting TCH Assignment to the dedicated MS. Subsequently, BSS will attempt to allocated free TCH for MS voice messaging. Once Assignment Command is received by MS, stating the availability of TCH for the MS, it will move to the dedicated TCH and responds with Assignment Complete. In turns, BSS will submit Assignment Complete to MSC as to complete the signal activity.Case :TCH CongestionTIPS :For TCH Congestion certain features can be enabled like TCH queuing , Directed Retry and Congestion Relief. In case of the TCH queuing feature is enable, MS will queue in the Original SDCCH , awaiting for the next available TCH. It is to be remainded that once Queuing timer expires. BSS willalso terminates transactions,in which case, call setup is termedas unsuccessfull due to TCH Congestion. The same situation also applies in situation where Congestion Relief feature is enabled. In the case of Directed Retry feature is enabled, MS will perform Handover to TCH of another cell if a valid handover neighbor is detected. The best thing to do is to add more radios in the cell to remove congestion.Interference analysis on a particular carier can be done through an optimization tools like Neptune. Once interfering frequencies are determind, the frequency plan can be cleanedfrom such frequencies.4. Hardware ProblemHardware failures also play major role for poor CSSR. Improper functinality of any BTS hardware can affect the overall performance of sites.TIPS :If there are no capacity or RF issues then equipment needs to be checked. Before starting the drivetest make sure that the cell site are free for any hardware alarms. The important parameter to check is the path balance. If path balances are not fine then start checking the power from radio to connected antennas. If we take the examples of GSM 900 scenario, the link budget defines that the radio should transmit 40 watts power and at the top of the cabinet, 20 watts are recaived ( Considering the 3 dB loss of combiner). While checking the power, if any components seems to procedure more losses than expected, change that component. Similarly check the power at antenna feeder ports. Some time due to the water ingress, connectors get rusty and needs to be replaced.

TCH-SMeasurement Point Of successful TCHseizuresMeasurement Point of successfull TCH seizures1. When CH_ACT_ACK message is received in the immediate assignment process. Since there is no SDCCH available, TCH channel is directly assigned.2. When CH_ACT_ACK message is received, the calling status is CS_WAIT_RR_EST(Waiting RR setup status) and the present channel is TCH.3. When assignment complete message is sent in process of assignment.4. When the MSG_ABIS_HO_DETECT message is received during incoming inter BSC inter cell handover, and the handover type is non-SDCCH handover.5. When the MSG_ABIS_HO_DETECT message is received during internal inter cell handover, and the handover type is non-SDCCH handover.6. When the CLEAR-CMD message with the cause of HO_SUCC or CALL_CTRL is received from the MSC during inter-BSC handover , and the handover cause is directed retry.Direct retry process:When the CLEAR-CMD message, whose cause values is HO_SUCC or CALL_CTRL, is received from the MSC during inter BSC handover , and at the same time the handover cause is direct retry, one measurement point will be counted and added to successful TCH seizures times

TCH -DRTCH Calldropcauses of TCH Call DropUsually, the typical causes for sending the Clear_Request mssg are as follows ;1. Radio Inteface Failure2. O & M Intervention3. Equipment Failure4. Protocol error5. Preemption