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Premium member Presentation Transcript OMF000603 Traffic Statistics Analysis: OMF000603 Traffic Statistics Analysis Issue 2.0Reference: Page 2 Reference 31160978-BSC Traffic Statistic Manual Volume I 31033203-BSS Troubleshooting ManualSlide 3: Page 3 Objectives Upon completion of this course, you will be able to: Know the traffic statistics system structure Understand some often-used traffic measurement items Locate some problems through the traffic statistics systemSlide 4: Page 4 Chapter 1 Brief introduction to BSC traffic statistics Chapter 2 Often-used traffic statistics items analysis Chapter 3 Locate problem through traffic analysis Chapter 4 Case study for traffic statistics ContentsMain Structure of Traffic Statistics System : Page 5 BM1 Call process data BM data Hardware data Signaling data BM AM/CM BAM WS1 WSn M2000 Server HUB Main Structure of Traffic Statistics SystemMenu Introduction to BSC Traffic Statistics: Page 6 Menu Introduction to BSC Traffic Statistics Task list management BSC traffic statistics platform provides the function of registering a new task, deleting a registered task and refreshing the task list. Task management BSC traffic statistics platform provides the function of modifying task name, modifying statistic period of permanent task, hanging up task, activating task, querying task information, querying task result and querying task running state.Menu Introduction to BSC Traffic Statistics: Page 7 Menu Introduction to BSC Traffic Statistics Template management Template management provides the function of defining item template, object template, time template, user-defined statistic items and refreshing all templates.Menu Introduction to BSC Traffic Statistics: Page 8 Menu Introduction to BSC Traffic Statistics Limitations The traffic measurement task is registered using the BSC traffic statistics console, the maximum number of tasks of each BM module is 200. The maximum number of subtasks in each BM module is 3000. One task can only include 60 original items. Items regarding to maximum/minimum value can not be repeatedly registered in all tasks.Brief Introduction to BSC Traffic Statistics Item: Page 9 Brief Introduction to BSC Traffic Statistics Item TCH Congestion Rate TCH Congestion Rate (excluding handover) = (TCH seizure failures for call + TCH seizure failures for very early assignment) / (attempted TCH seizures + attempted TCH seizures for very early assignment) * 100%Brief Introduction to BSC Traffic Statistics Item: Page 10 Brief Introduction to BSC Traffic Statistics Item TCH Congestion Rate TCH congestion rate (including handover)= (TCH seizure failures for call + TCH seizure failures for very early assignment + TCH seizure failures for intra BSC incoming cell handover (no radio resource) + TCH seizure failures for inter BSC incoming cell handover (no radio resource) ) / (attempted TCH seizures (all) + attempted TCH seizures for very early assignment + attempted TCH seizures for intraBSC incoming cell handover + attempted TCH seizures for interBSC incoming cell handover) * 100%Brief Introduction to BSC Traffic Statistics Item: Page 11 Brief Introduction to BSC Traffic Statistics Item TCH Congestion Rate TCH congestion rate (TCH overflow) = Attempted TCH seizures meeting a TCH blocked state / Attempted TCH seizures (all) * 100%Brief Introduction to BSC Traffic Statistics Item: Page 12 Brief Introduction to BSC Traffic Statistics Item SDCCH congestion rate (SDCCH overflow) SDCCH congestion rate (SDCCH overflow)= times of attempted seizures meeting an SDCCH blocked state / attempted SDCCH seizures (all) * 100%Brief Introduction to BSC Traffic Statistics Item: Page 13 Brief Introduction to BSC Traffic Statistics Item TCH Call Drop Rate TCH Call Drop Rate = TCH Call Drops / Successful TCH Seizures (all) *100% SDCCH Call Drop Rate SDCCH Call Drop Rate = SDCCH call drops / successful SDCCH seizures (all) *100%Brief Introduction to BSC Traffic Statistics Item: Page 14 Brief Introduction to BSC Traffic Statistics Item Handover Success Rate Inter cell handover success rate= (Successful incoming internal inter cell handovers + Successful incoming interBSC inter cell handovers + Successful outgoing internal inter cell handovers + Successful outgoing interBSC inter cell handovers) / (Attempted incoming internal inter cell handovers+ Attempted incoming interBSC inter cell handovers + Attempted outgoing internal inter cell handovers + Attempted outgoing interBSC inter cell handovers) *100%Brief Introduction to BSC Traffic Statistics Item: Page 15 Brief Introduction to BSC Traffic Statistics Item Handover Success Rate Inter cell radio handover success rate= (Successful incoming internal inter cell handovers + Successful incoming interBSC inter cell handovers + Successful outgoing internal inter cell handovers + Successful outgoing interBSC inter cell handovers) / (Incoming internal inter cell handovers + Inter BSC incoming cell handovers + Outgoing internal inter cell handovers + Inter BSC outgoing cell handovers) * 100%Exercise : Page 16 Exercise Write down the key items of the network Answer: The most important items for the network are: call drop rate, TCH congestion rate, SDCCH congestion rate, outgoing and incoming handover success rate, traffic volume etc.Brief Introduction to BSC Traffic Statistics Item: Page 17 Brief Introduction to BSC Traffic Statistics Item MTP Measurement Function Cell Measurement Function Power control Measurement Call Drop Measurement Site Initialization Measurement Function BSC Cell Broadcast Measurement Function BSC Measurement Function SCCP Measurement Function A-interface Operation and management statistic A-interface Equipment Maintenance statistic A-interface Trunk Board message statistic CPU Measurement FunctionBrief Introduction to BSC Traffic Statistics Item: Page 18 Brief Introduction to BSC Traffic Statistics Item Defined Adjacent Cell Measurement Function Receiving Quality Measurement Receiving Level Measurement Function Up-Down Link Balance Measurement Function LAPD Link Measurement Function Cell Frequency Scan BTS Initial Measurement Cell Broadcast Statistic Outgoing Inter cell handover Measurement Function Incoming Inter cell handover Measurement Function Undefined Adjacent Cell Measurement Function GPRS Related Measurement FunctionSlide 19: Page 19 Chapter 1 Brief introduction to BSC traffic statistics Chapter 2 Often-used traffic statistics items analysis Chapter 3 Locate problem through traffic analysis Chapter 4 Case study for traffic statistics ContentsOften-used Traffic Statistics Items Analysis: Page 20 Often-used Traffic Statistics Items Analysis Systematical logic From whole system to specific cell Integrality Observe the change trend of the items for more than one week and the changing trend of each day. Relativity Relationship between various kinds of traffic statistics itemsOften-used Traffic Statistics Items Analysis: Page 21 Often-used Traffic Statistics Items Analysis Analysis process First we shall analyze and compare the item of BSC measurement function to have a rough idea for the whole network. During analyzing, if any important items (such as call drop rate or handover success rate) are abnormal, we shall do further detailed analysis for the corresponding items.Often-used Traffic Statistics Items Analysis: Page 22 Often-used Traffic Statistics Items Analysis Analysis process Check the cell that has abnormal items (call drop, congestion, handover failure and so on). Base on whole percentage and absolute times (call drop, congestion, handover failure and so on), decide whether some further analysis should be considered or not.Often-used Traffic Statistics Items Analysis: Page 23 Often-used Traffic Statistics Items Analysis Circuit paging (A-interface) successful rate Immediate assignment successful rate TCH call drop rate TCH and SDCCH congestion rate Handover success rate Interference bandOften-used Traffic Statistics Items Analysis: Page 24 Often-used Traffic Statistics Items Analysis Circuit paging (A-interface) success rate Relate to “ATT ”, coverage area and random access performance. Relate to the paging re-send mechanism implemented by BSS or MSC.Often-used Traffic Statistics Items Analysis: Page 25 Often-used Traffic Statistics Items Analysis Immediate assignment success rate When BTS receives a Random Access message from MS, BTS will apply a channel from BSC. If there is no channel available, BSC will send immediate assignment rejected message which indicates the failure of immediate assignment. At the same time, MS’s access will be bared for some time. The interference and collision of random access will affect immediate assignment successful rate.Often-used Traffic Statistics Items Analysis: Page 26 Often-used Traffic Statistics Items Analysis TCH call drop rate Possible causes can be TCH lost radio connections (Connection failure). TCH lost radio connections (Error indication). Ground link disconnection when TCH seized (Abis). Call drop during handoverOften-used Traffic Statistics Items Analysis: Page 27 Often-used Traffic Statistics Items Analysis TCH call drop formula and measurement point TCH Call Drop Rate = TCH Call Drop / Successful TCH Seizures (all) *100%Often-used Traffic Statistics Items Analysis: Page 28 Often-used Traffic Statistics Items Analysis RF lost rate TCH RF Lost Rate = (times of radio link disconnection when TCH seized (connection failure) + times of radio link disconnection when TCH seized (error indication)) / successful TCH seizures (all) * 100% SDCCH RF Lost Rate = (times of radio link disconnection when SDCCH seized (connection failure) + times of radio link disconnection when SDCCH seized (error indication)) / successful SDCCH seizures (all) * 100%Often-used Traffic Statistics Items Analysis: Page 29 Often-used Traffic Statistics Items Analysis TCH congestion rate (TCH overflow) It is a key item used to estimate the cell load. When the load of the cell overruns the system limitation, try to distribute some traffic to adjacent cells.Often-used Traffic Statistics Items Analysis: Page 30 Often-used Traffic Statistics Items Analysis Causes of TCH congestion ( TCH seizure failure ) Assignment failure Equipment fault Invalid ground resource Ground resource already allocated Illegal message contents Radio interface failure and return to original channel No channel availableOften-used Traffic Statistics Items Analysis: Page 31 Often-used Traffic Statistics Items Analysis TCH Congestion Rate TCH congestion rate (including handover)= (TCH seizure failures for call + TCH seizure failures for very early assignment + TCH seizure failures for intra BSC incoming cell handover (no radio resource) + TCH seizure failures for inter BSC incoming cell handover (no radio resource) ) / (attempted TCH seizures (all) + attempted TCH seizures for very early assignment + attempted TCH seizures for intraBSC incoming cell handover + attempted TCH seizures for interBSC incoming cell handover) * 100%Often-used Traffic Statistics Items Analysis: Page 32 Often-used Traffic Statistics Items Analysis SDCCH congestion rate (SDCCH overflow) SDCCH congestion rate (SDCCH overflow)= times of attempted seizures meeting an SDCCH blocked state / attempted SDCCH seizures (all) * 100%Often-used Traffic Statistics Items Analysis: Page 33 Often-used Traffic Statistics Items Analysis SDCCH congestion measurement point Attempted SDCCH seizure meeting a SDCCH blocked state is counted when there is a SDCCH seizure but no SDCCH available. Attempted SDCCH seizures (all) Receive CH_REQ and the channel type is SDCCH. Incoming interBSC inter cell handover and the handover type is SDCCH handover. Incoming intraBSC inter cell and intra-cell handover and the handover type is SDCCH handover.Often-used Traffic Statistics Items Analysis: Page 34 Often-used Traffic Statistics Items Analysis Handover measurement point For different objects such as BSC, band (900/1800), incoming/outgoing, inter-cell/intra-cell handover and so on, there are different items. By analyzing different items, the problems can be located more rapidly.Often-used Traffic Statistics Items Analysis: Page 35 Often-used Traffic Statistics Items Analysis Handover Success Rate Inter cell handover success rate= (Successful incoming internal inter cell handovers + Successful incoming interBSC inter cell handovers + Successful outgoing internal inter cell handovers + Successful outgoing interBSC inter cell handovers) / (Attempted incoming internal inter cell handovers+ Attempted incoming interBSC inter cell handovers + Attempted outgoing internal inter cell handovers + Attempted outgoing interBSC inter cell handovers) *100%Often-used Traffic Statistics Items Analysis: Page 36 Often-used Traffic Statistics Items Analysis Causes of handover Power budget Poor uplink signal quality Poor downlink signal quality Low uplink signal strength Low downlink signal strength Too large TA value Other reasons Note: Handover types and times with all adjacent cells are listed in outgoing and incoming inter cell handover measurement function.Often-used Traffic Statistics Items Analysis: Page 37 Often-used Traffic Statistics Items Analysis Handover failure reasons No available channel Illegal frequency Timer timeout Illegal channel Illegal TA Other reasonsOften-used Traffic Statistics Items Analysis: Page 38 Often-used Traffic Statistics Items Analysis TCH interference band measurement The result in each TCH interference band shows the average number of idle TCH within this interference band in the statistic period, which reflects the average interference level. In urban and suburb area, because of different density of base station and the frequency reuse pattern, the acceptable interference level is different.Often-used Traffic Statistics Items Analysis: Page 39 Often-used Traffic Statistics Items Analysis Cell frequency scan Shows the signal strength received by main antenna and diversity antenna. Reflects the interference level for specific frequency. The difference between the measurement results of main and diversity antenna reflects the difference between the two antennas such as direction, gain, path loss and so on. It is an important way to know the diversity receiving performance.Often-used Traffic Statistics Items Analysis: Page 40 Often-used Traffic Statistics Items Analysis Receiving level measurement Receiving level measurement is based on TRX. The receiving level is divided into 6 bands Band 0 : -110~-100dBm Band1 : -100~-95dBm Band 2 : -95~-90dBm Band 3 : -90~-80dBm Band 4 : -80~-70dBm Band 5 : > -70dBmExercise: Page 41 Exercise List the often-used traffic statistics tasks that we use to locate and analyze the problem. Answer: the often-used traffic statistics tasks are BSC measurement function TCH and SDCCH measurement function Inter-cell and intra-cell handover measurement function Outgoing and incoming inter cell handover measurement function Up-down link balance measurement function Call drop measurement function Cell frequency scan, etc.Slide 42: Page 42 Chapter 1 Brief introduction to BSC traffic statistics Chapter 2 Often-used traffic statistics items analysis Chapter 3 Locate problem through traffic analysis Chapter 4 Case study for traffic statistics ContentsTraffic Statistics Analysis: Page 43 BSC Measurement Function High call drop rate High congestion rate Low handover success rate TCH performance Call drops SDCCH performance Link balance Outgoing handover Alarm data Alarm data TCH performance TCH performance Incoming handover Link balance Link Balance Alarm data Traffic Statistics Analysis General method for traffic analysisTraffic Statistics Analysis: Page 44 Traffic Statistics Analysis Combine traffic statistics analysis with other optimization method Drive test: simulate common subscriber’s behavior. Analyze objects Coverage Quality Handover Signaling OthersTraffic Statistics Analysis-TCH Call Drop: Page 45 Traffic Statistics Analysis-TCH Call Drop TCH call drop analysis Cell with high call drop rate Cell performance statistics Call drop times Interference band Causes of call drop Call drop measurement Average uplink level at TCH call drops Average down link level at TCH call drop Average downlink quality at TCH call drop Handover measurement Outgoing inter cell handover success rate Incoming inter cell handover success rate Handover failure and re-establish failure Alarm and hardware fault Average TA value at TCH call drop Average uplink quality at TCH call dropTraffic Statistics Analysis-TCH Call Drop: Page 46 Traffic Statistics Analysis-TCH Call Drop Call drop types Edge call drop: low receiving signaling strength, large TA. Short distance call drop: low receiving signal strength and small TA. BQ call drop: high receiving signal strength and poor quality. Sudden call drop: before call drop, the call is normal then call drop happened suddenly.Traffic Statistics Analysis-TCH Call Drop: Page 47 Traffic Statistics Analysis-TCH Call Drop Edge call drop Causes MS is out of cell’s effective coverage area. “Island” phenomenon caused by over shooting or missing neighbor. Isolated site. Solutions Add new site to guarantee the effective continuous coverage. Add the necessary neighbor. Adjust antenna height and antenna downtilt, use high gain antenna Modify some parameters: “SACCH multi-frames”, “Radio link timeout counter”, “handover threshold”, “handover statistic time”, etc..Traffic Statistics Analysis-TCH Call Drop: Page 48 Traffic Statistics Analysis-TCH Call Drop Short distance call drop Causes Poor coverage caused by complicated terrain or high dense building. Solutions Increase EIRP. Adjust antenna direction and downtilt, make the main lobe point to high traffic area. Adjust parameters related to call drop.Traffic Statistics Analysis-TCH Call Drop: Page 49 Traffic Statistics Analysis-TCH Call Drop BQ call drop( high signal strength) Causes High transmission bit error rate (BER). Uplink or downlink interference. Interference caused by repeater. Interference caused by radar or other similar equipment. Interference caused by improper frequency planning. Self-interference caused by BTS. Solutions Try to find the external interference source. Optimize frequency planning. Adjust antenna system, avoid “island”. Solve the problem of transmission quality.Traffic Statistics Analysis-TCH Call Drop: Page 50 Traffic Statistics Analysis-TCH Call Drop Overall process for call drop analysis Find out cells with high call drop rate. Classify the call drop according to the character. Analyze the cells’ traffic load and total call drop times. Analyze the call drop measurement function. Check the interference band. First of all, we shall know the type of the call drop.Traffic Statistics Analysis-TCH Call Drop: Page 51 Traffic Statistics Analysis-TCH Call Drop The main causes for call drop Interference (internal and external). Poor coverage (coverage hole and island). Improper handover (neighbor planning and handover parameter setting). Unbalanced up-down link (TMA, power amplifier, antenna direction). Improper parameter settings ( RLT and SACCH multi-frames). Equipment problem (TRX, power amplifier, and TMA).Traffic Statistics Analysis-TCH Call Drop: Page 52 Traffic Statistics Analysis-TCH Call Drop Interference analysis process Analyze the appearance period of the interference. Block TRX in turn and monitor the interference measurement results. Calculate the handover caused by poor quality and check the average receiving quality level for each TRX. In call drop measurement function, check the average signal strength and quality of call drops. Through drive test, check the interference and signal quality. Use spectrum analyzer to find the interference source. Dispose equipment fault (such as: TRX self-oscillation, antenna inter-modulation).Traffic Statistics Analysis-TCH Call Drop: Page 53 Traffic Statistics Analysis-TCH Call Drop Coverage problem analysis Traffic items In power control measurement function, the average uplink or downlink signal strength is too low. In receiving level measurement function, a lot of low signal strength records can be found. In inter-cell handover measurement function, the average receiving signal strength is too low when handover is triggered. In call drop measurement, the signal strength is too low when call drop happens, or the TA value is abnormal. In undefined adjacent cell measurement function, the potential neighbor cells with high average signal strength can be find.Traffic Statistics Analysis-TCH Call Drop: Page 54 Traffic Statistics Analysis-TCH Call Drop Coverage problem analysis Judgment method In Power Control measurement Check whether the average distance between MS and BTS comply with design. Check whether the maximum distance between MS and BTS is abnormal in several continuous periods. In outgoing inter-cell handover measurement function check whether the handover successful rate to some cells is low. check the number of unsuccessful handover with unsuccessful reversion (call drop caused by handover).Traffic Statistics Analysis-TCH Call Drop: Page 55 Traffic Statistics Analysis-TCH Call Drop Coverage problem analysis Disposing method Drive test in the suspected poor coverage area. Adjust the following parameters based on the drive test results BTS transmitting power Antenna downtilt and height RXLEVEL_ACCESS_MIN Add site to ensure the continuous coverage.Traffic Statistics Analysis-TCH Call Drop: Page 56 Traffic Statistics Analysis-TCH Call Drop Improper handover (neighbor planning and handover parameters ） Disposing method Check the handover parameters to see whether there are improper parameter settings. In inter-cell handover measurement function, check whether there are many unsuccessful outgoing cell handovers with unsuccessful reversions. In undefined adjacent cell measurement function, check whether the signal strength and the number of measurement reports for the undefined neighbor cell are high.Traffic Statistics Analysis-TCH Call Drop: Page 57 Traffic Statistics Analysis-TCH Call Drop Imbalanced up-down link (tower amplifier, power amplifier, and antenna directions) Disposing method Analyze “up-down link balance measurement function” statistics result and confirm whether the uplink and downlink are balanced. In call drop measurement function, analyze the average receiving signal strength and quality for both the uplink and downlink. In power control measurement function, analyze the average receiving signal strength for both the uplink and downlink.Traffic Statistics Analysis-TCH Call Drop: Page 58 Traffic Statistics Analysis-TCH Call Drop Balance between uplink and downlink Let D= (downlink receiving level − uplink receiving level) − (MS sensitivity − BTS sensitivity). Usually the MS sensitivity is -102 dBm and the BTS sensitivity is -108dBm. The formula can be simplified as D= downlink receiving level − uplink receiving level – 6dB If D=0, it means uplink and downlink are balanced If D>0, it means downlink is better than uplink If D<0, it means uplink is better than downlink Link balance rank Range of D 1 ≤ -15 2 -14 ~ -10 3 -9 ~ -6 4 -5 ~ -3 5 -2 ~ 0 6 0 7 1 ~ 2 8 3 ~ 5 9 6 ~ 9 10 10 ~ 14 11 ≥15Traffic Statistics Analysis-TCH Call Drop: Page 59 Traffic Statistics Analysis-TCH Call Drop Improper radio parameter setting (Radio Link timeout, SACCH multi-frames) Judgment method In system information data, check the radio link timeout In cell property data, check SACCH multi-frames, and the timer for radio link connection (T3105).Traffic Statistics Analysis-TCH Call Drop: Page 60 Traffic Statistics Analysis-TCH Call Drop Equipment problem (TRX, power amplifier, tower amplifier, etc.) Judgment method In TCH measure function, many TCH seizure failures due to A interface problem. In call drop measurement function, there are many call drops due to ground links. In TCH measurement function, there are many TCH seizure failures due to equipment failure. Disposing method Monitor transmission and board alarms (FTC board failure, A interface PCM synchronization alarm, LAPD link disconnected, TRX alarm); analyze whether transmission is disconnected or some boards are faulty.Traffic Statistics Analysis-SDCCH Call Drop: Page 61 Traffic Statistics Analysis-SDCCH Call Drop SDCCH call drop Refer to TCH call drop analysis. The cause and mechanism of SDCCH call drop are almost the same as TCH.Traffic Statistics Analysis-Handover: Page 62 Low Handover Success Rate Handover Measurement Function Alarm (Clock), Hardware Fault TCH Measurement Function Outgoing Inter Cell Failure Incoming Inter Cell Failure Outgoing Inter cell Handover Measurement Function Incoming Inter cell Handover Measurement Function Cause of Failure in BSC 1.Illegal Channels 2.Illegal Carrier 3.Illegal TA 4.Timer out 5.No available channel 6.Others Traffic Statistics Analysis-Handover Handover analysisTraffic Statistics Analysis-Handover: Page 63 Traffic Statistics Analysis-Handover Handover failure analysis Causes of handover failure Improper handover parameters. Hardware fault (TRX board fault). Congestion Interference Coverage Clock fault (Internal clock, external clock)Traffic Statistics Analysis-Handover: Page 64 Traffic Statistics Analysis-Handover Handover failure analysis Disposing method Find out the cells with low handover success rate. Find the out the cells with high handover failures. Compare the incoming cell handover failures and outgoing cell handover failures. Register the task to measure the incoming cell handover and outgoing cell handover. Find out handover failure relation (failure to all the neighbor cells or part of the neighbor cells).Traffic Statistics Analysis-Handover: Page 65 Traffic Statistics Analysis-Handover Improper parameter settings Disposing method Check whether the handover threshold such as TA, BQ and handover function switch are suitable or not. Check whether the successful TCH seizures for handover are much more than successful TCH seizures for call. If handover times divided by call times is larger than 3, then it indicates that there may be ping-pong handover. Check the parameter settings and adjust them (layer setting, layer handover hysteresis, inter cell handover hysteresis, PBGT threshold, etc.). Check whether the average signal strength is low when the handover happens. If so, it indicates the edge handover threshold is too low.Traffic Statistics Analysis-Handover: Page 66 Traffic Statistics Analysis-Handover Hardware fault Problem description The target cell has idle channels but when applying for the channels CH_ACT_NACK or TIMEOUT message appears. TCH availability is abnormal. If the call drop rate and congestion rate are both high, the equipment may have some fault.Traffic Statistics Analysis-Handover: Page 67 Traffic Statistics Analysis-Handover Hardware fault Disposing process Monitor transmission and board alarms (FTC board failure, A interface PCM sync alarm, LAPD link disconnected, TRX alarm). Analyze whether the transmission is disconnected or the boards have some fault (for example: the TRX is damaged). Check whether there is clock alarm.Traffic Statistics Analysis-Handover: Page 68 Traffic Statistics Analysis-Handover Congestion Objects needed to be analyzed Cells with low incoming handover success rate. Neighbor of the cell with low incoming handover success rate. Locating the problem In incoming inter cell handover measurement function, check whether many handover failures are caused by congestion. For low incoming handover success rate, check the cell’s traffic . For low outgoing handover success rate, check the neighbor cell’s traffic.Traffic Statistics Analysis-Handover: Page 69 Traffic Statistics Analysis-Handover Congestion Disposing process Adjust the cell’s coverage (adjust BTS transmitting power, RXLEVEL_ACCESS_MIN, RACH access threshold, and the antenna downtilt and height). Adjust parameters (CRO, load handover parameters, cell priority and handover parameters). Expand or adjust TRX configuration between high and low traffic cells.Question: Page 70 Question The item “radio handover success rate” is the ratio of successful handovers to handovers. The handovers are counted when sending or receiving HO_CMD or HO_REQ_RSP in the handover process. Please write down the possible reasons that can cause the low radio handover success rate between BSCs.Answer: Page 71 Answer There are two kinds of outgoing handovers. One is intra-BSC handover, and the other is inter-BSC handover. The possible reasons are list as following. For inter-BSC handover: If the uplink signal strength of the target cell is low, the MS cannot access the target cell. Thus the handover fails If the target cell is a wrong cell which has the same BCCH and BSIC as the expected target cell, MS will send access request to a wrong cell. Then MS cannot access. Thus the handover fails. If the CGI is wrong, MSC will send the handover request with wrong CGI. Then MS will send access request to a wrong cell. It has the same effect as the above one.Traffic Statistics Analysis-TCH Congestion: Page 72 Traffic Statistics Analysis-TCH Congestion TCH congestion Main causes Insufficient system capacity Interference Coverage Antenna and feeder problems Improper parameter setting (system information parameters)Traffic Statistics Analysis-TCH Congestion: Page 73 Traffic Statistics Analysis-TCH Congestion Insufficient system capacity or traffic imbalanced Judgment method The traffic is high and is imbalanced between cells. There are many channel request rejections due to channel busy. Incoming handover measurement shows that there are too many unsuccessful incoming cell handovers (congestion). Disposing process Expand or adjust the configuration between high and low traffic cells Adjust coverage (adjust BTS transmitting power, antenna direction, downtilt, height, etc.). Adjust parameters (CRO, Rx_Lev_Access_Min, load handover parameters, cell priorities, handover parameters).Traffic Statistics Analysis-TCH Congestion: Page 74 Traffic Statistics Analysis-TCH Congestion Interference (external and internal interference) Problem description Interference brings unacceptable BER which affects the assignment process. Downlink Interference makes MS’s DSC decrease to 0, then MS reselects to another cell with low signal strength, and this is a potential reason for TCH seizure failure. If TCH seizure failures (including handover) minus attempted TCH seizures meeting TCH overflow is large, then there may be some interference. Disposing process Refer to TCH call drop caused by interference.Traffic Statistics Analysis-TCH Congestion: Page 75 Traffic Statistics Analysis-TCH Congestion Antenna and feeder problem Disposing process In cell frequency scan measurement function, check the measurement results got from main receiving antenna and diversity receiving antenna. In Up-down link balance measurement function, check the measurement report numbers in each rank. Check antenna direction, downtilt and connection.Traffic Statistics Analysis-TCH Congestion: Page 76 Traffic Statistics Analysis-TCH Congestion Improper parameter settings Check the relevant parameters such as RXLEV_ACCESS_MIN, CRO, BTS transmitting power, handover threshold etc..Traffic Statistics Analysis-TCH Congestion: Page 77 Traffic Statistics Analysis-TCH Congestion Coverage Refer to coverage analysis for TCH call drop rate.Traffic Statistics Analysis-SDCCH Congestion: Page 78 Traffic Statistics Analysis-SDCCH Congestion SDCCH congestion Main causes Improper parameter settings (system information) Insufficient system capacity Improper LAC planning InterferenceTraffic Statistics Analysis-SDCCH Congestion: Page 79 Traffic Statistics Analysis-SDCCH Congestion Improper parameter settings Judgment method Successful immediate assignments / immediate assignment transmissions >85%. The above formula shows the ratio between number of EST_IND messages that MS sends to BSC and the immediate assignment commands that BSC sends to BTS. It indicate whether there are some improper parameters in the system information. Disposing process Adjust the access parameters (Random access error threshold, RACH minimum access level, MS Max Retrans, Tx-integer). Adjust the location update related parameters (dual-band network parameters such as CRO, cell reselection hysteresis, T3212).Traffic Statistics Analysis-SDCCH Congestion: Page 80 Traffic Statistics Analysis-SDCCH Congestion Insufficient system capacity Problem description Many location updates happen at the border of different location areas. Massive location updates happen simultaneously. Disposing method Properly plan the location area Configure more SDCCHs Use SDCCH dynamic allocation Add more TRXTraffic Statistics Analysis-SDCCH Congestion: Page 81 Traffic Statistics Analysis-SDCCH Congestion Improper LAC planning The border of different location area is the street. The border of different location area is at the high traffic area.Traffic Statistics Analysis-SDCCH Congestion: Page 82 Traffic Statistics Analysis-SDCCH Congestion Interference Problem description RACH minimum access level is low. Interference in the system, which will bring a lot of illusory SDCCH channel requests. Disposing process Properly set the RACH minimum access level Eliminate the interferenceSlide 83: Page 83 Chapter 1 Brief introduction to BSC traffic statistics Chapter 2 Often-used traffic statistics items analysis Chapter 3 Locate problem through traffic analysis Chapter 4 Case study for traffic statistics ContentsCase Study-One (Handover): Page 84 Case Study-One (Handover) Problem description Handover success rate is always very low because of the congestion (about 70%) In the evening of 3rd. Dec, site D located in urban is expanded from “S2/2/2” to “S3/3/3”. The busy hour handover success rate does not get improved after expansion. Sometimes handover success rate is lower than before. At the same time, lots of subscribers complain about the network quality. Refer to busy hour traffic statistics of 3rd. Dec.Case Study-One (Handover): Page 85 Case Study-One (Handover) Cell Handover success rate Radio handover success rate Intra-BSC incoming handover failures (no channel available) Intra-BSC incoming handover failures (others) TCH congestion D_1 53.41% 90.02% 397 18 47.53% D_2 49.82% 93.98% 389 2 67.23% D_3 57.67% 90.06% 314 51 48.31% C_3 61.25% 91.67% 502 25 40.61% A_2 78.40% 89.07% 0 33 0 A_3 77.14% 93.80% 0 20 0 F_2 76.36% 76.36% 0 12 0 E_1 66.22% 88.10% 26 63 5.33% E_2 92.73% 94.44% 0 2 0 E_3 83.25% 91.91% 0 6 0 B_3 83.48% 95.53% 0 5 0.75% Traffic statistics for 24th.NovCase Study-One (Handover): Page 86 Case Study-One (Handover) Cell Handover success rate Radio handover success rate Intra-BSC incoming handover failures (no channel available) Intra-BSC incoming handover failures (others) TCH congestion D_1 49.75% 52.95% 17 246 5.27% D_2 56.48% 58.56% 1 161 0.58% D_3 65.92% 66.08% 0 86 22.37% C_3 60.58% 66.3% 113 166 0.00% A_2 70.55% 71.71% 0 0 1.06% A_3 68.02% 68.95% 0 0 0.00% F_2 60.61% 60.61% 0 13 0.56% E_1 63% 64.08% 1 55 0.00% E_2 61.77% 62.69% 0 20 0.00% E_3 50.3% 50.3% 0 0 0.00% B_3 78.60% 82.45% 0 11 0.34% Traffic statistics for 13th.DecCase Study-One (Handover): Page 87 Case Study-One (Handover) Site locationCase Study-One (Handover): Page 88 Case Study-One (Handover) Analysis Analyzing the traffic statistics before expansion and after expansion, we find that before the expansion the handover failure is caused by congestion and the radio handover success rate is normal. In Urban area many cells’ radio handover success rate decreased after expansion, therefore we conclude that the cause of handover failure after expansion has been changed. Analyzing the urban site location diagram, we find lots of cells’ radio handover success rate are low and these cells have handover relationship with site D. Therefore we can suspect that the handover problem may be caused by site D.Case Study-One (Handover): Page 89 Case Study-One (Handover) Analysis After checking the hardware of site D through maintenance console, we find the state of TMU board is abnormal and clock is unstable. Finally we affirm the low handover success rate is caused by the wrong setting of switches in TMU board. For sure, the high call drop rate is caused by handover failures. The day after processing, the busy hour handover success rate is higher than 90%. Thus the problem is solved. Refer to busy hour traffic statistics of 17th. Dec.Case Study-One (Handover): Page 90 Case Study-One (Handover) Cell Handover success rate Radio handover success rate Intra-BSC incoming handover failures (no channel available) Intra-BSC incoming handover failures (others) TCH congestion D_1 86.58% 95.90% 47 10 13.00% D_2 93.09% 96.88% 10 15 3.40% D_3 95.57% 96.79% 0 10 0.00% C_3 86.84% 95.94% 80 7 18.26% A_2 88.43% 91.51% 1 21 0.48% A_3 92.56% 94.12% 0 6 0.00% F_2 98.47% 89.47% 0 1 0.00% E_1 93.69% 95.59% 1 6 1.44% E_2 93.55% 93.55% 0 2 0.00% E_3 97.40% 97.45% 0 1 0.00% B_3 91.80% 96.89% 10 1 7.92% Traffic statistics for 17th.DecCase Study-One (Handover): Page 91 Case Study-One (Handover) Conclusion and suggestion Pay attention to the difference between radio handover success rate and handover success rate because it can help us to locate handover problem efficiently. Handover problem sometimes is accompanied with call drops and others; it is an important clew for locating and solving problems.Case Study-Two (Call drop): Page 92 Case Study-Two (Call drop) Fault description When we analyze the traffic statistics, we find that a cell’s call drop rate in busy hour is large than 2%. In cell call drop measurement function, we find that the average uplink level of call drop is 1 (-109dBm), while the downlink level is 26 (-84dbm). High call drop rate is caused by imbalance between uplink and downlink. In up-down link balance measurement function: we find one TRX is normal, but there may be some problem with the other one. Result of rank 1 is 0, while that of rank 11 is 5833. It means the downlink is better than uplink.Case Study-Two (Call drop): Page 93 Case Study-Two (Call drop) Analysis We can exclude the problem of antenna and feeder because only one of the two TRXs is abnormal. Therefore we think that the problem may be caused by the uplink channel of TRX or CDU. After we change the CDU, the problem is solved.Case Study-Two (Call drop): Page 94 Case Study-Two (Call drop) Conclusion and suggestion To find the cause of call drop, we should register the following useful traffic statistics: TCH measurement function Call drop measurement function Inter cell handover measurement function Up-down link balance measurement function By analyzing the result of the above traffic statistics, we can locate the cause of the call drop (handover, interference, coverage etc.) and then register more detailed traffic measurement tasks. DT also is a effective method to find call drop problem.Case Study-three (SDCCH congestion): Page 95 Case Study-three (SDCCH congestion) Fault description In the network, the radio link connection success rate is low. After analyzing the traffic statistics, we find that it caused by SDCCH congestion and the congestion only exists in a few sites. Analyzing traffic statistics we find that in the congested cell, attempted SDCCH seizures are from 300 to 400 in a certain hour. The configuration of all the related BTSs is S1/1/1. Each cell has one SDCCH/8 channel. Normally, it can deal with 300-400 SDCCH seizures. But it is very strange that there are dozens of SDCCH congestions in busy hour.Case Study-three (SDCCH congestion): Page 96 Case Study-three (SDCCH congestion) Analysis Register “SDCCH measurement function” and analyze the result. We find that most of the SDCCH seizures are used for location update. After we analyze the site distribution, we find that the congested BTSs are located at the border of two location areas along the railway. So we can conclude that SDCCH congestion shall be caused by massive location updates. In SDCCH measurement function, we find that most of the location update happened in a specific 5 minutes. After checking the train timetable, we find that 4 or 5 trains passed by in this period. When the trains pass by, a large amount of location updates happen simultaneously. After adding more fixed SDCCHs and switching on “Dynamic SDCCH allocation” function, the problem is solved.Case Study-three (SDCCH blocking): Page 97 Case Study-three (SDCCH blocking) Conclusion and suggestion For SDCCH congestion, firstly we should register SDCCH measurement function, and then analyze the traffic statistics to find the cause of the problem (Location update, SDCCH handover, call setup etc.). Then check the parameter settings, interference, location area planning etc., to do further analysis. Adding SDCCH channels or enabling dynamic SDCCH allocation function can solve the congestion caused by insufficient capacity. Set the parameter and plan the location area properly to decrease the SDCCH congestion.Summary: Page 98 Summary Traffic statistics system basics Key traffic measurement items Traffic statistics analysis method Some cases Summary You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.
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Premium member Presentation Transcript OMF000603 Traffic Statistics Analysis: OMF000603 Traffic Statistics Analysis Issue 2.0Reference: Page 2 Reference 31160978-BSC Traffic Statistic Manual Volume I 31033203-BSS Troubleshooting ManualSlide 3: Page 3 Objectives Upon completion of this course, you will be able to: Know the traffic statistics system structure Understand some often-used traffic measurement items Locate some problems through the traffic statistics systemSlide 4: Page 4 Chapter 1 Brief introduction to BSC traffic statistics Chapter 2 Often-used traffic statistics items analysis Chapter 3 Locate problem through traffic analysis Chapter 4 Case study for traffic statistics ContentsMain Structure of Traffic Statistics System : Page 5 BM1 Call process data BM data Hardware data Signaling data BM AM/CM BAM WS1 WSn M2000 Server HUB Main Structure of Traffic Statistics SystemMenu Introduction to BSC Traffic Statistics: Page 6 Menu Introduction to BSC Traffic Statistics Task list management BSC traffic statistics platform provides the function of registering a new task, deleting a registered task and refreshing the task list. Task management BSC traffic statistics platform provides the function of modifying task name, modifying statistic period of permanent task, hanging up task, activating task, querying task information, querying task result and querying task running state.Menu Introduction to BSC Traffic Statistics: Page 7 Menu Introduction to BSC Traffic Statistics Template management Template management provides the function of defining item template, object template, time template, user-defined statistic items and refreshing all templates.Menu Introduction to BSC Traffic Statistics: Page 8 Menu Introduction to BSC Traffic Statistics Limitations The traffic measurement task is registered using the BSC traffic statistics console, the maximum number of tasks of each BM module is 200. The maximum number of subtasks in each BM module is 3000. One task can only include 60 original items. Items regarding to maximum/minimum value can not be repeatedly registered in all tasks.Brief Introduction to BSC Traffic Statistics Item: Page 9 Brief Introduction to BSC Traffic Statistics Item TCH Congestion Rate TCH Congestion Rate (excluding handover) = (TCH seizure failures for call + TCH seizure failures for very early assignment) / (attempted TCH seizures + attempted TCH seizures for very early assignment) * 100%Brief Introduction to BSC Traffic Statistics Item: Page 10 Brief Introduction to BSC Traffic Statistics Item TCH Congestion Rate TCH congestion rate (including handover)= (TCH seizure failures for call + TCH seizure failures for very early assignment + TCH seizure failures for intra BSC incoming cell handover (no radio resource) + TCH seizure failures for inter BSC incoming cell handover (no radio resource) ) / (attempted TCH seizures (all) + attempted TCH seizures for very early assignment + attempted TCH seizures for intraBSC incoming cell handover + attempted TCH seizures for interBSC incoming cell handover) * 100%Brief Introduction to BSC Traffic Statistics Item: Page 11 Brief Introduction to BSC Traffic Statistics Item TCH Congestion Rate TCH congestion rate (TCH overflow) = Attempted TCH seizures meeting a TCH blocked state / Attempted TCH seizures (all) * 100%Brief Introduction to BSC Traffic Statistics Item: Page 12 Brief Introduction to BSC Traffic Statistics Item SDCCH congestion rate (SDCCH overflow) SDCCH congestion rate (SDCCH overflow)= times of attempted seizures meeting an SDCCH blocked state / attempted SDCCH seizures (all) * 100%Brief Introduction to BSC Traffic Statistics Item: Page 13 Brief Introduction to BSC Traffic Statistics Item TCH Call Drop Rate TCH Call Drop Rate = TCH Call Drops / Successful TCH Seizures (all) *100% SDCCH Call Drop Rate SDCCH Call Drop Rate = SDCCH call drops / successful SDCCH seizures (all) *100%Brief Introduction to BSC Traffic Statistics Item: Page 14 Brief Introduction to BSC Traffic Statistics Item Handover Success Rate Inter cell handover success rate= (Successful incoming internal inter cell handovers + Successful incoming interBSC inter cell handovers + Successful outgoing internal inter cell handovers + Successful outgoing interBSC inter cell handovers) / (Attempted incoming internal inter cell handovers+ Attempted incoming interBSC inter cell handovers + Attempted outgoing internal inter cell handovers + Attempted outgoing interBSC inter cell handovers) *100%Brief Introduction to BSC Traffic Statistics Item: Page 15 Brief Introduction to BSC Traffic Statistics Item Handover Success Rate Inter cell radio handover success rate= (Successful incoming internal inter cell handovers + Successful incoming interBSC inter cell handovers + Successful outgoing internal inter cell handovers + Successful outgoing interBSC inter cell handovers) / (Incoming internal inter cell handovers + Inter BSC incoming cell handovers + Outgoing internal inter cell handovers + Inter BSC outgoing cell handovers) * 100%Exercise : Page 16 Exercise Write down the key items of the network Answer: The most important items for the network are: call drop rate, TCH congestion rate, SDCCH congestion rate, outgoing and incoming handover success rate, traffic volume etc.Brief Introduction to BSC Traffic Statistics Item: Page 17 Brief Introduction to BSC Traffic Statistics Item MTP Measurement Function Cell Measurement Function Power control Measurement Call Drop Measurement Site Initialization Measurement Function BSC Cell Broadcast Measurement Function BSC Measurement Function SCCP Measurement Function A-interface Operation and management statistic A-interface Equipment Maintenance statistic A-interface Trunk Board message statistic CPU Measurement FunctionBrief Introduction to BSC Traffic Statistics Item: Page 18 Brief Introduction to BSC Traffic Statistics Item Defined Adjacent Cell Measurement Function Receiving Quality Measurement Receiving Level Measurement Function Up-Down Link Balance Measurement Function LAPD Link Measurement Function Cell Frequency Scan BTS Initial Measurement Cell Broadcast Statistic Outgoing Inter cell handover Measurement Function Incoming Inter cell handover Measurement Function Undefined Adjacent Cell Measurement Function GPRS Related Measurement FunctionSlide 19: Page 19 Chapter 1 Brief introduction to BSC traffic statistics Chapter 2 Often-used traffic statistics items analysis Chapter 3 Locate problem through traffic analysis Chapter 4 Case study for traffic statistics ContentsOften-used Traffic Statistics Items Analysis: Page 20 Often-used Traffic Statistics Items Analysis Systematical logic From whole system to specific cell Integrality Observe the change trend of the items for more than one week and the changing trend of each day. Relativity Relationship between various kinds of traffic statistics itemsOften-used Traffic Statistics Items Analysis: Page 21 Often-used Traffic Statistics Items Analysis Analysis process First we shall analyze and compare the item of BSC measurement function to have a rough idea for the whole network. During analyzing, if any important items (such as call drop rate or handover success rate) are abnormal, we shall do further detailed analysis for the corresponding items.Often-used Traffic Statistics Items Analysis: Page 22 Often-used Traffic Statistics Items Analysis Analysis process Check the cell that has abnormal items (call drop, congestion, handover failure and so on). Base on whole percentage and absolute times (call drop, congestion, handover failure and so on), decide whether some further analysis should be considered or not.Often-used Traffic Statistics Items Analysis: Page 23 Often-used Traffic Statistics Items Analysis Circuit paging (A-interface) successful rate Immediate assignment successful rate TCH call drop rate TCH and SDCCH congestion rate Handover success rate Interference bandOften-used Traffic Statistics Items Analysis: Page 24 Often-used Traffic Statistics Items Analysis Circuit paging (A-interface) success rate Relate to “ATT ”, coverage area and random access performance. Relate to the paging re-send mechanism implemented by BSS or MSC.Often-used Traffic Statistics Items Analysis: Page 25 Often-used Traffic Statistics Items Analysis Immediate assignment success rate When BTS receives a Random Access message from MS, BTS will apply a channel from BSC. If there is no channel available, BSC will send immediate assignment rejected message which indicates the failure of immediate assignment. At the same time, MS’s access will be bared for some time. The interference and collision of random access will affect immediate assignment successful rate.Often-used Traffic Statistics Items Analysis: Page 26 Often-used Traffic Statistics Items Analysis TCH call drop rate Possible causes can be TCH lost radio connections (Connection failure). TCH lost radio connections (Error indication). Ground link disconnection when TCH seized (Abis). Call drop during handoverOften-used Traffic Statistics Items Analysis: Page 27 Often-used Traffic Statistics Items Analysis TCH call drop formula and measurement point TCH Call Drop Rate = TCH Call Drop / Successful TCH Seizures (all) *100%Often-used Traffic Statistics Items Analysis: Page 28 Often-used Traffic Statistics Items Analysis RF lost rate TCH RF Lost Rate = (times of radio link disconnection when TCH seized (connection failure) + times of radio link disconnection when TCH seized (error indication)) / successful TCH seizures (all) * 100% SDCCH RF Lost Rate = (times of radio link disconnection when SDCCH seized (connection failure) + times of radio link disconnection when SDCCH seized (error indication)) / successful SDCCH seizures (all) * 100%Often-used Traffic Statistics Items Analysis: Page 29 Often-used Traffic Statistics Items Analysis TCH congestion rate (TCH overflow) It is a key item used to estimate the cell load. When the load of the cell overruns the system limitation, try to distribute some traffic to adjacent cells.Often-used Traffic Statistics Items Analysis: Page 30 Often-used Traffic Statistics Items Analysis Causes of TCH congestion ( TCH seizure failure ) Assignment failure Equipment fault Invalid ground resource Ground resource already allocated Illegal message contents Radio interface failure and return to original channel No channel availableOften-used Traffic Statistics Items Analysis: Page 31 Often-used Traffic Statistics Items Analysis TCH Congestion Rate TCH congestion rate (including handover)= (TCH seizure failures for call + TCH seizure failures for very early assignment + TCH seizure failures for intra BSC incoming cell handover (no radio resource) + TCH seizure failures for inter BSC incoming cell handover (no radio resource) ) / (attempted TCH seizures (all) + attempted TCH seizures for very early assignment + attempted TCH seizures for intraBSC incoming cell handover + attempted TCH seizures for interBSC incoming cell handover) * 100%Often-used Traffic Statistics Items Analysis: Page 32 Often-used Traffic Statistics Items Analysis SDCCH congestion rate (SDCCH overflow) SDCCH congestion rate (SDCCH overflow)= times of attempted seizures meeting an SDCCH blocked state / attempted SDCCH seizures (all) * 100%Often-used Traffic Statistics Items Analysis: Page 33 Often-used Traffic Statistics Items Analysis SDCCH congestion measurement point Attempted SDCCH seizure meeting a SDCCH blocked state is counted when there is a SDCCH seizure but no SDCCH available. Attempted SDCCH seizures (all) Receive CH_REQ and the channel type is SDCCH. Incoming interBSC inter cell handover and the handover type is SDCCH handover. Incoming intraBSC inter cell and intra-cell handover and the handover type is SDCCH handover.Often-used Traffic Statistics Items Analysis: Page 34 Often-used Traffic Statistics Items Analysis Handover measurement point For different objects such as BSC, band (900/1800), incoming/outgoing, inter-cell/intra-cell handover and so on, there are different items. By analyzing different items, the problems can be located more rapidly.Often-used Traffic Statistics Items Analysis: Page 35 Often-used Traffic Statistics Items Analysis Handover Success Rate Inter cell handover success rate= (Successful incoming internal inter cell handovers + Successful incoming interBSC inter cell handovers + Successful outgoing internal inter cell handovers + Successful outgoing interBSC inter cell handovers) / (Attempted incoming internal inter cell handovers+ Attempted incoming interBSC inter cell handovers + Attempted outgoing internal inter cell handovers + Attempted outgoing interBSC inter cell handovers) *100%Often-used Traffic Statistics Items Analysis: Page 36 Often-used Traffic Statistics Items Analysis Causes of handover Power budget Poor uplink signal quality Poor downlink signal quality Low uplink signal strength Low downlink signal strength Too large TA value Other reasons Note: Handover types and times with all adjacent cells are listed in outgoing and incoming inter cell handover measurement function.Often-used Traffic Statistics Items Analysis: Page 37 Often-used Traffic Statistics Items Analysis Handover failure reasons No available channel Illegal frequency Timer timeout Illegal channel Illegal TA Other reasonsOften-used Traffic Statistics Items Analysis: Page 38 Often-used Traffic Statistics Items Analysis TCH interference band measurement The result in each TCH interference band shows the average number of idle TCH within this interference band in the statistic period, which reflects the average interference level. In urban and suburb area, because of different density of base station and the frequency reuse pattern, the acceptable interference level is different.Often-used Traffic Statistics Items Analysis: Page 39 Often-used Traffic Statistics Items Analysis Cell frequency scan Shows the signal strength received by main antenna and diversity antenna. Reflects the interference level for specific frequency. The difference between the measurement results of main and diversity antenna reflects the difference between the two antennas such as direction, gain, path loss and so on. It is an important way to know the diversity receiving performance.Often-used Traffic Statistics Items Analysis: Page 40 Often-used Traffic Statistics Items Analysis Receiving level measurement Receiving level measurement is based on TRX. The receiving level is divided into 6 bands Band 0 : -110~-100dBm Band1 : -100~-95dBm Band 2 : -95~-90dBm Band 3 : -90~-80dBm Band 4 : -80~-70dBm Band 5 : > -70dBmExercise: Page 41 Exercise List the often-used traffic statistics tasks that we use to locate and analyze the problem. Answer: the often-used traffic statistics tasks are BSC measurement function TCH and SDCCH measurement function Inter-cell and intra-cell handover measurement function Outgoing and incoming inter cell handover measurement function Up-down link balance measurement function Call drop measurement function Cell frequency scan, etc.Slide 42: Page 42 Chapter 1 Brief introduction to BSC traffic statistics Chapter 2 Often-used traffic statistics items analysis Chapter 3 Locate problem through traffic analysis Chapter 4 Case study for traffic statistics ContentsTraffic Statistics Analysis: Page 43 BSC Measurement Function High call drop rate High congestion rate Low handover success rate TCH performance Call drops SDCCH performance Link balance Outgoing handover Alarm data Alarm data TCH performance TCH performance Incoming handover Link balance Link Balance Alarm data Traffic Statistics Analysis General method for traffic analysisTraffic Statistics Analysis: Page 44 Traffic Statistics Analysis Combine traffic statistics analysis with other optimization method Drive test: simulate common subscriber’s behavior. Analyze objects Coverage Quality Handover Signaling OthersTraffic Statistics Analysis-TCH Call Drop: Page 45 Traffic Statistics Analysis-TCH Call Drop TCH call drop analysis Cell with high call drop rate Cell performance statistics Call drop times Interference band Causes of call drop Call drop measurement Average uplink level at TCH call drops Average down link level at TCH call drop Average downlink quality at TCH call drop Handover measurement Outgoing inter cell handover success rate Incoming inter cell handover success rate Handover failure and re-establish failure Alarm and hardware fault Average TA value at TCH call drop Average uplink quality at TCH call dropTraffic Statistics Analysis-TCH Call Drop: Page 46 Traffic Statistics Analysis-TCH Call Drop Call drop types Edge call drop: low receiving signaling strength, large TA. Short distance call drop: low receiving signal strength and small TA. BQ call drop: high receiving signal strength and poor quality. Sudden call drop: before call drop, the call is normal then call drop happened suddenly.Traffic Statistics Analysis-TCH Call Drop: Page 47 Traffic Statistics Analysis-TCH Call Drop Edge call drop Causes MS is out of cell’s effective coverage area. “Island” phenomenon caused by over shooting or missing neighbor. Isolated site. Solutions Add new site to guarantee the effective continuous coverage. Add the necessary neighbor. Adjust antenna height and antenna downtilt, use high gain antenna Modify some parameters: “SACCH multi-frames”, “Radio link timeout counter”, “handover threshold”, “handover statistic time”, etc..Traffic Statistics Analysis-TCH Call Drop: Page 48 Traffic Statistics Analysis-TCH Call Drop Short distance call drop Causes Poor coverage caused by complicated terrain or high dense building. Solutions Increase EIRP. Adjust antenna direction and downtilt, make the main lobe point to high traffic area. Adjust parameters related to call drop.Traffic Statistics Analysis-TCH Call Drop: Page 49 Traffic Statistics Analysis-TCH Call Drop BQ call drop( high signal strength) Causes High transmission bit error rate (BER). Uplink or downlink interference. Interference caused by repeater. Interference caused by radar or other similar equipment. Interference caused by improper frequency planning. Self-interference caused by BTS. Solutions Try to find the external interference source. Optimize frequency planning. Adjust antenna system, avoid “island”. Solve the problem of transmission quality.Traffic Statistics Analysis-TCH Call Drop: Page 50 Traffic Statistics Analysis-TCH Call Drop Overall process for call drop analysis Find out cells with high call drop rate. Classify the call drop according to the character. Analyze the cells’ traffic load and total call drop times. Analyze the call drop measurement function. Check the interference band. First of all, we shall know the type of the call drop.Traffic Statistics Analysis-TCH Call Drop: Page 51 Traffic Statistics Analysis-TCH Call Drop The main causes for call drop Interference (internal and external). Poor coverage (coverage hole and island). Improper handover (neighbor planning and handover parameter setting). Unbalanced up-down link (TMA, power amplifier, antenna direction). Improper parameter settings ( RLT and SACCH multi-frames). Equipment problem (TRX, power amplifier, and TMA).Traffic Statistics Analysis-TCH Call Drop: Page 52 Traffic Statistics Analysis-TCH Call Drop Interference analysis process Analyze the appearance period of the interference. Block TRX in turn and monitor the interference measurement results. Calculate the handover caused by poor quality and check the average receiving quality level for each TRX. In call drop measurement function, check the average signal strength and quality of call drops. Through drive test, check the interference and signal quality. Use spectrum analyzer to find the interference source. Dispose equipment fault (such as: TRX self-oscillation, antenna inter-modulation).Traffic Statistics Analysis-TCH Call Drop: Page 53 Traffic Statistics Analysis-TCH Call Drop Coverage problem analysis Traffic items In power control measurement function, the average uplink or downlink signal strength is too low. In receiving level measurement function, a lot of low signal strength records can be found. In inter-cell handover measurement function, the average receiving signal strength is too low when handover is triggered. In call drop measurement, the signal strength is too low when call drop happens, or the TA value is abnormal. In undefined adjacent cell measurement function, the potential neighbor cells with high average signal strength can be find.Traffic Statistics Analysis-TCH Call Drop: Page 54 Traffic Statistics Analysis-TCH Call Drop Coverage problem analysis Judgment method In Power Control measurement Check whether the average distance between MS and BTS comply with design. Check whether the maximum distance between MS and BTS is abnormal in several continuous periods. In outgoing inter-cell handover measurement function check whether the handover successful rate to some cells is low. check the number of unsuccessful handover with unsuccessful reversion (call drop caused by handover).Traffic Statistics Analysis-TCH Call Drop: Page 55 Traffic Statistics Analysis-TCH Call Drop Coverage problem analysis Disposing method Drive test in the suspected poor coverage area. Adjust the following parameters based on the drive test results BTS transmitting power Antenna downtilt and height RXLEVEL_ACCESS_MIN Add site to ensure the continuous coverage.Traffic Statistics Analysis-TCH Call Drop: Page 56 Traffic Statistics Analysis-TCH Call Drop Improper handover (neighbor planning and handover parameters ） Disposing method Check the handover parameters to see whether there are improper parameter settings. In inter-cell handover measurement function, check whether there are many unsuccessful outgoing cell handovers with unsuccessful reversions. In undefined adjacent cell measurement function, check whether the signal strength and the number of measurement reports for the undefined neighbor cell are high.Traffic Statistics Analysis-TCH Call Drop: Page 57 Traffic Statistics Analysis-TCH Call Drop Imbalanced up-down link (tower amplifier, power amplifier, and antenna directions) Disposing method Analyze “up-down link balance measurement function” statistics result and confirm whether the uplink and downlink are balanced. In call drop measurement function, analyze the average receiving signal strength and quality for both the uplink and downlink. In power control measurement function, analyze the average receiving signal strength for both the uplink and downlink.Traffic Statistics Analysis-TCH Call Drop: Page 58 Traffic Statistics Analysis-TCH Call Drop Balance between uplink and downlink Let D= (downlink receiving level − uplink receiving level) − (MS sensitivity − BTS sensitivity). Usually the MS sensitivity is -102 dBm and the BTS sensitivity is -108dBm. The formula can be simplified as D= downlink receiving level − uplink receiving level – 6dB If D=0, it means uplink and downlink are balanced If D>0, it means downlink is better than uplink If D<0, it means uplink is better than downlink Link balance rank Range of D 1 ≤ -15 2 -14 ~ -10 3 -9 ~ -6 4 -5 ~ -3 5 -2 ~ 0 6 0 7 1 ~ 2 8 3 ~ 5 9 6 ~ 9 10 10 ~ 14 11 ≥15Traffic Statistics Analysis-TCH Call Drop: Page 59 Traffic Statistics Analysis-TCH Call Drop Improper radio parameter setting (Radio Link timeout, SACCH multi-frames) Judgment method In system information data, check the radio link timeout In cell property data, check SACCH multi-frames, and the timer for radio link connection (T3105).Traffic Statistics Analysis-TCH Call Drop: Page 60 Traffic Statistics Analysis-TCH Call Drop Equipment problem (TRX, power amplifier, tower amplifier, etc.) Judgment method In TCH measure function, many TCH seizure failures due to A interface problem. In call drop measurement function, there are many call drops due to ground links. In TCH measurement function, there are many TCH seizure failures due to equipment failure. Disposing method Monitor transmission and board alarms (FTC board failure, A interface PCM synchronization alarm, LAPD link disconnected, TRX alarm); analyze whether transmission is disconnected or some boards are faulty.Traffic Statistics Analysis-SDCCH Call Drop: Page 61 Traffic Statistics Analysis-SDCCH Call Drop SDCCH call drop Refer to TCH call drop analysis. The cause and mechanism of SDCCH call drop are almost the same as TCH.Traffic Statistics Analysis-Handover: Page 62 Low Handover Success Rate Handover Measurement Function Alarm (Clock), Hardware Fault TCH Measurement Function Outgoing Inter Cell Failure Incoming Inter Cell Failure Outgoing Inter cell Handover Measurement Function Incoming Inter cell Handover Measurement Function Cause of Failure in BSC 1.Illegal Channels 2.Illegal Carrier 3.Illegal TA 4.Timer out 5.No available channel 6.Others Traffic Statistics Analysis-Handover Handover analysisTraffic Statistics Analysis-Handover: Page 63 Traffic Statistics Analysis-Handover Handover failure analysis Causes of handover failure Improper handover parameters. Hardware fault (TRX board fault). Congestion Interference Coverage Clock fault (Internal clock, external clock)Traffic Statistics Analysis-Handover: Page 64 Traffic Statistics Analysis-Handover Handover failure analysis Disposing method Find out the cells with low handover success rate. Find the out the cells with high handover failures. Compare the incoming cell handover failures and outgoing cell handover failures. Register the task to measure the incoming cell handover and outgoing cell handover. Find out handover failure relation (failure to all the neighbor cells or part of the neighbor cells).Traffic Statistics Analysis-Handover: Page 65 Traffic Statistics Analysis-Handover Improper parameter settings Disposing method Check whether the handover threshold such as TA, BQ and handover function switch are suitable or not. Check whether the successful TCH seizures for handover are much more than successful TCH seizures for call. If handover times divided by call times is larger than 3, then it indicates that there may be ping-pong handover. Check the parameter settings and adjust them (layer setting, layer handover hysteresis, inter cell handover hysteresis, PBGT threshold, etc.). Check whether the average signal strength is low when the handover happens. If so, it indicates the edge handover threshold is too low.Traffic Statistics Analysis-Handover: Page 66 Traffic Statistics Analysis-Handover Hardware fault Problem description The target cell has idle channels but when applying for the channels CH_ACT_NACK or TIMEOUT message appears. TCH availability is abnormal. If the call drop rate and congestion rate are both high, the equipment may have some fault.Traffic Statistics Analysis-Handover: Page 67 Traffic Statistics Analysis-Handover Hardware fault Disposing process Monitor transmission and board alarms (FTC board failure, A interface PCM sync alarm, LAPD link disconnected, TRX alarm). Analyze whether the transmission is disconnected or the boards have some fault (for example: the TRX is damaged). Check whether there is clock alarm.Traffic Statistics Analysis-Handover: Page 68 Traffic Statistics Analysis-Handover Congestion Objects needed to be analyzed Cells with low incoming handover success rate. Neighbor of the cell with low incoming handover success rate. Locating the problem In incoming inter cell handover measurement function, check whether many handover failures are caused by congestion. For low incoming handover success rate, check the cell’s traffic . For low outgoing handover success rate, check the neighbor cell’s traffic.Traffic Statistics Analysis-Handover: Page 69 Traffic Statistics Analysis-Handover Congestion Disposing process Adjust the cell’s coverage (adjust BTS transmitting power, RXLEVEL_ACCESS_MIN, RACH access threshold, and the antenna downtilt and height). Adjust parameters (CRO, load handover parameters, cell priority and handover parameters). Expand or adjust TRX configuration between high and low traffic cells.Question: Page 70 Question The item “radio handover success rate” is the ratio of successful handovers to handovers. The handovers are counted when sending or receiving HO_CMD or HO_REQ_RSP in the handover process. Please write down the possible reasons that can cause the low radio handover success rate between BSCs.Answer: Page 71 Answer There are two kinds of outgoing handovers. One is intra-BSC handover, and the other is inter-BSC handover. The possible reasons are list as following. For inter-BSC handover: If the uplink signal strength of the target cell is low, the MS cannot access the target cell. Thus the handover fails If the target cell is a wrong cell which has the same BCCH and BSIC as the expected target cell, MS will send access request to a wrong cell. Then MS cannot access. Thus the handover fails. If the CGI is wrong, MSC will send the handover request with wrong CGI. Then MS will send access request to a wrong cell. It has the same effect as the above one.Traffic Statistics Analysis-TCH Congestion: Page 72 Traffic Statistics Analysis-TCH Congestion TCH congestion Main causes Insufficient system capacity Interference Coverage Antenna and feeder problems Improper parameter setting (system information parameters)Traffic Statistics Analysis-TCH Congestion: Page 73 Traffic Statistics Analysis-TCH Congestion Insufficient system capacity or traffic imbalanced Judgment method The traffic is high and is imbalanced between cells. There are many channel request rejections due to channel busy. Incoming handover measurement shows that there are too many unsuccessful incoming cell handovers (congestion). Disposing process Expand or adjust the configuration between high and low traffic cells Adjust coverage (adjust BTS transmitting power, antenna direction, downtilt, height, etc.). Adjust parameters (CRO, Rx_Lev_Access_Min, load handover parameters, cell priorities, handover parameters).Traffic Statistics Analysis-TCH Congestion: Page 74 Traffic Statistics Analysis-TCH Congestion Interference (external and internal interference) Problem description Interference brings unacceptable BER which affects the assignment process. Downlink Interference makes MS’s DSC decrease to 0, then MS reselects to another cell with low signal strength, and this is a potential reason for TCH seizure failure. If TCH seizure failures (including handover) minus attempted TCH seizures meeting TCH overflow is large, then there may be some interference. Disposing process Refer to TCH call drop caused by interference.Traffic Statistics Analysis-TCH Congestion: Page 75 Traffic Statistics Analysis-TCH Congestion Antenna and feeder problem Disposing process In cell frequency scan measurement function, check the measurement results got from main receiving antenna and diversity receiving antenna. In Up-down link balance measurement function, check the measurement report numbers in each rank. Check antenna direction, downtilt and connection.Traffic Statistics Analysis-TCH Congestion: Page 76 Traffic Statistics Analysis-TCH Congestion Improper parameter settings Check the relevant parameters such as RXLEV_ACCESS_MIN, CRO, BTS transmitting power, handover threshold etc..Traffic Statistics Analysis-TCH Congestion: Page 77 Traffic Statistics Analysis-TCH Congestion Coverage Refer to coverage analysis for TCH call drop rate.Traffic Statistics Analysis-SDCCH Congestion: Page 78 Traffic Statistics Analysis-SDCCH Congestion SDCCH congestion Main causes Improper parameter settings (system information) Insufficient system capacity Improper LAC planning InterferenceTraffic Statistics Analysis-SDCCH Congestion: Page 79 Traffic Statistics Analysis-SDCCH Congestion Improper parameter settings Judgment method Successful immediate assignments / immediate assignment transmissions >85%. The above formula shows the ratio between number of EST_IND messages that MS sends to BSC and the immediate assignment commands that BSC sends to BTS. It indicate whether there are some improper parameters in the system information. Disposing process Adjust the access parameters (Random access error threshold, RACH minimum access level, MS Max Retrans, Tx-integer). Adjust the location update related parameters (dual-band network parameters such as CRO, cell reselection hysteresis, T3212).Traffic Statistics Analysis-SDCCH Congestion: Page 80 Traffic Statistics Analysis-SDCCH Congestion Insufficient system capacity Problem description Many location updates happen at the border of different location areas. Massive location updates happen simultaneously. Disposing method Properly plan the location area Configure more SDCCHs Use SDCCH dynamic allocation Add more TRXTraffic Statistics Analysis-SDCCH Congestion: Page 81 Traffic Statistics Analysis-SDCCH Congestion Improper LAC planning The border of different location area is the street. The border of different location area is at the high traffic area.Traffic Statistics Analysis-SDCCH Congestion: Page 82 Traffic Statistics Analysis-SDCCH Congestion Interference Problem description RACH minimum access level is low. Interference in the system, which will bring a lot of illusory SDCCH channel requests. Disposing process Properly set the RACH minimum access level Eliminate the interferenceSlide 83: Page 83 Chapter 1 Brief introduction to BSC traffic statistics Chapter 2 Often-used traffic statistics items analysis Chapter 3 Locate problem through traffic analysis Chapter 4 Case study for traffic statistics ContentsCase Study-One (Handover): Page 84 Case Study-One (Handover) Problem description Handover success rate is always very low because of the congestion (about 70%) In the evening of 3rd. Dec, site D located in urban is expanded from “S2/2/2” to “S3/3/3”. The busy hour handover success rate does not get improved after expansion. Sometimes handover success rate is lower than before. At the same time, lots of subscribers complain about the network quality. Refer to busy hour traffic statistics of 3rd. Dec.Case Study-One (Handover): Page 85 Case Study-One (Handover) Cell Handover success rate Radio handover success rate Intra-BSC incoming handover failures (no channel available) Intra-BSC incoming handover failures (others) TCH congestion D_1 53.41% 90.02% 397 18 47.53% D_2 49.82% 93.98% 389 2 67.23% D_3 57.67% 90.06% 314 51 48.31% C_3 61.25% 91.67% 502 25 40.61% A_2 78.40% 89.07% 0 33 0 A_3 77.14% 93.80% 0 20 0 F_2 76.36% 76.36% 0 12 0 E_1 66.22% 88.10% 26 63 5.33% E_2 92.73% 94.44% 0 2 0 E_3 83.25% 91.91% 0 6 0 B_3 83.48% 95.53% 0 5 0.75% Traffic statistics for 24th.NovCase Study-One (Handover): Page 86 Case Study-One (Handover) Cell Handover success rate Radio handover success rate Intra-BSC incoming handover failures (no channel available) Intra-BSC incoming handover failures (others) TCH congestion D_1 49.75% 52.95% 17 246 5.27% D_2 56.48% 58.56% 1 161 0.58% D_3 65.92% 66.08% 0 86 22.37% C_3 60.58% 66.3% 113 166 0.00% A_2 70.55% 71.71% 0 0 1.06% A_3 68.02% 68.95% 0 0 0.00% F_2 60.61% 60.61% 0 13 0.56% E_1 63% 64.08% 1 55 0.00% E_2 61.77% 62.69% 0 20 0.00% E_3 50.3% 50.3% 0 0 0.00% B_3 78.60% 82.45% 0 11 0.34% Traffic statistics for 13th.DecCase Study-One (Handover): Page 87 Case Study-One (Handover) Site locationCase Study-One (Handover): Page 88 Case Study-One (Handover) Analysis Analyzing the traffic statistics before expansion and after expansion, we find that before the expansion the handover failure is caused by congestion and the radio handover success rate is normal. In Urban area many cells’ radio handover success rate decreased after expansion, therefore we conclude that the cause of handover failure after expansion has been changed. Analyzing the urban site location diagram, we find lots of cells’ radio handover success rate are low and these cells have handover relationship with site D. Therefore we can suspect that the handover problem may be caused by site D.Case Study-One (Handover): Page 89 Case Study-One (Handover) Analysis After checking the hardware of site D through maintenance console, we find the state of TMU board is abnormal and clock is unstable. Finally we affirm the low handover success rate is caused by the wrong setting of switches in TMU board. For sure, the high call drop rate is caused by handover failures. The day after processing, the busy hour handover success rate is higher than 90%. Thus the problem is solved. Refer to busy hour traffic statistics of 17th. Dec.Case Study-One (Handover): Page 90 Case Study-One (Handover) Cell Handover success rate Radio handover success rate Intra-BSC incoming handover failures (no channel available) Intra-BSC incoming handover failures (others) TCH congestion D_1 86.58% 95.90% 47 10 13.00% D_2 93.09% 96.88% 10 15 3.40% D_3 95.57% 96.79% 0 10 0.00% C_3 86.84% 95.94% 80 7 18.26% A_2 88.43% 91.51% 1 21 0.48% A_3 92.56% 94.12% 0 6 0.00% F_2 98.47% 89.47% 0 1 0.00% E_1 93.69% 95.59% 1 6 1.44% E_2 93.55% 93.55% 0 2 0.00% E_3 97.40% 97.45% 0 1 0.00% B_3 91.80% 96.89% 10 1 7.92% Traffic statistics for 17th.DecCase Study-One (Handover): Page 91 Case Study-One (Handover) Conclusion and suggestion Pay attention to the difference between radio handover success rate and handover success rate because it can help us to locate handover problem efficiently. Handover problem sometimes is accompanied with call drops and others; it is an important clew for locating and solving problems.Case Study-Two (Call drop): Page 92 Case Study-Two (Call drop) Fault description When we analyze the traffic statistics, we find that a cell’s call drop rate in busy hour is large than 2%. In cell call drop measurement function, we find that the average uplink level of call drop is 1 (-109dBm), while the downlink level is 26 (-84dbm). High call drop rate is caused by imbalance between uplink and downlink. In up-down link balance measurement function: we find one TRX is normal, but there may be some problem with the other one. Result of rank 1 is 0, while that of rank 11 is 5833. It means the downlink is better than uplink.Case Study-Two (Call drop): Page 93 Case Study-Two (Call drop) Analysis We can exclude the problem of antenna and feeder because only one of the two TRXs is abnormal. Therefore we think that the problem may be caused by the uplink channel of TRX or CDU. After we change the CDU, the problem is solved.Case Study-Two (Call drop): Page 94 Case Study-Two (Call drop) Conclusion and suggestion To find the cause of call drop, we should register the following useful traffic statistics: TCH measurement function Call drop measurement function Inter cell handover measurement function Up-down link balance measurement function By analyzing the result of the above traffic statistics, we can locate the cause of the call drop (handover, interference, coverage etc.) and then register more detailed traffic measurement tasks. DT also is a effective method to find call drop problem.Case Study-three (SDCCH congestion): Page 95 Case Study-three (SDCCH congestion) Fault description In the network, the radio link connection success rate is low. After analyzing the traffic statistics, we find that it caused by SDCCH congestion and the congestion only exists in a few sites. Analyzing traffic statistics we find that in the congested cell, attempted SDCCH seizures are from 300 to 400 in a certain hour. The configuration of all the related BTSs is S1/1/1. Each cell has one SDCCH/8 channel. Normally, it can deal with 300-400 SDCCH seizures. But it is very strange that there are dozens of SDCCH congestions in busy hour.Case Study-three (SDCCH congestion): Page 96 Case Study-three (SDCCH congestion) Analysis Register “SDCCH measurement function” and analyze the result. We find that most of the SDCCH seizures are used for location update. After we analyze the site distribution, we find that the congested BTSs are located at the border of two location areas along the railway. So we can conclude that SDCCH congestion shall be caused by massive location updates. In SDCCH measurement function, we find that most of the location update happened in a specific 5 minutes. After checking the train timetable, we find that 4 or 5 trains passed by in this period. When the trains pass by, a large amount of location updates happen simultaneously. After adding more fixed SDCCHs and switching on “Dynamic SDCCH allocation” function, the problem is solved.Case Study-three (SDCCH blocking): Page 97 Case Study-three (SDCCH blocking) Conclusion and suggestion For SDCCH congestion, firstly we should register SDCCH measurement function, and then analyze the traffic statistics to find the cause of the problem (Location update, SDCCH handover, call setup etc.). Then check the parameter settings, interference, location area planning etc., to do further analysis. Adding SDCCH channels or enabling dynamic SDCCH allocation function can solve the congestion caused by insufficient capacity. Set the parameter and plan the location area properly to decrease the SDCCH congestion.Summary: Page 98 Summary Traffic statistics system basics Key traffic measurement items Traffic statistics analysis method Some cases Summary