og 205 traffic statistics analysis issue2.0

OMD6010 Traffic statistics analysis ISSUE1.131033203-BSS Troubleshooting Manual
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 system
HUAWEI TECHNOLOGIES CO., LTD.
Chapter 2 Often-used traffic statistics items analysis
Chapter 3 Locate problem through traffic analysis
Chapter 4 Case study for traffic statistics
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Traffic statistic is registered on OMC through background WS, runs at the host (MPU of BSC) and is read through the background WS. Due to the limitation of the host’s memory, the number of simultaneously running traffic measurement tasks are restricted. Similarly, due to the limitation of the communication bandwidth between foreground and background, it is suggested to get the traffic statistics result 10 minutes after the traffic statistics cycle.
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
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Template management
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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.
TCH Congestion Rate
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TCH Blocking Rate is one of the key items. In the formula, the numerator is the TCH seizure failures. There are two cases: Including and excluding handover.
TCH Seizure Failures are all of the seizure failures due to no available TCH channel and queue timeout after the SDCCH is allocated. It equals to “Assignment Failure (no radio resource available) Clear Request (no radio resource available) ”.
TCH Congestion Rate
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TCH Congestion Rate
TCH congestion rate (TCH overflow) = Attempted TCH seizures meeting a TCH blocked state / Attempted TCH seizures (all) * 100%
SDCCH congestion rate (SDCCH overflow)
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the measurement point of SDCCH congestion is attempted SDCCH seizure meeting a SDCCH blocked state, not simply SDCCH seizure failure.
TCH Call Drop Rate
TCH Call Drop Rate = TCH Call Drops / Successful TCH Seizures (all) *100%
SDCCH Call Drop Rate
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TCH call drop can be divided into three categories in more details. Understanding the difference of each category will be of great help for the further analysis of different TCH call drop reasons.
Main reason for TCH call drop:
TCH lost radio connections (connection failure)
TCH lost radio connections (error indication)
Ground link disconnection when TCH seized (Abis problem)
The definition of SDCCH call drop rate is almost the same as TCH call drop rate
Main reason for SDCCH call drop:
SDCCH lost radio connections (connection failure)
SDCCH lost radio connections (error indication)
Ground link disconnected when SDCCH seized (Abis problem)
Handover Success Rate
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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.
MTP Measurement Function
Cell Measurement Function
Power control Measurement
Call Drop Measurement
BSC Measurement Function
SCCP Measurement Function
A-interface Equipment Maintenance statistic
CPU Measurement Function
Huawei BSC traffic statistics consists of all the following measurement function.
BSC measurement function contains BSC overall running counters. This measurement result reflects the BSC running performance roughly.
Cell measurement function provides comprehensive traffic measurements about the cell including SDCCH measurement function, TCH measurement function, random access measurement function, inter-cell handover measurement function, intra-cell handover measurement function and other measurement functions. This measurement contraposes cells.
Power control measurement shows how BSC controls the power level and signal quality of the MS and BTS, which includes numbers of power control messages that BSC sends to BTS and MS, and the average signal strength and quality of uplink and downlink.
Call drop measurement function is base on the last valid measurement report of the SDCCH or TCH before call drop due to radio link problems, so it is helpful for the network operators to analyze the causes of call drop. This measurement contraposes cell.
Defined Adjacent Cell Measurement Function
Receiving Quality Measurement
LAPD Link Measurement Function
Undefined Adjacent Cell Measurement Function
GPRS Related Measurement Function
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Outgoing inter cell handover measurement function can be registered successfully only when the adjacent cells are defined. It is used to measure the details of intra-BSC and inter-BSC handovers,n including handover requests, successful handovers and unsuccessful handovers due to various handover cause..
Incoming inter cell handover measurement function is used to measure the detail of incoming handover from other adjacent cell to target cell, including handover requests, successful handovers and unsuccessful handovers due to congestion.
Undefined adjacent cell measurement function is used to measure the cells reported by MS which have not been defined in the cell adjacent relation table. The measurement includes BCCH, BSIC, average signal strength of undefined adjacent cells.
Up-Downlink balance measurement function is used to measure the TCH channel and the MR that BSC receives contains uplink receiving level and downlink receiving level.
Systematical logic
Integrality
Observe the change trend of the items for more than one week and the changing trend of each day.
Relativity
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From whole to specific, the problem cell can be located quickly. Observing items’ changing trend and reviewing the network operation records can be of great help for analyzing the causes of problems. Further more, items are closely related and mutually affected.
Analysis process
First we shall analyze and compare the item of BSC measurement function to have a rough idea for the whole network.
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Analysis process
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Those cells in which there are some abnormal items but small absolute times can be ignored. For example, one handover successful times among three handovers, then the handover successful rate is 33%. On the other hand, more attention shall be paid to the cells that have low index rate but high absolute times. The problems of such cells shall be solved quickly, because they affect the performance of whole BSC more seriously. For example, during 600 handovers, there are 540 successful handovers, then the handover successful rate is 90%. It is not very low. But 60 times of handover failure will bring much affect to the whole network.
Immediate assignment successful rate
TCH call drop rate
Handover success rate
Relate to , coverage area and random access performance.
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When the MS receives a paging message, it will access the network. When BSC receives the paging response message including the IMSI, it will take that the paging is successful. So, if the paging re-send mechanism is implemented at BSC, the paging successful rate will be better.
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.
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Excellent access performance is related to CCCH combination and Tx-integer setting. In addition, AGCH may also be the bottleneck of the system.
TCH call drop rate
Possible causes can be
Ground link disconnection when TCH seized (Abis).
Call drop during handover
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Analyze the main reason of call drop then do further analysis according to different causes.
TCH call drop formula and measurement point
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The current seized channel is TCH.
1, When ERR_IND message is received and it’s not in a handover process. Besides, the connection to the MS has been set up.
2, A call is cleared because the occupied resources are no longer unavailable ((BLOCKED or DISABLED).
3, A call is cleared because resource check fails.
4, The contents of the HO_DETECT message of incoming inter BSC handover is invalid.
5, The contents of the HO_CMP_UM message of incoming inter BSC handover is invalid.
6, Failed to send the HO_CMP message.
7, Timer waiting for HO_DETECT or HO_CMP message in incoming inter BSC handover times out.
8, Intra cell handover failed, or the timer waiting for HO_CMP message in outgoing intra BSC handover timeouts.
9, Timer waiting for HO_SUCCESS message in outgoing inter BSC handover times out.
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%
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The RF lost rate reflects the call drop rate due to the Um interface. Compared with call drop rate, the factor of ground link disconnection during assignment is ignored in the definition. The call drop rate minus the RF loss rate is the call drop rate caused by the ground link.
Often-used Traffic Statistics Items Analysis
TCH congestion rate (TCH overflow)
It is a key item used to estimate the cell load.
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Compare the traffic load of each cell to see whether the traffic load is much more different with each other .
Causes of TCH congestion ( TCH seizure failure )
Assignment failure
Equipment fault
No channel available
Detailed causes of seizure failure:
Ground resources are unavailable, such as circuit fault and CIC error.
Invalid message contents: some content in the assignment command is invalid.
Assignment failure: assignment failure due to some causes, such as interference or serious unbalanced link.
TCH Congestion Rate
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TCH seizure failure:
1. CH_ACT_NACK has been received and the channel type is TCH.
2. When the timer waiting for CH_ACT_ACK message times out.
3. When channel allocation failed after the CH_REQ message is received.
4. TCH seizure failure for very early assignment.
Often-used Traffic Statistics Items Analysis
SDCCH congestion rate (SDCCH overflow)
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Too many location updates is a main cause of SDCCH congestion. Modify parameters and add more SDCCH are reasonable solutions.
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.
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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.
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Successful incoming internal inter cell handovers measurement point:
1) Measured when the target cell (current cell) sends ASSIGNMENT COMPLETE to MSC after the MS has been successfully handed over to the target cell in the internal intercell handover (handover cause: directed retry).
2) Measured when the target cell (current cell) sends a HANDOVER PERFORMED message to MSC after the MS has been successfully handed over to the target cell in the internal intercell handover (handover cause: non-directed retry, e.g. signal quality, signal strength, TA, traffic load, rapid rxlevel drop, better cell, Response to MSC invocation, and O&M intervention).
Successful incoming interBSC inter cell handovers measurement point:
During the procedure of interBSC handover, the target (current) cell receives HANDOVER COMPLETE, and sends it to MSC.
Successful outgoing internal inter cell handovers measurement point:
During the procedure of internal intercell handover, the source cell (current cell) receives Inter Clear Request (cause: internal intercell handover succeeded) from the target cell.
Successful outgoing interBSC inter cell handovers measurement point:
During the procedure of interBSC handover, the source cell (current cell) receives the CLEAR COMMAND message (cause: handover success) from MSC.
Causes of handover
Other reasons
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In a normal network, more than 50% of the handovers shall be PBGT handover. If the proportion of a certain kind of handover (exclude PBGT handover) is too large, the network maybe has some problems such as equipment fault, interference, incomplete adjacent cells or improper parameter settings, etc..
PBGT handover: Power Budget handover, based on path loss.
Poor uplink or downlink signal quality: handover caused by that the uplink or downlink signal quality is lower than the threshold. It is emergency handover.
Low uplink or downlink signal strength: handover caused by that the uplink or downlink signal strength is lower than the edge handover threshold. It is edge handover.
Too large TA value: handover caused by that TA value is larger than the threshold.
Handover failure reasons
No available channel
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Those items show the causes of handover failure so that the problem can be found quickly.
No available channel: there is no channel available for the incoming handover.
Illegal frequency: the frequency include in the handover command is incorrect or erroneously coded.
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.
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BTS measures, calculates and reports the interference of the idle TCH channels. It is used by BSC as a criterion to allocate the channel. Interference is divided into six bands artificially according to the strength. The level used to classify the interference band is called interference band threshold. BTS uses this interference band threshold to know the level of the current signal’s interference strength and reports it to BSC through radio resources indication message. BSC will decide whether handover is necessary or not by comparing busy channels’ and idle channels’ resources included in radio resources indication message and measurement report. The interference measurement result can be used as a criterion to set the interference band threshold and analyze the interference. For more details please refer to protocols 0808, 0858, and 1221.
Default values:
Cell frequency scan
Shows the signal strength received by main antenna and diversity antenna.
Reflects the interference level for specific frequency.
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By comparing the receiving strength of the main antenna and diversity antenna, we know whether the direction, downtilt and receiving path of the two antennas are the same or not. Frequency scanning is an effective way for judging whether there is interference on specific frequency or not. This function can only be used for idle channels.
Receiving level measurement
The receiving level is divided into 6 bands
Band 0 : -110~-100dBm
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If there are excessive measurement reports with high level but poor quality, it indicates that there is interference existing in the system. This shall be confirmed through the analysis of interference band in TCH measurement function, drive test or frequency scan. This measurement type is implemented on TRX basis.
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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
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.
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In practice, the above graph can be used flexibly. With other features of the network, problems can be located quickly.
Drive test: simulate common subscriber’s behavior.
Analyze objects
TCH call drop analysis
Call drop measurement
TCH call drop
Average downlink quality
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.
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Respectively check relevant traffic statistics results according to the character of the four types of call drop.
For edge call drop, consider whether the adjacent cell is added and the adjacent cell is too busy.
For short distance call drop, check whether the coverage is insufficient.
For BQ call drop, emphasize on locating and solving interference problem.
The sudden call drop occurs accidentally and maybe caused by hardware or transmission.
Edge call drop
Isolated site.
Add the necessary neighbor.
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The core solution is to have a good coverage and eliminate island and make the handover executed quickly.
Short distance call drop
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.
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Note: Short distance call drops seldom occurs. Call drops in urban areas may be caused by decreasing BTS transmitting power or increasing downtilt for reducing interference. When increasing BTS power, we shall consider the interference brought to other cells.
BQ call drop( high signal strength)
Causes
Uplink or downlink interference.
Interference caused by repeater.
Interference caused by improper frequency planning.
Self-interference caused by BTS.
Optimize frequency planning.
Solve the problem of transmission quality.
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According to different causes, adjust the frequency plan to eliminate transmission BER or eliminate the external interference source. Repeater and over shooting are the most common causes for interference.
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.
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The main causes for call drop
Interference (internal and external).
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).
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The above list are the main causes for call drop. According to each causes, check the relevant traffic measurement items and solve them one by one.
Interference analysis process
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).
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The interference band is measured by idle TCH and sent to BSC via RF resources indication message. If the number of TCHs in interference band 3, 4 and 5 is not equal to 0, it means there’s some interference in the network. The internal interference will increase in accordance with the traffic load but external interference does not have relationship with traffic load.
During the cell handover measurement, the outgoing handover attempts caused by various causes are calculated. If there are excessive handovers due to poor quality, it indicates there is some interference. If the uplink quality is bad, it indicates there is some uplink interference; if the downlink quality is bad, it indicates there is some downlink interference.
Interference can also caused by overshooting. According to the actual situation, eliminate the interference by adjusting the BTS transmitting power, antenna downtilt, adjacent cell relationship and handover parameters or adjusting the frequency plan.
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.
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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
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Adjust the following parameters based on the drive test results
BTS transmitting power
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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.
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When the handover cannot be executed normally, call drop may happen. Causes for handover failure include data mistake, handover command sent to a wrong cell (co-BCCH and co-BSIC), no channel available in the target cell, interference or the small overlapping with adjacent cells. Using traffic statistics, the causes for handover failure can be located quickly.
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.
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The basic reason for call drop due to imbalanced links is that MS makes a call in a worse cell or handover to a worse cell. Only the downlink signals of the neighbor cells are measured during the cell reselection and handover. MS does not know the details about uplink. So, if the handover occurs towards a neighbor cell with high downlink signal strength but low uplink signal strength, the call drop or handover failure caused by bad uplink will occur.
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
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The absolute value of D shows how serious the uplink and downlink are imbalanced. According to the range of D, the MRs can be sorted into different ranks, showing the up-down link balance situation. Eleven ranks are defined as shown above. The result of each rank means the number of MRs. The sum of the results of all ranks of a TRX is the total number of MRs, which can show the traffic volume of the TRX.
Improper radio parameter setting (Radio Link timeout, SACCH multi-frames)
Judgment method
In system information data, check the radio link timeout
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Increasing the radio link timeout and SACCH multi-frames can reduce the call drops . And increasing the value of radio link connection timer can also reduce the call drops.
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
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If the availability of TCH is abnormal, it indicates some timeslots have problem. Excessive call drops due to ground link disconnection indicates transmission or circuits have some problems. In this case, it is required to check the alarms and the equipments.
SDCCH call drop
Refer to TCH call drop analysis.
The cause and mechanism of SDCCH call drop are almost the same as TCH.
1.Illegal Channels
2.Illegal Carrier
3.Illegal TA
4.Timer out
Analyze the incoming and outgoing handover first,
According to the first step, analyze handover of all of the adjacent cells or of a particular adjacent cell,
Associate with TCH measurement, alarm and other factor to find out the reason.
Congestion
Interference
Coverage
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Improper handover parameters: high inter cell handover hysteresis, very low load receiving threshold, very long P/N time, etc..
Clock problem is one of the main cause for handover failure.
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).
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.).
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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.
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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.
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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 .
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Handover failure (no channel available) in the traffic measurement indicates the handover failure due to congestion of the target cell.
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).
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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.
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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.
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Judgment method
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).
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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
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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.
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MS shall not reside in the cell with low signal strength, so set the RXLEV_ACCESS_MIN to balance the traffic carefully.
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Insufficient system capacity
Improper LAC planning
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Too many location updates are the common cause for SDCCH congestion. Insufficiency of system capacity can be indicated by TCH congestion. Interference and low random access threshold will cause illusory random access request.
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).
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Appropriately increasing T and S (maximum number of extended transmission timeslots) values can be of help to reduce the collisions on the random access channel, and appropriately increasing RACH minimum access level can improve the immediate assignment success rate. In urban and countryside, RACH minimum access level should be set to difference value according to frequency reuse pattern.
Problem description
Many location updates happen at the border of different location areas.
Massive location updates happen simultaneously.
Disposing method
Configure more SDCCHs
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As a basic principle, one SDCCH channel is needed for every two TRX. If the TRX number is odd, add one more SDCCH channel. Massive location update caused by the passing of the train can only be solved by configuring more SDCCHs.
The border of different location area is the street.
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Avoid setting two location areas in the urban area of a small and medium-sized city. Location areas overlapping with each other too much are also not recommended.
RACH minimum access level is low.
Interference in the system, which will bring a lot of illusory SDCCH channel requests.
Disposing process
Eliminate the interference
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.
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Intra-BSC incoming handover failures (others)
TCH congestion
TCH congestion
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.
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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.
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TCH congestion
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.
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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.
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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.
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To find the cause of call drop, we should register the following useful traffic statistics:
TCH 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.
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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.
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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.
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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.
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og 205 traffic statistics analysis issue2.0

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