12_OMF000603 Traffic Statistics Analysis

1HUAWEI TECHNOLOGIES CO., LTD. All rights reserved

www.huawei.com

Internal

Traffic Statistics Analysis

HUAWEI TECHNOLOGIES CO., LTD. Page 2All rights reserved

Reference

z 31160978-BSC Traffic Statistic Manual Volume I

z 31033203-BSS Troubleshooting Manual

2HUAWEI TECHNOLOGIES CO., LTD. Page 3All rights reserved

z 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


ChapterChapter 1 1 Brief introduction to BSC traffic Brief introduction to BSC traffic statisticsstatistics

ChapterChapter 2 2 OftenOften--used traffic statistics items used traffic statistics items analysisanalysis

ChapterChapter 3 3 Locate problem through traffic Locate problem through traffic analysisanalysis

ChapterChapter 4 4 Case study for traffic statisticsCase study for traffic statistics


BM1

Call process data

BM data

Hardware data

Signaling data

BM

AM/CMBAM

- -WS1 WSn

M2000 ServerHUB

Main Structure of Traffic Statistics System


Menu Introduction to BSC Traffic Statistics

z Task list management

>BSC traffic statistics platform provides the function of registering a new task, deleting a registered task and refreshing the task list.

z Task management

>BSC traffic statistics platform provides the function of modifying task name, modifying statistic period of permanent task, hanging up task, activating task, queryingtask information, querying task result and querying task running state.



z Template management

>Template management provides the function of defining item template, object template, time template, user-defined statistic items and refreshing all templates.



z 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

z 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%




>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 intra-BSC incoming cell handover + attempted TCH seizures for inter-BSC incoming cell handover) * 100%




>TCH congestion rate (TCH overflow) = Attempted TCH seizures meeting a TCH blocked state / Attempted TCH seizures (all) * 100%



z SDCCH congestion rate (SDCCH overflow)

>SDCCH congestion rate (SDCCH overflow)= times of attempted seizures meeting an SDCCH blocked state / attempted SDCCH seizures (all) * 100%



z TCH Call Drop Rate

>TCH Call Drop Rate = TCH Call Drops / Successful TCH Seizures (all) *100%

z SDCCH Call Drop Rate

>SDCCH Call Drop Rate = SDCCH call drops / successful SDCCH seizures (all) *100%



z Handover Success Rate

> inter-Cell handover success rate= (Successful incoming internal inter-Cell handovers + Successful incoming inter-BSC inter-Cell handovers + Successful outgoing internal inter-Cell handovers + Successful outgoing inter-BSC inter-Cell handovers) / (Attempted incoming internal inter-Cell handovers+ Attemptedincoming inter-BSC inter-Cell handovers + Attempted outgoing internal inter-Cell handovers + Attempted outgoing inter-BSC inter-Cell handovers) *100%




> inter-Cell radio handover success rate= (Successful incoming internal inter-Cell handovers + Successful incoming inter-BSC inter-Cell handovers + Successful outgoing internal inter-Cell handovers + Successful outgoing inter-BSC inter-Cell handovers) / (Incoming internal inter-Cell handovers + incoming inter-BSC inter-Cell handovers + Outgoing internal inter-Cell handovers + outgoing inter-BSC inter-Cell handovers) * 100%




Exercise

z Write down the key items of the network

z 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.



zMTP Measurement Function

zCell Measurement Function

zPower control Measurement

zCall Drop Measurement

zSite Initialization Measurement Function

zBSC Cell Broadcast Measurement Function

zBSC Measurement Function

zSCCP Measurement Function

zA-interface Operation and management statistic

zA-interface Equipment Maintenance statistic

zA-interface Trunk Board message statistic

zCPU Measurement Function

10



zDefined Adjacent Cell Measurement Function

zReceiving Quality Measurement

zReceiving Level Measurement Function

zUp-Down Link Balance Measurement Function

zLAPD Link Measurement Function

zCell Frequency Scan

zBTS Initial Measurement

zCell Broadcast Statistic

zOutgoing inter-Cell handover Measurement Function

zIncoming inter-Cell handover Measurement Function

zUndefined Adjacent Cell Measurement Function

zGPRS Related Measurement Function






11


Often-used Traffic Statistics Items Analysis

z Systematical logic

>From whole system to specific cellz Integrality

>Observe the change trend of the items for more than one week and the changing trend of each day.

z Relativity

>Relationship between various kinds of traffic statistics items



z Analysis process

>First we shall analyze and compare the item of BSCmeasurement 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.

12



zAnalysis process

>Check the cell that has abnormal items (call drop, congestion, handover failure and so on).

>Base on whole percentage and absolute timesabsolute times(call drop, congestion, handover failure and so on), decide whether some further analysis should be considered or not.

Those cells in which there are some abnormal items butsmall absolute times can be ignored.

On the other hand, more attention shall be paid to the cells that have low index rate but high absolute times.



z Circuit paging (A-interface) successful rate

z Immediate assignment successful rate

z TCH call drop rate

z TCH and SDCCH congestion rate

z Handover success rate

z Interference band

13



z 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.



z 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, MSs access will be bared for some time.

>The interference and collision of random access will affect immediate assignment successful rate.

Excellent access performance is related to CCCH combination and TX-integer setting.

In addition, AGCH may also be the bottleneck of the system

14



z Immediate assignment success rate

> Immediate Assignment Success Ratio = (Successful Immediate Assignments / Immediate Assignment Requests) 100%

>Formula of the BSC6000 with short index names: Immediate Assignment Success Ratio = ( (A3030A + A3030B + A3030C +

A3030D + A3030E + A3030F + A3030G + A3030H + A3030I + A3030J + A3037A + A3037B + A3037C + A3037D + A3037E + A3037G + A3037H + A3037I + A3037J + A3038A + A3038C + A3038E + A3038H + A3038I + A3038J) / (A300A + A300C + A300D + A300E + A300F)) 100%

>Summary formula of the BSC6000: Immediate Assignment Success Ratio = (Call Setup Indications (Circuit

Service) / Channel Requests (Circuit Service)) 100%



z 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 handover

15



z TCH call drop formula and measurement point

>TCH Call Drop Rate = TCH Call Drops / Successful TCH Seizures (all) *100%



z RF lost rate (call drop rate due to the Um interface)

>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%

16



z Summary formula of the Call Drop Ratio on TCH (BSC6000):

>Call Drop Ratio on TCH (including handover) = Call Drops on TCH / (Successful TCH Seizures (Signaling Channel) + Successful TCH Seizures (Traffic Channel) + Successful TCH Seizures in TCH Handovers (Traffic Channel)) 100%

= CM33 / (K3023 + K3013A + K3013B) 100%

>Call Drop Ratio on TCH (excluding handover) = Call Drops on TCH / Successful TCH Seizures (Traffic Channel) 100%

= CM33 / K3013A


Baseline of Call Drop Ratio on TCH of the BSC6000

1.64%1.57%1.15%0.90%Call drop ratio on TCH(excluding handover)

0.77%0.68%0.51%0.24%Call drop ratio on TCH(including handover)

Class D Network

Class C Network

Class B Network

Class A NetworkKPI Name

17



z TCH congestion rate (TCH overflow)

> It is a key item used to estimate the cell load.>When the load of the cell overruns exceed the system

limitation, try to distribute some traffic to adjacent cells.



z 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 available

18




>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 intra-BSC incoming cell handover + attempted TCH seizures for inter-BSC incoming cell handover) * 100%



z SDCCH congestion rate (SDCCH overflow)

>SDCCH congestion rate (SDCCH overflow)= times of attempted seizures meeting an SDCCH blocked state / attempted SDCCH seizures (all) * 100%

19


Congestion Ratio on SDCCH

z Formula of the BSC6000 with short index names:

>Congestion Ratio on SDCCH (Failed SDCCH Seizures due to Busy SDCCH) = ((R3127A + H3020A + H3220A + H3420A) / (R3100A + H3000 + H3200W + H3200X + H3200Y + H3200Z + H3400W + H3400X + H3400Y + H3400Z)) 100%

z Summary formula of the BSC6000:

>Congestion Ratio on SDCCH (Failed SDCCH Seizures due to Busy SDCCH) = (Failed SDCCH Seizures due to Busy SDCCH / SDCCH Seizure Requests) 100%



9.57%0.38%0.09%0.01%Congestion ratio on SDCCH

Class D Network

Class C Network

Class B Network


20



z SDCCH congestion measurement point

>Attempted SDCCH seizure meeting a SDCCH blocked state is counted when there is a SDCCH seizure but no SDCCH available.

z Attempted SDCCH seizures (all)

>Receive CH_REQ and the channel type is SDCCH.> Incoming inter-BSC inter-Cell handover and the handover

type is SDCCH handover.

> Incoming intra-BSC inter-Cell and intra-cell handover and the handover type is SDCCH handover.



z 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.

21



z Recommended Formula

>Handover Success Ratio = Successful Handovers / Handover Requests

>Radio Handover Success Ratio = Successful Handovers / Handover Commands




> inter-Cell handover success rate= (Successful incoming internal inter-Cell handovers + Successful incoming inter-BSC inter-Cell handovers + Successful outgoing internal inter-Cell handovers + Successful outgoing inter-BSC inter-Cell handovers) / (Attempted incoming internal inter-Cell handovers+ Attempted incoming inter-BSC inter-Cell handovers + Attempted outgoing internal inter-Cell handovers + Attempted outgoing inter-BSC inter-Cell handovers) *100%

22


Summary formulas of the BSC6000 Handover Success Rate

z Handover Success Ratio = (Successful Incoming Internal Inter-Cell Handovers + Successful Outgoing External Inter-Cell Handovers) / (Incoming Internal Inter-Cell Handover Requests + Outgoing External Inter-Cell Handover Requests) 100%

z Radio Handover Success Ratio = (Successful Incoming Internal Inter-Cell Handovers + Successful Outgoing External Inter-Cell Handovers) / (Incoming Internal Inter-Cell Handover Responses + Outgoing External Inter-Cell Handover Commands) 100%

z Intra-Cell Handover Success Ratio = (Successful Intra-Cell Handovers / Intra-Cell Handover Requests) 100%

z Intra-Cell Radio Handover Success Ratio = (Successful Intra-Cell Handovers / Intra-Cell Handover Commands) 100%

z Internal Handover Success Ratio = (Successful Intra-Cell Handovers + Successful Incoming Internal Inter-Cell Handovers) / (Intra-Cell Handover Requests + Incoming Internal Inter-Cell Handover Requests) 100%


Summary formulas of the BSC6000Handover Success Rate

z Internal Radio Handover Success Ratio = (Successful Intra-Cell Handovers + Successful Incoming Internal Inter-Cell Handovers) / (Intra-Cell Handover Commands + Incoming Internal Inter-Cell Handover Responses) 100%

z Incoming BSC Handover Success Ratio = (Successful Incoming External Inter-Cell Handovers / Incoming External Inter-Cell Handover Requests) 100%

z Incoming BSC Radio Handover Success Ratio = (Successful Incoming External Inter-Cell Handovers / Incoming External Inter-Cell Handover Responses) 100%

z Outgoing BSC Handover Success Ratio = (Successful Outgoing External Inter-Cell Handovers / Outgoing External Inter-Cell Handover Requests) 100%

z Outgoing BSC Radio Handover Success Ratio = (Successful Outgoing External Inter-Cell Handovers / Outgoing External Inter-Cell Handover Commands) 100%

23



z 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

z Note: Handover types and times with all adjacent cells are listed in outgoing and incoming inter-Cell handover measurement function.



zHandover failure reasons

>No available channel >Illegal frequency>Timer timeout>Illegal channel>Illegal TA>Other reasons

24



88.84%92.54%95.00%97.03%Outgoing BSC radio handover success ratio

81.10%87.42%91.58%95.00%Outgoing BSC handover success ratio

86.01%92.45%94.34%96.83%Incoming BSC radio handover success ratio

87.05%91.94%94.44%96.30%Incoming BSC handover success ratio

93.52%94.80%96.1%97.91%Internal radio handover success ratio

85.20%92.20%95.70%97.81%Internal handover success ratio

90%95%97%98.2%Radio handover success ratio

88%92%96.91%98.11%Handover success ratio

Class D Network

Class C Network

Class B Network




z 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.

25



z 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.



z Receiving level measurement

>Receiving level measurement is based on TRX.z 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 : > -70dBm

26


Exercise

z List the often-used traffic statistics tasks that we use to locate and analyze the problem.

z 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.






27


BSC Measurement Function

High call drop rate High congestion rate Low handover success rate

TCH

performance

Call drops

SDC

CH

performance

Link balance

Outgoing handover

Alarm

data

Alarm

data

TCH

performance

TCH

performance

Incoming handover

Link balance

Link Balance

Alarm

data


General method for traffic analysis



z Combine traffic statistics analysis with other optimization method

>Drive test: simulate common subscribers behavior.z Analyze objects

>Coverage>Quality>Handover>Signaling >Others

28


Traffic Statistics Analysis-TCH Call Drop

z 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 atTCH call drop

Average downlink qualityat TCH call drop

Handovermeasurement

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 atTCH call drop

Average uplink quality atTCH call drop



z 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.

29



z Edge call drop>Causes

MS is out of cells 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..



z 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.

30



z 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.



z 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.

z First of all, we shall know the type of the call drop.

31



z 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).



z 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).

32


Traffic Statistics Analysis-TCH Call Dropz 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 Dropz 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).

33



z 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.



z 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.

34



z 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.



zBalance 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

35



z 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).



z 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 failuresdue 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 someboards are faulty.

36


Traffic Statistics Analysis-SDCCH Call Drop

SDCCH call dropSDCCH call drop

Refer to TCH call drop analysis.

The cause and mechanism of SDCCH call drop are almost the same as TCH.


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 Channels2.Illegal Carrier3.Illegal TA4.Timer out5.No available channel6.Others

Traffic Statistics Analysis-Handover

Handover analysis

37



z Handover failure analysis

>Causes of handover failure Improper handover parameters.

Hardware fault (TRX board fault).

Congestion

Interference

Coverage

Clock fault (Internal clock, external clock)



z 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).

38


Traffic Statistics Analysis-Handoverz 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.



z 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.

39



z 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.



z 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 cells traffic .

For low outgoing handover success rate, check the neighbor cells traffic.

40



z Congestion

>Disposing process Adjust the cells 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.


Traffic Statistics Analysis-TCH Congestion

z TCH congestion

>Main causes Insufficient system capacity

Interference

Coverage

Antenna and feeder problems

Improper parameter setting (system information parameters)

41



z 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).



z Interference (external and internal interference)

>Problem description Interference brings unacceptable BER which affects the

assignment process.

Downlink Interference makes MSs 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.

42



z 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.



z Improper parameter settings

>Check the relevant parameters such as RXLEV_ACCESS_MIN, CRO, BTS transmitting power, handover threshold etc..

43



z Coverage

>Refer to coverage analysis for TCH call drop rate.


Traffic Statistics Analysis-SDCCH Congestion

z SDCCH congestion

>Main causes Improper parameter settings (system information)

Insufficient system capacity

Improper LAC planning

Interference

44



z 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).



z 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 TRX

45



z Improper LAC planning

>The border of different location area is the street.>The border of different location area is at the high traffic

area.



z 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 interference

46







Case Study-One (Handover)

z 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.

47



0.75%5095.53%83.48%B_3

06091.91%83.25%E_3

02094.44%92.73%E_2

5.33%632688.10%66.22%E_1

012076.36%76.36%F_2

020093.80%77.14%A_3

033089.07%78.40%A_2

40.61%2550291.67%61.25%C_3

48.31%5131490.06%57.67%D_3

67.23%238993.98%49.82%D_2

47.53%1839790.02%53.41%D_1

TCHcongestion

Intra-BSCincoming handover failures(others)

Intra-BSCincoming handover

failures(no channel available)

Radio handoversuccess rate

Handoversuccess rateCell

Traffic statistics for 24th.Nov



0.34%11082.45%78.60%B_3

0.00%0050.3%50.3%E_3

0.00%20062.69%61.77%E_2

0.00%55164.08%63%E_1

0.56%13060.61%60.61%F_2

0.00%0068.95%68.02%A_3

1.06%0071.71%70.55%A_2

0.00%16611366.3%60.58%C_3

22.37%86066.08%65.92%D_3

0.58%161158.56%56.48%D_2

5.27%2461752.95%49.75%D_1

TCHcongestion





Handoversuccess rate

Cell

Traffic statistics for 13th.Dec

48



Site location



z 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 cellsradio 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.

49



z 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.



7.92%11096.89%91.80%B_3

0.00%1097.45%97.40%E_3

0.00%2093.55%93.55%E_2

1.44%6195.59%93.69%E_1

0.00%1089.47%98.47%F_2

0.00%6094.12%92.56%A_3

0.48%21191.51%88.43%A_2

18.26%78095.94%86.84%C_3

0.00%10096.79%95.57%D_3

3.40%151096.88%93.09%D_2

13.00%104795.90%86.58%D_1

TCHcongestion





Handoversuccess rateCell

Traffic statistics for 17th.Dec

50



z 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)

z Fault description

>When we analyze the traffic statistics, we find that a cells 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.

51



z Analysis

>We can exclude the problem of antenna and feederbecause 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.



z 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.

52


Case Study-three (SDCCH congestion)

z 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)

z 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 locationupdate 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.

53


Case Study-three (SDCCH blocking)

z 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 SDCCHallocation function can solve the congestion caused by insufficient capacity.

>Set the parameter and plan the location area properly to decrease the SDCCH congestion.


Summary

z Traffic statistics system basics

z Key traffic measurement items

z Traffic statistics analysis method

z Some cases

SummarySummary

54

www.huawei.com

Thank You

Documents

12_OMF000603 Traffic Statistics Analysis