Case Study of WCDMA Optimization

8/21/2019 Case Study of WCDMA Optimization

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Case Study of WCDMA Optimization

Performance Analysis of Nastar


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Introduction to Genex Nastar

Contents

Typical cases

Summary

Performance analysis process


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Modules of Nastar:

Performance analysis

Coverage analysis

Interference analysis

Adjacent cell analysis

Configuration analysis

Access analysis

Call drop analysis

Major Function Modules of Nastar

This training material describes some application cases of the

performance analysis part only.


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Major functions of the

performance analysis module:

Traffic statistics analysis

Performance Query

Performance Report

CHR analysis

CHR Analysis

Major Functions of Performance Analysis Module

The above functions are often used during analysis and their specific applications are described in the typical cases that will

follow. Below is a brief introduction to the operations for various functions. Please refer to the online help or relevant

operation guide of Nastar for details.

Note: The TOP N Query in the above figure is also a traffic statistics analysis function of Nastar . It can automatically

complete some sorting & analysis work, but it can only analyze cell measurement indices rather than RNC and SPU

measurement indices. This limitation makes it inconvenient to use and so we do not describe this function for the time being.

You may refer to the online help of Nastar if you are interested in it.


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Operation Overview of Performance Analysis Module

Performance Query provides flexible traffic measurement index query. Before querying traffic measurement

indices, we must first make the analysis theme (a table composed of relevant traffic measurement indices is

called an analysis theme), so as to query the traffic measurement indices accordingly.

There are some default analysis themes in Nastar, as shown in the figure on the right.

Operation overview of performance query

The default analysis themes are simple and inflexible.

Moreover, performance problems occur to a wide scope

and various features are correlated. Obviously the default

analysis themes cannot satisfy the needs of routine

problem monitoring and analysis. Therefore, the analyzer

often needs to make the analysis theme by himself/herself.

It is a basic performance analysis skill for us to master the

methods of making and querying analysis themes.


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Operation Overview of Performance Analysis Module

What follows are the specific operation steps of making and querying analysis themes (here

we takeCell TOPN monitoring as an example)

Note:A table composed of relevant traffic measurement indices is called an analysis theme.


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Operation Overview of Performance Analysis Module (Continued)

Step 1: Right clickPerformance Query and then selectNew Perf

Func, as shown in the right figure.

Step 2: SelectCELL Algorithm and Performance Measurement in the

Query Type dialog box, as shown in the right figure.


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Step 3: Input the name of the analysis theme in the Name text box

and then clickQuery List Setting, as shown in the right figure.

Step 4: Select the indices involved in the analysis theme from the

left index tree in the Query List Setting dialog box and then click

>, as shown in the right figure.


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Step 5: The Query List box shows the selected indices. Click OK,

as shown in the right figure.

Step 6: ClickUp and/orDown to adjust the sequence of the

indices displayed in the Avail Items List box (the topmost item is the

first line of data to be output) , and then click OK to finish making the

analysis theme, as shown in the right figure.


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Step 7: The Performance Query node on the navigation tree shows

the analysis theme you have just made. Double click the analysis

theme. The Query dialog box pops up, as shown in the right figure.

Step 8: Select the begin date and end date of the data to be

analyzed as well as the time granularity on the Time Range tab

page, as shown in the right figure.


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Operation Overview of Performance Analysis Module(Continued)

Step 9: Select the cell(s) to be analyzed on the Query Object tab page,

as shown in the right figure. Finally, click OK. The program will start

executing the query according to the analysis theme you have specified.

Step 10: Click theALL icon to display all the query

results. Select a certain cell in the first line and then

click theZA icon to sort the output data

according to the selected cell (or you can sort the

output data by other cells you select). Finally, click the

X icon to convert the outputs into Microsoft Office

Excel for display, as shown in the right figure. Till now,

the operation ends.


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We may combine analysis themes to form templates so as to improve the efficiency of analysis. As these

templates can be kept and transferred, repeated operations are avoided and there is great convenience in

experience accumulation and sharing. Each time you make an analysis, you just need to output reports

according to the templates you specify. This is the traffic statistic analysis mode of Performance Report.

Nastar has integrated some report templates based on experience, as shown in the following figure. It also

provides the custom report template function, that is, you can make report templates according to your own

experience. To distinguish them, here we call the integrated templates as Self-contained report templates

of Nastar and call the custom templates as Custom report templates of Nastar.

Operation overview of performance report

No matter whether it is a self-contained report template or a custom

report template of Nastar, the operation of outputting the report is

basically the same. Below we take the operation of outputting the RNC

Weekly Report as an example.

Note: Please refer to the online help or relevant operation guide of

Nastar for how to make a custom report template.


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Operation Overview of Performance AnalysisModule (Continued)

Step 1: Double click RNC Weekly Report, as shown in the right figure.

Step 2: In the dialog box that pops up, select the path to save the report,

the analyzed object and the start date and end date of the data to be

analyzed, as shown in the right figure. Finally, clickOK. The program

will immediately generate a report and the operation thus ends.


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Nastar provides the CHR analysis function, through which the other failure causes of traffic measurement

and the doubtful & exceptional traffic statistics can be further analyzed so as to obtain more detailed

failure causes and learn the detailed exceptional process.

Below is a brief description of relevant operations of CHR analysis:

Operation overview of CHR analysis


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Step 1: Double click SPU Subscribers Log Analysis, as shown

in the right figure.

Step 2: In the dialog box that pops up, select the start date and

time of the data to be analyzed, end date and time, abnormal

case, UE ID, procedure (by default all are selected) and the

analyzed object, and then click OK, as shown in the right

figure.


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Step 3: See the following figure for the CHR analysis interface. Please refer to the relevant guide, e.g.

Instructions on Use of BSC6800V100R002B03D306 Testability Log, for a detailed description and analysis

method of this interface.


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Contents

Typical cases

Summary



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Performance Analysis Process

Network-wide

KPI monitoring

Cell TOPN

monitoring

Clearly

located?

Solution

CHR

analysis

Clearly

located?

Problem location test

& signaling trace

analysis(troubleshooting)

No

Yes

Yes

No

General process of performance analysis

Cell analysis

Parameter configuration analysis


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Performance Analysis Process (Continued)

Description of the performance analysis process

Network-wide KPI monitoring: Monitor the KPIs of the entire network. Exceptions indicate that the network

has severe problems, for example, when a certain KPI in the weekly/daily report is displayed in red, it means

that index is abnormal in the entire network.

Cell TOPN monitoring: Monitor the KPI TOPN distribution of cells at the monitoring time granularity of a

matter of hours, so as to avoid the case where the performance deterioration of a certain cell in a certain time

span is concealed in space and time (thus we may avoid the situation where the KPIs of the entire network are

all normal but the performance of a certain cell in a certain time span has severely deteriorated). Besides, we

can also monitor some non-KPI metrics, e.g. uplink RTWP, cell out of service, co-channel/inter-channel/inter-

system handover preparation success rate, board CPU utilization, etc.

Cell analysis: Analyze the failure that occurred to the specific cell in the specific time and classify the failure

causes by cause analysis in the traffic statistics; analyze if the specific network conduct is abnormal or not, for

example, analyze if such network conducts as the proportion of RRC setup request types, RAB setup

distribution, RB distribution and DCCC rise/fall are abnormal or not.


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Parameter configuration analysis: Analyze if the relevant parameter configuration is abnormal or not.

CHR analysis: Further analyze the causes unknown in cell analysis, e.g. Other causes; or analyze if the

specific procedure is abnormal or not when the specific failure cause is known through cell analysis but the

correlation analysis results indicate that the cause may be wrong (possible due to statistical error or other

problems).

Problem location test and signaling trace analysis: Perform the location test on the severest cell(s), trace the

signaling of various interfaces and all the other data that may help problem analysis & location, and then

comprehensively analyze the collected data till the problem is solved. This process is called troubleshooting.

Solution: Put forward the solution.



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Mapping from the performance analysis process to

Nastar performance analysis function

Nastar flexibly supports network-wide KPI monitoring, cell TOPN monitoring, cell analysis and CHR analysis

through various analysis functions. The figure below shows the correspondence:

Network-wide

KPI monitoring

Cell analysis

CHR analysis

Cell TOPN

monitoring

Note: The red lines indicate the major analysis functions.



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Contents

Typical cases

Summary



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Case 1Plenty of Non-Service RRC Requests due to Wrong

Setting of CN Denial Cause Value

A network has little traffic but there are plenty of non-service RRC setup requests, as shown in the following

table:

As can be seen from the above table, the number of non-service RRC setup requests is 33 times

(112391/3389=33) that of service RRC setup requests. This ratio may be abnormal.

Network-wide KPI monitoring

Note: You can get the above table via RNC Daily Report/RNC Weekly Report or custom report of Nastar.

Case 1 Plent of Non Ser ice RRC Req ests d e to Wrong


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Cell analysis

According to the types of RRC setup requests for all cells, the number of RRC connection setup requests for

registration in some cells accounts for over 99% of the total RRC connection setup requests, as shown in the

following table:

Through the above cell analysis, we are sure that the ratio of non-service RRC setup requests to service RRC

setup requests is abnormal.

Note: You can get the above table via custom report or Performance Query of Nastar.


Setting of CN Denial Cause Value (Continued)

Case 1 Plenty of Non Service RRC Requests due to Wrong


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RNC signaling analysis

Through further RNC LMT interface signaling trace, we find that there are indeed quite many RRC connection

setup requests of registration type and most of them are repeated requests from the same IMSI, as shown in

the following figure:





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After querying the 3G HLR, we know that the IMSI 460019115045990 shown in the above figure is not a registered 3G

user. Certainly the users registration request will always be denied and thus the registration will always fail. The

problem here is why the RRC request of the same IMSI keeps appearing. According to protocol analysis, when a UE

enters the 3G system and if its registration request is denied by the CN, the UE may take one of the following actions:

a) if the denial cause is #17 cause value (network failure), then the UE will start the T3211 timer (15s). After this timer

expires, the UE will attempt three times (the Attempt Counter of the timer is then 4) and then enter the restricted state.

If in this period the T3212 timer expires, then the above procedure will be triggered again. If the LAI changes, the UE

will make the above attempt immediately in the new LAI.

b) If the denial cause is #15 cause value (no suitable cells in LA), the UE will record this LAI in the Forbidden LA list

and will not make multiple attempts as in the above case (#17 cause value). The UE will not initiate the registration

procedure again till an LA not in the Forbidden LA list appears or the UE is switched on again. After confirming with

the CN side, we know that the cause value is indeed set to #17. So the root cause is found.

In general, if 2G and 3G use the same PLMN ID in the 3G coverage area and if the 2G IMSI uses a 3G UE, the above

problem will immediately occur after the user is dropped from the 2G network. Therefore, plenty of non-service RRC

setup requests will arise and consume plenty of power, code, transport and other resources and may cause congestion.

Problem analysis & location





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Modify the cause value of CN denial from #17 (network failure) to #15 (no suitable cells in LA). After the

modification, the ratio of non-service RRC setup requests to service RRC setup requests in the entire network

becomes 3467/15912 = 4.59, which is normal (the normal ratio should be less than 10 according to the data

statistics of various commercial offices), as shown in the following table:

Solution




Case 2 Transport Congestion due to IUB Bandwidth


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Case 2Transport Congestion due to IUB Bandwidth

Configuration Error

Both the service RRC connection setup success rate and the non-service RRC connection setup success rate

are low in a network, as shown in the following table:



AccessRRC Connection Setup Success Rate(service)(>95%) 89.17%(10700/12000)

RRC Connection Setup Success Rate(other)(>95%) 91.05%(118396/130038)



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Cell analysis

As can be seen from the right

table, the major cause of RRC

connection setup failure is that

plenty of RRC connection

requests are denied when Cells

0, 1 and 2 are busy and the RRC

connection denial rate is up to

62%. In most cases, the denial

cause is due to AAL2 setup

failure. According to routine

experience and the reply from

R&D, AAL2 setup failure is mostly

caused by transport congestion.

The three cells belong to the

same Node B.



Configuration Error (Continued)



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As can be see from the indices in green on the right side of the above table, the uplink/downlink RLC mean throughput and the

maximum quantity of uplink/downlink CE resources occupied are not large in the case of transport congestion, so possibly the

transport congestion is caused by IUB bandwidth configuration error.

Open the RNC MML configuration script and find the IUB configuration of the Node B with transport congestion as follows:

The Node B has two pairs of E1 and the bearer type is IMA.

The total bandwidth (PCR) configured for NCP, CCP, ALCAP and IPOA is 302 kbps. There are two AAL2 paths. One is configured for HSDPA service and the bandwidth is 2442 kbps; the other is

for R99 service and the bandwidth is 891 kbps.

The two pairs of E1 in IMA bearer mode can provide 1860 * 2 = 3720 kpbs ATM transport capability. Excluding the common

bandwidth occupied by NCP, CCP, ALCAP and IPOA, they should be able to provide 3720 - 302 = 3418 kbps bandwidth for

traffic channels. Moreover, there are two AAL2 paths and the sharing mode should be configured between AAL2 paths, that is,

the bandwidth of each AAL2 path should be set to the maximum transport capability of traffic channels.

Therefore, the bandwidth of HSDPA and that of R99 AAL2 paths should be both set to 3418 kbps. Obviously, the bandwidth of

R99 AAL2 paths is set to 891 kbps (too small). Even without considering soft handover, 891 kbps cannot satisfy the access

needs of two 384 kbps services (R99 services), so transport congestion may occur.





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Solution

Configure the AAL2 path bandwidth of HSDPA and that of R99 to 3418 kbps. After the modification, the service

RRC connection setup success rate and the non-service RRC connection setup success rate both reach the

normal KPI requirement and the problem is thus solved, as shown in the following table:




Case 3 Low Paging Success Rate due to Paging Cycle


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Case 3Low Paging Success Rate due to Paging Cycle

Coefficient Setting Error

The paging success rate of a certain network is less than 35% (very low), as shown in the following figure:


Note: You can get the above table via RNC Weekly Report of Nastar.

Moreover, users say that the paging response time is rather long.



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Open the RNC MML script. The CN domain paging cycle coefficient DrxCycleLenCoef is set to 8 and the

paging resend count MACCPageRepeat is set to 1.

Moreover, we know from the CN side that the CS paging resend count is set to 3, the interval between the first

paging and the second paging is 3 seconds, and the resend interval of the third paging is 4 seconds.


Coefficient Setting Error (Continued)



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As can be seen from the above settings, the paging detection cycle of the UE in the idle mode, that is, the DRX

(discontinuous reception) cycle is 2^8 = 2.56s. Each paging message from the CN will be sent twice in the

RNC and the paging interval is 2^8 = 2.56s. In other words, at least 22^8 = 5.12s is needed before each

paging resent by the RNC can be responded by the UE. Generally, the paging resend count and resend

interval of the CN must be considered along with the resend of the UTRAN. If the UTRAN resends the paging

once, then the resend interval of the CN should be more than two DRX cycles. Obviously, the resend interval of

the CN (3s) is less than two DRX cycles (5.12s) and so the CN starts to resend the next paging message

before the UTRAN finishes sending and resending the preceding paging message. Therefore, no paging

response is obtained and this problem is shown as paging failure in the traffic statistics of the RNC.

For the UE in the idle mode, the DRX cycle is 2^8 = 2.56s and the UEs paging response time is more than

2.56s, so the paging response time is longer than we actually feel.






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Solution

Modify the paging cycle coefficient of the CN domain DrxCycleLenCoef from 8 to 6 (baseline). After the

modification, the DRX cycle is reduced from 2.56s to 0.64s and the paging success rate of the entire network is

larger than 85%, as shown in the following figure. The problem is thus solved.




Case 4 Low Paging Success Rate due to 2G&3G


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Case 4 Low Paging Success Rate due to 2G&3G

Combined Paging

The paging success rate of a certain network is less than 10% (very low), as shown in the following figure:



Case 4Low Paging Success Rate due to 2G&3G


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Because the paging success rate kept being rather low for a number of days, we preliminarily determined that

there was little possibility of weak coverage. We checked the CN and found that the 2G&3G combined paging

policy was set in the MSC, that is, any paging message destined to 2G or 3G would be initiated to all the LACs

in the 2G and 3G networks so as to guarantee paging response.

Site investigation


Check the RNC MML script. The parameter configurations related to paging are found normal.

Case o ag g Success ate due to G&3G

Combined Paging (Continued)

Case 4Low Paging Success Rate due to 2G&3G Combined


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The above combined paging policy will surely cause the 3G paging success rate to be low. Because there

are quite many 2G subscribers at the site, plenty of paging messages to 2G subscribers will also be sent in

the 3G network and because the called subscribers are 2G subscribers, the 3G network will surely not

receive any paging response. Therefore, the 3G paging success rate will surely be low. The more paging

messages to 2G subscribers, the lower 3G paging success rate.

The 2G/3G combined paging policy may be used in some scenarios to improve the paging response

probability to some extent, but it may also bring the following troubles:

1. Paging channel congestion;

2. The PCHs consume plenty of power;

3. Increased air interface interference.

In sum, the 2G&3G combined paging policy has little gain but may easily bring other severe performance

problems. It is seldom used.

g g

Paging (Continued)

Case 4Low Paging Success Rate due to 2G&3G Combined


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Solution

Change the CN paging policy to the normal policy, that is, paging by LAC. After the modification, the paging

success rate of the entire network is higher than 85% and the problem is solved, as shown in the following

figure:


g g

Paging (Continued)

Case 5Abnormal Load due to Unreasonable Common


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Cell Max. Tx Power Empty Load Power Ratio

Channel Power Ratio Configuration

In a network with many cells

empty-loaded, the ratio of the

power to the total power (i.e.

the downlink load) is between

3% and 38%, as shown in the

right table. Normally, the loadof a cell empty-loaded should

be about 20%, so the value

between 3% and 38% is

severely abnormal.

Cell TOPN monitoring

Note: You can get the above

table by combining

Performance Query of

Nastar and Excel.

Case 5

Abnormal Load due to Unreasonable Common Channel


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The load abnormality in the case of empty load is usually caused by unreasonable common channel power ratio configuration.

Below is a comprehensive analysis of the script settings:

In the above table, the load of some cells empty-loaded is very huge. Lets take 38% here to make the calculation. After we deduct

the load of the empty-loaded cell, the admission redundancy (20%) and the power (30%) statically allocated to HSDPA, the power

left for R99 services is only 12% (100% - 38% -20% -30% = 12%), which is little and may very easily cause power congestion, that

is, the capacity is restricted.

Whats more, the load of some cells empty-loaded is very little, e.g. 3%, which is also abnormal. We may conclude through

calculation that such cells cannot be accessed due to pilot Ec/Io deterioration when the load of these cells is about 30%, so the

maximum load of such cells will be about 30%. Again because for the admission algorithm (Algorithm 1), load control algorithm and

other algorithms it is necessary to compare the current load with the corresponding threshold value (e.g. 75%) so as to decide

whether to start the corresponding algorithm, possibly the current load cannot be more than the corresponding threshold value and

the algorithms may fail.

We further check the script configuration and find that the following problems exist for the power ratio configuration of the cells with

abnormal load:

1. The pilot power configuration is from 27 dBm to 37.8 dBm whereas the maximum transmit power of the cells is

mostly set to 44.8 dBm.

2. The power ratio configuration of common channels such as PSCH, SSCH, PCH and FACH is far larger than the

baseline configuration.


Power Ratio Configuration (Continued)

Case 5



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Because the power of other channels uses pilot power as a reference, too high or low pilot power is the major reason why the load of cells

empty-loaded is too high or low. The pilot power should be reasonably set according to the maximum power of the cell. According to the

planning (simulation) requirements, the pilot power should be 10 dB less than the maximum transmit power of the cell. Too high pilot power

will result in capacity loss as mentioned above, whereas too low pilot power will cause the algorithms to fail and may bring other problems

such as mute. If we need to reduce the pilot power in special cases, we should also lower the configured maximum transmit power of that

cell, so that the pilot power is 10 dB less than the maximum transmit power of the cell. For instance, suppose we set the pilot power to 27

dBm, then we should configure the maximum transmit power of the cell to 37 dBm.

In some guidance documents about RF optimization, we are often told to modify pilot channel power as an optimization means. We do not

recommend this. Because the modification of pilot power in a large scope will result in numerous problems such as uplink-downlink

unbalance, service coverage void in the soft handover area and severe adjacent cell interference in the uplink. Therefore, we should start

with antenna parameters to solve RF problems such as weak coverage and pilot pollution. We should not adjust the pilot power unless in

special cases.

When the power ratio configuration of common channels such as PSCH, SSCH, PCH and FACH is far larger than the baseline

configuration, the load of cells empty-loaded may be too high. The baseline configuration of power ratio for common channels has been

verified in Beta tests and commercial offices. We should not modify the baseline configuration as a routine RF optimization means.

Moreover, we should use the smaller power ratio to attain a better balance between common channel coverage and traffic channel coverage

during the optimization, so that the common channel power ratio after the optimization is not far larger than the baseline configuration.


Case 5



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Cell Max. Tx Power Empty Load Power Ratio

Solution

Take the following measures:

1. Optimize the configurations of the pilot power and cell maximum transmit power, so that the pilot power

is 10 dB or more less than the cell maximum transmit power, for example, Pcpich = 27 dBm, TCP = 37

dBm, Pcpich = 34.8 dBm and TCP = 44.8 dBm.

2. Restore the power ratio configuration of common channels (PSCH, SSCH, PCH, FACH, etc. )t to the

corresponding baseline configuration.

After the above measures are taken, the cell loads restore to normal and the problem is thus solved without bringing

any other troubles, as shown in the following table:

Note: You can get the above table by combining Performance Query of Nastar and Excel.


Case 6Access Failure and Call Drop due to


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External Interference

In a certain network, the average RTWP of quite many cells during some days is above 85 dBm, as shown in

the following table:


As can be seen from the above table, the cells with a high average RTWP have normal services (they are not

out of service) and very little traffic, so very probably external interference may cause the RTWP to raise.




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Correlation analysis of RRC setup failure and interference

As can be seen from the above table, the cause of RRC setup failure is that the UE does not reply and for the

cells whose failure rate is high with many failures, the average RTWP is above95 dBm (rather high).

Moreover, there is very little traffic in these cells. Therefore, very probably the abnormal raise of RTWP may

cause plenty of RRC setup failures.


p

External Interference (Continued)



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As can be seen from the above table, the cause of CS RAB setup failure is air interface failure (mostly RB no

response) and for the cells whose failure rate is not high but with many failures, the average RTWP is above

92 dBm (very high). Moreover, there is very little traffic in these cells. Therefore, very probably the abnormal

raise of RTWP may cause CS RAB setup failure.



Correlation analysis of RAB setup failure and interference



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As can be seen from the above table, the cause of CS call drop is RF failure (mostly uplink synchronization

failure and UU interface no response). For the cells whose failure rate is high with many failures, the average

RTWP is above92 dBm (very high). Moreover, there is very little traffic in these cells. Therefore, very

probably the abnormal raise of RTWP may cause CS call drop.



Correlation analysis of CS call drop and interference



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Correlation analysis of PS call drop and interference

As can be seen from the above table, the cause of PS call drop is RF failure (mostly uplink synchronization

failure and UU interface no response). For the cells whose failure rate is high with many failures, the average

RTWP is above95 dBm (rather high). Moreover, there is very little traffic in these cells. Therefore, very

probably the abnormal raise of RTWP may cause PS call drop.





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According to the routine interference monitoring results and the correlation analysis between RRC setup

failure/RAB setup failure/call drop and the average RTWP, we may infer that possibly there exists strong

external interference that causes the RTWP of some cells to abnormally raise. The plenty of RRC setup

failures, RAB setup failures and call drops are all closely linked to the abnormal raise of RTWP.

For this reason, we carefully surveyed the radio environment at the site and searched for interference.

Through tests and problem location, we found that the strong interference came from the radio equipment

of the army. With our efforts, the customer requested the local radio commission to remove the existing

interference source or lower the power of the radio equipment. These external interference was gradually

reduced. The latest statistics show that the number of cells with abnormal raise of RTWP will decrease

with the weakening of abnormal raise of the average RTWP.



E l I f (C i d)


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Solution

Continue to push the customer and the local radio commission to shut off the interference source or reduce the

transmit power of the interference source so that the interference is within the acceptable range.


Case 7 Power Congestion due to Resource Restriction


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Case 7 Power Congestion due to Resource Restriction

Power congestion occurs to many cells in a network, as shown in the following table:


As can be seen from the above table, power congestion mainly occurs in the PS RAB setup phase and

accounts for over 50% of all congestions. The congestion rate during PS RAB setup is as high as 16.55%.

Obviously, power congestion is quite severe.


Case 7Power Congestion due to Resource

R t i ti (C ti d))


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Open the MML script to see the call admission parameter configuration of the cells with power congestion:

The downlink call admission algorithm uses Algorithm 1

(NBMDLCACALGOSELSWITCH=ALGORITHM_FIRST)

The maximum transmit power of the cell is 20W (MAXTXPOWER=430)

The call admission threshold of PS services is 75% (DLOTHERTHD=75)

Therefore, the power threshold for access denial of PS services is 10lg (20000*75%) = 41.76 dBm. We can

see from the above table that the transmit power of the cells with power congestion is above 41.92 dBm,

which is more than the admission threshold 41.76 dBm. Thus we know that the power congestion is normal.

Moreover, the maximum number of CEs in the downlink reaches 97 when congestion occurs, indicating that

there is indeed big traffic and power resource congestion is a fact.


Restriction (Continued))

Case 7Power Congestion due to Resource Restriction

(C ti d))


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Solution

Solve power resource congestion by the following means:

1. Optimize PS policies (e.g. DCCC, state transition, etc.)

2. Increase carrier frequencies

3. Increase micro cells in hot spots

4. Cell splitting

5. Introduce HSDPA

6. Other means

Select the specific solution according to the actual situation.

(Continued))

Case 8Code Congestion due to Resource Restriction


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Code congestion occurs to quite many cells in a network, as shown in the following table:


As can be seen from the above table, code congestion mainly occurs in the PS RAB setup phase and accounts

for 100% of all congestions. The congestion rate during PS RAB setup is as high as 7.78%. Obviously, code

congestion is quite severe.


g


(Continued))


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As can be seen from the right green part in the above table, the average code utilization rate is over 60% when

code congestion occurs. Therefore, code congestion may easily occur. Moreover, the maximum number of CEs

in the downlink reaches 105 when the congestion occurs, indicating that there is indeed big traffic and code

resource congestion is a fact.

Correlation analysis of code congestion, code utilization rate and traffic

(Continued))


(Continued))


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Solution

(Continued))

The same as power resource congestion, we may solve code resource congestion by the following means:


2. Increase carrier frequencies


4. Cell splitting

5. Introduce HSDPA

6. Other means


Case 9IUB Transport Congestion due to Resource


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Transport congestion occurs to quite many cells in a network, as shown in the following table


As can be seen from the above table, IUB transport congestion mainly occurs in the PS RAB setup phase and

accounts for over 90% of all congestions. The congestion rate during PS RAB setup is as high as 31.33%.

Obviously, IUB transport congestion is quite severe.


Restriction

Case 9 IUB Transport Congestion due to Resource


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Here we select Cell1211 to make an analysis. Open the MML scrip to see the relevant IUB transport bandwidth

configuration as follows:

The Node B to which the cell belongs has a pair of E1s and the bearer type is UNI

There is one AAL2 path for R99 services and the bandwidth is 1812 kbps

As can be seen from the above configuration, the IUB bandwidth configuration of the Node B is OK for the

physical bandwidth of one E1. However, we can see from the right green part in the above table that the

average downlink throughput is as high as 104.85 kbps when IUB transport congestion occurs to the cell and

so the cell traffic is rather high. Moreover, the Node B has two cells and the traffic of the two cells together will

be even higher. Therefore, one E1 cannot satisfy the actual bearer requirements and thus IUB transport

congestion may easily occur.

Therefore, IUB transport congestion is caused by limited transport resources.





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Solution



Solve transport resource congestion by the following means:


2. Expand the capacity of transport resources


4. Other means


Case 10

Plenty of RRC Connection Setup Failures due to

Node B Version Defect


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Node B Version Defect

The RRC connection setup success rate in a network is rather low, as shown in the following table:



Case 10


Node B Version Defect (Continued)


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RRC connection setup failure mostly occurs to such cells as 30843, 30863, 30252 and 30382. It is nearly 100%

for these cells and the major failure cause is that the UE does not reply, as shown in the following table:

Cell analysis



Case 10




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As can be seen from the right green part in the above table, the cells are in normal service, the RTWP is about -106

dBm and the maximum transmit power of the cells is about 36 dBm when RRC connection setup failed, so there is no

transport problem or uplink interference.

Assisted by the onsite engineers, we performed the dialing test on Cell 30843 and started IOS tracing. The failure

symptom is as follows: After receiving RRC CONNCET REQ, the RNC normally sends RRC CONNECT SETUP.

However, RRC connection setup failed because RRC CONNECT SETUP COMPLETE is not received. Finally, the

RNC initiates RL to release the link. See the figure below:



Case 10




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Open the RRC CONNCET REQ message, as shown in the following figure:

As can be seen from the above figure, the downlink Ec/No is about (44-49)/2 = -2.5 dB when the RRC

connection setup request is initiated. Therefore, the downlink signal quality is OK and there should be no

downlink weak coverage or downlink interference problem.


Case 10Plenty of RRC Connection Setup Failures due to



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Try deactivating the cells and then activating them. The cells can be connected, as shown in the following figure:

Therefore, the problem is caused by Node B equipment fault.

The R&D confirmed that the problem was due to software version (V16 041) defect of Node B of BTS3812E

type and could be solved by upgrading the software version to V16 061.


Case 10




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SolutionUpgrade the software version of the Node B of BTS3812E type to V16 061. After the software version upgrade,

the RRC connection setup success rate in the network reaches the normal KPI requirements and thus the

problem is solved, as shown in the following table:


Case 11

Power Congestion due to UnreasonableAdmission Parameter Setting


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g

Power congestion occurs to

the cells in the right figure

(mainly 50201 and 50203) in

the RRC connection setup

phase and RAB setup phase.

According to the maximum

number of CEs when the

congestion occurs, we know

that the traffic is not very big.


Note: You can get the table on

the right via custom report or


Nastar.

Power congestion in RRC setup

Power congestion in RAB setup

Case 11

Power Congestion due to UnreasonableAdmission Parameter Setting (Continued)


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Open the MML script. The uplink call admission algorithm of the two cells uses Algorithm 2. We can see

from the traffic that there is no uplink congestion. The downlink call admission algorithm uses Algorithm 1.

The downlink threshold of the conversational AMR voice service is 70%, that of conversational non-AMR

voice service is 70% and that of other services is 60%. Below are relevant MML commands:

ADD CELLCAC:CELLID = 50201, DLCONVAMRTHD = 70, DLCONVNONAMRTHD = 70,

DLOTHERTHD = 60

ADD CELLCAC:CELLID = 50203, DLCONVAMRTHD = 70, DLCONVNONAMRTHD = 70,

DLOTHERTHD = 60

Comparing the above with the baseline configurations and the corresponding settings of various

commercial offices, we can see that the values of the above call admission thresholds are too small.

g ( )

Case 11

Power Congestion due to Unreasonable AdmissionParameter Setting (Continued)


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Solution

Change the downlink thresholds of conversational AMR voice service, conversational non-AMR voice service

and other services respectively to 80%, 80% and 75% (the baseline values of RNC1.5). Then the power

congestion problem disappears.

g ( )

Case 12

Code Congestion due to Unreasonable Setting of

DCCC and Soft Handover Parameters


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Code congestion often occurs to Cells 50201 and 50203.


Note: You can get the table on the right via custom report or Performance Query of Nastar.

Case 12


DCCC and Soft Handover Parameters (Continued)


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As viewed from RB distribution, in the downlink at 20:00 the two cells had quite many DL PS384k services,

some PS144k streaming services as well as some other services:

Correlation analysis (1)

Note: You can get the above table via Performance Query of Nastar.

( )

Case 12


DCCC and Soft Handover Parameters


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Further analysis reveals that the actual average RB traffic of PS high-speed service is not high:


So the DCCC related parameter configuration may be unreasonable.

Case 12

Code Congestion due to Unreasonable Setting ofDCCC and Soft Handover Parameters


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The DCCC monitoring results show that there is no channel switching and there is no DCCC-related RB

reconfiguration in the entire network, as shown in the following table:


Possibly the DCCC switch is off.

Case 12



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Parameter configuration analysis (1)

Open the MML scrip. The DCCC switch is indeed off (SET CORRMALGOSWITCH:CHSWITCH =

DCCC_SWITCH-0).

We recommend that the DCCC switch be on (the DCCC-related parameters may temporarily use the default

ones or they can be optimized as needed so as to ensure that the users will not obviously feel the change).

When the DCCC switch is on, the code resources that do not need to be occupied will be released and the

corresponding power resources will also be released. In this way, code congestion and power congestion can

be alleviated to a certain extent.

Case 12



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As can be seen from the following table, the ratio of 1A events to 1B events is even higher than 100.

Correlation analysis (2)


Case 12



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Most of the weak links in the active set release resources by the out-of-sync mechanism, as can be verified in the

following table:


Case 12



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Parameter configuration analysis(2)

Open the MML script. The relevant threshold of RNC-level 1B is set to 14 (7 dB) and the trigger time is set to

2560 (2560 ms), which will make it hard to trigger the 1B event.

When the 1B event cannot be timely triggered, some links cannot be timely released and as a result some

code resources that do not need to be occupied will be occupied, thus easily causing code congestion.

Moreover, transport congestion and power congestion are likely to occur, too.

Lets have a look at Hong Kongs settings:The relative threshold of RNC-level 1B is set to 14 (7dB) but the

trigger time is set to 640 (640 ms). The ratio of 1A events to 1B events is within 2 and so the set values are

reasonable.

Case 12



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Solution


1. Open the DCCC switch.

2. Modify 1B parameters with reference to Hong Kongs relevant parameter configuration: the

relative threshold of RNC-level 1B is 14 (7 dB) and the trigger time is 640 (640 ms).

After the above are done, code congestion has disappeared.

Case 13

High Call Drop Rate due to Unreasonable Setting of 1DParameters and Inter-System Handover Parameters


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Call drop occurs to the following cells:


Note: You can get the

table on the right via

custom report or


Nastar.

As can be seen from the

above table, many cells in

the entire network have a

high CS or PS call drop

rate, mainly because of

RLC reset, uplink out-of-

sync and UU interface no

response.

Case 13

High Call Drop Rate due to Unreasonable Setting of1D Parameters and Inter-System Handover

Parameters (Continued)


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Parameter configuration analysisThe above call drop is usually caused by weak coverage. We can find some problems from the MML:

1. The RNC soft handover 1D hysteresis is set to 10 (5 dB) and the 1D trigger time is set to 1280

(1280 ms), which will make it hard to trigger the 1D event. So the list of best cells cannot be timely

updated, causing the UE unable to obtain the appropriate adjacency and ultimately resulting in no

handover at all or delayed handover, which will further cause call drop (e.g. RLC reset, uplink out-

of-sync, UU interface no response , etc.). The below soft handover failure due to UE no response is

a case of call drop due to UU interface no response:



Case 13




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Lets have a look at the settings in Hong Kong and Brunei: 1D hysteresis is set to 8 (4 dB) and the

1D trigger time is set to 640 (640 ms), so the 1D event is more easily to trigger, which can be

verified by the ratio of 1D events to 1A events. In Hong Kong and Brunei, 1D events are about half

of 1A events, but in this case the ratio is 1/8. So we recommend that the settings be changed to

the same as in Hong Kong and Brunei so that soft handover becomes more smooth and the call

drop rate can be improved.

2. In inter-system handover, RSCP is used as the measurement (RNC level) and the compressed

mode enable threshold INTERRATPSTHD2DRSCP is set to -115 dBm. This threshold value is

too low, as a result the compressed mode may not be enabled before the call drop or call drop

may occur very easily in the inter-system handover after the compressed mode is enabled. These

call drop causes are also shown as RLC reset, uplink out-of-sync and UU interface no response.

Therefore, we recommend that the value of INTERRATPSTHD2DRSCP be changed to -105 dBm

or larger.


Case 13




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Solution


1. Modify 1D parameters with reference to relevant parameter configuration in Hong Kong and

Brunei: 1D hysteresis is set to 8 (4 dB) and the 1D trigger time is set to 640 (640 ms).

2. Change the value of INTERRATPSTHD2DRSCP to -105dBm or a greater value, so as to

avoid call drop due to weak signals during signal switching.

After the above are done, both the CS call drop rate and the PS call drop rate are improved, as shown in

the following table:



Case 14

High Call Drop Rate due to RNC TrafficMeasurement Defect


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Call drop occurs to the following cells:


Note: You can get the

table on the right via

custom report or


Nastar.

We can see from the right

table that the PS call drop

rate is very high for cells

3062, 1362, 1403, etc.and most are due to

Other causes.

Case 14

High Call Drop Rate due to RNC TrafficMeasurement Defect (Continued)


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Because the call drop cause is Other, we should first check the relevant CDL log.

Below is the log of Cell 1403 on May 3:

CDL analysis

======No. 57======

Interface: RNCAP_NBM_NBAP_INTERFACE

Msg: NBAP_RL_RECFG_READY

======No. 58======

Interface: RNCAP_INTRA_INTERFACE

Msg: RNCAP_RL_SYNC_RECFG_RSLT

======No. 59======

FSM ID:RNCAP_RB_FSM_ID

CSS:RB SETUP

CS:RNCAP_CSS_RB_WAIT_UE_RB_SETUP_FAIL

======No. 60======

Alarm in RNCAP_AlcfgAlSetupConnType1Rsp:Received Iub AAL2 type1 setup responce message

from AL but result is 85 not success!

======No. 61======


Msg: RNCAP_MAIN_RUNTIME_ABNORMAL_MSG

RL

reconfiguration is

complete

AL configuration failed

Case 14



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======No. 62======

Interface: RNCAP_CCB_STATE_TIMER_INTERFACE

Msg: RNCAP_TI_RB_WAIT_UE_RB_SETUP_FAIL

======No. 63======FSM ID:RNCAP_RB_FSM_ID

CSS:RB SETUP

CS:RNCAP_CSS_RB_WAIT_UE_RB_SETUP_RSP

======No. 64======

Interface: RNCAP_RNCAP_RRC_INTERFACE

Msg: RRC_RB_SETUP_CMP

======No. 65======


Msg: RNCAP_RB_SETUP_SUCC

======No. 72======


Msg: RNCAP_RAB_SETUP_RSLT

======No. 73======RAB Setup Procedure Succeed.

======No. 74======

FSM ID:RNCAP_IDLE_FSM_ID

CSS:IDLE

CS:RNCAP_CSS_IDLE

RB setup begins

RB setup iscomplete

Signaling plane setup succeeded

and the RNC returns the RAB

setup success message to the CN

Case 14



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======No. 75======

ENTER RNCAP_MainBackupRabSetupD2D . usCcbIndex = 127

======No. 76======

Err in RNCAP_CcbCheckAbnormalFlags: User Plane Fail!RAB Fail Cn Domain id = 1, Rab Id = 5

======No. 77======

Err In RNCAP_CcbCheckAbnormalFlags: User Plane Fail! Table Type is : 9, Table Index is 2252

======No. 78======

Err In RNCAP_CcbCheckAbnormalFlags: User Plane Fail! Cause is 184945367

======No. 79======

Enter in RNCAP_RabRelReq for PS: Cause = 184945367, enRabRelReqType = 4.

According to the above CDL procedure analysis: a) the RNC returns the RAB setup success message to the CN after completing

RL reconfiguration and RB setup (this is merely the setup success in the NBAP signaling plane); b) the limited transport bandwidth

caused the user plane setup failure during the NBAP user plane setup, so the RNC then initiates the RAB release procedure. The

Other cause in the above traffic statistics means the abnormal release here.

User plane setup

failed

The error code 184945367 can be interpreted as

RR_ERR_RNCAP_ALCFG_IUB_AAL2_MAX_BIT_RATE_FOR_FW_NOT_A

VAIL, that is, the limited transport bandwidth caused user plane setup failure.

The RNC enters the RAB release procedure

Case 14



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The above analysis shows that the call drop in traffic statistics is actually access failure and the RNC should

not count theRAB release procedurethat follows as call drop.

The R&D has confirmed that this is a known bug of the current RNC version (R005C03B065) and it can be

avoided by installing the SP05 patch.


Case 14



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After the SP05 patch is installed for the RNC, almost all the call drops with the cause being Other have

disappeared and the PS call drop rate is obviously lower, as shown in the following table. The problem is thus

solved.

Solution


Case 15

Power Congestion due to HSDPAMeasurement Switch Off


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The PS RAB setup success rate in a network is 79% (extremely low), as shown in the following table:



Case 15

Power Congestion due to HSDPA MeasurementSwitch Off (Continued)


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Cell analysis

The cell analysis results show that the PS RAB setup failure mostly occurs to such cells as 8881, 8882

and 25282 and the major failure cause is power congestion, as shown in the following table:


Case 15

Power Congestion due to HSDPA MeasurementSwitch Off (Continued)


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As shown in the above table, when power congestion occurs, the maximum transmit power of the cell is 39 dBm

(not high) and it should not cause power congestion. Further analysis of CDL reveals that the PS RAB setup

failure is due to power congestion that is caused by access denial (in many cases the denial based on the

equivalent user number) . Because the script parameters useAlg_First, there should not be any judgment of

the equipment user number. The only possibility is that the power cannot be predicted. Because the cell is H

cell and the power occupied by H channel needs to be known during the call admission, the algorithm provides

a switchHSDPA measurement. The measurement can be made and call admission based on power

prediction can be performed only when this switch is on. In the script, this switch is off for the network and thus

the call admission uses the equivalent user number to make the power prediction and a big deviation arises

(this is also why we should avoid using the equivalent user number for call admission) to cause the denial that

should not happen. Thats the reason why we see power congestion in the traffic statistics although the actual

power is not high.


Case 15

Power Congestion due to HSDPAMeasurement Switch Off (Continued)


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Open the HSDPA measurement switch, as shown in the following figure to solve the problem.

Solution

Note: The NCP bandwidth should be above 100 kbps if we want to open the HSDPA measurement switch.

After the switch is on, the PS RAB setup success rate of the entire network reaches the normal KPI

requirements and the problem is solved, as shown in the following table:


Case 16

Rising PS Call Drop Rate due to Incorrect Setting ofSupport Capability for PS Inter-System Handover


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The PS call drop rate of a network is larger than 30% (extremely high), as shown in the following table:



Case 16

Rising PS Call Drop Rate due to Incorrect Setting of Support

Capability for PS Inter-System Handover (Continued)


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Cell analysis

The cell analysis results show that the cells with severe call drop are 24181, 3783, 19083, etc. and the majorcauses of call drop are RLC reset, uplink synchronization failure, UU interface no response or other RF

problems, as shown in the following table:


Case 16Rising PS Call Drop Rate due to Incorrect Setting of Support



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The call drop with the cause being RF problems is often due to weak coverage. However, the results of

checking and analyzing the MML script show that the 2G cell support capability needed for inter-system

handover of PS services in the network is EDGE (ADD TYPRABBASIC REQ2GCAP= EDGE whereas it is

GPRS (ADD GSMCELL RATCELLTYPE=GPRS) in GSM cell attribute configuration. Because the capability

required by the services is higher than the support capability of GSM cells, PS services will not start the

compressed mode for inter-system handover. Therefore, PS service call drop may easily occur at the edge of

the network with the call drop cause being RF problems.


Case 16Rising PS Call Drop Rate due to Incorrect Setting of Support



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Change REQ2GCAP=EDGE in the PS service attributes to REQ2GCAP=GPRS. The PS service call drop

rate is improved to a certain extent, as shown in the following table:

Solution


Case 17

PS Inter-System Handover Success Rate Is Zero due toRNC Traffic Measurement Defect


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The PS inter-system handover success rate of a network is 0, as shown in the following table:



Case 17

PS Inter-System Handover Success Rate Is Zero due toRNC Traffic Measurement Defect (Continued)


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Cell analysis

The cell analysis results show that the PS inter-system handover failure mostly occurs to such cells as 45552,

5552, 25652 and 45151 and the major failure cause is Other, as shown in the following table:

RNCId Cell Id Cell Name Date VS.IRATHO.FailO

utPSUTRAN.Cell

VS.IRATHO.AttO

utPSUTRAN

IRATHO.FailOut

PSUTRAN.Cfg

Unsupp

IRATHO.FailOut

PSUTRAN.Phy

ChFail

VS.IRATHO.Fail

OutPSUTRAN.

Other

72 45552 CELL:45552 2006-4-17 44 44 0 0 44

72 5552 CELL:5552 2006-4-17 38 38 0 1 37

72 5553 CELL:5553 2006-4-17 32 32 0 1 31

72 16033 CELL:16033 2006-4-17 29 29 0 0 29

72 2333 CELL:2333 2006-4-17 22 22 0 1 21

72 5243 CELL:5243 2006-4-17 22 22 0 1 21

72 23543 CELL:23543 2006-4-17 21 21 0 1 20

72 44552 CELL:44552 2006-4-17 19 19 0 0 19

72 26741 CELL:26741 2006-4-17 16 16 0 0 16

72 23541 CELL:23541 2006-4-17 13 13 0 0 13

RNCId Cell Id Cell Name Date VS.IRATHO.FailO

utPSUTRAN.Cell

VS.IRATHO.AttO

utPSUTRAN

IRATHO.FailOut

PSUTRAN.Cfg

Unsupp

IRATHO.FailOut

PSUTRAN.Phy

ChFail

VS.IRATHO.Fail

OutPSUTRAN.

Other

74 25652 CELL:25652 2006-4-17 54 54 0 3 51

74 45151 CELL:45151 2006-4-17 24 24 0 0 24

74 20451 CELL:20451 2006-4-17 18 18 0 0 18

74 18492 CELL:18492 2006-4-17 12 12 0 2 10

74 22352 CELL:22352 2006-4-17 12 12 0 0 12

74 11892 CELL:11892 2006-4-17 11 11 0 2 9

74 25292 CELL:25292 2006-4-17 10 10 0 0 10

74 25393 CELL:25393 2006-4-17 10 10 0 1 9

74 25291 CELL:25291 2006-4-17 9 9 0 0 9

74 45152 CELL:45152 2006-4-17 9 9 0 0 9


Case 17



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We tested the cells with frequent failures at the site and found that the PS inter-system handover actually succeeded

but the RNC PS traffic statistics indicated failure.

Through further signaling trace and analysis, we found that the CN did not send the SRNC CONTEXT REQUEST

message during PS inter-system handover whereas at present the RNC will not count the success unless it receives

the SRNC CONTEXT REQUEST message (so the PS inter-system handover success count is always 0 in the

statistics). At present, our CN will send the SRNC CONTEXT REQUEST message, so we failed to discover this

problem during the test of V15 office. (On the earlier days, the RNC would directly judge the cause value of IU RELCMD but later we discovered in Uruguay Beta Test that the CN (not our CN) would always send the release command

even if the 2G system did not support inter-system handover and the RNC would count the handover as being

successful as long as the release cause value was Normal Release , so we changed the rule to the present way so

as to avoid incorrect measurement: the RNC will not count the handover as being successful unless it receives the

SRNC CONTEXT REQUEST message).

It is not stipulated in the protocols that the CN should send the SRNC CONTEXT REQUEST message during PS inter-

system handover. Instead, the CN does not need to send this message if it is not necessary to restore the PDP

context.

Therefore, the PS inter-system handover success rate being 0 is due to the incorrect traffic measurement method of

RNC.

Case 17



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Change the measurement method of PS inter-system handover success as follows: During the PS inter-system

handover, if the RNC receives the IU RELEASE COMMAND message after sending the CELL CHANGE

ORDER FROM UTRAN message and if the cause value in the IU RELEASE COMMAND message is

Successful Relocation orNormal Release or an other normal cause value, then it indicates that the PS

inter-system handover procedure succeeded and the success should be counted. Merge this change into the

RNC V17 version.

There still exists this problem: When the CN sends the IU RELEASE COMMAND message that carries the

normal cause value in the case of inter-system handover failure, the RNC will also count the handover as being

successful. This problem cannot be avoided and at present our RNC cannot solve it.

Solution

Case 18

High PS Call Drop Rate due to FACHState Support Defect


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The PS call drop rate of a certain network is higher than 30% (extraordinarily high), as shown in the following table:



Case 18

High PS Call Drop Rate due to FACH StateSupport Defect (Continued)


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Network conduct analysis

According to RB reconfiguration conduct analysis, channel switching between common channels

(FACH) and dedicated channels occurred many times:


Case 18



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Open the MML script. The BE service state transition switch is already on. It is learned from the R&D that the

present RNC has defect in the support for FACH state, that is, the channel switching between common

channels and dedicated channels may easily cause call drop. Therefore, a major reason of the high call drop

rate may be that this function switch is on.

Case 18



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Close the BE service state transition switch. The PS service call drop rate is greatly lowered, as shown in thefollowing table:

Solution


Case 19

Low CS Inter-System Handover Success Rate due to2G Parameter Configuration Error


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CS inter-system handover failure frequently occurs to the following cells and the failure rate is even as high as

100% with the major failure cause being physical channel failure, as shown in the following table:



Case 19

Low CS Inter-System Handover Success Rate due to2G Parameter Configuration Error (Continued)


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Physical channel failure is generally caused by weak signals of 2G cells, interference at the 2G side or other

problems. Later these causes were ruled out at the site and ultimately we found that the problem was because

the 2G MSC did not set cell encryption in the handover response message after the AMR function was

provisioned for the GSM of the customer.

Till now, we were sure that the problem was caused by 2G MSC.


Case 19

Low CS Inter-System Handover Success Rate due to2G Parameter Configuration Error (Continued)


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Because the 2G network was provided by our competitor E, we asked the customer to push E to handle theproblem. After then, the CS inter-system handover failure rate obviously decreased and the problem was thus

solved, as shown in the following table:

Solution


Case 20

High VP Service Call Drop Rate due to Too High LogicChannel Priority


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After the RNC version of a network is upgraded from BSC6800V100R003 to BSC6800V100R005, the VP call

drop rate rises from less than 1.44% to about 3.39% , as shown in the comparison of KPIs below (the left table

is the data before the upgrade and the right table is the data after the upgrade):

Case 20

High VP Service Call Drop Rate due to Too High LogicChannel Priority (Continued)


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Cell analysis

The cell analysis results show that VP call drops are randomly distributed in space and time and the call drop is

due to RF problems. The cells are in normal service and the RTWP is also normal when the call drop occurs,

as shown in the following table:


Case 20



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The RF-attributable call drop is generally caused by weak coverage, but there was little possibility that the coverage changed a

lot in a large scope within the two days of upgrade, so we suspected that the rise of the VP call drop rate was closely related

with the RNC upgrade.

Through troubleshooting, we found that BSC6800V100R003 and BSC6800V100R005 had slight difference in the specific

implementation: In RNC V1.3, the priority allocation of logical channels is implemented in the codes and cannot be modified via

any command, whats more, signaling priority is higher than service priority; in RNC V1.5 and later versions, flexibility is added

and the priority allocation is configurable via the background with such factors as service type differentiation fully considered,

meanwhile default configurations are provided for priority parameters.

We found through the verification test on the simulation platform that the service priority in the default configurations of RNC

V1.5 was too high and the logical channel priority of some services was even higher than signaling priority, which caused cell

coverage edges. When the transmit power of the UE is close to the maximum value, the UE will enter the uplink TFC selective

sending state and then the uplink signaling cannot be sent, thus causing call drop. The relationship between logical channel

priority and transport channels is not clarified in the protocols. According to the test results, it is this parameter that helped the

VP call drop rate of various commercial offices to decrease.

Case 20



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Change the default value of logical channel priority of VP service RB in BSC6800V100R005 from 1 to 4 (SET

LOCHPRIO: CSCONVLOCHPRIO=4 ), so that the service priority is not larger than the signaling priority. The

VP call drop rate obviously decreases and the problem is thus solved, as shown in the following table:

Solution


Contents


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Typical cases

Summary


Experience Summary


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Experience 1: Get familiar with traffic measurement indices

Performance analysis is largely based on traffic statistics, so we should be familiar with traffic measurement indices.

We are sure which to analyze only after we know the traffic measurement indices and their meanings and measuring

time.

The Help file of RNC traffic measurement provides the structure diagram of traffic measurement indices (index tree) as

well as a description of the index meanings and measuring time. We should understand all the indices covered in this

Help file. Of all the indices, the indexes of cell measurement and RNC overall performance measurementare

especially important. We must completely master them.

The raw traffic measurement indices in Nastar

come from the RNC product and the index

trees of the two are the same, as shown in the

right figure (the left is the index tree of RNC

and the right is that of Nastar). Therefore, you

will be familiar with the traffic measurement

index structure of Nastar and find it easy to

use once you are familiar with the Help file of

traffic measurement.

Experience Summary (Continued)


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Experience 2: Be good at designing analysis themes

As we mentioned before, a table composed of relevant traffic measurement indices is called an analysis theme. There is no

constraint for the design of analysis themes. Any group of relevant traffic measurement indices can become an analysis theme, as

long as they can guide the discovery or analysis of problems. The aforesaid cases have given many examples of analysis themes.

Although there is no constraint for the design of analysis themes, analysis themes have a lot in common in terms of the analysis

principle, for example, most performance problems are related to equipment state, interference, capacity and coverage, so we may

combine the indexes related to equipment state, interference, capacity and coverage into a standardcorrelated index setto

serve as a reference for analyzing a specific performance problem. Practice shows that the correlated index set may have a great

role: It enables the analyzer to analyze problems from a wider angle and to further confirm problems or discover new exceptions.

Below is the correlated index set often used inCell TOPN monitoring andCell analysis. It is given here for your reference

only.



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How well you design analysis themes and how efficient they can help problem discovery and problem analysis will depend on how well

you understand the traffic measurement indices, master the systematic knowledge and accumulate analysis experience. Moreover, as

mentioned before, analysis themes can be integrated in templates to enable knowledge transfer and experience sharing. Therefore, the

analysis theme function of Nastar is a powerful weapon to expand your thoughts and bring into play your wisdom and potentials. It

enables your experience to be conveniently shared to others.

Below are some common analysis themes based on a summary of past experience. There are already report templates accordingly for

your reference, which provide the basic information needed for routine monitoring and analysis of performance problems and he lp you

efficiently complete performance monitoring & analysis.

A link toreport

template. It is

for your

reference only.

Example of Analysis

Theme Report Template of

Nastar



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Experience 3: Get familiar with auxiliary problem analysis & lo

Case Study of WCDMA Optimization

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