57828159-investigating degradation due to 7745

1/10 Technical Documentation Radio Access BTS Alarm troubleshooting

INVESTIGATING BSS PERFORMANCE DEGRADATION

- A Description about its relation to 7745 and 7604 alarms -


I. Description

Performance degradation in BSS can be affected by many factors.

As we all know, BSS is comprised of hardware and software equipment.

The degradation can be affected by both factors. But here, we try to look for

every cause instead of software factors, in order to improve BSS.

In this description, we will also explain about 7745 and 7604 alarms

and its impact to performance degradation. These alarms analysis are

based on our experience in this life. Thus, if anyone who has experience

with these alarms and its solution, it will be our precious experience

together, in order to improve our customer’s network.

II. BSS Performance

BSS performance is affected by TRx performance. So, it is important

to look at how TRx operate and work properly under its cell. The explanation

below, will describe how to check and maintain TRx, cells and BTS

performance, especially with its relation to 7745 and 7604.

Check Neighbors

Every cells have some neighbors. Neighbors must be created and

planned properly, in order to maintain every calls handover to its neighbors.

Look at the picture below.

Figure. Cell A has cell B and C as its neighbours

Cell A BSIC = p Freq = q

Cell C BSIC = y Freq = x

Cell B BSIC = y Freq = x


From figure above, we see that cell A have neighbor cell B and cell

C which is having same BSIC and same Frequency Channel. Our

experience shows that this condition will make whether TRx’s under cell B

or cell C will have 7745 alarms. Because when MS from cell A is going to

handover, it detects two cells with same BSIC and Frequency. These two

cells will interference each other. We found this situation at some cells in

Central Java. You can check this condition from MML using common ZEAT.

And remember, check also neighbors of every cells which having 7745

alarms, which can be perform with command ZEAO or from RNW for its

simplicity.

Check TRx’s TSC (Training Sequence Code)

TRx’s have TSC parameter as its Training Sequence Code of the

carrier. We have to make sure, that TSC must have same value with its

BCC. If TSC is different with its BCC, it will raise 7745 alarms at the TRX’s.

Check TRx’s TSC using ZERO command. And check BCC of its cell using

ZEQO command. Make sure they have same value.

Switch BCCH Frequency to another TRX

7745 alarms can be raise in every different case. Every case has

different analysis and solutions. We will try to identify and analyze 7745 and

7604 alarms in some example situation below.

- 7745 at one TRX only

Before you do the site visit, make sure that you have to perform

parameter check (TSC), neighbours and perform the TRX’s test at the

TRx remotely. If you go to do site visit, remember to check the SMA Cable

at Tx connector to WCxA of the TRx. Make sure it is properly tight

connected. Replace the TRx, BB2F and SMA cables if needed.

- 7745 at two TRX.


parameter check (TSC), neighbours and perform the TRx test at the TRx


remotely. For example: we have 3 or 4 TRx under one cell, which are TRx

1, 2, 3 and/or TRx4. If the alarms exist at TRx 1 and 2, and BCCH

frequency is at TRX 1 or 2, try to switch the BCCH frequency to TRx 3 or

TRx 4. If the alarms still appear at TRX 1 or 2, then it is possible that TRX

1 and 2 have a partial cross feeder. It is just our temporary conclusion.

You have to do site visit to make sure. Replace TRx, BB2F, WCxA or

DVxA if needed. Also remember to check alarms on the other sector to

ensure our analysis.

- 7745 at all TRX’s under same cell


parameter check (TSC), neighbours and perform the TRx test at the TRx

remotely. Also remember to check alarms on the other sector. Many

possibilities here, including full partial cross feeder, bad feeder quality and

its connection, interference, broken DVxA, etc.

The most important things if we have BTS performance degradation,

specially related to 7745 is :

1. Perform remote solution first.

o Parameter check

o Neighbours check

o Alarms collection at least 3 or 4 days before.

o Remote TRx test

o Use ND report to strengthen our analysis. Usually ND report

195, 196 and 208 will be useful. For example :

UL, DL Quality and UL Inteference per TRX (Part 1) between 20070118 and 20070118 sorted by bsc_name,bcf_name,bts_name asc q0 q1 q2 q3 q4 q5 q6 q7 (%) (%) (%) (%) (%) (%) (%) (%) ************************************

BSC Name Segment Name (ID) TRX UL UL UL UL UL UL UL UL Call min BCF Name BTS Name (ID) ID DL DL DL DL DL DL DL DL Call dif ----------------------------------------------------------------------------------------------------------------------- SIDOARUM GONDOMANAN3 (30) 12 1 1 1 1 1 1 2 100 40 GONDOMANAN GONDOMANAN3 (30) 5 5 5 5 5 5 5 100 86


From report 196 examples above, we found bad uplink and downlink

quality of TRX12. We have to replace this TRx. In performance

analysis, we usually take a look at band q5. If q5 value is under 90%,

then we suspect that the TRx have bad quality whether uplink or

downlink. Collect information as many as you can, in order to

strengthen our analysis. Then we will know what are we going to do.

2. After we have all analysis and findings, and the problems cannot be

solve remotely, and then we have to do the site visit. Make sure that

you have brought all of the spare part unit needed, tools and also site

master for VSWR check. If feeder is broken, usually 7604 will raise.

Bad connection of SMA cables at RxMain and RxDiv side, it will also

raise 7604 alarms.

III. 7745 and 7604, what is happening ?

If we have 7745 alarms in our network, what is really happening ?

and 7604, what is exactly happen ? Take a look at figure below.

Figure. One sector 4 TRx configurartion

7745 alarm is usually related to degraded transmit quality of one

sector or one TRx. Transmit quality degradation as we discussed above


could be affected by many factors such as neighbours interference,

different TSC-BCC value. Then, if all parameters related have been

checked, we can find out from hardware related by checking its transmit

path from TRx unit, Tx port, SMA-cables from Tx port to WCxA, WCxA

itself, and so on, until its feeder connection and antenna.

Thus, 7604 alarm is usually related to degraded receive quality of

one sector or one TRx. From hardware point of view, we can check its

receive path from TRx unit, Rx main and RxDiv port, SMA cables from Rx

port to M2xA, M2xA itself, and so on, until its feeder connection and

antenna. So, we can conclude by now, if we have feeder antenna cable

broken, it may raise 7745 and 7604 as feeder is used as transmit and

reveice paths.

Problems with 7745 Traffic Channel failures which h ave no sign of a specific failure cause.

Traffic Channel Failure is defined simply as a failure that occurs

during an active call which is using a traffic channel. There are various

faulty scenarios which can cause the 7745 Traffic Channel Failure to

become active. Some primary examples of these faulty scenarios which

can cause the 7745 alarms are BTS unit hardware failures, transmission

failures and network setup problems. This document will cover a scenario

of the Network Setup problem and how it can cause the 7745 alarm. The

specific type of Network Setup problem discussed pertains to incorrect

neighbor cell settings.

The fault scenario can be seen when no relevant alarms are found

within the BTS or BSC alarm histories and no errors are found in the site

setup files.

The alarm history files pertain to ZEOH for BTS alarm types and

ZAHP for BSC alarm types.


The site setup file types pertain to the Hardware Configurator file,

Hub Manager file and Site Information file.

If no other faults are apparent such as transmission degrading

issues or hardware unit failures then an RF site level investigation is

needed.

Performing a drive test on the site in order to find the exact point of

call or handover failure can be very useful in discovering the root cause of

these failure types. If a handover is found to be failing between the source

cell and two or three neighbors but not with all neighbors then the neighbor

settings need to be evaluated for discrepancies.

One primary failure occurrence happens when the site contains a

boarder cell between two BSCs. If the cell is on the BSC boarder then

check the neighbor settings between the BSC bordered cells. An example

of an incorrect setting which will cause the 7745 failure is the ‘FREQ’

setting. The frequency of neighboring cells is a specific parameter which is

part of the adjacent cell settings within command type ZEA_. The frequency

setting is mandatory for inter BSC adjacencies.

The network and RF planning of the adjacent cells to the 7745

alarming site are also common causes of these traffic channel failures.

When a call is improperly released during a handover from the source cell

to the adjacent cell it can then cause a traffic channel failure to occur for the

source cell.

If the drive tests are not easily available then Abis traces can be

done from BSC site. The abis traces can be a very time consuming method

to find the network or RF planning issues so it is strongly suggested that the

drive tests are done if at all possible. The abis traces are a very good

source of information if in-depth further analysis is required.


Within the abis trace the calls can be tracked on an individual bases

to show receive and quality levels. From the Abis trace the call receive level

and quality levels along with timing advance values should be viewed. The

call can be handed into the cell or originated within the cell. At some point a

mobile moving though the source cell will need to be handed out to the

neighboring cell. The mobile should be expected to handover based on the

degraded receive and quality levels which can be seen within the

measurement report found within the abis trace for that active call. When

neighbors are defined incorrectly or the RF plan is improperly implemented

then these Traffic Channel Failures can occur alone with no other alarm

types to explain specific area of fault.

Antenna setup errors are normally found by degraded RSSI values.

Antenna setup issues should be found within the initial investigation from

alarm histories in the form of 7604 or 7607 Operation degraded alarms.


Troubleshooting Method:

1)We have cabled all the sites for diversity. Receiver Diversity

(RDIV) parameter in BSC is off by default. If we have not changed it till

now, enable this parameter in BTS (value Y).

2) In order to troubleshoot this alarm, take the alarm history for 7745

alarm for two days and make a list of Sites/TRXs and Timeslots from where

this alarm is being reported.

3) If this alarm is being reported repeatedly from same TRXs swap

this TRX with a healthy TRX in that sector. If the alarm shifts with the TRX,

the problem is with that TRX. In that case the TRX has to be replaced. If the

alarm stays on that TRX, then check the back plane and the feeder cable.

The following example will make is clear.

Lets say that TRX 3 of BTS 1 is having 7745 alarm on a number of

TSLs.

- The first step would be to swap TRX 3 and 4. If the alarm shifts to

TRX 4, the problem is most likely with the TRX. Replace the TRX and

observe the new TRX.

- If the alarm stays on TRX 3 even after swapping it with TRX 4, then

the problem is either with the Back plane pins or with the feeders/antenna

connections.

- Check the pins at the back plane for TRX

- To eliminate the antenna connection problem, swap the cables for

the antenna connection at the duplexer. Swap the cables between the

antennas for TRX 3 and 4 with the antenna for TRX 1 and 2. If the problem

shifts with the antenna, check the VSWR, returt loss and insertion loss for

the feeders.


- If this does not help swap the multicoupler cables for TRX 3&4 with

the multicoupler cables for TRX 1&2.

These steps will help to greately reduce the number of 7745 alarms.

If after doing all these steps, these alarms are still observed escalate this

problem to the planning team in your respective circles.

Conclusion: The best trouble shooting practice for traffic channel

failures is to check alarm histories and next step is real time drive test.

Just remember to collect any information as many as you can even

from all alarms, trx test, NDreport, etc , then make a deep analysis to locate

the suspect fault, and then you will know what are you going to do. These

alarms clearing will take many days, because after we perform some

replacement, troubleshooting, etc, we have to monitor the result, at least for

one day. So, it is better if you write on a note, about all activities have been

done on one site.

Please note that this alarm means that the rate of calls terminating in

failure on a channel is above the threshold value set by the operator. This alarm is

used to supervise the functioning of traffic and signaling channels, and to detect

the possible faulty channels. This alarm does not necessararily mean that there is

a fault in the equipment. This means that a call has failed a number of times on a

particular timeslot. This failure can be due to a number of reasons. It can due to

poor coverage, due to interference, due to malfunctioning of TRX etc. If we are

sure that we have checked all installation aspects in the BTS and this alarm is still

coming from some TRXs, then we can escalate this to our planiing team. But

before doing this we have to be very sure that there is no problem with the

TRX/feeder/backplane etc.

57828159-investigating degradation due to 7745

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