General Guidelines for RF Hidden Faults Rectification

Purpose:

The purpose of this document is to provide the general guidelines for RF hidden faults (Main/diversity, link imbalance & TRX Efficiency Issues) rectification for both field teams as well as the back office team.

Issues:

Mostly hidden faults are the result of some intra/inter sector swap or some faulty equipment. Below is the pictorial description of some of the issues which can be observed and actions to counter them both for BTS 3012 & BTS 3900.

BTS 3012

BTS 3900

BO team should check all the TRX level stats (main/diversity, link imbalance & TRX efficiency) before addressing any issue. Also check the alarms, output power & transmit/receive mode (single/double feeder etc.).In addition team should verify configuration with the filed team for rectification. Audit Guidelines:

1. First and foremost step is to confirm the co-ordinates of the site so as to negate the difference between planned and physical data.

2. Then check the azimuths of all sectors both for 2G and 3G. In case site has separate antennas for 900 & 1800 band note the azimuth for both antennas separately.

3. Note the type of antenna being used e.g. dual band, single 900 & single 1800 etc.

4. Check the Mechanical tilts and electrical tilts (900 & 1800 separate in case of dual band antenna).

5. Check the antenna height in each sector.

2G Cable Tracing:

1. First identify the sector e.g. A, B or C etc with the help of compass and then do the feeder cable tracing.

2. Do the cable tracing from the antenna to the BTS cabinet not the other way around.

3. Before tracing the cables, confirm the running configuration of boards from M2000 with the help of back office P.O.C. Board numbering usually starts from 0 and goes till 5. Sometimes we have separate cabinets for 900 & 1800 so it is very important to confirm the board configuration before doing any changes.4. Always do cable tracing one by one, say 900, at a time and not mess up all the things.

5. Make sure all the cables are terminating at the correct boards as per configuration.

6. Check for transmit/receive swap (details given below).7. Check for Main/Diversity swap (details given below).

8. Check for CPRI cable swap (details given below).9. Check for diplexer swap (details given below).Below is the simple block diagram for Antenna system to identify different parts.

2G Possible Issues:

Below are some of the cases which can result in partial/sector swap. i. Inter-sector swap

i. 900 cables of one sector are going in the 900 board of other sector.

ii. 900 cables of one sector are going in the 1800 board of other sector.

iii. 1800 cables of one sector are going in the 900 board of other sector.

iv. 1800 cables of one sector are going in the 1800 board of other sector.

ii. Intra-sector swap

i. 900 cables are going to 1800 board.

ii. 1800 cables are going to 900 board.

iii. Transmit & Receive swap

i. Transmit is going to receive & receive is going to transmit within the same sector.

ii. Transmit is going to receive of other sector.

iii. Receive is going to transmit of other sector.

iv. Transmit is going to transmit of other sector.

v. Receive is going receive of other sector.iv. Main & diversity swap

i. Main is going to diversity & vice versa within same sector.ii. Main 1800 is going to main 900 & vice versa within same sector.

iii. Main 1800 is going to main 900 & vice versa of other sector.

iv. Diversity 1800 is going to diversity 900 & vice versa within same sector.

v. Diversity 1800 is going to diversity 900 & vice versa of other sector.vi. Main of one sector is going to main of other sector.

vii. Diversity of one sector is going to diversity of other sector.

v. CPRI cable swap

i. CPRI cable of one sector connected to the board of other sector. This can be confirmed with back office support.vi. Cable terminating in wrong Diplexer

i. 900 cables terminating in 1800 diplexer and vice versa.

ii. 900 cable going directly to board whereas 1800 comes through diplexer.

Some of the issues observed during recent activities are listed below:

3G Cable Tracing:

CP cable coming from RRUs should terminate in correct WBBU board. Ports are in sequence i.e. port 1 for sector 1, port 2 for sector 2 and port 3 for sector 3.

TRX Efficiency & Link Imbalance Issue:

For TRX efficiency & Link imbalance issues you need to check connectors/jumpers connections and their condition (sometimes water sticks in connectors & they get rusty) in addition to the steps mentioned above. If nothing is obvious use site master for sweep test.Note:

Most of the cases can be resolved by keeping above cases in mind but please note that rectification may not be limited to only these cases.

Back Office Support:

Responsibilities of back office support for hidden faults rectification are listed below: Clearly communicate the problem to the field team e.g. which sector has the issue, either 900 or 1800 TRXs are suffering with hidden faults, suspected sectors for swap from DT results etc. Confirm the site configuration in coordination with the FME i.e. ask the FME to turn off the particular board and confirm the same from M2000. Activate the 15 minutes MRs(to save the time of field teams) on the M2000 for counters S4556 & S4557 for diversity; S462A,S462B,S462C,S462D,S462E,S462F,S462G,S462H,S462I,S462J & S462K for UL/DL ; CR440A, CR440B, CR443A, CR443B, R4419A & R4419B for Immediate Assignment Success Rate, Handover Success Rate & Assignment Success respectively. Please note that all these MRs to be checked at TRX level. After the rectification pull out the MRs against the counters mentioned above to ensure:

For Diversity Issues:

Main Level (dBm) =10*log(S4556)-120

Diversity Level (dBm) = 10*log(S4557)-120

Main Level (dBm)-Diversity Level (dBm)< |+/-8| For UL/DL Issues:

Downlink Path Imbalance Issue >>> [(Level1 + Level 2)/(Level1+Level2+Level11)]*100>30%Uplink Path Imbalance Issue >>> [Level 11/(Level1+Level2+Level11)]*100>25% For TRX Efficiency:

ASR_900 TRXs> 85%ASR_1800 TRXs> 90%HSR_900 TRXs> 85%HSR_1800 TRXs> 90% Also check the traffic carried by the particular cell through monitor channel status in M2000 after the activity.

If the problem still persists after all the activities ask the FME to do sweep test with site master to look for faulty connectors, jumpers etc.

Note: It is advisable to check the busy hour stats on the morning of next day to ensure that issue is rectified fully & ask the FME to revisit the site if need be.

THE END

Inverse connection of antennas between cells: inter-cell handover counters

Fault of the TX:

Power query and comparison

Fault of the RX:

Difference between the main antenna level and the diversity antenna level

counters

Fault of an antenna:

1. VSWR alarms

2. Difference between the main antenna level and the diversity antenna level

3. Difference in average downlink level among tunnels counters

Crossed pair of antennas between cells: difference between the main antenna level and the diversity antenna level

counters

Inverse connection of antennas between cells: inter-cell handover counters

Fault of the connecting line between modules:

Difference between the main antenna level and the diversity antenna level

Fault of an antenna:

1. VSWR alarms

2. Difference between the main antenna level and the diversity antenna level

3. Difference in average downlink level among tunnels counters

Crossed pair of antennas between cells: difference between the main antenna level and the diversity antenna level

counters

Straight Jumper being used rather than curve