Troubleshooting Faults on Main and Diversity RX Channels Due to Incorrect Antenna Connections This section describes how to troubleshoot faults on main and diversity RX channels due to incorrect antenna connections.
Symptom Alarms such as ALM-4176 Main receive channel alarm and ALM-4178 Diversity receive channel alarm are reported. The BTSs that report these alarms encounter problems. For example, the BTS coverage decreases, MSs have difficulty accessing the network, call drops due to handovers increase, and the packet switched (PS) service rate decreases. Swapped BTSs are more likely to encounter antenna connection errors than newly deployed BTSs. Field engineers can use traffic statistics and signaling data in the early phase to locate such problems.
Background Information The following are the performance counters related to main and diversity RX channels:
S4556:Average Main Level in the Customized MR
S4557:Average Diversity Level in the Customized MR
The following are the formulas for calculating the main and diversity RX signal levels:
Main RX signal level (dB) = 10 x log10(S4556) - 120
Diversity RX signal level (dB) = 10 x log10(S4557) - 120
Location Procedure Figure 1 shows the procedure for locating faults on main and diversity RX channels due to incorrect antenna connections.
Figure 1 Procedure for locating faults on main and diversity RX channels due to incorrect antenna connections
Troubleshooting Procedure 1. Check whether the cables between the TRXs and the radio frequency (RF) modules are faulty. Calculate the main and diversity RX signal levels according to the preceding formulas mentioned in background information. For the carriers of the TRXs connecting to the same RF module, if the main RX signal level is different from the diversity RX signal level, check whether any cables between the TRXs and the RF module are faulty.
If yes, replace the faulty cables. Then, go to Step 2.
If no, go to Step 3.
2. Check whether the alarms related to the main and diversity RX channels are cleared.
If yes, no further action is required.
If no, go to Step 3.
3. Check whether a jumper or feeder connected to an antenna connector for the RF module is faulty. Calculate the main and diversity RX signal levels according to the preceding formulas mentioned in background information. For the carriers of all the TRXs connecting to the same antenna connector, if the main RX signal level is different from the diversity RX signal level, check whether a jumper or feeder connected to an antenna connector for the RF module is faulty.
If yes, replace the faulty jumper or feeder. Then, go to Step 4.
If no, go to Step 5.
4. Check whether the alarms are cleared.
If yes, no further action is required.
If no, go to Step 5.
5. Check whether the antenna connections between two cells are crossed. Calculate the main and diversity RX signal levels according to the preceding formulas mentioned in background information. For the carriers of all the TRXs in two cells under the same BTS, if the main RX signal level is different from the diversity RX signal level, check whether the antenna connections between the two cells are crossed pairs.
If yes, correct the antenna connections. Then, go to Step 6.
If no, return to Procedure for locating main and diversity receive channel faults.
6. Check whether the alarms are cleared.
If yes, no further action is required.
If no, return to Procedure for locating main and diversity receive channel faults.
Typical Symptoms of Incorrect Antenna Connections
BTS Type BTS3012
BTS3900
Fault Type
Symptom
Faults in cables between the TRXs and the DFCU or DDPU
For the carriers of some TRXs connected to the DFCU or DDPU, if the main RX signal level is different from the diversity RX signal level, the RXM or RXD cables between the TRXs and the DFCU or DDPU may be faulty.
Faults in the feeder or jumper connected to an antenna connector for the DFCU or DDPU
For the carriers of all the TRXs connected to the same antenna connector, the main RX signal level is different from the diversity RX signal level.
Crossed pairs between the main and diversity RX channels of the two cells
For the carriers of all the TRXs in two or more cells under the same BTS, the main RX signal level is different from the diversity RX signal level.
Incorrect configuration of the TRX send and receive modes
For all carriers of a TRX connected to an RF module, the main RX signal level is different from the diversity RX signal level.
Faults in antennas connected to TRXs
When there are two TRXs in combined-cabinet mode:
There is a great difference in the RX signal level between the main and diversity RX channels of only one cell under the BTS.
For all carriers of one TRX, the main RX signal level is lower than the diversity RX signal level; for all carriers of another TRX, the diversity RX signal level is lower than the main RX signal level.
When there is only one TRX:
Crossed pairs between the main and diversity RX channels of two cells
There is a great difference in the RX signal level between the main and diversity RX channels of only one cell under the BTS.
For all carriers of the TRX, the main RX signal level is different from the diversity RX signal level.
When there are two TRXs in combined-cabinet mode:
There is a great difference in the RX signal level between the main and diversity RX channels of two or more cells under the BTS.
For all carriers of one TRX, the main RX signal level is lower than the diversity RX signal level; for all carriers of another TRX, the diversity RX signal level is lower than the main RX signal level.
When there is only one TRX:
BTS3900/BTS3012 Inappropriate thresholds for the RX signal level of the main and diversity RX channels
There is a great difference in the RX signal level between the main and diversity RX channels of two or more cells under the BTS.
For all carriers of the TRX, the main RX signal level is different from the diversity RX signal level.
For the BTS3012, the threshold is set to 6 dB or larger; for the BTS3900, the threshold is set to 10 dB or larger.
BTS Type
Fault Type Low RX signal level of main and diversity RX channels
Symptom The main and diversity RX signal level is lower than -98 dB. (This can be used as a supplementary method to determine incorrect antenna connections.)
Typical Case Symptom A site frequently encounter problems such as interference, one-way audio, sharp decreases in the RX signal level, and MS access failures. Cause Analysis The feeders for the main and diversity RX channels of the two cells are crossed. As a result, the main and diversity RX signal level difference exceeds 10 dB. Location Procedure 1. Query the performance measurement results by choosing MR Measurement(MR) > User defined MRs per TRX > User defined MRs per TRX > TRX_EXT_MAIN_RX_AVR_LEV on the M2000. 2. Calculate the main and diversity RX signal levels of the two cells according to the preceding formulas. 3. Analyze the main and diversity RX signal level of all carriers in the two cells. The main and diversity RX signal level difference exceeds 10 dB. In addition, the RX signal level of path A in cell 1 is high and that of path B in cell 1 is low, whereas the RX signal level of path A in cell 2 is high and that of path B in cell 2 is low. This indicates that the antenna connections between the two cells are crossed. 4. Check for crossed pairs of feeders onsite and reconnect the feeders. The alarms are cleared. Parent topic: Faults on Main and Diversity RX Channels
