Troubleshooting guide for RSSI, RX level l evel and VSWR alarms. Flexi Multiradio
Items needed •
Test phone with test software.
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7/16 Torque wrench (25 Nm -18.5 ft-lb).
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Laptop with latest BTS manager.
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Dummy loads if available
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Note: For detailed antenna system troubleshooting sweep gear is needed.
(2G) RSSI Alarms
Understanding RSSI Values
BSS10063 Rx Antenna Supervision by Comparing RSSI The purpose of Rx Antenna Supervision is to monitor t he Rx antenna condition. Rx antennas can be monitored for major problems by taking a long-term average of the difference between the Main Rx RSSI and the Div Rx RSSI. The monitoring is based on the principle that all received bursts where the Rx level of main or diversity branch is above the defined limit value (-100 dBm) are accepted as samples and used in the averaging process. A minimum of 160000 samples in one hour must be collected for the BTS to assume that the results are reliable and therefore could be used to raise an alarm. The differences of the TRXs connected to t he same antennas are counted up, and the average difference for main and diversity antennas is calculated. If the difference is above the threshold (default value 10 dB), and the number of samples indicate that the results should be reliable, an alarm is activated. The threshold default value of 10 dB can be changed by a parameter at the BSC between 3 and 64. The functionality of the feature can be disabled. It is still possible that both antennas are damaged simultaneously and the samples from both antennas remain below -100 dBm limit value. Therefore, the difference algorithm cannot detect the fault. For this reason, t he BSC also observes the assignment and handover success rate.
Settable RSSI sample limit The number of received signal strength indicator (RSSI) samples, needed for a valid RSSI calculation, can be configured using t he Element Manager according to the traffic density. The RSSI sample can be configured to values: 80000, 1600 00 (default), 350000 and 7500 00. The value 80000 is preferred when the BTS is located in a rural area and when the traffic density is low. The values 350000 or 750000 are preferred when the BTS is located in an urban area and has high capacity utilization . In areas with intermediate traffic density it is preferred to use the default value 160000. The RSSI sample value may also be configured during the commissioning phase.
Alarm Start and Cancel The BTS estimates the number of samples it would receive for high/medium traffic profiles by setting an internal threshold val ue, which is a multiple of the user defined RSSI sample count. This value is an internal value and is not visible to the user.
The RSSI alarm is raised when: In the first hour, the received sample count is greater than the internal threshold and the RSSI alarm conditions are valid. In the first hour the received sample count is greater than the user configured RSSI sample threshold, but less than the inte rnal RSSI alarm threshold. Then, the BTS software waits for the next hour to determine whether the RSSI alarm is to be raised. In the consecutive second hour the received sample count is greater than the internal RSSI alarm threshold or the user configured RSSI sample threshold and the RSSI alarm conditions are valid. If t he user configurable sample count is changed during this hour then the monitoring is reset and the process restarts from the first hour. The alarm is cancelled automatically in the next hour if the sample count is greater than the user configured sample count and the alarm condition has been cleared.
How the RSSI values are calculate Depending on how the sample count is set in BTS manager will determine how many samples are needed for the calculation . For example 160000 valid sample readings for each TRX in a sector. (This equates to about 2.4% usage over the 1 hour period). One sample equals one TDMA frame and one TDMA frame is 4.615ms. Therefore, one continuous call for one hour will generate 780,065 samples. (12.3minutes). This means that 1TSL needs to be active for a total of 12.3minutes. Real world situations normally have more time slots (TSL) active. If al l 8 TSL are being used each TSL only needs to be active for 115.4 seconds to trigger the feature. This approximately equals to 2.4% usage of the TRX. The system still needs the complete 1 hour testing period before the RSSI Values are calculated and displayed.
Check RSSI from BTS manager
Troubleshooting RSSI Related Alarms: 1. Determine the faulty sector by checking RSSI values in BTS manager. Any difference greater than 10 should be checked. 2. Swap the main and diversity line at the RF module. Be sure the connectors are properly torque (25 Nm / 18.5 ft-lb) after the swap. An alternative to swapping the main and diversity lines could be to use dummy loads if available. Matching dummy loads should be used. Lastly if both lines are suspected to be faulty a sector swap can be completed during the maintenance window. RESET the module after the swap then monitor!! 3. The sample value can be changed to the lowest value 80000 so that less test calls are needed to generate the alarm. Note: Once troubleshooting is complete the value should be changed back to correct value. 160000 for rural area and 750000 for urban area. 4. Perform test calls. Note: you will need a test phone so that you can verify you are camping on the correct sector. Make the needed test calls based on the sample rate that is set in the BTS. NOTE: For RSSI sample to generate traffic is needed. Perform test calls as needed. 5. If the issue follows the antenna line then additional antenna system troubleshooting is needed. (sweeps!) If the fault stays on the same line then the RF module should be replaced.
Fault Example The weakest signal (Ant 2 -119) should be investigated. If after swapping the antenna line and the -119 moves to antenna one the antenna system should be checked. If the issue stays on antenna 2 (port 2) then the RF module should be replaced.
NED Product documentation
(3G)Rx levels differ too much between main and diversity antennas Flexi Multiradio Troubleshooting Guide
Understanding RX level Alarms RAN119: Antenna Alarm with Receiver Signal Comparison
This feature is used for monitoring the performance of the antenna line. The antenna alarm gives information to the operator if, for example, an antenna is broken. By comparing the signal levels in both receiver antennas, an alarm is raised if there is > 7 dB difference in the received wideband noise between the main and diversity branches. If both main and diversity branches are under -112 dBm, a cell fault and an alarm is raised for both branches. BTS RX level output is prx noise when site has no calls, below is the description from NED. Uplink noise (also known as system noise) is the sum of all stationary noise, not just thermal noise. It is very important that the uplink noise is estimated accurately, as it has a direct effect on the capacity of the cell in question. Uplink noise can either be set to a fixed value at the radio network planning stage, or allowed to fluctuate according to the current conditions, with the help of an autotuning algorithm. The autotuning algorithm of Uplink noise level (PrxNoise) can be switched on or off on a cell-by-cell basis using the management parameter PrxNoise autotuning allowed (PrxNoiseAutotuning). Naturally, the uplink noise level can only be measured when the cell is unloaded, or under a very low load. Therefore, the updating of uplink noise is dependent on PrxUnloaded measurements. When the cell is unloaded, PrxTotal is the same as PrxUnloaded. The cell is considered to be unloaded when the following conditions controlled with a PRFILE parameter are met:
NED Product documentation information Fault name Rx signal level failure Meaning The RX signal level is less than -112dBm or the difference between the maximum and minimum power levels of all RX antennas in the same cell and sector is more than the limit (Flexi 7dB). Cell capacity is decreased. Reported alarms 7654 CELL OPERATION DEGRADED LED display Blinking red (7654) Instructions Check BTS Site Manager for the received signal levels to find out which RX is causing the problem. 2. If an MHA is alarming, replace the MHA unit and check if the RX signal level failure alarm is canceled. 3. Check the antenna cables. The radio module, antenna feeder, or antenna is faulty on the antenna line which has the inadequate RX level. Check and replace the faulty equipment. Note: The RX value in BTS Site Manager is refreshed at one minute intervals.
Checks from BTS manager
Troubleshooting RX level Alarms: 1. Determine the faulty sector by checking RX levels from BTS manager. Any difference greater than 7dB or any line lower than -112dBm should be checked. 2. Swap the main and diversity line at the RF module. Be sure the connectors are properly torque (25 Nm / 18.5 ft-lb) after the swap. An alternative to swapping the main and diversity lines could be to use dummy loads if available. Matching dummy loads should be used. Lastly if both lines are suspected to be faulty a sector swap can be completed during the maintenance window. RESET the RF module after the swap then monitor!! 3. After the swap recheck the level from BTS Manager. 4. If the issue follows the antenna line then additional antenna system troubleshooting is needed.
