Troubleshooting RTWP FaultsThis section provides information required to troubleshoot RTWP faults. The information includes fault descriptions, background information, possible causes, fault handling method and procedure, and typical cases. Fault Description An RTWP-related alarm is reported if there are received total wideband power (RTWP) faults in the radio frequency (RF) channels of an RF unit. Related Information Related alarms are as follows: ALM-26522 RF Unit RX Channel RTWP/RSSI Unbalanced ALM-26521 RF Unit RX Channel RTWP/RSSI Too Low Possible Causes The setting of attenuation on the RX channel of the RF unit is incorrect. The feeder connected to the RF unit is faulty. Passive intermodulation (PIM) exists. External interference exists. The feeder is improperly connected to the antenna. The hardware in an RF module is faulty. Faults may be caused by other uncertain factors. Troubleshooting Flowchart a. Subrack No..) . If such an alarm is reported. run the MOD RXBRANCH command to modify the configuration. and Slot No.c. If it is configured as planned.Figure 1 Troubleshooting flowchart for RTWP faults Troubleshooting Procedure 1. Run the LST ALMAF command to check whether alarms related to ALD or TDM are reported (applicable only to 3900 series base stations). Command output for 3900 series base stations (The values of Cabinet No. clear the alarm by referring to Troubleshooting ALD Link Faults. Run the LST RXBRANCH command to check whether attenuation of the RX channel of the RRU is configured as planned. are 0 for the BTS3202E. If it is not configured as planned. b. Rectify the faults and modify the improper settings. go to 1.. For example. PIM interference exists.1dB) = 0 RTWP Initial1(0.1dB) = 0 RTWP Initial3(0.1dB) results = 1) No. = of RX Channel = ON Attenuation(0. the existence of PIM interference can be determined. SimLoadCfgIndex=9.Cabinet No. = 0 RX Channel No. ADD CELLSIMULOAD: LocalCellId=x. PIM interference exists. and then compare the received signal strength indicator (RSSI) values before and after the simulated load is added. From the main menu on the M2000 client. clear the alarm by referring to ALM-26522 RF Unit RX Channel RTWP/RSSI Unbalanced or ALM-26521 RF Unit RX Channel RTWP/RSSI Too Low. . Using this typical characteristic. the scheduling performance cannot be ensured. there is no PIM interference and go to 3. If values on all RSSI curves are basically the same. An RSSI tracing task is created. If either of the alarms is reported. = 0 Subrack 0 Logical Switch 0 RTWP = 0 RTWP = 0 RTWP = 0 RTWP = 0 (Number of c.1dB) = 0 RTWP Initial5(0. Check whether PIM interference exists. If the values on one RSSI curve are significantly greater than the values on other RSSI curves. Then.1dB) Initial6(0. NOTE: Note that load simulation is mainly used in interference tests. If the uplink interference increases significantly with the transmit power. = 62 Slot No.5dB) = Initial0(0. If the ALM-26522 RF Unit RX Channel RTWP/RSSI Unbalanced alarm cannot be cleared by referring to ALM-26522 RF Unit RX Channel RTWP/RSSI Unbalanced. PIM has a typical characteristic: The level of the intermodulation products increases with the transmit power. You are advised not to use load simulation for a cell with more than six active UEs. Check whether the ALM-26522 RF Unit RX Channel RTWP/RSSI Unbalanced or ALM-26521 RF Unit RX Channel RTWP/RSSI Too Low alarm is reported. choose Monitor > Signaling Trace > Signaling Trace Management.1dB) = 0 RTWP Initial7(0. b. Figure 2 shows an example of RSSI tracing results. The procedure is as follows: a.1dB) Initial4(0. The simulated load and transmit power have a positive correlation with the value of the SimLoadCfgIndex parameter.1dB) Initial2(0. Otherwise. Otherwise. perform 2 to 6.List RxBranch Configure Information ----------------------------------. You can increase the transmit power by adding a downlink simulated load. choose LTE > Cell Performance Monitoring > Interference RSSI Statistic Detect Monitoring. Start RSSI tracing. click New in the right pane. Run the ADD CELLSIMULOAD command to add a simulated load. PIM interference does not exist. 2. In the left navigation tree. PIM interference is introduced by the device or cable before this breakpoint. PIM interference is not caused by the RF unit. PIM interference is caused by the RF unit. disconnect the cable at breakpoint 1. Add a simulated load and shake the cable segments by segments from the RF unit top to the antenna port. connect the breakpoint to a matched load or a low-intermodulation attenuator. For example. If RSSI values change dramatically when shaking a segment. b. and add a downlink simulation load. PIM interference is introduced by this segment. Ensure the inserted attenuator has low intermodulation interference so that it will not add additional PIM interference to the cable. Perform the similar steps to the other breakpoints. connect breakpoint 1 to a low-intermodulation attenuator. set four breakpoints from the RF unit top to the antenna port. Disconnect the cable at the breakpoints one by one along the direction from the RF unit top to the antenna port. and check whether the RTWP values increase. use either of the following methods to determine the location or device where PIM is introduced: a. as shown in Figure 3. If the RTWP values increase. Breakpoint-based PIM detection: By using breakpoints. If RTWP values do not change.Figure 2 RSSI tracing result If PIM interference exists according to the preceding investigation. If RTWP values increase. At first. Each time the cable is disconnected at a breakpoint. add a downlink simulated load. divide the cable connecting the RF unit top to the antenna port into several segments by using breakpoints. . If the interference is removed. and investigation results to Huawei technical support for fault diagnosis. running logs of RF units. replace the cable and then check whether the interference still exists. no further action is required. RTWP variations of different RF channels are uncorrelated. replace the RF unit. The ALM-26522 RF Unit RX Channel RTWP/RSSI Unbalanced alarm caused by a crossed pair connection has the following characteristics: a. Then. the RF unit will have different RTWP values.Figure 3 Schematic diagram for breakpoint-based PIM detection If the interference is caused by the RF unit. see Monitoring eNodeB Performance in Real Time > Spectrum Detection in 3900 Series Base Station LMT User Guide. The purpose is to ensure the consistency between the direction and coverage of an antenna so that balanced RTWP values are obtained. If the RF channels of an RF unit are used by different sectors. If the interference persists. The alarm is reported in at least two sectors under the same eNodeB. b. send the local tracing results. Check whether a crossed pair connection exists (applicable only to 3900 series base stations). Monitor the results in Broadband on-line frequency scan for at least 30 minutes or until the 26522 RF Unit RX Channel RTWP/RSSI Unbalanced alarm is reported. If the interference is caused by the cable. check whether the interference exists in the antenna. For the procedure for performing Broadband on-line frequency scan. Description RF channels in an RF unit must be used by the same sector except in MIMO mutual-aid scenarios. Note that the ALM-26522 RF Unit RX Channel RTWP/RSSI Unbalanced alarm is reported only when the number of UEs is significantly different between two cells with a crossed pair connection. . the services of the peer mode carried by this RF unit are also interrupted. This test cannot be applied to 1T2R RF units if RRU combination is not used.c. respectively. a cross pair connection exists between the two sectors. or cells under the eNodeB with an omnidirectional antenna. RTWP variations are similar in different sectors. where the UE is located. Detailed information about the sectors with a crossed pair connection is displayed in the detection result. The result is shown as follows: +++ HUAWEI 2012-02-02 10:54:58 O&M #453 %%STR CROSFEEDTST:. NOTE: Note the following before starting a crossed pair connection test: This test is an offline test and the execution of this command interrupts services. cell 1). for the external filter. distributed cells. Otherwise. specify the Start Test Frequency and End Test Frequency parameters to the start frequency and end frequency. the execution output is not reliable. If the UE accesses another cell (for example. Report Type = Cross Feeder Test Progress Status = Success Session ID = 65537 . If the VSWR is greater than 2. This test cannot be performed simultaneously with the VSWR test or distance to fault (DTF) test. Check whether the UE accesses cell 1. The result is similar to the following: To start a cross feeder test. This command applies to the scenario where RF modules are in 2T2R mode.%% RETCODE = 0 Progress report. If the antenna system is not equipped with an external filter. Run the STR CROSFEEDTST command to start a crossed pair connection test. Perform drive tests and trace signaling without interrupting the services. Troubleshooting Method The cells with a crossed pair connection can be determined by using either of the following two methods: d. the antennas of cells 1 and 3 are cross-connected. the result may be incorrect. This command does not apply to the scenario where all antennas of one sector are connected to another sector. If the antenna system is equipped with an external filter. e. Make a phone call in a cell (for example. Do not start this test if the number of sectors that work in the same frequency band and support the test is less than two. You are advised to perform a high-precision VSWR test before running this command. The test will be performed in the test frequency band supported by the RF unit. Operation succeeded. the Start Test Frequency and End Test Frequency parameters do not need to be specified. This command does not apply to multi-RRU cells. If this command is executed on a multi-mode RF unit or an RF unit connected to an antenna shared by the local and peer modes. the result may be incorrect. cell 3). run the following command: STR CROSFEEDTST:. The VSWR test has a great impact on the precision of this test because the VSWR will cause a gain loss. If the bandwidth between the start frequency and end frequency of the external filter is less than 10 MHz. you are not advised to run this command. Session ID = 65537 (Number of results = 1) --END +++ HUAWEI 2012-02-02 10:55:15 O&M #452 %%STR CROSFEEDTST:. If RESULT is Crossed for two sectors. The Crossed value of RESULT appears in pairs. If this command is executed in other scenarios.%% RETCODE = 0 Operation succeeded.5. Sector No. contact Huawei technical support. adjust their antenna connection. contact Huawei technical support. Typical Cases None If the fault persists. and diversity-diversity). several rounds of antenna adjustment may be required before the test result verifies no crossed pair connection. Therefore. Since there are three types of crossed pair connections (main-main. maindiversity. If the fault is not caused by the preceding factors.Cross Feeder Test Result -----------------------. RESULT 0 Normal 1 Normal (Number of results = 2) --END Handling Suggestion After the sectors with a crossed pair connection are determined. ignore it if the RTWP imbalance alarm is not frequently triggered. it may be caused by random electromagnetic interference. . If the RTWP imbalance alarm is frequently triggered. Check whether random electromagnetic interference exists. Occasional electromagnetic interference has a small impact on the network performance.