Loopback Bit Error Ratio Troubleshooting

Possible Setup Issues

• To perform the Loopback BER measurement while in Active Cell Operating Mode , you must be on an RB test mode call, with Channel Type set to a symmetrical RMC. Loopback BER can not be measured for Asymmetrical RMCs .
• The UE must be configured in loopback mode 1 or 2 (see UE Loopback Type ). When using FDD Test Operating Mode , you must manually configure the UE during testing; no overhead messaging or signaling is provided to set up the mobile station in this operating mode. See UE Control During FDD Test Mode Operation .
• If the Confidence Test Result is Max Bits Tested , you may need to increase the Number of Bits to Test to enable a Pass or Fail result.
• Uplink DTCH RMC CRC Presence must be set to Present .
• Loopback Delay results can not be obtained when DL DTCH Data is set to All Zeros or All Ones .
• During remote operation of the loopback bit error ratio measurement, you should configure the trigger arm to single. See SETup:WBERror and Triggering of Measurements .
• This measurement always uses protocol triggering. A measurement cannot be made unless the UE is synchronized to the test set's downlink signal and is transmitting a corresponding uplink signal.
• Synchronization requirements

  In order for the test set to synchronize to the UE's signal and perform the BER measurement, the following must occur:

  • The loopback delay must be less than 50 transmission time intervals of the DTCH.
    Note, some UEs buffer data during a Physical Channel Reconfiguration (handover), then increase the loopback delay to compensate. As a result, after several handovers, the loopback delay may be too great for the test set to synchronize to the UE's signal. To correct the problem, set RB Test Mode PCR Loopback Messaging State to On before performing the Physical Channel Reconfiguration (this clears the UE's buffer and resets its loopback delay as part of every Physical Channel Reconfiguration), or perform a Transport Channel Reconfiguration to the same RMC after the Physical Channel Reconfiguration to reset the loopback delay in the UE.
  • The bit error ratio must be less than 10% on a block-by-block basis for three consecutive blocks.
    If necessary, increase Cell Power or decrease AWGN Power to decrease BER and allow the test set to synchronize to the uplink signal.

• Measurement results are affected by any amplitude offsets that are entered, since the level into the UE is altered.

Other Considerations

• During front panel operation of the loopback BER measurement, intermediate results are always displayed (i.e. as bit errors are detected the current bit error ratio for the test is updated). This may cause the bit error ratio to vary throughout execution of the measurement. You should use the final bit error ratio reported to determine the BER result for the measurement, not the intermediate results.
     

  NOTE

  If trigger arm is set to continuous, it may be difficult to determine the final bit error ratio result. Watching the bits tested increment will help you determine when the measurement is reporting the final result. (The test set will then immediately begin the next measurement.)

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• The test set may return a Confidence Test Result of Max Bits Tested even when the Bit Error Ratio result is above the specified BER Requirement . This is because as testing progresses, the bit error ratio trajectory converges to a value (see 3GPP TS 34.121 Figure F.6.1.9 ). The test set attempts to predict if the BER value the UE is converging to will be above or below the BER Requirement . The BER trajectory may temporarily exceed the BER Requirement yet still converge to a value below the BER Requirement . A result of Max Bits Tested is returned by the test set if it can not accurately predict whether the trajectory is converging to a value above or below the BER Requirement .

• When Confidence State is Off , you may set the number of data bits to test during the measurement using the Number of Bits to Test setting. However, the actual number of bits tested is always the largest multiple of the number of bits needed to fill a DTCH transport block for the transmitted format. For example, for the 12.2 kbps reference measurement channel (RMC) the transport block is 244 bits. So if you set the number of bits to test to 1000, the actual number of bits tested will be 1220 (1000 bits/244 bits per block = 4.1 blocks, so 5 blocks are required to test at least 1000 bits. 5 blocks x 244 bits per block = 1220 bits).

  When Confidence State is On , you may set the maximum number of bits to test during the measurement using the Number of Bits to Test setting. However, the actual number of bits tested will be less than this number if an early pass or early fail event occurs (see Confidence Test Result ). If a Confidence Test Result of Max Bits Tested is returned, then the actual number of bits tested is the largest multiple of the number of bits needed to fill a DTCH transport block for the transmitted format.

• The loopback block error ratio and loopback bit error ratio measurements can not be run concurrently. If a BLER measurement is initiated while a BER measurement is active, the BER measurement will be aborted and the measurement will be closed (and vice versa).

Interpreting Integrity Indicator Values

• If Measurement Timeout (2) is returned:
  • The measurement timeout value you entered for the measurement may be too small for the number of bits being used. In this case, either reduce the number of bits to test or increase the timeout value.
  • The measurement may not have started because it could not align the received data with the transmitted data. This happens if any of the following conditions occur:
    • The test set is unable to synchronize to the uplink signal. See Synchronization requirements .
    • The UE is not configured for the proper loopback mode.
    • The UE is not configured for the proper uplink transport format.
• Questionable MS-to-Cell Data (28) is returned if a CRC Error or Missing Block is detected (see CRC Errors and Missing Blocks ).

Related Topics

Integrity Indicator

+200 through +299 Error Message Descriptions

Loopback Bit Error Ratio (BER) Measurement Description