The test set must be set to operate as a base station transmitting in DTX mode. In this mode, there are periods where no transmission occurs. The BFI measurement is made by transmitting GMSK modulated pseudo-random bit sequence (PRBS) data in the periods where no transmission should occur. The mobile station should indicate these frames as bad by setting all the bits to zero before looping them back to the test set. From the number of frames with bits not set to zero, the test set returns results indicating the rate of undetected bad frames.
The BFI measurement in the test set supports full-rate (FR), half-rate (HR), adaptive full-rate (AFS) and adaptive half-rate (AHS) speech channel modes. See Channel Mode Setup for more information about channel modes.
For expected results, the test set must be properly configured. See How do I make a GSM Bad Frame Indication (BFI) Measurement? or Programming a GSM Bad Frame Indication (BFI) Measurement for the proper procedure.
The mobile station's loopback delay expressed in frames. The default setting for this parameter is 5. However, this value is mobile station specific. You may not get expected results if this is not configured correctly. You can determine the speech frame delay using the test set. To do this, perform the Bit Error Measurement and use the value it automatically displays for the Loopback Delay.
The GPIB command to set this parameter is SETup:<BFINdication|BFI>:SFDelay .