Theoretical Bit Error Rate Performance of the Kalman Filter Excisor for FM Interference
DEFENCE RESEARCH ESTABLISHMENT OTTAWA (ONTARIO)
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This technical report develops a theoretical bit error rate expression for a Kalman filtering technique that is used for filtering narrowband interferers out of direct sequence spread spectrum signals. The approach is based on the digital phase-locked loop Kalman filter and is close to optimum in so far as demodulating an FM-type of interferer. Because the interference is assumed to be much stronger than either the signal or noise, the Kalman filter locks onto the interference and produces estimates of its phase and envelope. Several assumptions are made in the development of the theoretical bit error rate expression and these are expanded upon. It is shown and illustrated that theory agrees well with simulation as long as the bandwidth of the low pass filter used to determine the envelope of the interference is much less than the sampling rate, otherwise the interference estimate at the input to the interference canceller will have significant cross-correlation with the signal, leading to some cancellation of the spread spectrum signal.
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