A frequency tracking RAKE demodulator for multipath channels

The structure and performance of a frequency-tracking RAKE receiver for spread-spectrum HF communications are discussed. The receiver uses a frequency-tracking loop that compensates for the Doppler-induced phase offset between the correlator output signal and the channel reference to maximize the resulting signal-to-noise ratio at the output. The processing estimates the average multipath phase offset and rotates the complex samples at the correlator output to remove the estimated phase error. The performance of the loop is analyzed for single and multiple path channels in additive white Gaussian noise (AWGN), and simulation results are presented on the bit-error-rate (BER) performance of the tracking receiver. The results show that by properly setting the bandwidth of the loop it is possible to achieve BER performance within a few tenths of a decibel of an ideal RAKE demodulator