Comparison of four FFT-based frequency acquisition techniques for Costas loop BPSK signal demodulation

This paper discussed four open-loop frequency acquisition techniques for suppressed-carrier BPSK signals. The techniques, which do not require accurate symbol timing nor a data preamble sequence, employ fast Fourier transforms (FFT´s) on the Costas loop phase detector output to detect the Doppler frequency offset. Performance of the full-, half-, and staggered-symbol integration techniques as well as the low-pass filter technique are compared in terms of the error signal output SNR´s. Then, the probability of detecting the frequency offset is computed for the special case when the frequency of the tone to be detected coincides with one of the FFT-bin center frequencies. It is shown that the performance of the integration techniques depends strongly on the symbol timing offset. On the other hand, the detection probability for the one-pole arm filter technique depends directly on the filter bandwidth. The staggered integration technique is shown to have comparable performance to the low-pass filter technique for low-to-medium symbol SNR´s but the latter is superior at high symbol SNR´s