A Novel Approach to Improve Doppler Tolerance of Polyphase Code

Polyphase codes have a large mainlobe-to-sidelobe ratio in matched filter processing. However, the conventional matched filter processing of polyphase codes suffer severe signal loss in performance under large Doppler environment. The basic approach for overcoming the Doppler effect is to use a bank of Doppler-matched filters. Each of the Doppler-matched filters is designed to match a different Doppler frequency. However, the brute force method causes heavily computed burden. This paper proposed a novel correlator based on partial match filter (PMF), followed by the FFT and maximum output selector. The method can simultaneously search all possible Doppler frequencies. The processing scheme can cancel the phase rotation resulted from Doppler frequency, therefore, improve Doppler tolerance when detecting polyphase codes. The performance for the Doppler tolerance improves with decreasing of size of partial correlator and FFT. The scalloping loss can be compensated by zero-padding FFT.