Abstract:

Since the Doppler frequency offset and Doppler rate-of-change caused by the accelerated motion of the moving targets are hard to tract and eliminate in high-dynamic environment,which seriously affects the performance of the receiver,we propose a carrier synchronization method for joint pilot and Viterbi decoding per-survivor-processing (PSP).First,an open-loop acquisition is performed based on the minimum mean square error (MMSE) principle,and the frequency offset is modeled in the form of the Taylor series expansion.Then,a known sequence is used to estimate the Doppler frequency offset and Doppler rate-of-change,thereby limiting the frequency offset and rate-of-change to a small range.Meanwhile,to overcome the performance degradation caused by the accumulation of long-term phase errors,the closed-loop tracking is implemented by the PSP technology,and the soft information determined by Viterbi symbol-by-symbol is input to the third-order phase-locked loop (PLL).Moreover,the frequency synthesizer is adjusted according to the error of the phase detector.Then this action is iteratively performed to minimize the error of the phase detector and realize the carrier synchronization.Finally,coherent demodulation reception is achieved.Simulation results show that when the normalized frequency offset is less than 0.1 and the normalized rate-of-change is less than 10^-3,the proposed method can track the carrier accurately.Furthermore,under the bit-to-error (BER) constraint of 10^-5,there is only 0.8dB difference in S/N ratio between the proposed decoding synchronization cascade tracking algorithm and the ideal carrier synchronization without the Doppler frequency offset and rate-of-change.In addition,the propose algorithm is significantly superior to the traditional phase-locked loop and MMSE algorithm.

Key words: high-dynamic, carrier synchronization, pilot, per-survivor-processing, phase-locked loop