Research On Synchronization And Demodulation Algorithm Of SOQPSK

With the growth of the wireless terminals, the available frequency resources are limited seriously. In order to make full use of the frequency resource, the modulation formats with high frequency spectrum utilization have attracted a large number of studies. SOQPSK (Shaped offset quadrature phase shift keying) signal has become a hotspot for its high frequency spectrum utilization. In this paper, the model of SOQPSK, synchronization and demodulation algorithm have been investigated.Firstly, the model of SOQPSK is studied. The phase tree of the MIL-SOQPSK, SOQPSK-A and SOQPSK-B signals has been investigated. Then the encoding and modulation characteristics of the SOQPSK signals are analyzed and the modulation function of SOQPSK-A and SOQPSK-B signals are proposed. Finally, the spectrum among the three types of SOQPSK signals, OQPSK and MSK signal are compared.Secondly, the synchronization algorithm of the SOQPSK signal is studied. According to the characteristics of the phase trajectory, a new nonlinear quartic symbol timing estimation algorithm is proposed. Then the joint symbol timing and carrier phase estimation algorithm is proposed, and the performance bounds of the estimator have been analyzed. The frequency estimation algorithm of the SOQPSK signals has also been investigated. Then the factors of the symbol timing, carrier phase and the carrier frequency are considered together, the joint synchronization algorithm has been investigated. Simulation experiments show that the performances of the estimators are close to the modified Cramer-Rao bound (MCRB).Finally, the demodulation algorithms of the SOQPSK signals are investigated. Based on the analysis of the simplified demodulation algorithm for MIL-SOQPSK, the simplified demodulation algorithm for SOQPSK-A and SOQPSK-B are investigated, in which the approximate matched filters are calculated. The simplified demodulation algorithm decreases the computational complexity. Meanwhile, another simplified demodulation algorithm based on the linear waveform decomposition is compared. Simulation results show that the bit error ratio (BER) performance of the proposed simplified demodulation based on matched filters is better.In this thesis, the phase trajectory of the SOQPSK signal is investigated carefully, based on which, the synchronization and demodulation algorithms are proposed. The synchronization algorithms improve the estimation performance of the parameters, and the simplified demodulations decrease the computational complexity.