| How to use power and bandwidth more efficiently is a primary goal for wireless channel which is limited in power and bandwidth,such as deep space communications, satellite communications, mobile communications and ultra-short wave radio communications channel and so on.In order to improve the validity and reliability of wireless communications system, we should adopt efficient modulation scheme and consider how to realize effective carrier synchronization at low Signal-to-Noise Ratio(SNR) and large frequency offset conditions.The singal generated by constant envelope modulation technology has a highly power efficient. Constant envelope modulation is divided into continuous and discontinuous phase modulation based on phase continuity. The continuous phase modulation(CPM) signal is more suitable for transmission in the wireless communications channel for its highly bandwidth efficient,so this paper makes a deep research on CPM signal.In CPM signals, SOQPSK signal has more excellent performance in power utilization ratio and frequency utilization. Firstly, the basic concept of CPM is introduced and SOQPSK signal modulation technology is studied. A reduced-complexity demodulation algorithm for recursive/nonrecursive SOQPSK-MIL and recursive/nonrecursive SOQPSK-TG is studied. The two-state decision feedback demodulation algorithm for recursive SOQPSK-TG is made an in-depth study and two state detection for nonrecursive SOQPSK-TG is poposed. Then, to solve the carrier recovery problem with large frequency offset at extremely low SNR for CPM, a joint time-domain and frequency-domain carrier synchronization algorithm is proposed,it can achieve optimal BER performance. Besides, the proposed algorithm is very suitable for Wireless communications with short pilot cost and low complexity.Finally, a quasi-coherent demodulation algorithm of CPM based on DSP TMS320C5510 of TI Company was finished and the performance of this algorithm is tested. |
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