Search

Deep space communications has played an important role in deep space exploration. Compared with common satellite and terrestrial communications, deep space communications faces more challenging environment. The paper investigated the unique features of deep space communications in detail, discussed the key technologies and its development trends for deep space communications.

It is a challenging problem to design a high performance modulation for mobile satellite communications due to the limited power and bandwidth resource. The paper improves Feher patented Quadrature Phase Shift Keying (FQPSK) by redefining the waveform. The novel FQPSK, with constant envelope, can be used to improve the power efficiency and frequency efficiency of mobile satellite communication. The study shows that the improved FQPSK outperforms conventional FQPSK over AWGN and is immune to the non-linearity of high power amplifier. At last, the impact of flat fading and multi-path fading of channel on the BER performance of improved modulation is analyzed.

As the raised cosine shaping filter is often employed in practical satellite communication system, the envelope fluctuation at the symbol transition point is decreased which leads to the failure of the common wavelet algorithm under low SNR. Accordingly, a method of blind symbol rate estimation using signal preprocessing and Haar wavelet is proposed in this paper. Firstly, the effect of filter shaping can be reduced by the signal preprocessing. Then, the optimal scale factor is searched and the signal is processed and analyzed by the Haar wavelet transform. Finally, the symbol rate line is extracted and a nonlinear filter method is inducted for improving the estimation performance. Theoretical analysis and computer simulation show the efficiency of the proposed algorithm under low SNR and small roll-off factor.