Study Of QPSK-demodulated Algorithms Based On Processing Transponders

In communication satellites'processing transponders, the on-board demodulation is an important technology, which can improve the transmission qualities of satellite signals. Because of the satellite resources limited, the complexity and power consumption are considered in on-board demodulation. This paper mainly researches and analyzes QPSK-demodulated algorithms based on processing transponders. The demodulation of QPSK signals includes non-coherent demodulation and coherent demodulation. For the non-coherent and coherent demodulation of QPSK signals, the paper discusses the non-coherent demodulation in the differential QPSK-modulated system and two algorithms of carrier phase estimation-V & V algorithm and LBAR algorithm, and appropriately improves LBAR algorithm. Comparing with the performance, we conclude that the non-coherent demodulation of QPSK signals in the performance is not as good as the coherent demodulation, but it has the low complexity; we conclude that the improved LBAR algorithm for estimation of QPSK-demodulated carrier phase improves the accuracy of the estimators and reduces the computing complexity, relative to V & V algorithm and LBAR algorithm. In the MATLAB simulation environment, the performance of several algorithms such as the BER (bit error rate) is carried out. Through the hardware platform system, the BER of the algorithms is tested and verified. The results show that because of its low computational complexity and low power consumption, the QPSK-demodulated algorithms in the paper is more suitable for on-board demodulation system.