说明：  深空信道是一种典型功率受限信道，其频带利用率高，但是由于传输环境特 殊性，较大的传输距离和时延导致信道的信噪比极低。除此之外，侦察通信中， 由于传输距窝较远也导致信道信噪比较低。如何将低信噪比条件下的信号准确的 恢复出来是现在急需研究的难点。针对这些问题，在阅读了大量文献的基础上， 本文对低信噪比下ＱＰＳＫ信号解调中的关键技术进行了研巧。
(Deep space channel is a typical power-constrained channel with high bandwidth utilization. However, due to the particularity of the transmission environment, the signal-to-noise ratio of the channel is very low due to the large transmission distance and delay. In addition, in reconnaissance communication, the long transmission distance also leads to the low signal-to-noise ratio of the channel. How to recover the signal accurately under the condition of low signal-to-noise ratio (SNR) is a difficult problem that needs to be studied urgently. In view of these problems, on the basis of reading a large number of literatures, the key technologies of QPSK signal demodulation under low signal-to-noise ratio are studied in this paper.)