针对深空通信极低信噪比环境下,通信距离大,信号衰减大等特点,阐述了深空通信对低码率码字的需求。介绍低码率码字的发展情况后,引入GLDPC码,分析了LDPC码和Hadamard码进行级联时存在的度为1的节点问题。将LDPC-Hadamard级联码进行优化,对优化后的LDPC-Hadamard码进行仿真。结果表明,极低信噪比下,低码率LDPC-Hadamard码性能较好,一定程度上能够满足深空通信等恶劣信噪环境下的需求。 Aiming at the characteristics of very low signal-to-noise ratio (SNR) in deep space communications, such as large communication distance and large signal attenuation, the demand for low bit rate codewords in deep space communication is expounded. After introducing the development of low bit rate code words, the introduction of GLDPC code, the analysis of the LDPC code and Hadamard code cascade exists when the degree of 1 node problem. The LDPC-Hadamard concatenated code is optimized to simulate the optimized LDPC-Hadamard code. The results show that LDPC-Hadamard code performs well under very low signal-to-noise ratio and can meet the needs of bad signal-noise environment such as deep space communication to a certain extent.