中文摘要：

为了减少在低信噪比区的平均迭代次数和削弱LLR值的振荡,分析了中短码长LDPC码错误帧对应校验节点对数似然比及校验和变化的规律,提出了一种基于消息振荡及校验更新的改进BP译码算法。该算法通过提前结束迭代译码的准则来减少在低信噪比区的平均迭代次数,并通过修正校验节点的更新来削弱LLR值的振荡来提高译码性能。仿真结果表明,相对于BP算法：在低信噪比区,该算法减少了平均迭代次数且译码性能没有损失;而在中高信噪比区,该算法提高了译码性能而平均迭代次数无须增加。

英文摘要：

To reduce the average number of decoding iterations in the region of low SNR（signal to noise ratio） and weaken the oscillation of the LLR（logarithm likelihood ratio）,discovered the variation law of the check nodes＇LLR and the checksum,in the error frame of the short and middle length LDPC codes.Based on the law,proposed an improved BP algorithm of LDPC decoding.In the algorithm,developed an early stopping criterion to reduce the average number of decoding iterations in the region of low SNR.And to improve the decoding performance by weakening the oscillation of the LLR,modified the update algorithm of check node.Simulation results show that,the algorithm reduces the number of iteration while the performance is not reduced in the region of low SNR,the decoding performance is improved while the number of iteration is not changed in the region of middle and high SNR.