Conditional Error Probability Analysis in HARQ Process

In hybrid automatic repeat request (HARQ) process,the failure of the first transmission is the condition of the retransmission.The distribution of the noise after combining is not zero-mean-Gaussian. Unfortunately,the assumption of zero-mean-Gaussian noise is widely used in the analysis of HARQ,as well as some similar technologies.Therefore,the estimation of the conditional error probability is smaller than the exact one.In this paper,the conditional error probability under non-zero-mean-Gaussian noise is exactly analyzed.An approximate expression of the exact conditional error probability is also presented for simplicity of application.The difference between the real error probability and estimation based on zero-mean-Gaussian noise assumption is more obvious if the number of symbols in a packet is small and the channel of retransmission is worse than that of the first transmission.