Analysis of the threshold in adaptive demodulation

A new adaptive demodulation(ADM) scheme based on rateless code and Maximum a Posteriori Probability compute the log-likelihood ratio(LLR) of each bit in the modulated symbol, if the LLR of this bit is larger than the pre-set threshold, demodulate this bit, else delete it. Because the channel state information(CSI) is known by the receiver, this scheme select the bit to demodulate based on the CSI, so it improve the channel usage. The demodulate threshold in this algorithm determines the demodulation order, hence it has great influence on system performance. This paper analyses the demodulation threshold in this adaptive demodulation algorithm, and find out the optimal threshold by simulation, in order to achieve the optimal performance.