Low-complexity rate compatible modulation with hybrid weight set

Rate Compatible Modulation (RCM) is an efficient technique for high spectral efficiency seamless transmission over highly dynamic wireless channels. However, its high decoding complexity at the receiver prevents it from being applied in scenarios where computation resources are limited. To alleviate this problem, an RCM with variable weight sets (RCM-VWS) was presented in the literature to significantly reduce its complexity by employing weight sets of different complexities for channels at different signal-to-noise-ratio (SNR). However, RCM-VWS has to introduce an undesired feedback channel for the transmission of SNR information that is estimated at the receiver and transmitted back to the transmitter for weight set selection. To achieve a low computational complexity while avoiding feedback transmission at the same time, a novel RCM scheme with hybrid weight set (RCM-HWS) is introduced in this paper. A low complexity of decoding is allowed by gradually reducing the complexity of weight sets based on the number symbols already sent. It also avoids the feedback of SNRs since we can deduce SNRs from the number of the symbols transmitted and use a hybrid weight set we have designed. The theoretical analysis and simulation results show that the proposed scheme has the advantages of low demodulation complexity and not requiring feedback channel while maintaining the same transmission throughput as that of the conventional RCM. Therefore, the proposed scheme has a wider range of applications, especially in the case that feedback channel is not available.