Efficient seamless rate compatible modulation

In order to avoid channel information feedback and improve the performance of the adaptive coded modulation (ACM) system in space communication, this paper proposes an improved rate compatible modulation (RCM) scheme to approach the channel capacity for the time-varying channel. RCM is a seamless rate adaptive technology, in which modulation signals are incrementally generated from information bits through weighted mapping. Rate adaptation is achieved through varying the number of modulated signals. The paper suggests an adaptive RCM based on construction of sub-block generation matrix of RCM in order to improve the performance of traditional RCM at different Signal-Noise Ratio (SNR), and simulations show that the improved scheme can provide a higher throughput than existing ones. Finally, a low complexity decoding algorithm is proposed.