Abstract
Rate-compatible modulation (RCM) can achieve adaptive transmission in a variable channel environment. However, there are two problems with conventional RCM. Firstly, there is a large number of four rings in the mapping matrix of the conventional RCM, which blocks the delivery of messages in the decoding. Secondly, in the conventional decoding of RCM, the soft information of the last decoding will be discarded when cyclic redundancy check (CRC) is failed, which decreases the performance significantly. In order to address these two problems, in this paper, we propose a new method to construct a mapping matrix without four rings (MMwoFR) and an improved belief propagation (IBP) algorithm for RCM decoding. On the one hand, by using MMwoFR, the constructed matrix is able to prevent the existence of four rings which have much side influence of reliability performance. On the other hand, the IBP is able to make the most use of the soft information in RCM decoding. Simulation results show that using MMwoFR and IBP can bring at least 12% goodput gain for RCM at the high signal-to-noise ratio (SNR) region while maintaining the same performance in the low and moderate SNR regions. Moreover, complexity analysis shows that the new scheme has comparable complexity compared with a conventional RCM.
Highlights
High transmission rate is an important parameter in wireless communications over time-varying channels
Original Rate Compatible Modulation In Rate-compatible modulation (RCM), source bits are directly mapped to symbols
When the weight set is {±1, ±2, ±4, ±4}, RCM2 achieve the rate of 6.25 bits/s/Hz at 30 dB, while mapping matrix without four rings (MMwoFR) achieve the same rate at 27 dB, improved belief propagation (IBP) at 24 dB and MMwoFR-IBP at 23 dB
Summary
High transmission rate is an important parameter in wireless communications over time-varying channels. Adaptive coding and modulation (ACM) is an effective way to achieve high transmission rate, which has been adopted in 802.11a [1,2]. In order to achieve seamless transmission and overcome the problem of channel estimation at the same time, several rateless codes [4,5,6,7] have been proposed. An ACK signal acts as a feedback to notify the transmitter starting to transmit symbols generated by another block of bits In this way, RCM is able to achieve seamless rate adaptation under time-varying channel conditions. The existence of four rings will decrease the reliability performance of RCM Another problem of RCM is that the process of iterative decoding loses lots of useful information. The design RCM mapping matrix can combine the construction method of QC-LDPC codes.
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