Rate-Splitting Multilevel Codes over an AWGN Channel

This paper deals with a novel multilevel coding technique for an additive white Gaussian noise (AWGN) channel, referred to as rate-splitting multilevel codes (RS--MLC), which is capable of achieving the Shannon capacity limit in the high signal-to-noise regime by stacking up low-rate capacity-approaching codes. The rate-splitting concept originally occurred in a work for Gaussian multiple access channels by Rimoldi and Urbanke. RS--MLC has the advantage of allowing comparatively low-complexity successive cancelation decoding, also known as multistage decoding. Unlike classic multilevel codes where the rates at each level should be appropriately chosen via an information-theoretical approach, this scheme removes this limitation and admits a rigorous capacity achievability proof from multiuser information theory. Analysis of error propagation of multistage decoding is presented, providing guidelines for power and rate allotment among different levels. Application examples are illustrated in an analytical manner. As a byproduct, a new synchronization scheme suitable for TC and LDPC codes is described. Finally, we investigate the coding latency inherent in RS--MLC via random error exponent. It is shown that RS--MLC exhibits poor performance in terms of coding latency. The implication is that an asymptotic-optimal coding scheme may not necessarily be ideal, particularly for applications with rigid system delay.

Keywords: AWGN, Shannon Capacity, Multiple Access, Multilevel Codes, Turbo Codes, LDPC, Coding Latency