Coded modulation design for two-way relay channels

In this paper, we present and analyze high efficiency joint coded modulation schemes for two-way relay channels. Depending on how the side information is utilized, two relay-to-destination decode-and-forward approaches are investigated. The first one, termed joint modulation relaying (JMR), jointly modulates two source messages by applying the side information at the modulator and the demodulator. The second one, termed bit-cooperative coded modulation relaying (BCCMR), is a new joint coded modulation scheme for coded relay systems. In particular, we propose new constellation mapping for the JMR and establish the corresponding optimal constellation labeling criterion. For the BCCMR, the joint coding-modulation design introduces the benefits of increased minimum Euclidean distance and the Hamming distance by exploiting the side information in the demapping and decoding. The advantages of the low-density parity-check (LDPC)-coded BCCMR and JMR are analyzed using the density evolution approach. Numerical results are provided to illustrate the significant gains for the symmetric and asymmetric relaying on Rayleigh fading channels.