Cooperative Amplify-and-Forward with Trellis Coded Modulation

In a cooperative communication network, individual users are encouraged not only to transmit their own data, but also relay other user´s data. This relaying transmission creates spatial diversity to combat the effect of individual severe fading and path loss. Since cooperative users utilize some degree of their transmission freedom for relaying other user´s data, cooperative transmission results in lowering each user´s transmission spectral efficiency. Therefore, a coding scheme with high spectral efficiency and optimized performance would be desirable for a cooperative network. This paper proposes the Trellis Coded Modulation (TCM) scheme to be incorporated with the cooperative Amplify-and- Forward (AF) systems. A criterion for designing good TCM codes for AF systems is also derived and two cooperative AF systems achieving 1 bits/sec/Hz and 1.5 bits/sec/Hz for each user are presented. Analyses in this paper show that cooperative TCM schemes can not only achieve high spectral efficiency, but also outperform convolutional codes with a high order modulation scheme.