Distributed trellis coded modulation for multi-source cooperative networks

At the expense of spectral efficiency loss, cooperation among users improves error performance by enhancing the diversity provided by slow fading channels. Recently, multi-source cooperation (MSC) has been introduced to improve cooperative diversity and bandwidth efficiency relative to cooperative schemes which rely on repetition coding. The overall code rate of MSC, however, is still less than 1. In this paper we put forth a distributed trellis coded modulation (DTCM) MSC system which reaches the bandwidth efficiency of a non-cooperative TDMA system. This is accomplished by partitioning transmissions into frames. In each frame, each user\´s transmission consists of two parts: the new message from current frame, and DTCM relayed messages from the previous frame. The proposed system is compatible with existing TDMA networks, and gives each user flexibility to cooperate or not. We show that in a cooperative network with K active users, the maximum diversity order is upper bounded by min(d_min, 1 + └K/2┘) when using a convolutional code with rate 1/2 and minimum (free) Hamming distance d_min. As a result, the proposed system improves error performance without sacrificing rate.