Two new approaches to bandwidth-efficient partnering for cooperative diversity

This paper presents two new techniques employing bandwidth-efficient modulation to enable two partners to cooperatively convey their data to a common destination. Both approaches integrate relaying and channel coding, exploiting the fact that each partner knows the data relayed by the other partner to enhance the partner-to-partner link. The first approach is based on bit-interleaved coded modulation (BICM); a key innovation is the use of set-partition (SP) labelling that enables the receiving partner to demodulate and decode based on a sparse subset of the original constellation. The second approach is based on trellis coded modulation (TCM); the local and relayed data are multiplexed together prior to encoding, and the receiving partner prunes the trellis edges inconsistent with the known relayed data. In both approaches, the receiver at the common destination benefits in two ways - indirectly from the increased diversity made possible by the enhanced partner-to-partner link, and directly by exploiting the SP-labeling/trellis-pruning in its decoding protocol. Simulations indicate that the new techniques offer significant performance gain over conventional cooperation based on time-sharing - a gain of 2.50 dB for the 16-QAM BICM system and a gain of 3.0 dB for the 8-PSK TCM system, both at a frame error rate of 10^-2.