Link Adaptive Transmission Techniques In Cooperative Communication

In cooperative communication, cooperation among two or more single antenna users can generate space diversity gain, which will effectively increase end to end spectral efficiency. In order to combat with the challenges brought by time-variant channel and multi-hop transmission, link adaptive transmission techniques for cooperative communication is investigated to farthest utilize cooperative diversity gain in this dissertation.Firstly, the widely used adaptive modulation and coding technique is introduced, we also analyze the problems of adaptive modulation, power allocation and subcarrier allocation in single-relay cooperative system where a single forwarding scheme is involved, and give some adaptive schemes for AF and DF cooperative system respectively. Then we investigate the performance of cooperative system using multiple forwarding scheme, including a hybrid forwarding strategy in OFDM based single-relay cooperative system, i.e., adaptively selecting forwarding scheme on each subcarrier, and a hybrid forwarding strategy in multiple-relay cooperative system, i.e., selecting the best forwarding scheme for each relay. Simulation result shows wireless resources is better utilized under this hybrid forwarding scheme stategy.In addition, to avoid the feedback of channel state information (CSI) from receiver to sender, fountain codes, and we describe how to apply belief propagation algorithm to the decoding of fountain codes under wireless noisy channel. From the encoding and decoding procedure we can see why fountain codes can realize adaptive transmission. Then we study the performance of applying fountain codes in cooperative communication system, and point out that decoded-and-forward cooperation cannot bring significant cooperative diversity. Considering this, we propose an amplify-and-forward cooperative communication scheme combined with adaptive demodulation. Simulation result shows, compared to direct transmission and decode-and-forward cooperative communication using fountain codes, this scheme does have lower bit error rate as well as faster decoding.This dissertation summarizes and absorbs a lot of achievements in adaptive communication, some new ideas are proposed as well and validated via simulation.