Research On Distributed Space-time Coding And Related Techniques In Cooperative Communication

In order to improve the transmission rate and the reliability of wirelesscommunication system, cooperative communication technology has been proposed.The key idea of the cooperative scheme is that each user of the wireless networkserves as a relay and forwards the information signals from its partner to thedestination. By sharing the antennas of the other users, the virtual multi-in multi-out(MIMO) system can also been built. In this manner, the spatial diversity gain can beobtained, and the transmission power of the users can be reduced. Besides, thenetwork coverage can also be expanded. Therefore, the cooperative communicationtechnology has been widely concerned, and it will be the key technology of the fourthgeneration mobile communication system.In this dissertation, we focus on the novel transmission scheme and the encodingand decoding technology of the distributed space-time code in cooperativecommunication system. Specifically, the estimation and cancellation schemes forinter-symbol-interference (ISI) in the asynchronous cooperative communications andthe full rate transmission schemes in half-duplex relay network have been studied inthis dissertation. The main contributions of this dissertation are summarized asfollows.Firstly, the ISI estimation and cancellation scheme for noncoherent detection hasbeen designed for asynchronous cooperative communication system. In theconventional ISI cancellation schemes, the channel state information (CSI) and thetiming error information need to be well known at the destination node, which wouldinduce high estimation complexity. In order to solve this problem, a simple detectionalgorithm for asynchronous distributed differential space-time code is proposed. In theproposed algorithm, ISI is estimated and cancelled without any CSI or timing errorinformation at the destination node. The simulation results show that the proposedalgorithm can cancel ISI effectively.Then, the half-duplex relay network with full transmission rate has been studied.In order to solve the problem that the transmission rate from the source to thedestination of the half-duplex relay network is halved, the two path successive relay(TPSR) scheme and the full rate conventional relay scheme have been proposed. Thesymbol error rates (SERs) of these two schemes have been calculated and comparedin this dissertation. The analysis and simulation results show that, in the case of lowerspectral efficiencies, the performance of the full rate conventional relay scheme is slightly better than the TPSR scheme. However in the case that higher modulationalphabets are chosen, the SER of the TPSR scheme is much lower. So the TPSRscheme is particularly useful for higher spectral efficiencies.At last, two inter-relay interference (IRI) cancellation schemes, which are namedas partial IRI cancellation scheme and the signal-space diversity (SSD) baseddifferential transmission scheme, respectively, have been proposed for the TPSRnetwork. In the partial IRI cancellation scheme, parts of the IRI signals are retained atthe destination node during the decoding process to improve the performance. Besides,to reduce the decoding complexity of the proposed scheme, the iteration maximalratio combining (I-MRC) decoding algorithm is designed. Then, we analyse thediversity gain of the proposed scheme and the result shows that the proposed partialIRI cancellation scheme can obtain extra diversity gain and improve the performanceof the TPSR network. In the SSD based differential transmission scheme, as the SSDencoding scheme is considered, IRI can be easily cancelled by the relay. Besides, inthis scheme, the destination node does not need to know any CSI, and the relays onlyneed to estimate the CSI of inter-relay channel. So, this scheme is with low decodingcomplexity and low CSI estimating complexity.