The Research On Equalization Schemes For Space-time Coded Cooperative Systems With Insufficient CP

In the cooperative communication system, since relay nodes are decentralize,signals from therelay nodes are not synchronized at time. Therefore,combating time delays is one of main problemsin the studies for cooperative communications.Orthogonal frequency division multiplexing (OFDM)technology is applied to combat the time delays. However,CP that is added can reduce the symboltransmission rate.So,on the reseach for cooperative OFDM system,reducing data redundancy isbecoming one of the major problems. This paper introduces decision feedback equalizer (DFE) atthe receiver and nonlinear precoder at the relay nodes to reduce data redundancy.The main contentsare as follows:(1) This paper describes the three basic protocols at the relay nodes in cooperativecommunications. Moerover, asynchronous cooperative communications system model is analyzedin detail. Finally,this paper also study using OFDM techniques to eliminate the influence of thedelay,as long as the cyclic prefix (CP) is not less than time-delay length, time delay error can beeffectively avoided.(2) This paper studies equalization schemes and asynchronous distributed space-time codingschemes for cooperative communications system with sufficient CP. Alamouti space-time blockcodes are analyzed as an example of asynchronous distributed space-time block codes. Forasynchronous distributed space-time block codes, time-reversal and complex operation are adoptedto achieve reconstruction of space-time code.(3) This paper introduces decision feedback equalizing scheme for cooperativecommunications system with insufficient CP. Respectively, zero forcing(ZF) decision feedbackequalizer and minimum mean square error(MMSE) decision feedback equalizer are designed forthis system. MMSE decision feedback equalizer outperforms ZF decision feedback equalizer,butthe complexity of the receiver is increased.(4) Nonlinear precoding scheme is introduced for cooperative OFDM systems with insufficientCP.Respectively nonlinear precoder are designed at the relay nodes.As for nonlinear precodingscheme, the inter-symbol interference is added at the relay node, added intersymbol interferenceand residual inter-symbol interference cancel each other out.So structure of space-time code withfull diversity can be can be obtained simply by linear equalizing at the receiver.