Research On Technologies Of Relay Forwarding Strategy Optimization And Coded Cooperation

Currently,the wireless cooperative communications have become the research hot spot due to their reliable transmission,higher efficiency and wide coverage.But they still have some disadvantages,such as high complexity,difficulty to approach the theoretical value and so on.So the relaying strategies and coded cooperation technologies are researched in this dissertation to alleviate the above problems.Firstly,the background,development and current research status of the cooperative communications are briefly introduced.Then,the existing wireless cooperative communications model,combining technique and relaying strategies are investigated briefly,and the link adaptive regeneration(LAR)strategy is also introduced.Finally,the innovations of the optimized LAR strategy,quantize-and-forward(QF)strategy and Raptor coded cooperation are carried out in the cooperative communications.The main content and contributions are listed as follows:1.The theoretical analysis about the LAR strategy is introduced to improve the problem that the decode-and-forward(DF)relay system can not achieve diversity gains.Firstly,the realization process of the LAR strategy and a low complex single relay selection scheme based on the LAR strategy are investigated.Then,the approximately analytical expression of the bit error rate(BER)and outage probability with high signal-to-noise ratio(SNR)are derived.Finally,Simulations indicate that the BER performance of the LAR scheme is better than that of the amplify-and-forward(AF),the DF and the selective decode-and-forward(SDF)scheme,with 3.5d B,7dB and 7dB SNR performance gains,respectively,at BER of 10-3.And the outage probability performance of the LAR scheme is also improved with the increase of the relay number.2.To overcome the higher computational complexity,an improved low complex QF scheme is proposed for the current QF relay system.The computational complexity is decreased by the combination of the low order modulation and quantization together.At the destination node,it tackles the quantization information and directly transmits information by maximum ratio combining(MRC),which efficiently reduce the BER of the whole system.Simultaneously,the QF relay system is further optimized with relay selection strategy and optimum power allocation scheme.Finally,the BER performance of the 1-bit,2-bit and 3-bit QF relay system is simulated.Simulation results indicate that the 3-bit QF scheme has about 4.5~7.5 dB and 1~2.5 dB SNR performance gains than the 1-bit and 2-bit QF schemes,at BER of 10-2,respectively.And when the relay node located nearly to the destination node,the system has better BER performance.For the2-bit QF,the scheme of the source-relay distance with 0.9 has about 5dB,7.5dB,9dB and 15 dBSNR performance gains than those of the distance with 0.7,0.5,0.3 and 0.1,respectively,at BER of10-3.In addition,the proposed optimum power allocation saves about 2.5dB much more relay power on average than that of the equal power allocation.3.Based on the rateless nature of the fountain codes,a novel Raptor coded cooperation(CC)scheme is proposed to overcome the difficulty to estimate the channel state information(CSI)of the wireless communications.In this scheme,different Raptor codes are employed at the source and relay nodes.Therefore,after receiving the data transmitted from different independent links,the destination node tries to decode them jointly by the intrinsic relationship among them,which can achieve much higher coding gains and full diversity gains in high SNR regime.In addition,in order to reduce the complexity of Raptor encoding and decoding,the quasi-cyclic low-density parity-check(QC-LDPC)codes constructed by integer sequence are adopted as the pre-coding.Simulation results indicate that the proposed Raptor CC scheme obtains about 2dB and 1dB SNR gains than that of the traditional DF based one,a scheme with the combination of a Raptor code,and a distributed space-time block code(DSTBC),respectively,at BER of 10-4.Moreover,the SNR performances of the proposed scheme are improved about 2dB and 7dB at outage probability of 10-2,when compared with the schemes of the CC strategy and DF strategy,respectively.By optimization and improvement of the relaying strategies and coded cooperation technologies,this dissertation contributes to improve the performance of the cooperative communications.And those innovations in this thesis all can be implemented with low complexity,which are easy to apply to engineering with significant application value.