The Research On Effective Transmission Schemes For SWIPT Relay Cooperative Systems

In the era of the Internet of everything,the amount of the interaction between information is already higher than expected.The spectrum resources and energy resources of communication field are gradually unable to meet the needs of people.Fortunately,the emergence of simultaneous wireless information and power transfer(SWIPT)technology,which utilizes the radio frequency(RF)signals as the carrier of information to realize the transmission of information and energy in parallel,has alleviated this problem to some extent.Due to the path loss and multipath fading in wireless communication,especially in the long-distance communication,people start to combine the SWIPT with cooperative communication.Thus,not only the coverage of communication can be extended,but also the capacity and service quality of system can be improved.This thesis mainly studies the design of relay transmission scheme based on decode-and-forward(DF)protocol in SWIPT relay cooperative system.From the perspective of system energy and network lifetime,it focuses on the issue of best relay selection(BRS)under the two receiving structures,i.e.,power splitting(PS)and time switching(TS).Instead of the much commonly used relay selection criteria,we choose the maximization of system remaining energy as our selection criterion.In addition,we apply the proposed criterion to the multi-relay forwarding system,that is,the partial relay selection(PRS).Finally,the simulation results demonstrate that the proposed scheme provides longer lifetime as compared to the conventional ones.The main work and contributions are summarized as follows:At first,a lifetime-oriented transmission scheme based on the maximization of system remaining energy is proposed in the PS-based relay cooperative network,namely BRS-PS.The PS factor and the forwarding power of relays are jointly optimized by constructing the decoding set and forwarding set.The simulation results have proved the feasibility and reliability of the proposed scheme by comparing with another two schemes,that is non-EH(energy harvesting)scheme and the relay transmission scheme based on the maximal capacity of relay-destination.Based on the work 1,the selection criterion,i.e.,“maximizing the remaining energy of system”,can also be applied to the TS-based relay cooperative network.Due to the differences between the PS and TS transmission model,we optimize the TS factor and select the best relay(BRS-TS)according to the local conditions.Simulation results have affirmed the advantages of the proposed selection criterion “maximum remaining energy” in prolonging the network life span.For further study,this thesis extends the issue of optimal relay selection to the best partial relay selection(PRS)based on the work 1.Combined with the beamforming technology,the system's PS factor is optimized by maximizing the remaining energy of system.What's more,the suboptimal forwarding set is obtained by means of greedy combination,and the optimal beamforming vector can be solved by an iterative algorithm.The simulation results indicate that the network survival time of PRS scheme is longer than that of BRS scheme.