Research On Multi Relay Coding Selective Decode-and-Forward Technology Of 5G Internet Of Things

At present,5G Internet of things(Io T)technology is developing rapidly.As its key technology,the research on wireless sensor network(WSN)has attracted extensive attention.For many WSN application scenarios,reducing system energy consumption and improving signal transmission reliability are the primary problems.Therefore,this thesis mainly studies the cooperative technology of multi relay coding selective decode-and-forward(SDF).Firstly,a multi relay node SDF for cooperative communication and the corresponding power allocation method are proposed to reduce the outage probability.Then,a polar coded SDF relay cooperation scheme is proposed to improve the reliability of signal transmission.In addition,aiming at the problem of battery energy loss of relay nodes,the power division protocol of synchronous wireless information and power transmission(SWIPT)technology is optimized,and an adaptive power division energy collection communication system based on multiple relay SDF is proposed.The research contents and contributions of this thesis are concluded as follows:1.To solve low success probability of information transmission in cooperative relay space communication network,a multi relay node SDF and corresponding power allocation method for cooperative communication are proposed.The multi relay SDF scheme based on channel state information can dynamically select the relay set of the lowest system outage probability according to current SNR.Aiming at low energy consumption utilization and low frequency band utilization of multi relay SDF scheme,an optimal relay node selection and power allocation scheme are proposed,which improves the system outage performance and reduces the complexity.The simulation results show that the smaller the threshold,the smaller the outage probability of the optimal relay node selection and the corresponding power allocation scheme.When the system outage probability is 10^-3,the optimal relay node selection and corresponding power allocation scheme with the threshold set to 0.1,0.3 and 0.5 have about 10d B,7d B and 4d B performance gain compared with the multi relay SDF scheme based on channel state information,and the optimal relay node selection and corresponding power allocation with the threshold set as 1 have about 3d B performance loss compared to the multi relay SDF scheme based on channel state information.But with the increase of SNR,the multi relay SDF scheme based on channel state information decreases faster.When the SNR is high enough,the outage probability will be lower than the optimal relay node selection and corresponding power allocation scheme.2.To improve the reliability of information in wireless cooperative communication systems,a polar coded SDF relay cooperation is proposed.A decision factor of relay selection is proposed to discard error information.In the process of confidence propagation(BP)decoding of polar codes,a variable iterative threshold is constructed to stop the iterative update calculation of nodes with high reliability,which reduces the average number of decoding iterations.When the likelihood ratio of all information bit nodes is reliable,the iterative decoding decision operation is directly stopped,which improves the decoding efficiency and reduces the complexity of the traditional BP decoding.Simulation results show that the proposed BP decoding algorithm with reduced complexity reduces the decoding iterative operation time by about 80%,when compared with that of the traditional BP decoding.At BER of 10^-4,the performance of proposed scheme is 1.5d B and 3d B higher than these of the LDPC coded SDF and polar coded DF,respectively.3.To solve battery energy loss in relay nodes,an adaptive power division energy collection communication system based on multi relay SDF is proposed.Aiming at the energy defect of relay node,SWIPT is used to adopt power division protocol.The proposed scheme uses the adaptive power division factor to maximize the end-to-end instantaneous signal-to-noise ratio according to channel characteristics,and it selects the relay node with the largest instantaneous signal-to-noise ratio in multiple relay nodes for transmission,which maximizes the ergodic capacity of the system and reduces the overall outage probability.Simulation results show that,at outage probability of10^-3,the performance of the proposed optimal relay scheme is about 15d B higher than that of the random scheme.When the system outage probability is 10^-5,the performance of the proposed adaptive power division factor scheme is about 3.5d B,1.7d B and 1.5d B higher than that of the schemes with fixed power division factors of 0.3,0.5 and 0.7,respectively.Therefore,the simulation results verify the correctness of the analytical expression,and the performance is better than the existing schemes.The multi relay node selective decoding forwarding and corresponding power allocation method of cooperative communication studied in this thesis solves the problem of low information transmission success probability of cooperative relay space communication network,and proposes a polar coded SDF relay cooperation scheme,which improves the system bit error rate(BER)performance and reduces the complexity of polar code BP decoding.Combined with SWIPT,an adaptive power splitting and energy harvesting communication system based on multi relay SDF is proposed,which solves the battery energy loss of relay nodes.It is very suitable for 5G Internet of things cooperative wireless sensor networks with energy limited nodes.