Research On Beamforming Based On Two-way Relay Network

With the Internet of things and wireless sensor networks entering a new stage of development,they put forward higher requirements for wireless communication transmission in terms of coverage,transmission rate,spectrum efficiency,etc.The two-way relay network based on physical layer network coding technology integrates the advantages of cooperative communication,significantly improves the transmission rate of the network,and the spectral efficiency.In order to support the needs of mass information transmission in the future Internet of things,non-orthogonal multiple access technology has attracted much attention because it supports multiple users to share a block of orthogonal time-frequency resources.It can provide higher spectrum efficiency and greater convenience for saving resources.In addition,with the enhancement of device functions in the Internet of things,the problem of energy consumption will become increasingly prominent,which will become a key factor restricting the improvement of network performance.With the emergence of energy harvesting technology,wireless energy carrying communication technology based on radio frequency(RF)signal provides a direction to solve the energy shortage.Meanwhile,beamforming technology can be used to improve the transmission performance of system.In order to realize green communication and mass information transmission,it is necessary to study the beamforming technology in the two-way relay network,considering the two scenarios of simultaneous wireless information and power transfer and non-orthogonal multiple access.Based on those,this thesis accomplishes the following two aspects of research work:In order to achieve green communication,we have studied a novel distributed beamforming scheme for realizing simultaneous wireless information and power transfer in the two-way relay channel.Simulation results have effectively illustrated the feasibility of the proposed scheme.Specifically,it is assumed that perfect channel state information(CSI)is available.We design the beamforming through minimization of the upper bound of average mean squared error(MSE)subject to the total transmit power constraint at the relays and the energy harvesting constraint at the energy harvesting(EH)receiver.Firstly,we propose the local optimal beamforming scheme.Via a series of mathematical manipulation,the initialoptimization problem can be transformed into a standard semi-definite programming problem,and then the local optimal solution can be obtained effectively using the interior point method.The closed-form beamforming design scheme is proposed owing to the high computation complexity of local optimal beamforming scheme.A closed-form solution is obtained via recasting the initial problem to the form of Rayleigh-Ritz ratio.Numerical results are provided and analyzed to demonstrate that the proposed two beamforming schemes have tradeoffs between system speed and computational complexityTo solve the problem of limited spectrum resources,the non-orthogonal multiple access(NOMA)technology is applied to the two-way relay network,and the optimization design of beamforming matrix variables is studied.The simulation results verify the superiority of the proposed scheme in improving network capacity.We consider the objective is to maximize the sum rate under the transmit power of relay constraint and the achievable rate of weak user constraint.Concerning the non-convex intractable optimal problem,the optimization problem is transformed into a second-order cone programming problem by mathematical transformation.Then finding an optimal solution by using the proposed iterative algorithm based concave-convex procedure(CCCP).Simulation results illustrates that the proposed scheme is prior to the existing scheme in terms of system rate.