Research On Resource Allocation Algorithms Of Realy Network Based On Energy Harvesting

With the development of mobile services,the number of terminals increases greatly,and energy consumption increases rapidly,which puts forward higher requirements for wireless system capacity,communication quality,and battery life.Cooperative relay communication can improve system capacity and effectively solve the problem of weak coverage at the edge of cellular network.Energy harvesting technology can effectively utilize environmental energy and realize green communication.Therefore,cooperative relay system based on energy harvesting has become a research hotspot.How to design appropriate resource allocation scheme is very important to make full use of the harvested energy to improve the communication quality of the system.In this thesis,the multi-relay cooperative communication system with energy harvesting is taken as the research object,considering different energy harvesting methods of relays,theoretical and simulation analysis of throughput,outage probability and energy efficiency are carried out,and the resource allocation algorithm is optimized.The main research contents and innovations are as follows:(1)For the multi-relay cooperative communication scenario with energy buffering and data buffering functions,a joint optimization algorithm for relay pair selection and power allocation is proposed.Under the constraints of energy causality,energy capacity,data causality and data capacity,the throughput maximization problem is constructed.In order to solve this NP-hard problem,the optimization problem is divided into two sub-problems.The first sub-problem is the relay pair selection problem,and a relay pair selection mechanism is proposed to determine the optimal transmitting relay and receiving relay in the current time slot.The two sub-problems are the optimization of relay transmit power,and the optimal transmit power is obtained by using the Lagrange multiplier iterative method.Simulation results show that the proposed optimal relay pair selection mechanism can effectively improve the system throughput performance.(2)The performance of the two-hop half-duplex relay system based on SWIPT energy harvesting is analyzed,and a joint optimization algorithm of energy threshold and power division factor is proposed.Among them,the relay has the functions of energy collection and storage,and combined with the adaptive AF/DF(Amplify-Forward/Decode-Forward)transmission strategy and the TS-PS(Time Switching-Power Splitting)protocol,the relay selection scheme is Energy Optimal Select(EOS),Gain Optimal Select(GOS),and Energy and Gain Optimal Select(EGOS).Based on the finite state Markov chain,the energy arrival and use states of each relay are modeled,and the energy transfer steady state matrix is obtained,and the analytical expression of the system outage probability is deduced using the Gauss-Chebyshev formula.The optimization models under the EOS and GOS schemes that minimize the probability of communication interruption by optimizing the power division ratio and the optimization model under the EGOS scheme that jointly optimize the energy threshold and power division ratio to minimize the probability of communication interruption are constructed.A one-dimensional search algorithm based on golden section and a two-dimensional search algorithm based on iteration are used to solve the problem respectively.The simulation results show that the relay selection scheme of EGOS is the best among the three schemes,and the influence of parameters such as source node transmit power,minimum transmission rate,and relay location on outage performance is analyzed.(3)Considering the nonlinear energy harvesting model,a power allocation algorithm based on nonlinear energy harvesting is proposed for the multi-relay cooperative forwarding scenario in the two-hop half-duplex relay system.In order to reduce the complexity,a piecewise linear model is used to approximate the nonlinear model,and under the constraints of energy causality,transmission rate and the total transmit power of multiple relays,a joint optimization of the relay transmit power and power division ratio is constructed to maximize the system energy efficiency.The energy efficiency maximization problem is a nonlinear fractional programming problem.First,the problem is decoupled into a single-relay probabilistic optimization problem.Based on the Dinkelbach iterative algorithm,the single-relay power is optimally allocated.It is proved that the optimization problem after iterative simplification is a convex programming problem.For different energy harvesting model broken lines,the corresponding simplified expressions of the joint optimization problem are obtained respectively,and the closed-form solutions are obtained by mathematical methods such as monotonicity,Lagrange multiplier method,KKT condition and Cardan formula.The simulation results show that in the energy harvesting relay system,the energy efficiency of the multi-relay system is higher than that of the single-relay system.Compared with the linear energy harvesting model,the algorithm proposed in this paper can achieve better performance.