On The Study Of Joint Information And Energy Transmissions In Cooperative Relay Systems

In recent years,with the development of wireless power communication and relay technology,cooperative relay based j oint information and energy transmission technology has received extensive attention for its ability to extend the coverage of communication networks,enhance transmission reliability and improve energy efficiency.However,in cooperative relay transmission,the loss of energy transmission is severe,and the transmission spectrum efficiency is reduced since the energy transmission needs to occupy time and frequency resources.Therefore,the cooperative relay transmission strategy needs to be jointly designed to improve energy harvesting efficiency and spectrum efficiency.To solve the above problems,in this paper,we study the resource allocation problem and spectrum sharing mechanism of joint information and energy transmissions in cooperative relay systems,the main research contents are summarized as follows:(1)The resource allocation of information and energy transmission with a passive relay is studied.Ajoint optimization algorithm for subcarrier and power allocation is proposed to maximize the harvested energy.Since the original problem is an integral non-convex problem,the dual decomposition method is used to decouple the original problem and achieve the optimal system performance.Numerical results show that the proposed algorithm has significant improvement on the system performance.(2)The spectrum sharing of information and energy transmission with a cognitive relay is studied.We propose an adaptive spectrum sharing mechanism,that is,cognitive relay adaptively selects a mechanism between energy cooperation only and joint information and energy cooperation to help the information transmission of primary system.The closed-form solution of the throughput of each link in the system is derived.Afterwards we get secondaiy system performance maximized with primary system performance by optimizing the adaptive factor and the time allocation coefficient.Simulation results show that the performance of the proposed spectrum sharing mechanism has significantly improved compared to that of other non-adaptive mechanisms.(3)The spectrum sharing of backscattering assisted joint information and energy transmission with a cognitive relay is studied.Ambient backscatter technology enables energy-constrained nodes to realize their own information modulation and transmission by modifying and reflecting ambient RF signals,which can simultaneously improve energy efficiency and spectrum efficiency.Therefore,a spectrum sharing mechanism is proposed,where the secondary user not only assists the primary system in information and energy transmission,but also the secondary user uses the ambient backscatter technique to modulate the surrounding energy signals to realize its own information transmission and energy harvesting,thereby improving energy efficiency and spectral efficiency.The closed-form solution of the primary and secondary system thr-oughput under this mechanism is analyzed,and the overall system throughput is maximized by optimizing the time allocation coefficient to meet the performance limitations of the primary system.Simulation results show that the performance of the proposed spectrum sharing mechanism is much better than that of non-cooperative mode.