Study On Optimal Transmission Strategy Design In Wireless Powered Communications With User Cooperation

Wireless power transfer(WPT),where the smart terminals can harvest the energy from the far-field radio-frequency signals provided by energy access point(EAP),becomes a new approach to avoid replacing or recharging the batteries,reduce total cost and prolong the lifetime.On the other hand,cooperation communication,where near user assists far user to forward information,is an effective way to improve total throughput and system coverage.Combing WPT and cooperation communication,it can further improve the performance in wireless communication systems.For this reason,this paper mainly focuses cooperative strategy and resource allocation problems of wireless powered communications(WPC)with user cooperation.The main content of this paper can be summarized in two aspects:(1)First,we propose a pricing mechanism in wireless powered communication networks(WPCN)to incentive the assist user to forward source user's information.In this mechanism,all data transmission need to be charged with different price for different users.Then we propose a harvest-then-transmit protocol.For the best-effort cooperative WPCN,we solve the utility efficiency maximization and best user selection problem by reformulating it to a standard convex problem.For the WPCN with a Quality-of-Service(QoS)constraint,we propose an effective scheme to meet the source user's QoS requirement with the minimum price cost.Simulation results show that our proposed schemes can improve the system cost utility significantly.(2)Second,we propose a new communication protocol in multicast device-to-device(D2D)communications with simultaneous wireless information and power transfer(SWIPT)technology.In the first slot,source user transits information and power to help user.In the second slot,help user uses the cellular spectrum and forwards the information to multiple receivers by using harvested energy.The objective is to maximize system transmission rate.This problem is solved in two steps.In the first step,the resource allocation problem is solved by linear programming.In the second step,the power-splitting coefficient value is obtained by taking the benefit of help user into account.Numerical results show that the proposed strategy not only improve the total throughput and spectral efficiency,but also motivate the cooperation.Given the above,building a suitable communication protocol and allocating resources properly in wireless communications with WPT and user cooperation will improve the communication system performance and incentivize the cooperative communications between users.