Resource Optimization For OFDM Systems With Energy Harvesting

Orthogonal Frequency Division Multiplexing(OFDM)is the key technology of the fourth generation mobile communication system and the good method to realize high-speed wireless data communication.However,as the demand for high data rate services increases quickly,it is accompanied by a surge in energy use all over the world.With the reduction of fossil and deterioration of the environment,since 2008,green communication and networks have become research hotpots in mobile communication systems.Energy Harvesting has become a hot topic as a promising green communication technology in recent years.This paper studies the resource optimization problem of OFDM system by using Simultaneous Wireless Information and Power Transfer(SWIPT)technology and hybrid energy harvesting technology:Aiming at the multi-dimensional resource optimization problem of AF-OFDM system based on SWIPT,we established a single-cell single-relay and multi-user OFDM downlink system model which relay is equipped with radio frequency energy harvester.In order to maximize the overall achievable rate in AF-OFDM system,multiple degrees of freedom(power allocation,subcarrier assignment,incremental policy,power splitting ratio)are jointly optimized,and subjected to the transmission power as well as the quality of service constraints.The optimization problem is a mixed-integer nonlinear programming and the corresponding solution has a high computational complexity.In order to have a better tradeoff between performance and complexity,we propose a suboptimal solution.The simulation verifies the convergence of the optimization problem,and we compare the proposed algorithm with the exhaustive algorithm and different dimensional degenerate algorithms.The results show that our proposed algorithm is a progressive suboptimal solution with low complexity and has a better performance than all other degenerate algorithms.The proposed algorithm is more robust.In addition,when solving the nonconvex optimization problem,we prove that the dual gap is zero even the problem is non-convex.Hence,the Lagrange duality theory can be used to solve the optimization problem,and the sub-gradient algorithm is used to update the objective function.The optimization variables are solved one by one during each iteration.Aiming at the problem of downlink multi-user resource optimization of OFDM systems based on hybrid energy harvesting,a single-cell and multi-user system model is established in this paper.Considering that the base station has a huge impact on the energy consumption in any communication network,we let the base station powered by renewable energy and a stable power grid at the same time to make full use of renewable energy and reduce the carbon emissions in the base station.This paper designs an optimization problem with the goal of maximizing system energy efficiency,which takes subcarrier assignment,transmit power and base station circuit power as variables and models the dynamic energy acquisition and channel state time-varying process.Considering energy constraints,battery capacity constraints,and proportionality requirements of rate between users,the proposed algorithm improves the energy efficiency of the system while ensuring fairness among users.Simulation results verify the correctness of the proposed scheme.