| With the rapid growth of wireless communication technology and the popularization of mobile devices,the energy consumption of networks and environment pollution are becoming increasingly serious.On the other hand,the contradiction between limited wireless spectrum resources and rapid growth of high-speed wireless service demand has become increasing prominent.Therefore,research on green communication with low energy consumption and high energy efficiency becomes a key issue in the new generation of wireless communication systems.Energy harvesting(EH)is a new technology of green communications,which can enable devices to acquire renewable energy from the surrounding environment and convert it into electrical power for use.This dissertation focuses on the energy-efficient resource allocation combined with energy harvesting in wireless networks.The main contributions of this dissertation are summarized below.First,the downlink resource reuse scheme is more complicated than the uplink one because the downlink transmitting power of base station is the power coupling of all cell users.This dissertation investigates energyefficient downlink resource reuse and power control strategies for device-to-device(D2D)communications underlaying cellular networks.Each D2 D link is allowed to reuse the resource blocks(RBs)of multiple cellular users and each RB can only be reused by one D2 D link.We aim to maximize the total energy efficiency of all D2 D pairs while guaranteeing the quality of service(QoS)of cellular users and the power requirements for both base station and D2 D pairs.Because of the fractional form of objective function,the optimization problem is a non-convex fractional programming problem.In order to solve the problem,we first derive the optimal downlink transmitting power of base station according to the QoS requirement of cellular users.Based on this basis,the original optimization problem is transformed into an equivalent subtractive-form problem based on the theory of nonlinear fractional programming.The subtractive-form non-convex problem can be transformed into a convex optimization problem according to the definition of perspective function,and further solved by KKT optimality conditions.Simulation results show that the proposed energy-efficient downlink resource reuse and power control strategies can significantly improve the energy efficiency of D2 D communications.Then,to improve the spectral efficiency,each D2 D link in our work is allowed to reuse the resource blocks(RBs)of multiple cellular Users and each RB can be reused by different D2 D links.By utilizing an overlapping coalition formation game,we aim to maximize the sum rate of all D2 D pairs in D2 D communications underlaying cellular networks without sacrificing the QoS of each cellular user(CU)and D2 D pair.In the initial phase,each D2 D pair chooses one or multiple RBs to reuse according to the cross-tier interference level,and user equipments(D2D pairs and CU)sharing the same resource block can be considered as a coalition.In the second phase,a cooperative game with overlapping coalitions is further proposed to maximize the system utility in terms of the sum rate of all D2 D pairs.In this phase,each D2 D pair can make a decision on whether to leave current coalition to join a new coalition or not.Each time the D2 D pair changes the coalition which it is currently participating in,both the individual payoff and total payoff of the new formed coalitions should be improved.Through the analysis of convergence and stability,and also the simulation results,we can conclude that user equipments can cooperate to form a stable and the most beneficial coalitional structure with overlapping coalitions.Next,EH can reduce carbon emission and realize the self-sustain ability of system compared to traditional energy.Thus,we study an energy-efficient power control algorithm with max-min fairness for energy harvesting ad hoc networks.Fairness-aware energy-efficient power control schemes can avoid serious unfairness among different users.In addition,EH can reduce the limit of battery capacity on performance of system.By guaranteeing the energy causality constraint and QoS of each node,we formulate an optimization problem aim at maximizing the individual energy efficiency.Because of the existence of co-channel interference terms and fractional form of objective function,the original problem is a non-convex optimization.To make the problem tractable,we propose a two-loop iterative algorithm to obtain a near optimal solution of the original problem.In the outer loop,the original fractional form problem is transformed into an equivalent subtractive-form problem via parametric approach,and in the inner loop,a combinational framework of successive convex approximation(SCA)and geometric programming(GP)is adopted to solve the subtractive-form problem.Simulation results show that the proposed fairness-aware energy-efficient power control algorithm can provide a greater fairness in energy harvesting ad hoc networks.Finally,due to the uncertainty of renewable energy in nature,we investigate an off-line energy-efficient resource allocation scheme in timesharing multiuser system with a hybrid energy harvesting transmitter.The goal of the proposed scheme is to maximize the energy efficiency of timesharing multiuser system while considering jointly allocation of power and transmission time.The optimization problem is a non-convex fractional programming problem and is hard to solved.To make it tractable,we transform the original fractional form problem into an equivalent subtractive-form problem via Dinkelbach method.Based on this basis,we adopt perspective function to transform it into a convex optimization problem and solve the convex optimization problem by using Lagrange dual decomposition method.In addition,we prove that the transmitting power for each user remains constant during its transmission time.Simulation results show that the proposed energy-efficient resource allocation scheme can improve the energy efficiency of timesharing multiuser system significantly. |
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