Resource Management For Green Communications In Heterogeneous Networks

Heterogeneous networks(Het Nets)is a key cellular paradigm shift for the next generation wireless communications.Het Net can adopt lower transmission power and derive higher spectrum efficiency with the deployment of the lower power femtocell or the device-to-device(D2D)communications,which has drawn the attention from both the industry and academia.On the other hands,the concept of green communication is deeply rooted.The purpose of green communication is sustainable,energy-efficient communication and the targets are energy-efficient Het Nets,wireless powered communication networks(WPCN),etc.Femtocell users(FUEs)and D2 D users(DUEs)can reuse the spectrum of the macrocell users(MUEs),which will introduce interference to the MUEs.Resource management such as power allocation,scheduling and access control can be adopted to mitigate the interference.On the other hand,in WPCN,time allocation is implemented for users to harvest energy and transmit information.Different time allocation strategy will lead to different performance and the coupled time and power make the problem difficult.The critical investigation is to find the resource management algorithms.Nowadays,mobile users are battery-limited equipments and green communication is seeking the sustainable and energy-efficient communication,which means the resource management for green communications in Het Nets is very important.In this dissertation,we will investigate the resource management for green communications with various scenarios in Het Nets.The main contributions of the dissertation are listed as follows:1.The energy efficient optimization problem is analyzed for the downlink macro-femto Het Nets.Since the quality of service(Qo S)of MUEs should be guaranteed in the full frequency reuse Het Nets,the femtocells cannot be allowed to transmit simultaneously,and the scheduling scheme can be adopted to tackle the situation.The energy efficiency is found to be correlated in a negative manner with the time of the scheduling.Therefore,an energy efficient scheduling scheme is proposed,which can lead to a fast schedule and the transmit and receive signal designs are obtained at the same time.Based on the scheduling scheme,the problem is transformed into a power allocation problem.The effective power allocation algorithm is proposed to solve the non-convex problem,which can improve the energy efficiency.Simulation results are presented to show the effectiveness of the proposed algorithm compared with the previous work,which means that the proposed algorithm is of higher application value in terms of green communication.2.The robust energy efficient algorithm is proposed for the uplink D2D-cellular Het Net in which bounded channel state information(CSI)error is considered.With the columnwise uncertainty and ellipsoidal uncertainty,the user-centric and network-centric energy efficient power control problems are analyzed.The price based cost function is introduced into the objectives of DUE,which will discourage the transmission of the DUEs and guarantee the Qo S of cellular user equipments(CUE).The user-centric problem is formulated into the form of a Stackelberg game.The robust power allocation is proposed and the relationship between the price and Nash equilibrium is analyzed.In the network-centric method,maximizing the collective energy efficiency of CUEs and DUEs is studied and the objective function is an NP-complete sum of ratios problem.Theoretical analysis shows that with the appropriate mathematical transformation,the network-centric D2 D power control problem has the identical local solution to that of a special case of the user-centric problem,where a special price is given.The simulation results validates the robustness of the proposed algorithms.3.The novel concurrent transmission framework is proposed for the WPCN.Assuming the random transmission of the users,the feasible framework for both time constraint and energy constraint is proposed with the help of the interference coupled model.The proposed feasible framework can help the operator to judge the working state of the WPCN.Based on the proposed transmission framework,the minimum throughput maximization problem is investigated,which is a non-convex problem.By variable substitution,the non-convex minimum throughput maximization problem can be transformed into an equivalent convex one.Moreover,the sum rate maximization problem is analyzed.The relationship between the optimal time and power allocation is derived,and with the relationship,the time and power optimization problem is transferred into the power allocation problem.Theoretical analysis shows that the sum rate optimization problem can be appropriately computed with a series of subproblems.A bisection method based algorithm is proposed to solve the subproblems.The converged solution is the KKT point of the original problem.The resource allocation problem is analyzed for the wireless powered femtocell and macrocell networks.The macrocell and femtocell optimization problem is proposed based on the Stackelberg game model.With optimal power condition,the macrocell problem is transformed into an equivalent convex problem.The close-formed solution for the power allocation is derived by solving the KKT conditions.Simulation results indicate that the proposed feaibility framework can judge the network statements and the proposed algorithms can outperform the ones in the existing works,which means the proposed algorithms are of higher application value in terms of green communication.4.The energy efficiency for the time switching WPCN is investigated.The time switching strategy is adopted for that the orthogonal time allocation will reduce the reuse of the time resource.The sum energy efficiency optimization problem is formulated.After deriving the condition of the energy node,the iterative time and power allocation algorithm is proposed.The power allocation problem is sum of ratios problem and the time allocation problem is linear programming.By solving the problem,the power allocation scheme is derived which can converge to the KKT point and the close-formed time allocation scheme is also derived.Simulation results show that compared with the existing literature,the joint optimization algorithm of time and power can obtain higher energy efficiency.