Research On Energy Efficiency Optimization For D2D Communications

With the development of the fifth generation mobile communication technology and the popularity of smart terminal devices,the data service demand of mobile users increases dramatically,and the energy consumption problem becomes more and more serious.D2D communication technology is one of the key technologies for the fifth generation mobile communication system because of its high spectral efficiency,fast transmission rate and low power consumption.However,the introduction of D2D technology in traditional cellular networks may cause serious interferences to the original users and thus affect the performance of cellular networks.Therefore,it is an important research topic for D2D communication to reduce network energy consumption and improve system energy efficiency with reasonable interference coordination while ensuring the quality of service for cellular users.In this thesis,the corresponding energy efficiency optimizations are conducted for three different D2D communication models by means of power control and resource allocation.The main work is as follows:1.For D2D communications in UAV-assisted access networks,the energy efficiency optimization is studied.A UAV is used as an airborne base station to provide services to ground users.When multiple D2D user-pairs share the same channel resources allocated by the UAV,the individual energy efficiency of each user-pair and the total energy efficiency of the D2D network are optimized respectively.The individual energy efficiency problem uses the maximum-minimum fairness criterion to ensure that all D2D user-pairs are treated fairly,and the total energy efficiency problem jointly optimizes the deployment of the UAV and the transmit power of each D2D transmitter.To solve the individual energy efficiency problem,the original problem is transformed into an equivalent subtractive counterpart with side parameters.Then,the new problem can be solved via a standard convex optimization method after constraining the co-channel interferences.Similarly,the total energy efficiency problem can also be transformed into an equivalent subtractive counterpart.Then,the new problem is divided into two sub-problems,which are solved via alternative optimization method for transmit power and UAV location respectively.The simulation results show that the proposed scheme achieves a good tradeoff between energy efficiency and computational complexity.2.The energy-efficient resource allocation for D2D communications powered by energy harvesting technology is studied,where the energy is collected from the radiation of a UAV.Therefore,two operation models,i.e.“harvest-then-transmit” and “harvest-transmit-store” are put forward and the corresponding resource allocation schemes for energy efficiency maximization are designed respectively.For the energy-efficient resource allocation problem under the “harvest-then-transmit” model,the Dinkelbach method and the iterative gradient method are used to solve the problem based on the fractional programming theory and D.C.programming theory.For the energy-efficient resource allocation problem under the“harvest-transmit-store” model,the original problem is transformed into a mixed-integer nonlinear programming problem by the Lagrangian relaxation method,and then solved by the successive convex optimization algorithm and downward rounded golden section method.The simulation results show that the proposed schemes have good energy efficiency performances for above two models.3.For a heterogeneous cellular network with multiple D2D user-pairs,there exist adjacent channel interferences between user-pairs due to adjacent resource blocks been used.The total energy efficiency maximization of D2D networks is investigated in terms of downlink resource reuse and power control.The resource reuse problem is an assignment problem,which can be solved by the Hungarian algorithm.The power control problem is solved by the Dinkelbach method nested with the interference constraint method.The simulation results show that the proposed scheme has good convergence behaviors,and its energy efficiency performance is better than that of the random allocation method.