Joint Mode Switching And Power Allocation For Energy-Efficient D2D Communications

Recently,green networks have aroused great attention,which aim to save energy consumption as much as possible.Device-to-Device(D2D)communication is expected to save energy by reducing the transmit power.When integrating D2 D communication technology into cellular networks,three transmission modes can be used for D2 D communication.In the relay mode,cellular users benefit from low power consumption.In the underlay mode,spectral efficiency is improved as D2 D users share the in-band spectrum with cellular users.In the overlay mode,the battery life of D2 D user equipment(UE)can be extended while the transmit power is reduced.A potential D2 D UE can select a communication mode and dynamically adopts the mode selection according to the time-varying link quality.Thus,the spectral efficiency and energy efficiency can be improved meanwhile enhancing the system capacity and achieving the construction of green network from long run.Both the transmission time and transmit power under each transmission mode will affect the battery life of the UEs,which will have effect on the energy efficiency.Therefore,the limited battery life of UEs should be considered when D2 D UEs dynamically adopt the mode selection.Meanwhile,the time-varing quality of the communicaiton channel shuold be better taken into consideration.What's more,it is necessary to consider the problems of time allocation and power allocation under the cooperative mode when operating the collaborative technology in the cellular D2 D hybrid network.In view of the above problems,this paper studys the D2 D cooperative communication scenario where a D2 D user helps carry the traffic of a cellular user with the relay mode and then transmits its own data with overlay mode.Meanwhile,the sutuation is taken into consideration where the D2 D UE with low battery level has data to transmit.To allocate the transmission time and transmit power under the two transmission modes,an constrained particle swarm algorithm is proposed to maximize the battery life of the users.Furthermore,based on the D2 D cooperative relay technology,a dynamic mode selection criterion based on the cellular user communication status is proposed as the communication modes of D2 D users can be dynamically adopted.Considering that the average transmission time of D2 D users working in different modes will affect the battery life of the equipment,a linear programming-Newton iterative algorithm is designed to allocate the transmit power and average transmission time of the three modes,aiming at maximizing the battery life of the users.The simulation results show that the resource allocation algorithms designed in this paper can prolong the battery life of the UEs and improve the energy efficiency under the rate requirement of D2 D user and cellular user.