Power Control And Resource Allocation For Relay-assisted D2D Communications

In Long Term Evolution-Advanced(LTE-A)system,device-to-device(D2D)communication enables proximity users to transmit signals directly.It can reduce transmission delay,lower energy consumption,and offload the traffic of base station and core network.Meanwhile,introducing relay technology into LTE-A system can not only improve the quality of service for D2 D users who are in the margin of cellular network or out of network coverage,but also weaken the mutual interference between cellular communications and D2 D communications,i.e.,weaken the co-channel interference,since the transmit power of relay-assisted D2 D users can be reduced.On one hand,with the concept of green radio being put forward,the future mobile communication systems need take energy consumption into consideration while providing reliable transmissions.Therefore,it is imperative to control power for relay-assisted D2 D communications from the view of improving energy efficiency.On the other hand,proximal single-antenna transmitters can obtain space diversity gain by being cooperating relays in a multi-user network,but the wireless users are universally selfish.Hence,it is necessary to manage resources among cooperating D2 D users from the perspective of fairness.In order to solve these two problems,this paper mainly makes the following contributions.Firstly,in order to achieve green communication,an energy-efficient power control method for half/full duplex relay-assisted D2D(HD/FD RA-D2D)communications is proposed in this paper.A HD/FD RA-D2 D communication model in LTE-A system is first established,where one D2 D user reuses the same spectrum resource with one cellular user.After analyzing the co-channel interference,we get the energy efficiency expressions of HD/FD RA-D2 D links,respectively.Then the power control problems of D2 D transmitter and D2 D relay are formulated aiming at maximizing the energy efficiency of RA-D2 D links while satisfying the minimum data-rate requirement of cellular uplink.And the power control problems of HD/FD RA-D2 D links are solved by using convex programming and nonlinear fractional programming,respectively.Simulation results show that RA-D2 D communications can make better use of energy with the proposed power control method,which corresponds to green radio requirements.Secondly,considering the selfishness of wireless users,a proportional fair resource allocation and relay selection method among D2 D transmitters is proposed.A local D2 D network is first constructed,where D2 D users can act as not only a D2 D source but also a potential relay for other D2 D links.And cooperative communications will occur on condition that all cooperating D2 D users can benefit from this cooperation.Next,a proportional fair resource allocation problem among cooperating D2 D users is formulated as a Nash bargaining game.And the closed-form resource allocation results for both single relay-assisted situation and double relay-assisted situation are got,respectively.Then a simple relay selection strategy is given,allowing the D2 D user who has priority to relay selection to select the best one or two devices as its cooperating relays.Simulation results prove the proportional fairness of resource allocation and the effectiveness of relay selection.