Research On Resource Scheduling In Relay-assisted D2D Communication System Under Different Cellular Network Coverage Scenarios

With the rapid development of mobile communication technology and the large-scale popularization of smart terminals,mobile data traffic in the network has explosively increased,which puts higher requirements on the capacity and quality of service(QoS)for wireless communication system.Meanwhile,the contradiction between the scarce wireless spectrum resource and the growing QoS demand is becoming more and more apparent,which restricts the further development of wireless communication.Device-to-Device(D2D)communication enables direct communication between two nearby mobile devices without traversing the Base Station(BS)or core network,which can improve the data rate,increase the system capacity,reduce the transmission delay and the energy consumption,mitigate the traffic load on the BS.At the same time,D2D users(DU)can reuse the spectrum resource of cellular users(CU),hence significantly improving the spectrum utilization.Besides,DU can autonomously establish communication connection with each other and manage them autonomously,which can easily use the scenarios that there is no cellular infrastructure or large-scale networks where designated control central entity is infeasible due to excessive signaling overhead.When the distance between the D2D transmitter(DT)and the D2D receiver(DR)is relatively long or the channel condition between them is inferior,the introduction of relay technology can further improve the data transmission rate,enhance the reliability and flexibility of D2D communication,enlarge the coverage of cellular networks.Therefore,the combination of D2D communication and relay technology is a research hotspot currently.The 3rd Generation Partnership Project(3GPP)organization divides the research scenarios of D2D communication into three categories,namely,D2D communication within the cellular network coverage,D2D communication out of the cellular network coverage and D2D communication under partial coverage of cellular network.According to the scenario classification of 3GPP,this thesis mainly studies the resource scheduling problem for relay-assisted D2D communication system in the first two cellular network coverage scenarios.The main research contents of this thesis are as follows:(1)Considering the D2D communication scenario within the cellular network coverage,a simultaneous wireless information and power transfer(SWIPT)-enabled relay-assisted D2D communication system model is established.In the system model,each CU occupies a pre-assigned independent and orthogonal subchannel,and the D2D link can only established by reusing the downlink spectrum resource of CU,assume that there is no direct communication link between the DT and DR,so that a half-duplex decode-and-forward(DF)relay is required to assist the communication.In order to alleviate the problem of limited energy,relay nodes(RN)employ the SWIPT technology to harvest energy.Based on the above system model,an optimization model of joint channel allocation and transmit power control of DT and RN is formulated to maximize the sum rate of D2D subsystem while satisfying the constrains of channel allocation,energy causality,minimum transmission rate demands of CU and maximum transmit power limit of DT,and a joint channel and power scheduling algorithm is developed.Specifically,this thesis emploies the concept of bi-level optimization to decompose the formulated non-convex mixed-integer non-linear programming(MINLP)problem into an inner power control problem and an outer channel allocation problem.For the inner power control problem,this thesis converts the non-convex optimization problem into a convex problem by leveraging the assumption that the signal to interference plus noise ratio(SINR)of the DT-RN link is equal to the SINR of the RN-DR link,then employ the Lagrangian duality approach to solve this problem;For the outer channel allocation problem,the Hungarian algorithm is used to.Simulation results show that the proposed resource scheduling algorithm can significantly improve the sum rate of D2D subsystem.(2)Considering the D2D communication scenario out of the cellular network coverage,a social-aware based relay-assisted D2D communication system model is established.In the system model,each DT contends for one shared channel by random access based on a slotted contention model,and each DU can autonomously switch between the direct communication mode and the relay communication mode according to the network conditions.When the DU operate in relay communication mode,a half-duplex DF relay which has social relationship with the DR is required to assist the DT completing communication.Based on the above system model,to address the issue of low spectrum utilization caused by multi-pairs of DU collision and the time-varying nature of wireless channel,as well as the selection of optimal RN set to be probing,a statistical model of distributed channel access process is formulated to maximize the statistical average throughput of system,and a distributed channel scheduling method is developed.Simulation results show that the proposed channel scheduling method can achieve the desired trade-off between throughput gain via cooperative communication and signaling overhead of establishing cooperative relaying.