Study On Transmission Rate And Energy Efficiency For Cellular-D2D Hybrid Systems

D2D communication(Device-to-Device)has been standardized by LTE-advance as an important near-scene communication technology in 5G.With the development of the Internet and the continuous improvement of user requirements,the traditional cellular system can no longer meet the requirements of wireless communication network and the local small-scale communication scenario with hierarchical structure will become an important complement to cellular systems.As a result,D2D communication will be-come an important extension of cellular users.D2D communication,as a short-distance communication mode,has the advantages of low relay,low power consumption and high transmission rate.Utilizing licensed frequency resources in underlay mode,it not only improves spectrum efficiency but also allows users to have good quality of service,which will be guaranteed.So D2D communication will be an important form of future wireless communications.This thesis firstly considers the cellular-D2D hybrid system model.The lower ex-pressions of transmission rate are analyzed for D2D users under direct mode and cellu-lar mode.The hybrid system on D2D underlay mode is studied emphatically,and the user distribution is described by the Poisson Point Process(PPP)of stochastic geometry.The transmission probability(coverage probability)expressions for cellular users and D2D users are analyzed.Based on this,a single-band power control and user allocation proposal is obtained,and a multi-band power distribution proposal based on carrier ag-gregation is further analyzed in depth.The simulation results reveal that the user can ef-fectively improve the performance of the hybrid system by power control,which is con-sistent with the theoretical results,and the multi-band power allocation proposal can find the maximum transmission rate,under the specific D2D user density,while im-proving the frequency utilization.Then,the thesis considers a Massive MIMO-D2D hybrid system model,while the user distribution is described by the PPP theory.Two conditions of hybrid system shar-ing downlink and uplink frequency resources are analyzed respectively.Expressions are derived for the uplink transmission rates.The relationship between the transmission rate,energy efficiency and the number of antennas,D2D user density and other factors is si-mulated,and three actual scenarios of user distributions are discussed.The simulation results reveal that the hybrid system can find the maximum value of the total transmis-sion rate under a certain D2D user density.When the user density is small,the transmis-sion rate increases significantly with the growth of the number of antennas.The energy efficiency,however,is limited by the total power consumption.Finally,a joint optimi-zation of the minimum transmit power and the access threshold is utilized for the uplink D2D user,thereby achieving the purpose of saving power consumption and improving energy efficiency.