Research On Licensed And Unlicensed Spectrum Access Scheme For Hybrid Cellular And D2D Networks

With the development of society and the continuous evolution of wireless communication technology,the demand for data traffic services has exploded.In order to solve the contradiction between demand and supply of the bandwidth,the academic community has proposed Device-to-Device(D2D)communication,which enables adjacent nodes to communicate directly without passing base stations with high speed and low latency.D2D communication is considered to be a key technology to improve the spectrum efficiency and system throughput of cellular networks(CNs).However,D2D communication is not a long-term solution.Mobile communication users are growing rapidly,and the limited resources in licensed spectrum are becoming more and more difficult to meet the needs of future wireless network traffic data.Based on this,the academic community has expanded Long Term Evolution(LTE)in unlicensed spectrum(LTE-U),which can effectively increase network capacity.Inspired by LTE-U,research on the D2D in Unlicensed Spectrum(D2D-U)is also being carried out.However,few authors consider the scenario in which the cellular users and D2D users both can access the unlicensed spectrum,and the protocols of LTE communication and Wireless Fidelity(WiFi)technology are not the same.Therefore,there are still many problems on the good coexistence of LTE-U,D2D-U and WiFi users,and it is a challenge that should not be underestimated.This article conducts in-depth discussion and research on the above problems.First,we propose a hybrid cellular and D2D network in licensed and unlicensed spectrum.D2D users reuse the uplink of cellular communication in the licensed spectrum to reduce interference complexity.At the same time,both cellular users and D2D users can access the unlicensed spectrum which occupied by WiFi users.Secondly,in order to make LTE-U,D2D-U and WiFi networks coexist well and ensure the Quality of Service(QoS)of all users,we have made improvements based on the original duty cycle mechanism,and proposed a duty cycle method based on fairness.With a flexible duty cycle mechanism,the system automatically adjusts the proportion of LTE-U and D2D-U in the entire time slot based on the data transmission flow change of the WiFi network.Finally,since the user access in the cellular and D2D hybrid network under the licensed and unlicensed spectrum is a mixed integer nonlinear programming problem,in order to optimize the transmission rate of the communication system,we propose a matching-iteration based joint resource allocation and user access algorithm.The simulation results show that the proposed algorithm can significantly improve the network capacity,transmission rate and spectrum utilization of the network.