| In recent years,with the rapid development of new technologies such as smart cities,intelligent transportation and industrial Internet,frequent communication between a large number of intelligent terminals such as autonomous vehicles,industrial cooperative robots and wearable intelligent devices has put forward higher requirements on the carrying capacity and communication delay of wireless networks.In the traditional cellular communication mode,data must be uploaded to the base station and core network before being sent to the peer user even though the two communication parties are very close,resulting in a waste of spectrum resources and extra communication delay.For this reason,the Fifth Generation mobile communication system(5G)New Radio Sidelink eliminates the need for user data to be forwarded by the base station and core network by allowing users to establish PC5 links for end-to-end communication.Thus,NR Sidelink and has higher spectrum utilization rate and lower transmission delay,enabling the development of intelligent manufacturing,automatic driving and other vertical industries.As 5GAdvanced(5G-A)applies NR Sidelink to more diverse scenarios,the Third Generation Partnership Project(3GPP)organizes standardization studies of NR Sidelink communication enhancements to meet communication rate and coverage requirements in new application fields.In this thesis,the NR Sidelink technology for 5G-A was studied in depth.The main innovations achieved are as follows:(1)Aiming at the problem of extra transmission delay caused by the uncertainty of Listen Before Talk(LBT)when NR Sidelink accesses the unlicensed frequency band,this thesis proposes an unlicensed access mechanism of NR Sidelink based on terminal autonomous interception.In this mechanism,the concept of "candidate reserved subchannel" is introduced.By activating and releasing candidate reserved subchannel resources,the access success rate of NR Sidelink in the unlicensed frequency band is improved,and the influence of LBT uncertainty on the unlicensed access delay of NR Sidelink is reduced.Based on the above access mechanism,a dynamic update algorithm of candidate reserved subchannel is proposed.Secondly,mathematical modeling and analysis were carried out on the proposed mechanism and algorithm,and the node transmission probability and collision probability of NR Sidelink and WiFi systems were derived respectively,thus obtaining the access success rate and saturation throughput of the two systems.Finally,the proposed mechanism was verified by simulation,and the simulation results showed that compared with the traditional unlicensed access mechanism,the proposed mechanism increased the success rate of NR Sidelink unlicensed access by about 28%.(2)Aiming at the route discovery process of NR Sidelink User-toUser(U2U)multi-hop relay,a route discovery mechanism based on the Model A and Model B discovery process of NR Sidelink is proposed.This mechanism is compatible with the existing NR Sidelink communication standard process and protocol,and integrates route discovery into the Sidelink direct discovery process,so that users can initiate route discovery before establishing communication links with neighboring nodes.So as to solve the traditional route discovery premise that communication links between neighboring nodes are established in advance which results in additional system overhead issues.In addition,the packet frame structure of the U2U multi-hop relay is redesigned to support the multi-hop relay transmission of discovery messages.Finally,the signaling cost,end-to-end delay,routing success rate and other performance parameters of the proposed mechanism are simulated and analyzed,and the feasibility of the proposed mechanism in route discovery of NR Sidelink U2U multi-hop relay of is verified. |
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