Research On The Scheduling Scheme Of Non-Orthogonal Multiple Access For Urban Vehicular Networks

Urban vehicular networks play an important role in intelligent transportation systems.In an urban vehicular network,the quality-of-service constraints include low latency,ultra reliability and high transmission rate,which poses severe challenges to the system's resource scheduling scheme.By utilizing non-orthogonal multiple access(NOMA)for resource scheduling,the freedom of traditional multiple access communications can be expanded,and thus,the quality of service can be improved.Therefore,the investigation of NOMA-based scheduling schemes is of great significance for urban vehicular networks.In this thesis,the algorithms of user scheduling and resource allocation based on NOMA are designed under the urban traffic models.The purpose of the proposed algorithms is to improve the average spectral efficiency,the lower bound of transmission reliability,and the semi-persistent scheduling(SPS)period.The main work of this thesis is described as follows.1)The joint optimization strategy of digital precoding and user scheduling is investigated.When the optimization of total throughput is obtained,there exists a fairness problem between the cell-center users and the cell-edge users in NOMA systems.To handle this challenge,full-duplex cooperative NOMA is introduced.A precoding scheme based on the centroid of users' channel vectors in each NOMA cluster is designed to improve the performance of spatial filtering.Then,a heuristic user scheduling algorithm is proposed to improve the flexibility of NOMA clustering under the uneven vehicle distribution scenes.Finally,simulation results show that the proposed strategy has higher average spectral efficiency and better user fairness than the typical schemes.2)The joint optimization strategy of power allocation and user scheduling is investigated.To shorten the latency,millimeter wave NOMA is first introduced in the design of SPS.The joint optimization problem in terms of user scheduling and power allocation is formulated to minimize the scheduling period.This problem is then proved to be NP-hard by being reduced into a vertex coloring problem.To solve it with polynomial complexity,we decouple it into two sub-problems,i.e.,the power allocation problem and the user scheduling problem,and calculate them by iteration.For one sub-problem,a novel power allocation algorithm is proposed to obtain the optimal lower bound of the packet reception rate in each time slot.For the other sub-problem,a beam division and user clustering algorithm is proposed,and the user scheduling is implemented by solving a bilateral many-to-many matching with peer effects.The analytical results on stability,convergence and computational complexity are presented.Finally,simulation results show that the proposed scheduling strategy outperforms the existing typical schemes.