Research And Simulation On Applications Of NOMA Technology In V2I Communications

Vehicle-to-everything(V2X)communication is the information exchange between a vehicle and other vehicles,pedestrians,transport infrastructure and internet gateways in the intelligent transportation system(ITS).Because of the widely deployed infrastructure,the LTE network has been considered as a promising candidate to support the V2 X communication.However,with a massive number of devices accessing the V2 X network in the future,the conventional OFDMA-based LTE network faces serious congestion problem due to its low efficiency of orthogonal access.The non-orthogonal multiple access(NOMA)technique has been well recognized as an effective solution for the future 5G for higher spectrum efficiency and larger capacity.Therefore,in the framework of LTE,this thesis mainly studies vehicle-to-infrastructure(V2I)communication based on NOMA technology.First of all,in this thesis we establish V2I communication simulation platform under the LTE framework,including network topology model,road side unit(RSU)model,vehicle user model,and the selection of V2I communication channel model.We also investigate the influence of RSU spacing on system performance based on the platform.The result shows that when the vehicle density is constant,the bigger the RSU spacing is,the worse the system performance will be.Then,we apply the NOMA technology to the built simulation platform and investigate some different multi-user pairing and power allocation schemes in a downlink system level.Multi-user pairing schemes include pre-group pairing and channel state sorting pairing scheme.The result shows that the former has a better performance and moderate search complexity,and also takes accounts of user fairness(edge user throughput).In pre-group pairing scheme,two user groups with different user numbers are considered,the result of which shows that when the number of users in the two groups is equal,maximum user fairness and sub-optimal performance can be achieved.Two power allocation schemes including fixed power allocation(FPA)and frational transmit power allocation(FTPA)are applied,and the result shows that the latter which utilizes the channel gaps between paired users can provide better system performance with acceptable complexity.In the end,on the V2I simulation platform based on NOMA technology,the precoding schemes of MIMO are investigated,including transmit diversity,open-loop multiplex and closed-loop multiplex schemes.The result shows that the transmit diversity precoding scheme based on NOMA-MIMO system gets the most performance improvement on OFDMA-MIMO system,but the closed-loop multiplex scheme shows the best performance at the cost of maximum signaling overhead.The performance of open-loop multiplex precoding is quite close to that of closed-loop multiplexing precoding with moderate signaling overhead,which suggests the feasibility of openloop scheme in practical system.In addition,error propagation(EP)problem in NOMA-MIMO V2I communication system is invesigated in this thesis,the existence of which is shown to reduce the performance of vehicles greately by simulation results.