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A Research On Non-Orthogonal Multiple Access(NOMA) For 5G/B5G Networks

Posted on:2021-02-20Degree:MasterType:Thesis
Country:ChinaCandidate:M S ZhangFull Text:PDF
GTID:2428330614471796Subject:Communication and Information System
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The 5G commercialization has been issued in major areas in main cities of China by the year 2020,which not only provides users with higher communication quality,but also promotes the development of emerging technologies.How to efficiently use the limited spectrum resources and how to effectively allocate the resources according to the service requirements are important problems to be solved in the research of new generation mobile communication systems.As a key technology of 5G,non-orthogonal multiple access(NOMA)technology can theoretically achieve higher user accessibility and higher transmission reliability than traditional orthogonal multiple access(OMA)strategy.Considering new communication scenarios,and with the goal of efficiently using limited spectrum resources,supporting massive connections,and achieving low-latency and high-reliability communication,this dissertation studies the NOMA technology for 5G/B5 G mobile communications,and makes progress in the application of non orthogonal code access(NOCA)technology in URLLC scenario and the resource optimization of power domain NOMA in massive MIMO system.Non-orthogonal coded access(NOCA)is one of the 5G candidate multiple access schemes.NOCA uses QPSK-based low cross-correlation sequence codebook to spread user's transmission symbols over multiple subcarriers,and uses parallel interference cancellation(PIC)mechanism at the receiver to distinguish multiple users and reduce the inter-user interference,so as to achieve the multiplexation of users on the same timefrequency resource.NOCA scheme combined with proactive retransmission scheduling strategy is proposed to reduce transmission latency and enhance reliability in URLLC scenario.Through system level simulation,this dissertation evaluates the latency and reliability performance of NOCA schemes with different spreading length in URLLC scenario,and with reactive and proactive retransmission modes.The simulation results show that the proactive retransmission scheme can achieve more transmission opportunities within 1ms delay,and the NOCA scheme can further eliminate the interuser interference and improve the transmission reliability.Finally,an adaptive NOCA spreading length strategy is proposed for different user density and packet arrival rate scenarios.As a key technology of transmission layer in 5G/B5 G,massive MIMO expands the spacial dimension by configuring multiple antennas at the transmitter of base station.The combination of massive MIMO and NOMA can bring benefits: on the one hand,multiple users in the cell can multiplex and communicate with the base station on the same timefrequency resource achieving higher spectral efficiency;on the other hand,the diversity gain brought by multiple antennas can further improve the power efficiency.This dissertation investigates the power minimization problem of general downlink multi-cell multi-input and single-output-NOMA(MISO-NOMA)systems,under the condition that each user in the cell satisfies a certain data rate constraint.Distributed iterative algorithms are designed to jointly solve the three subproblems,i.e.,user clustering,beamforming and power control.Firstly,the Semi-Orthogonal User Selection(SUS)algorithm is adopted to select beamforming users,and the Zero-Forcing(ZF)beamforming strategy is used to construct the precoding matrix.Then,two distributed user clustering strategies are proposed,i.e.,channel condition-based user clustering(CCUC)algorithm and power consumption-based user clustering(PCUC)algorithm.Finally,with the fixed user grouping strategy and beamforming matrix,the analytical solution of the optimal power allocation strategy is derived theoretically,and the convergence of the distributed iterative algorithm is proved.The numerical results show that the proposed scheme is superior to the traditional MISO-NOMA strategy and non-clustered MISO-NOMA strategy in terms of power consumption,outage rate,energy efficiency and connectivity efficiency.
Keywords/Search Tags:non-orthogonal multiple access (NOMA), ultra reliable low latency(URLLC), uplink grant-free transmissions, massive MIMO, power allocation, beamforming, user clustering
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