User Pairing Scehems In Different NOMA Communication Scenarios

In non-orthogonal multiple access(NOMA)system,multiple users are multiplexed in the power domain and share the available communication re-source.Which users share the same resource has an important effect on system performance,so it is necessary to study user pairing scheme.In this thesis,we study user pairing scheme in three NOMA communication scenarios,includ-ing downlink NOMA communication scenario,cooperative downlink NOMA communication scenario and downlink millimeter-wave non-orthogonal multi-ple access(mmWave NOMA)communication scenario.In the following,we will introduce the contributions of our thesis.Firstly,we propose two novel user clustering schemes in the downlink NOMA communication scenario.In the proposed system,an N-antenna base station(BS)selects and serves 2N users from K single antenna user equipments(UEs)(K>2N and K is even).In particular,we propose a signal difference and alignment(SDA)framework to achieve fair and spectral efficient user clus-tering for NOMA with flexible performance-complexity tradeoff.To be more specific,the BS sorts UEs according to their large-scale fading(LSF)gains and selects N primary UEs with the highest LSF gains to guide the downlink zero-forcing beamforming(ZFBF)vector.Then the BS selects N complementary UEs from the second half of the sorted UE set based on the principle of signal space alignment(SSA).Unlike conventional user scheduling,SDA framework uses the ordered set to create signal strength difference for NOMA while em-ploying opportunistic SSA method to select complementary UEs with minimal inter-cluster interference leakage.Moreover,the SDA framework can enable distributed implementation with graceful performance at lower system over-head.Numerical results verify that the proposed schemes improve the perfor-mance in downlink NOMA system.Secondly,we propose two user pairing schemes in the cooperative down-link NOMA communication scenario.In the proposed system,a BS equipped with N antennas selects N pairs of users equipped with single antenna to serve.One pair includes a near user and a far user,whose signals are superposed at the transmitter side,and successive interference cancellation(SIC)is applied to the receiver side.According to SIC,the near user has prior information about the message of the far user,which is exploited to forward the signal of the far user in the proposed NOMA system.Simultaneous wireless information and power transfer(SWIPT)technique is employed at the NOMA system,in which the near user harvests energy from BS to forward the information to the far user.In addition,ZFBF is used to remove the inter-pair interference of the near user,and in order to minimize the inter-pair interference of the far user,the two user pairing algorithms are proposed.To guarantee the performance of users,we propose a power allocation scheme.Simulation results show the proposed algorithms can improve the performance in the cooperative downlink SWIPT NOMA system.Finally,we propose three user pairing schemes in the downlink mmWave NOMA communication scenario.In the proposed system,the application of millimeter-wave(mmWave)to NOMA system is investigated,including one M-antenna BS and multiple single-antenna users,and mm Wave and NOMA are two key technologies in 5th generation(5G)network.In order to reduce the sys-tem overhead,three user pairing schemes based on the distance between users and the BS are proposed,i.e.,random near user and random far user(RNRF),nearest near user and nearest far user(NNNF)and nearest near user and far-thest far user(NNFF).The signals of the two user within one pair are super-posed at the transmitter and SIC is utilized at the receiver.In addition,the proposed scheme focus on a single beam and random beamforming is applied to mmWave NOMA systems which can further reduce the system overhead.Stochastic geometry is used to characterize the performance of the proposed mm Wave NOMA transmission system.Closed-form expressions for the out-age probability and sum rate are derived for the three schemes.The Monte Carlo simulations demonstrate the performance of the mm Wave NOMA sys-tem is improved and verify the accuracy of the derived analytical results.