Theory And Method Of Multiuser Opportunistic Beamforming

The fifth generation(5G)mobile communication technology provides more highspeed,reliable and lower delay communication services.In order to achieve better communication performance,it is necessary to adopt higher spectrum utilization communication techniques with the limited wireless resources.MIMO is one of the core schemes,which utilizes space domain to improve spectrum efficiency.One of the most important techniques of MIMO is precoding,where base station(BS)pre-processes the transmitted signals with precoding matrices.There are many criterions to generate the precoding matrices,including zero forcing(ZF),regularized channel inversion(RCI),block diagonalization(BD)criterions,etc.However,for most of the criterions,perfect channel state information(CSI)is required in BS.In order to obtain perfect CSI for precoding,channel estimation techniques are required.The complexities of channel estimation techniques are extremely high,and the latency is also large,which limit the applications of precoding techniques.To degrade the limitations,opportunistic beamforming(OBF)was proposed,where opportunistic precoding and multiuser selection are combined to obtain multiuser diversity gain with little CSI.Compared to the conventional precoding techniques,a distinct advantage of OBF is the little CSI characteristic,where users are only required to feed back their instantaneous signal-to-noise ratio(SNR).The BS picks the user with the largest SNR to transmit signals.Therefore,OBF systems can achieve high spectrum efficiency with low complexity.In order to further study the opportunistic beamforming techniques and further promote the application of OBF in the future wireless communication systems.In this paper,OBF is studied from four aspects: the basic theory of OBF,the extended OBF system with multiple receiving antennas,the optimal selected weight OBF system based on non-orthogonal multiple access(NOMA)and the joint design of transmitting and receiving.Aiming at the basic theory of OBF,this paper firstly presents the model of OBF system and proposes the transmission mechanism based on the maximum capacity criterion.For two typical wireless channels,i.e.Rayleigh and Rician fading channels,this paper deduces the statistical characteristics of the equivalent channels.According to the statistical characteristics,the closed-form expressions of ergodic capacities in both Rayleigh and Rician fading channels are given.In order to further analyze the performances of the system,the upper and lower bounds of bit error rate(BER)are derived.Aiming at the problem of OBF multiple receiving antenna expansion,this paper firstly presents the system model of multiuser multiple receiving antennas OBF,and proposes three criterions to combine the received signals of multiple antennas.Then,in order to improve the applicability of OBF system,channel model is extended to Nakagami-M fading channel,and the equivalent channel and statistical characteristics of Nakagami-Mfading channel are derived.Furthermore,the closed-form expressions of ergodic capacity of the system are given.At the same time,considering the real physical scene,where users can not feed back accurate SNR to the BS,this paper proposes a channel quality indication quantization scheme.In order to solve the problem of multiple access in OBF system,this paper proposes a non-orthogonal multiple access scheme,and designs the optimal beamforming weight jointly.Then,the optimization function aiming at maximizing the spectrum efficiency is established,and the optimal resource allocation algorithm considering the weight selection,user pairing and power allocation is proposed.Then,the simplified algorithms are proposed to reduce the complexity of the algorithm.At the same time,the theoretical values of BERs of all the users are derived.In order to solve the joint design problem of the transmitter and receiver in OBF system,this paper firstly proposes an OBF system with joint optimal selection of beamforming weight and multiple receiving antennas,where multiple access,optimal weight and multiple antenna receiving are jointly considered.Then,aiming at the unfairness among the users in OBF systems,this paper proposes a user pairing strategy based on the proportional fairness constraint.Then,based on the proportional fairness constraint,an optimization function aiming at maximizing the spectrum efficiency is established.A joint iterative optimal resource scheduling algorithm to meet both the fairness between and high spectrum efficiency is presented.