Research On Hybrid Precoding Techniques In Millimeter-wave Massive MIMO-NOMA Systems

With the rapid development of mobile Internet technology,the available spectrum resources have been seriously insufficient.At the same time,with the continuous growth of user data services,facing the communication demands of higher transmission rate and lower latency,the fifth generation(5G)mobile communication system emerged.In order to meet the needs of large-capacity and high-speed data services,millimeter wave(mm Wave)technology not only provides abundant spectrum resources,but also provides higher transmission rates.The massive multiple input multiple output(m MIMO)technology can dramatically improve spectrum efficiency of the system and compensate for the path loss,making mm Wave m MIMO communication possible.In addition,it's difficult for traditional orthogonal multiple access(OMA)to adapt to the5 G massive interconnection scenario,and non-orthogonal multiple access(NOMA)technology is considered to be another key technology of 5G communication because it can greatly increase the number of concurrent service users,thereby further the system capacity.Therefore,in order to achieve higher data transmission rates and massive terminal interconnection,the combination of mm Wave,m MIMO and NOMA technologies will become inevitable,i.e.,to form the mm Wave m MIMO-NOMA system.This thesis is oriented to the mm Wave m MIMO-NOMA system.For the issues of the high hardware cost and power consumption,based on Fixed Sub-Connected Hybrid Architecture(FSC-HA)and Dynamically Sub-Connected Hybrid Architecture(DSC-HA),two precoding schemes are proposed.The main contents are summerized as follows.1.Design of precoding scheme based on FSC-HA in mm Wave m MIMO-NOMA system.Firstly,use Equal Gain Transmission(EGT)/Maximal Ratio Combining(MRC)methods to alternately optimize the analog precoding vector and the analog combination vector to maximize the sum of the effective channel gains of each NOMA cluster users to make the received signal power maximized.Secondly,alternately optimize the digital precoding matrix and power allocation coefficient with the optimization goal of system sum rate maximization to weaken the interference between NOMA inter-clusters and intra-cluster users.Considering that the optimization problems are all non-convex optimization,when the power distribution coefficient is given,the digital precoding optimization problem is expressed as a Difference of Convex(DC)problem,and iteratively solved by the Successive Convex Approximation(SCA)algorithm according to the DC programming theory.Given the digital precoding matrix,the power allocation problem is expressed as a sub-problem of user power optimization between inter-clusters and intra-clusters,and then the Lagrangian function is used to solve it.Finally,numerical simulation shows that the system sum rate and energy efficiency of the proposed scheme are better than the corresponding OMA scheme,and the system energy efficiency is better than the Fully-Connected Hybrid Architecture(FC-HA)scheme,which proves that the proposed scheme has excellent performance in mm Wave m MIMO-NOMA system and is more suitable for practical scenarios.2.Design of precoding scheme based on DSC-HA in mm Wave m MIMO-NOMA system.Firstly,On the basis of user clustering,based on the principle of maximizing equivalent channel gain,the analog precoding optimization problem is transformed into the joint design problem of transmitting antenna grouping and analog precoding,and using the Kuhn-Munkres algorithm to design the DSC network to realize the radio frequency chain and the transmitting antenna dynamically connected,and then the analog precoding vector is designed based on the antenna grouping result,which breaks the diagonal constraint of the analog precoding matrix in FSC-HA.Secondly,ZF algorithm is used to design the digital precoding vector to eliminate inter-cluster interference.Finally,based on the system sum rate maximization,the power allocation of the users of intra-cluster is solved to eliminate inter-user interference.Numerical simulation shows that the system sum rate and energy efficiency of the proposed DSC-HA scheme are better than the FSC-HA scheme and the corresponding OMA scheme,and its system sum rate is close to the FC-HA scheme.