Research On Spectrum Efficiency Of Millimeter Wave Massive MIMO Systems In LOS Environment

Millimeter wave communication and massive MIMO,as the key technologies of 5G communication,are more and more concerned by academics and industry naturely.Short-wavelength millimeter-wave communication facilitates the distribution of massive antenna arrays,while massive MIMO provides high directional beams by beamforming to compensate for the transmission loss of millimeter-wave signals.The fusion of the two can improve system performance effectively.However,millimeter-wave massive MIMO systems are susceptible to environmental factors,making them more suitable for propagation in line of sight(LOS)environments.Therefore,this paper mainly studies the spectral efficiency of millimeter?wave massive MIMO systems in LOS environment.In the LOS environment,the spectral efficiency of the millimeter-wave massive MIMO downlink multi-user system when the base station is configured with a uniform linear antenna array and the maximum specific transmission scheme is used is first studied.The closed-form expression of the achievable spectral efficiency is analyzed,and a user scheduling scheme based on angle information is proposed.This scheme can reduce the interference to zero between users,thereby achieving the optimization of the achievable spectrum efficiency,and a closed expression for the maximum achievable spectral efficiency is derived.The simulation results show that the achievable spectrum efficiency has been improved greatly after applying the user scheduling scheme.In order to improve the versatility,this paper studies two kinds of three-dimensional antenna arrays,Uniform rectangular planar array(URPA)and Uniform Cylindrical Array(UCYA),and considers the user,s azimuth and elevation angle.This paper further studies the impact of power injection algorithm with unequal power distribution on performance.The simulation results show that,compared with the equal power distribution scheme,the unequal power distribution scheme improves the spectrum efficiency of the system obviously;although the peak gain of the URPA configuration is large,the side lobes are too much,and its performance is not as good as the UCYA configuration.Then this paper studies the hybrid precoding optimization algorithm based on successive interference cancellation(SIC)in single-user scenarios.It makes the spectral efficiency optimization problem decomposed into a series of spectral efficiency optimization problems,and also studies the performance impact of channel state information on the performance of this precoding algorithm.The simulation results show that the SIC-based hybrid precoding algorithm is not only less complex,but also has good achievable spectral efficiency.Then the hybrid precoding scheme based on phase shifter in multi-user scenario is studied,and the upper bound of the achievable spectral efficiency of the scheme is deduced.Aining at the fact that the radio frequency(RF)chain can,t obtain the user phase information accurately,a hybrid precoding seheme based on quantization phase shifter is proposed.In addition,an actual power consumption model is considered,and the system's achievable energy efficiency is explored and its closed-form expression is derived.The simulation results show that compared with the all-digital scheme,the phase shifter-based hybrid precoding has higher energy efficiency,and the higher the quantization bit,the better the performance.It also studies the block precoding based on block diagonalization(BD)in multi-user scenarios.It considers the processing of the received signal at the receiving terminal and applies a power injection algorithm that considers the fairness between users to improve performance.The simulation results show that the BD-based hybrid precoding can approach the performance of the traditional digital precoding.