Research On Modulation And Access Technology In Mm Wave Massive MIMO Systems

With the rapid development of the mobile Internet and the Internet of Things(Io T),the fifth-generation mobile communication(5G)system has been given higher requirements,such as: higher connectivity,greater reliability,and faster data rates.The current mobile communication technology is difficult to meet the above needs,so it is a general trend to propose new communication mechanisms and research emerging technologies.In this paper,the key technologies in 5G mobile communications: millimeter wave(mm Wave)communications,Massive multiple input multiple output(Massive MIMO),non-orthogonal multiple access(NOMA)and spatial modulation(SM)are effectively combined to improve system connectivity and communication reliability.The main research contents are summarized as follows:Firstly,a spatial modulation scheme for low-cost,small-sized terminals in mm Wave massive MIMO systems is proposed.In order to use the spatial index to transmit part of the information for terminals with only a few transmit antennas deployed,an antenna-switching based spatial modulation technology is adopted.At the first,through the analysis of the theoretical upper bound of the average bit error rate(ABER),we optimized the design of the transceiver in the point-to-point communication scenario.The array gain brought by beamforming technology at the receiving end compensates for the serious path loss in mm Wave communication,and the optimized design of spatial modulation signals at the transmitting end,including the design of spatial modulation constellations and mapping rules,overcomes the difficulty in identifying index bits caused by the channel correlation between adjacent transmitting antennas in the mm Wave communication system.Next,the communication scenario is extended to a single base station serving multiple users.In order to eliminate the interference caused by strong user signals at the receiving end to weak user signals,we proposed a signal detection algorithm based on SIC.The simulation results show that the proposed spatial modulation scheme significantly improves the reliability of system communication.Secondly,an uplink joint time and beam domain NOMA scheme is designed to improve the system's ability to accommodate connected devices.We aim to achieve full coverage and separability of user signals under the condition of supporting high user overload rates,utilize the correlation and difference of the channels to achieve beam-domain NOMA,and utilize nonorthogonality of spreading sequence to achieve time-domain NOMA.With the optimization goal of improving the communication reliability of the system,this scheme constructs and solves the optimization problem of the joint domain sparse access matrix.Since multi-user information is sparse in the joint domain,message passing algorithm(MPA)can be used for efficient and reliable user signal detection.In order to reduce the decoding complexity while suppressing the influence of beam domain interference on the system decoding performance,we reconstruct the obtained joint domain access matrix and add the interference cancellation operation to the iterative process of the receiving end message passing algorithm(MPA).The simulation results show that the proposed multiple access scheme supports high overload rate while ensuring decoding performance.Finally,for scenarios where users are distributed over a wide range and cannot use spatial correlation to achieve full coverage of user signals,a joint domain multiple access scheme based on beam splitting is proposed.The so-called beam splitting refers to dividing an antenna array connected to a radio frequency link into multiple sub-arrays to form multiple sub-beams to serve multiple users in different directions.The design of this scheme mainly includes two aspects:joint domain resource allocation and signal detection algorithm optimization.Because the technology based on beam splitting is adopted,the allocation of beam domain resources needs to be determined according to the beam direction of multiple users,the situation of users accessing joint domain resources,and the division of arrays in each resource element.At the receiving end,since the new beamforming technology introduces inter-beam interference,a reconstruction algorithm based on channel quality is used for the joint domain access matrix.This scheme overcomes the shortcomings in the previous work,and enables users with unrelated spatial distribution to share a beam access to achieve the full coverage goal of the system.