Research On Massive MIMO Cooperative Communication Technology In Multi-user Scenarios

The rapid development of high-speed railways has greatly facilitated people’s travel.At the same time,the characteristics of high-speed rail communication scenarios such as high carriage penetration loss,strong information privacy,and high demand put forward new requirements for the design of high-speed rail-oriented wireless communication systems.Cooperative communication technology can effectively expand signal coverage,improve communication quality,and improve information transmission security from the physical layer.Therefore,it is widely used in high-speed rail communications.In addition to traditional relay,passive intelligent reflecting surface(IRS)technology can not only help increase system gain,but also avoid additional power consumption.This paper mainly studies the sum rate and energy efficiency of massive MIMO systems assisted by cooperative relay and IRS in multi-user communication scenarios.First of all,most of the current physical layer security research does not consider the impact of channel estimation errors on security performance,a full-duplex two-way relay networks security performance based on imperfect channel state information is studied.The optimal relay selection scheme is adopted,and the expressions of system security capacity and secrecy outage probability are derived based on the principle of maximum and minimum.The main factors affecting the security performance of the system are further analyzed,and the performance difference between full-duplex and half-duplex systems is compared.The simulation results show that the system secrecy performance is best when the relay node is at the midpoint between users.Meanwhile,reducing the channel estimation error,the average signal-to-noise ratio of the eavesdropping link and the residual self-interference can effectively reduce the system secrecy outage probability.Properly increase the number of relays can achieve better security performance.Secondly,in view of the problem of large energy consumption in massive MIMO,the sum rate and energy efficiency of the multi-user relay-assisted massive MIMO downlink are studied.Low resolution digital-to-analog converters(DACs)are equipped at both the base station(BS)and amplify-and-forward relay.Under the Rician fading channel,closed-form approximate expressions for the sum rate are derived with perfect and imperfect channel state information,respectively.A more general power scaling law is extracted to save signal transmission power without reducing the sum rate.A local optimal power allocation scheme is proposed to improve the channel capacity of active users.Finally,the trade-off between sum rate and energy efficiency is discussed.The simulation results show that the sum rate is not affected by the channel estimation error under the condition of strong line-of-sight channel.And it is more valuable to increase the DAC quantization bit at the relay when the BS antennas number is larger than relay.The best tradeoff between sum rate and energy efficiency can be obtained when the DAC quantization bit is 4.Finally,in order to further reduce system energy consumption and improve signal utilization,IRS is introduced to replace traditional relays in multi-user scenarios.The IRS is divided into blocks according to the number of users to serve each user separately.Through local optimization at the BS and IRS,the closed-form expression of the achievable sum rate of the system under the Rician fading channel is derived.A power consumption model is established,and the trade-off between sum rate and energy efficiency is analyzed.The simulation results show that increasing the number of BS antennas can effectively increase the system sum rate.When the BS transmission power is about 28 dBm,the energy efficiency reaches the maximum value,and a considerable achievable sum rate can be guaranteed.Finally,the proposed optimal power allocation scheme can effectively improve the system transmission rate.