Research On Non-orthogonal Multiple Access Under Practical Constraints

With the scarcity of spectrum resources,how to solve the large-scale access problem caused by the continuous development of mobile Internet and Internet of things has become a key challenge.In recent years,researchers have proposed a new method,that is non-orthogonal multiple access(NOMA).The basic principle of NOMA is to use superposition coding technology at the transmitter and serial interference cancellation(SIC)at the receiver to separate multi-user signals,so as to improve the access capacity and spectrum efficiency.In this paper,we aim at the cost,power consumption,time delay,CSI error and other constraints caused by the actual communication system,deeply study the achievable performance of NOMA system,and reveal the mechanism of key factors that affect the system performance.Firstly,aiming at Cell-free massive MIMO-NOMA system under low-cost constraints,this paper studies the transmission rate of each user in the downlink system under imperfect SIC,and derives the closed form expression of any achievable rate.The result reveals that the Cell-free massive MIMO-NOMA system has the advantages of high ergodic capacity and high coverage.The simulation shows that increasing the number of antennas and access points is of great importance to the system performance.And it is helpful to reduce the cost on the premise of ensuring certain performance by using low-precision ADC.Secondly,aiming at IRS-assisted NOMA system with imperfect channel state information(CSI)constraints,this paper studies the transmission rate of each user of SIMO-NOMA system,and deduces the closed form expression of the achievable rate of each user under different CSI constraints.The result reveals the importance of accurate channel estimation of Lo S channel for the improvement of system performance.The advantages of NOMA over OMA in multi-user system are also verified by simulating.Finally,aiming at the low-delay NOMA system with imperfect SIC constraints,this paper studies the reliability of each user in SIMO-NOMA downlink system,and derives the closed form expression of any user's block error rate,as well as the approximate expression of special user's block error rate under high SNR.The results show that increasing the number of users can improve the reliability of users with better channels,but it will reduce the reliability of users with worse channels.While with low SNR,increasing the number of users will reduce the reliability of all users.The simulation results verify this conclusion.