Research On Non-orthogonal Multiple Access Technology Based On Multi-user Superposition Coding

In recent years,with the rapid development of mobile communications,the number of users and data services have shown explosive growth.On the one hand,this situation poses more complex scenarios for mobile communications,and on the other hand,it also challenges the sustainable development of green communications.However,it's hard for the orthogonal multiple access technology,represented by orthogonal frequency division multiple access(OFDMA)in the fourth generation(4G)mobile communication system,to meet the demand.Therefore,the industry proposed the non-orthogonal multiple access(NOMA)technology,which increases accessed users while improving resource utilization efficiency.Thus,this graduation thesis builds a non-orthogonal multiple access system based on multi-user superposition coding,optimizes the system from the perspective of power allocation and modulation,and combines the system with collaboration communication to extend the application scenario.This thesis firstly introduces the principle of NOMA from the power domain and the coding domain respectively,including principles and characteristics of several representative NOMA technologies.Next,the system model is built,where the design schemes of the transmitter and receiver are elaborated respectively.Based on the many-to-one model and the many-to-many model,the system is optimized from two directions:first,for power allocation,using coordinate alternation method and genetic algorithm as tools to study characteristics of constellation points and reachable sum rate of the system;second,from the perspective of modulation,using genetic algorithm to study the characteristics of constellation points and reachable sum rate of the system.Finally,the application of NOMA in collaborative communication scenarios is studied,the optimal design of power allocation scheme in cooperative communication scenario is completed.The research results show that for power allocation,reachable sum rate and bit error rate performance of the design scheme are better than the equal power allocation,and it is suitable for different superposition structures and modulation schemes.Meanwhile,for the modulation,the design scheme can improve reachable sum rate,which is better than single modulation,and it is applicable for different superposition structures.In addition,we design joint optimization scheme for power allocation in cooperative communication scenarios,which can approach maximum reachable sum rate of the system when the signal to noise ratio is high.