下行时间反转非正交多址接入系统的设计与优化

Design and Optimization of Downlink Time Reversal Non-Orthogonal Multiple Access System

针对时间反转多址接入系统在用户相关性较大时,用户间干扰严重,导致系统和速率下降问题,提出一种将时间反转多址接入技术与功率域非正交多址接入技术相结合的下行多址系统方案.将相关性较高的用户分为一组,组内用户符号采用非正交叠加传输的方式,不同用户组的符号采用时间反转滤波器进行预处理,实现多用户符号的同时同频传输.给出了一种用户分组算法,进一步在用户最小速率和基站的总发送功率约束下,采用迭代信干噪比注水算法优化用户的发送功率以最大化系统和速率.仿真结果表明,本文方案在配备单根发送天线、预滤波器采用迫零准则设计时高发送功率下的系统和速率比常规的时间反转多址接入方案约高30%;天线数目越多,性能优势越明显.

The sum rate of the time-reversal division multiple access(TRDMA)system decreases due to the severe in⁃ter-user interference when the users'channels have high correlation.To solve the problem,a downlink multiple access scheme combining TRDMA with the power domain non-orthogonal multiple access(NOMA)is proposed.The users with high channel correlation are grouped into a cluster.The symbols of the users in the same cluster are superimposed.The sym⁃bols of each cluster are pre-processed by its own time-reversal pre-filter.A clustering algorithm is presented.To maximize the sum rate of the system,the iterative SINR water-filling algorithm is used to optimize the transmission power of the us⁃ers'symbols under the constraints of the minimum rate of each user and the total power.The simulation results show that the sum rate of the proposed scheme is about 30%higher than that of the TRDMA scheme at high transmission power when one transmitting antenna is installed and the prefilter is designed according to the zero forcing criterion.The more the num⁃ber of antennas,the more obvious the performance advantage.