随着卫星通信向低轨巨型星座演进,信道快速变化与多用户干扰已成为制约系统容量的关键因素。针对仅已知信道协方差信息的多波束低轨卫星下行传输,本文提出一套由理论最优逐步逼近工程实用的四类统计信道状态信息(Channel State Informat...随着卫星通信向低轨巨型星座演进,信道快速变化与多用户干扰已成为制约系统容量的关键因素。针对仅已知信道协方差信息的多波束低轨卫星下行传输,本文提出一套由理论最优逐步逼近工程实用的四类统计信道状态信息(Channel State Information, CSI)预编码方案:(1)以最大化遍历和速率为目标的理论基准;(2)以蒙特卡罗平均和速率为目标的采样近似方案;(3)基于逐采样加权最小均方误差(Weighted Minimum Mean Square Error, WMMSE)的性能最优方案;(4)在方案(3)的基础上进一步对导频响应取统计期望,采用复杂度最低且性能损失可忽略的实用方案。针对多用户单天线与多天线场景,分别推导了可达速率表达式,构建了相应的非凸优化问题,并采用梯度下降结合流形优化的方法进行求解。仿真结果表明:所提出的WMMSE结合导频期望方案,在和速率性能上可达理想信道状态信息下迫零算法的80%,显著优于基于信道统计信息的迫零算法,并且在仅依赖统计CSI的低轨卫星多用户场景下,该方案通过对导频响应取统计期望,实现了导频开销降低约90%,同时算法收敛速度较传统逐采样WMMSE提升约8~10倍。本研究为高动态信道条件下的高效预编码设计提供了重要理论依据与实现指导。展开更多
In addition to conventional antenna-based array,the reconfigurable intelligent surface(RIS)holds promise as an alternative technology for manufacturing massive multi-input multi-output(MIMO)array for beyond 5G communi...In addition to conventional antenna-based array,the reconfigurable intelligent surface(RIS)holds promise as an alternative technology for manufacturing massive multi-input multi-output(MIMO)array for beyond 5G communications.This paper designs a fast algorithm to optimize the RIS-based MIMO precoder for maximizing the spectral efficiency,which includes the digital precoder and the RIS reflection phases.We evaluate the optimality of the algorithm by deriving an RIS channel capacity upper bound utilizing majorization theory.Our scheme can work for an RIS in both frequency flat and frequency selective channels,with either continuously or discretely tunable phases.The simulation results show that the proposed algorithm can achieve the capacity upper bound in some scenarios,which empirically proves its optimality.It is also shown that our algorithm is one-to-two orders of magnitude faster than the state-of-the-art methods in the literature.展开更多
文摘随着卫星通信向低轨巨型星座演进,信道快速变化与多用户干扰已成为制约系统容量的关键因素。针对仅已知信道协方差信息的多波束低轨卫星下行传输,本文提出一套由理论最优逐步逼近工程实用的四类统计信道状态信息(Channel State Information, CSI)预编码方案:(1)以最大化遍历和速率为目标的理论基准;(2)以蒙特卡罗平均和速率为目标的采样近似方案;(3)基于逐采样加权最小均方误差(Weighted Minimum Mean Square Error, WMMSE)的性能最优方案;(4)在方案(3)的基础上进一步对导频响应取统计期望,采用复杂度最低且性能损失可忽略的实用方案。针对多用户单天线与多天线场景,分别推导了可达速率表达式,构建了相应的非凸优化问题,并采用梯度下降结合流形优化的方法进行求解。仿真结果表明:所提出的WMMSE结合导频期望方案,在和速率性能上可达理想信道状态信息下迫零算法的80%,显著优于基于信道统计信息的迫零算法,并且在仅依赖统计CSI的低轨卫星多用户场景下,该方案通过对导频响应取统计期望,实现了导频开销降低约90%,同时算法收敛速度较传统逐采样WMMSE提升约8~10倍。本研究为高动态信道条件下的高效预编码设计提供了重要理论依据与实现指导。
基金supported by National Natural Science Foundation of China Grant No.61771005。
文摘In addition to conventional antenna-based array,the reconfigurable intelligent surface(RIS)holds promise as an alternative technology for manufacturing massive multi-input multi-output(MIMO)array for beyond 5G communications.This paper designs a fast algorithm to optimize the RIS-based MIMO precoder for maximizing the spectral efficiency,which includes the digital precoder and the RIS reflection phases.We evaluate the optimality of the algorithm by deriving an RIS channel capacity upper bound utilizing majorization theory.Our scheme can work for an RIS in both frequency flat and frequency selective channels,with either continuously or discretely tunable phases.The simulation results show that the proposed algorithm can achieve the capacity upper bound in some scenarios,which empirically proves its optimality.It is also shown that our algorithm is one-to-two orders of magnitude faster than the state-of-the-art methods in the literature.
