In high-speed multiuser Time Reversal(TR)downlink systems,the transmission rate is degraded due to the presence of severe inter-user and inter-symbol interference.Moreover,maximizing the weighted sum rate in such syst...In high-speed multiuser Time Reversal(TR)downlink systems,the transmission rate is degraded due to the presence of severe inter-user and inter-symbol interference.Moreover,maximizing the weighted sum rate in such systems is a critical objective,since the weighting factors represent the priority of different users in different applications.However,it faces significant challenges as it is an NP-hard and non-convex problem.In order to suppress these interferences and maximize the weighted sum rate,in this paper we present a novel approach for the joint design of the pre-filters.The proposed method applies successive convex approximation to transform the original problem into a Second-Order Cone Programming(SOCP)problem.Then,a low-complexity iterative algorithm is provided to effectively solve the resulting SOCP problem.According to the simulation results,the proposed method reaches a local optimum within a few iterations and demonstrates superior performance in terms of weighted sum rate compared to the current algorithm.展开更多
The application of Non-Orthogonal Multiple Access(NOMA) technology into satelliteaerial-ground integrated networks can meet the requirements of ultra-high rate and massive connectivity for the Sixth-Generation(6G) com...The application of Non-Orthogonal Multiple Access(NOMA) technology into satelliteaerial-ground integrated networks can meet the requirements of ultra-high rate and massive connectivity for the Sixth-Generation(6G) communication systems. We consider an uplink NOMA scenario for such a satellite-aerial-ground integrated network where multiple users communicate with satellite under the help of an Unmanned Aerial Vehicle(UAV) as an aerial relay equipped with a phased array. Supposing that buffer-aided decode-and-forward protocol is adopted at the UAV relay, we first formulate an optimization problem to maximize Ergodic Sum Rate(ESR) of the considered system subject to individual power constraint and quality-of-service constraint of each user.Then, with known imperfect channel state information of each user, we propose a joint power allocation and robust Beam Forming(BF) iterative algorithm to maximize ESR for the user-to-UAV link. Besides, to take the advantages of Free-Space Optical(FSO) and millimeter Wave(mmWave)communications, we present a switch-based hybrid FSO/mmWave scheme and a robust BF algorithm for the UAV-to-satellite link to achieve higher rate. Moreover, a closed-form ESR expression is derived. Finally, the effectiveness and correctness of the proposed solutions are verified by numerical simulations, and the performance evaluation results show that the proposed solutions not only achieve performance enhancement and robustness, but also outperform the orthogonal multiple access significantly.展开更多
The research for the Intelligent Reflecting Surface(IRS)which has the advantages of cost and energy efficiency has been studied.Channel capacity can be effectively increased by appropriately setting the phase value of...The research for the Intelligent Reflecting Surface(IRS)which has the advantages of cost and energy efficiency has been studied.Channel capacity can be effectively increased by appropriately setting the phase value of IRS elements according to the channel conditions.However,the problem of obtaining an appropriate phase value of IRs is difficult to solve due to the non-convex problem.This paper proposes an iterative algorithm for the alternating optimal solution in the Single User Multiple-Input-Multiple-Output(SU-MIMO)systems.The proposed iterative algorithm finds an alternating optimal solution that is the phase value of IRS one by one.The results show that the proposed method has better performance than that of the randomized IRS systems.The number of iterations for maximizing the performance of the proposed algorithm depends on the channel state between the IRS and the receiver.展开更多
In this paper, the asymptotic sum rate of a multi-user distributed antenna system （DAS） is analyzed. To mitigate inter-user interference, minimum mean squared error （MMSE） receivers are utilized to cooperatively p...In this paper, the asymptotic sum rate of a multi-user distributed antenna system （DAS） is analyzed. To mitigate inter-user interference, minimum mean squared error （MMSE） receivers are utilized to cooperatively process received signals in the uplink. It shows that inter-user interference is efficiently mitigated and the uplink sum rate of a multi-user DAS is greatly improved by adopting MMSE receivers. For very large number of users and remote antennas, the asymptotic uplink sum rate of MMSE receivers is derived by using virtue of the random matrix theory, which can be The approximation is verified to be quite accurate by Monte Carlo simply calculated in an iterative way simulations.展开更多
The distributed antenna system （DAS） is considered as a promising architecture for future wireless access. This paper describes the uplink of a power-controlled circular-layout DAS （CL-DAS） with minimum mean-squar...The distributed antenna system （DAS） is considered as a promising architecture for future wireless access. This paper describes the uplink of a power-controlled circular-layout DAS （CL-DAS） with minimum mean-square error （MMSE） receivers. Results from random matrix theory are used to show that for such a DAS, the per-user sum rate and the total transmit power both converge as the number of users and antennas goes to infinity with a constant ratio of antennas to users. The relationship between the asymptotic per-user sum rate and the asymptotic total transmit power is given for all possible values of the radius of the circle on which antennas are placed. This rate-power relationship is then used to find the optimal radius. With this optimal radius, the CL-DAS is proved to offer a significant gain compared with a traditional co-located antenna system. Simulation results demonstrate the validity of the analysis and the superiority of the DAS.展开更多
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
A non-orthogonal multiple access(NOMA) power allocation scheme on the basis of the sparrow search algorithm(SSA) is proposed in this work. Specifically, the logarithmic utility function is utilized to address the pote...A non-orthogonal multiple access(NOMA) power allocation scheme on the basis of the sparrow search algorithm(SSA) is proposed in this work. Specifically, the logarithmic utility function is utilized to address the potential fairness issue that may arise from the maximum sum-rate based objective function and the optical power constraints are set considering the non-negativity of the transmit signal, the requirement of the human eyes safety and all users' quality of service(Qo S). Then, the SSA is utilized to solve this optimization problem. Moreover, to demonstrate the superiority of the proposed strategy, it is compared with the fixed power allocation(FPA) and the gain ratio power allocation(GRPA) schemes. Results show that regardless of the number of users considered, the sum-rate achieved by SSA consistently outperforms that of FPA and GRPA schemes. Specifically, compared to FPA and GRPA schemes, the sum-rate obtained by SSA is increased by 40.45% and 53.44% when the number of users is 7, respectively. The proposed SSA also has better performance in terms of user fairness. This work will benefit the design and development of the NOMA-visible light communication(VLC) systems.展开更多
基金partially supported by the following funding sources:The National Natural Science Foundation of China(No.61771084)the Chongqing Graduate Scientific Research Innovation Project(No.CYB21200)。
文摘In high-speed multiuser Time Reversal(TR)downlink systems,the transmission rate is degraded due to the presence of severe inter-user and inter-symbol interference.Moreover,maximizing the weighted sum rate in such systems is a critical objective,since the weighting factors represent the priority of different users in different applications.However,it faces significant challenges as it is an NP-hard and non-convex problem.In order to suppress these interferences and maximize the weighted sum rate,in this paper we present a novel approach for the joint design of the pre-filters.The proposed method applies successive convex approximation to transform the original problem into a Second-Order Cone Programming(SOCP)problem.Then,a low-complexity iterative algorithm is provided to effectively solve the resulting SOCP problem.According to the simulation results,the proposed method reaches a local optimum within a few iterations and demonstrates superior performance in terms of weighted sum rate compared to the current algorithm.
基金co-supported by the Key International Cooperation Research Project,China(No.61720106003)Jiangsu Province Science and Technology Project,China(No.BE2021031)+4 种基金the Shanghai Aerospace Science and Technology Innovation Foundation,China(No.SAST2019-095)NUPTSF(No.NY220111)the Research Project of Science and Technology on Complex Electronic System Simulation Laboratory,China(No.DXZT-JC-ZZ-2019-009)the National Natural Science Foundation of China(No.61801234)the Postgraduate Research and Practice Innovation Program of Jiangsu Province,China(No.KYCX210739)。
文摘The application of Non-Orthogonal Multiple Access(NOMA) technology into satelliteaerial-ground integrated networks can meet the requirements of ultra-high rate and massive connectivity for the Sixth-Generation(6G) communication systems. We consider an uplink NOMA scenario for such a satellite-aerial-ground integrated network where multiple users communicate with satellite under the help of an Unmanned Aerial Vehicle(UAV) as an aerial relay equipped with a phased array. Supposing that buffer-aided decode-and-forward protocol is adopted at the UAV relay, we first formulate an optimization problem to maximize Ergodic Sum Rate(ESR) of the considered system subject to individual power constraint and quality-of-service constraint of each user.Then, with known imperfect channel state information of each user, we propose a joint power allocation and robust Beam Forming(BF) iterative algorithm to maximize ESR for the user-to-UAV link. Besides, to take the advantages of Free-Space Optical(FSO) and millimeter Wave(mmWave)communications, we present a switch-based hybrid FSO/mmWave scheme and a robust BF algorithm for the UAV-to-satellite link to achieve higher rate. Moreover, a closed-form ESR expression is derived. Finally, the effectiveness and correctness of the proposed solutions are verified by numerical simulations, and the performance evaluation results show that the proposed solutions not only achieve performance enhancement and robustness, but also outperform the orthogonal multiple access significantly.
基金supported by the MSIT(Ministry of Science and ICT),Korea,under the ITRC(Information Technology Research Center)support program(IITP-2022-2018-0-01423)supervised by the ITP(Institute for Information&Communications Technology Planning&Evaluation)supported by Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Education(2020R1A6A1A03038540).
文摘The research for the Intelligent Reflecting Surface(IRS)which has the advantages of cost and energy efficiency has been studied.Channel capacity can be effectively increased by appropriately setting the phase value of IRS elements according to the channel conditions.However,the problem of obtaining an appropriate phase value of IRs is difficult to solve due to the non-convex problem.This paper proposes an iterative algorithm for the alternating optimal solution in the Single User Multiple-Input-Multiple-Output(SU-MIMO)systems.The proposed iterative algorithm finds an alternating optimal solution that is the phase value of IRS one by one.The results show that the proposed method has better performance than that of the randomized IRS systems.The number of iterations for maximizing the performance of the proposed algorithm depends on the channel state between the IRS and the receiver.
文摘In this paper, the asymptotic sum rate of a multi-user distributed antenna system （DAS） is analyzed. To mitigate inter-user interference, minimum mean squared error （MMSE） receivers are utilized to cooperatively process received signals in the uplink. It shows that inter-user interference is efficiently mitigated and the uplink sum rate of a multi-user DAS is greatly improved by adopting MMSE receivers. For very large number of users and remote antennas, the asymptotic uplink sum rate of MMSE receivers is derived by using virtue of the random matrix theory, which can be The approximation is verified to be quite accurate by Monte Carlo simply calculated in an iterative way simulations.
基金Supported by the National Natural Science Foundation of China (No. 90204001)
文摘The distributed antenna system （DAS） is considered as a promising architecture for future wireless access. This paper describes the uplink of a power-controlled circular-layout DAS （CL-DAS） with minimum mean-square error （MMSE） receivers. Results from random matrix theory are used to show that for such a DAS, the per-user sum rate and the total transmit power both converge as the number of users and antennas goes to infinity with a constant ratio of antennas to users. The relationship between the asymptotic per-user sum rate and the asymptotic total transmit power is given for all possible values of the radius of the circle on which antennas are placed. This rate-power relationship is then used to find the optimal radius. With this optimal radius, the CL-DAS is proved to offer a significant gain compared with a traditional co-located antenna system. Simulation results demonstrate the validity of the analysis and the superiority of the DAS.
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。
文摘针对具有星间链路(inter-satellite links,ISL)的低轨(low earth orbit,LEO)多卫星系统,提出了一种基于多卫星协作传输的和速率(sum rate,SR)最大化预编码算法.传统的预编码算法需要复杂的星上计算来得到数值解,这导致低轨卫星系统面临较大的计算开销和延迟问题.为解决上述关键问题,设计了一种基于交替方向乘子法(alternating direction method of multipliers,ADMM)的高吞吐量、低复杂度、具有闭式解的分布式预编码算法.该算法通过构建辅助变量和问题分解,将预编码设计问题转化为多个子问题并行求解,每个子问题仅有一个约束条件,并在每次迭代后仅通过星间链路交换设计的数据矩阵,从而有效实现分布式预编码.仿真结果表明,与典型的两步和速率最大化算法相比,所提出的算法可以实现更高的和速率,同时大幅降低计算复杂度.
基金supported by the Cooperative Research Project between China Coal Energy Research Institute Co.,Ltd. and Xidian University (No.N-KY-HX-1101-202302-00725)the Key Research and Development Program of Shaanxi Province (No.2017ZDCXL-GY-06-02)。
文摘A non-orthogonal multiple access(NOMA) power allocation scheme on the basis of the sparrow search algorithm(SSA) is proposed in this work. Specifically, the logarithmic utility function is utilized to address the potential fairness issue that may arise from the maximum sum-rate based objective function and the optical power constraints are set considering the non-negativity of the transmit signal, the requirement of the human eyes safety and all users' quality of service(Qo S). Then, the SSA is utilized to solve this optimization problem. Moreover, to demonstrate the superiority of the proposed strategy, it is compared with the fixed power allocation(FPA) and the gain ratio power allocation(GRPA) schemes. Results show that regardless of the number of users considered, the sum-rate achieved by SSA consistently outperforms that of FPA and GRPA schemes. Specifically, compared to FPA and GRPA schemes, the sum-rate obtained by SSA is increased by 40.45% and 53.44% when the number of users is 7, respectively. The proposed SSA also has better performance in terms of user fairness. This work will benefit the design and development of the NOMA-visible light communication(VLC) systems.
文摘将无人机与频谱共享技术相结合,可建立高质量通信链路,提高频谱资源利用效率。然而,由于主、次用户间交叉链路干扰的存在,实现次用户的高可达速率变得十分困难。为了解决该问题,设计了一种智能反射面(Intelligent Reflective Surface,IRS)辅助的无人机认知中继通信网络。通过联合优化无人机的位置部署、次基站的波束成形和IRS的相移矩阵,最大化频谱共享网络中次用户的加权和速率(Weighted Sum Rate,WSR)。为了解决所建立的非凸问题,将其解耦为3个子问题,然后提出了一种交替优化算法来迭代优化变量。利用连续凸逼近(Successive Convex Approxi‑mation,SCA)法对无人机的位置进行优化;利用直接分式规划(Dire ct Fractional Programming,DFP)法对次基站的波束成形进行优化;利用DFP结合交替方向乘子法(Alternating Direction Method of Multipliers,ADMM)对IRS的相移矩阵进行优化。仿真结果表明,与基准算法相比,所提算法能实现更高的次用户WSR。
