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Frontiers of Information Technology & Electronic Engineering 2017年第6期18卷 796-807页

作者： Zhen-hua YUAN Chen CHEN Xiang CHENG Guo-cheng LV Liu-qing YANG Ye JIN State Key Laboratory of Advanced Optical Communication Systems and Networks Peking University Department of Electrical & Computer Engineering Colorado State University

This article is focused on secure relay beamformer design with a correlated channel model in the relay-eavesdropper network. In this network, a single-antenna source-destination pair transmits secure information with the help of an amplify-and-forward (AF) relay equipped with multiple antennas, and the legitimate and eavesdropping channels are correlated. The relay cannot obtain the instantaneous channel state information (CSI) of the eavesdropper, and has only the knowledge of correlation information between the legitimate and eavesdropping channels. Depending on this information, we derive the conditional distribution of the eavesdropping channel. Two beamformers at the relay are studied for the approximate ergodic secrecy rate:(1) the generalized match-andforward (GMF) beamformer to maximize the legitimate channel rate, and (2) the general-rank beamformer (GRBF).In addition, one lower-bound-maximizing (LBM) beamformer at the relay is discussed for maximizing the lower bound of the ergodic secrecy rate. We find that the GMF beamformer is the optimal rank-one beamformer, that the GRBF is the iteratively optimal beamformer, and that the performance of the LBM beamformer for the ergodic secrecy rate gets close to that of the GRBF for the approximate secrecy rate. It can also be observed that when the relay has lower power or the channel gain of the second hop is low, the performance of the GMF beamformer surpasses that of the GRBF. Numerical results are presented to illustrate the beamformers' performance.

关键词： Physical layer security Relay beamforming correlated channels Ergodic secrecy rate

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Uplink transmission design for crowded correlated cell-free massive MIMO-OFDM systems

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Science China(Information Sciences) 2021年第8期64卷 127-142页

作者： Junyuan GAO Yongpeng WU Yongjian WANG Wenjun ZHANG Fan WEI The Department of Electronic Engineering Shanghai Jiao Tong University The National Computer Network Emergency Response Technical Team/Coordination Center of China

In cell-free massive multiple-input multiple-output(MIMO) orthogonal frequency division multiplexing(OFDM) systems, user equipments(UEs) are served by many distributed access points(APs),where channels are correlated owing to finite angle-delay spread in realistic outdoor wireless propagation environments. Meanwhile, the number of UEs is growing rapidly for future fully networked society. In this paper, we focus on the uplink transmission design in crowded correlated cell-free massive MIMO-OFDM systems with a limited number of orthogonal pilots. For the pilot transmission phase, we identify active UEs based on non-orthogonal pilot phase shift hopping patterns and non-orthogonal adjustable phase shift pilots(APSP). We derive a closed-form expression of mean square error of channel estimation(MSE-CE) and obtain an optimal condition for minimizing MSE-CE. According to this condition, the APSP set allocation scheme is proposed. Furthermore, for the data transmission, the max-min power control algorithm is devised to maximize the minimum spectral efficiency(SE) lower bound among active UEs. Simulation results indicate significant performance gains in terms of MSE-CE for the proposed APSP set allocation scheme. The proposed power control scheme can further improve the minimum SE among active UEs. Hence, they are crucial for crowded correlated cell-free massive MIMO-OFDM systems.

关键词： APSP set allocation cell-free massive MIMO-OFDM correlated channels crowded scenarios power control

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Performance Analysis of Spatially correlated Massive MIMO with Hardware Impairments

Performance Analysis of Spatially Correlated Massive MIMO wi...

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作者： Zeeshan Samad 上海交通大学

学位级别：硕士

Multiple-input multiple-output(MIMO) system with very large number of base station(BS)antennas has attained a lot of attention in recent years. Since, it improves the overall system capacity as well as Bit Error Rate(BER) by exploiting the advantages of high degrees of freedom and better spatial multiplexing. Performance analysis described in this thesis mainly concern with two serious *** Impairments: Implementation of large number of antennas on a BS expected to have low power consumption and low-budget radio frequency(RF) components which are prone to hardware impairments. Phase noise(PN), high power amplifier(HPA) nonlinearities, or in phase/quadrature-phase(I/Q) imbalance) are some reasons of introduction such impairments that can drastically effect the performance of large scale MIMO *** mitigation schemes are used to overcome the impact of hardware impairments but unfortunately, these schemes are not perfect enough such that a certain amount of residual RF hardware impairment always *** Correlations: Deployment of large number of antennas on both the transmit and the receive side introduces cross correlations between multiple transmission *** reason of such correlations is the narrow space between adjacent antenna elements. It is essential to consider such correlations during analyzing the system *** the design of practical cellular systems, the actual benefit of multi-antenna transmission is limited by a variety of factors such as hardware impairments and the correlation between multiple transmission channels. In this thesis, we design a new system model for MIMO system by taking transmit RF impairments into account and consider it as an additional distortion during transmission. We further define a spatially correlated channel model to investigate the impact of channel correlations on system capacity. Next a general capacity expression is derived to analyze the performance of massive MIMO in various

关键词： s-MIMO correlated channels channel capacity transmit-RF impairment

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