Wireless Physical Layer Security with Imperfect Channel State Information: A Survey

Physical layer security is an emerging technique for improving wireless communication security, which is widely regarded as a complement to cryptographic technologies. To design physical layer security techniques for practical scenarios, uncertainty and imperfections in the channel knowledge need to be taken into account. This paper is a survey of recent research on physical layer security that considers imperfect channel state information （CSI） at communication nodes. We first give an overview of the main information-theoretic measures of secrecy performance with imperfect CSI. Then, we describe several signal processing enhancements in secure transmission designs. These enhancements include secure on-off transmission, beamforming with artificial noise, and secure communication assisted by relay nodes or in cognitive radio systems. Recent studies of physical layer security in large-scale decentralized wireless networks are also summarized. Finally, open problems for on-going and future research are discussed.

Robust MIMO Precoding for Cognitive Multiuser Relay Networks with Imperfect Channel State Information

In this paper, a novel robust precoder with imperfect channel state information(CSI)is proposed for multi-input multi-output(MIMO)cognitive multiuser networks equipped with relays. In the proposed model, the secondary users(SUs)are allowed to share the spectrum with the primary users(PUs)when the interference temperature(IT)is below a specific threshold. The transmitting strategy of relays is amplify-and-forward(AF), and the CSI error is characterized in terms of spherical uncertainty region. A minmax problem for the transmit power of the relays is considered when the mean square error(MSE)of SUs and the IT of PU meet their corresponding thresholds, and it is transformed into a semi-definite programming(SDP)problem to search for the solution. Numerical simulations demonstrate the effectiveness of the proposed precoder.

Adaptive Energy-Efficient Power Allocation for DAS with Imperfect Channel State Information and Antenna Selection

Considering that perfect channel state information(CSI) is difficult to obtain in practice,energy efficiency(EE) for distributed antenna systems(DAS) based on imperfect CSI and antennas selection is investigated in Rayleigh fading channel.A novel EE that is defined as the average transmission rate divided by the total consumed power is introduced.In accordance with this definition,an adaptive power allocation(PA) scheme for DAS is proposed to maximize the EE under the maximum transmit power constraint.The solution of PA in the constrained EE optimization does exist and is unique.A practical iterative algorithm with Newton method is presented to obtain the solution of PA.The proposed scheme includes the one under perfect CSI as a special case,and it only needs large scale and statistical information.As a result,the scheme has low overhead and good robustness.The theoretical EE is also derived for performance evaluation,and simulation result shows the validity of the theoretical analysis.Moreover,EE can be enhanced by decreasing the estimation error and/or path loss exponents.

Resource allocation algorithm in LTE uplink SC-FDMA system for time-varying channel with imperfect channel state information

In long term evolution （LTE） uplink single carrier frequency division multiple access （SC-FDMA） system, the restriction that multiple resource blocks （RBs） allocated to a user should be adjacent, makes the resource allocation problem hard to solve. Moreover, with the practical constraint that perfect channel state information （CSI） cannot be obtained in time-varying channel, the resource allocation problem will become more difficult. In this paper, an efficient resource allocation algorithm is proposed in LTE uplink SC-FDMA system with imperfect CSI assumption. Firstly, the resource allocation problem is formulated as a mixed integer programming problem. Then an efficient algorithm based on discrete stochastic optimization is proposed to solve the problem. Finally, simulation results show that the proposed algorithm has desirable system performance.

Joint Optimization of Spectral and Energy Efficiency for Multi-Pair Full-Duplex Two-Way Relay Networks with Imperfect Channel State Information

An iterative algorithm is proposed for jointly optimizing spectral and energy efficiency in a multipair full-duplex (FD) two-way relaying (TWR) system with imperfect channel state information (CSI). Based on Dinkelbach method, a Taylor expansion based approximation method and the Generalized Lagrange Multiplier Method have been applied iteratively to obtain the near optimal relay amplified matrix and power allocation, respectively. And the simulation results illustrate the effectiveness of the proposed algorithm and the algorithm can converge quickly. © 2017, Shanghai Jiaotong University and Springer-Verlag Berlin Heidelberg.

可重构智能表面辅助多用户NOMA网络鲁棒资源分配

在不完美信道状态信息(Channel State Information,CSI)和不完美串行干扰消除(Successive Interference Cancellation,SIC)的场景下,研究了可重构智能表面(Reconfigurable Intelligent Surface,RIS)辅助多用户非正交多址接入(Non-Orthogonal Multiple Access,NOMA)网络的鲁棒资源分配问题.在考虑两类用户(信息用户和能量用户)服务质量(Quality of Service,QoS)和信息用户SIC约束下,建立了基站发射功率最小化的优化问题.该问题是一个多变量耦合的非凸优化问题.为了求解该问题,本文使用松弛变量、线性近似、S-程序、符号定性法转化该问题的非凸约束.然后将优化问题分解为两个子问题,最后使用交替优化方法迭代求解两个子问题,直到发送功率收敛.仿真结果表明:该文算法具有较好的收敛性,实现了资源的鲁棒分配,同时有效地降低基站发射功率.

智能反射面辅助的多入单出共生无线电鲁棒安全资源分配算法

针对信道不确定性影响、无线信息泄露和障碍物阻挡导致通信质量下降等问题,该文提出一种基于智能反射面(RIS)辅助的多输入单输出(MISO)共生无线电(SR)鲁棒安全资源分配算法。考虑主用户的安全速率约束、次用户的最小速率约束、RIS最小能量收集约束,基于有界信道不确定性,建立了一个联合主被动波束赋形优化的资源分配问题。利用半正定松弛、S-procedure和变量替换法将含参数摄动的非凸问题转化为确定性的凸优化问题,并提出一种基于半正定松弛的鲁棒资源分配算法。仿真结果表明,与现有算法相比,该文算法具有较好的收敛性和鲁棒性。

非完美CSI下的全双工中继网络的能效谱效均衡

为优化非完美信道状态信息下的解码转发全双工中继网络的能效和谱效,提出了一种基于该网络模型的能效谱效均衡策略。通过构建能量效率和频谱效率的折中优化函数,将一个非凸的多目标优化问题转换为一个凸的单目标优化问题,利用求导法和拉格朗日乘子法求解在不同折中因子下的最优中继发射功率。仿真结果表明,可以通过改变折中因子来优化系统的能效和谱效值,获得最优能效和谱效的性能折中。

基于队列稳定性的卫星安全波束成形算法

针对频谱共享且存在受窃听风险的空天地一体化网络,提出了一种基于窃听者非完美信道状态信息的鲁棒安全波束成形方法。首先,在卫星、无人机和基站均采用多播技术服务地球站和地面用户,且实现频谱资源共享的情况下,建立长期平均功耗的最小化为目标,用户服务质量、窃听概率、发送功率预算和数据队列稳定性为约束条件的联合优化问题;其次,为了解决长期平均约束,利用李雅普诺夫优化技术将随机优化问题转化为每个时隙的惩罚发送功率最小化问题,并提出了一种迭代算法,结合伯恩斯坦不等式和连续凸逼近算法,以获取波束成形权向量以实现空天地一体化网络的安全可靠传输。最后,仿真结果证实了提出的方案可以显著提高保密性能,同时在功耗和队列稳定性之间取得良好的折中。

Joint Energy-Efficient Power Allocation and Beamforming Design for mm Wave-NOMA System with Imperfect CSI

The joint power allocation(PA)and beamforming(BF)design problem is studied to maximize the energy efficiency of a two-user downlink millimeter-wave system with non-orthogonal multiple access under imperfect channel state information(CSI).By means of block coordinate descent,convex-concave procedure,and successive convex approximate,we propose a suboptimal joint PA and BF design scheme to address this non-convex problem.Simulation results verify that the proposed joint PA and BF design scheme is more effective when compared to some existing schemes.

Cross-layer design of combining AMC with HARQ in cooperative relay system with perfect and imperfect CSI

A cross-layer design which combines adaptive modulation and coding (AMC) at the physical layer with a hybrid automatic repeat request (HARQ) protocol at the data link layer (LL) is presented, in cooperative relay system over Nakagami-m fading channels with perfect and imperfect channel state information (CSI). In order to maximize spectral efficiency (SE) under delay and packet error rate (PER) performance constraints, a state transition model and an optimization framework with perfect CSI are presented. Then the framework is extended to cooperative relay system with imperfect CSI. The numerical results show that the scheme can achieve maximum SE while satisfying transmitting delay requirements. Compared with the imperfect CSI, the average PER with perfect CSI is much lower and the spectral efficiency is much higher.

Underwater video transceiver designs based on channel state information and video content

Underwater hostile channel conditions challenge video transmission designs. The current designs often treat video coding and transmission schemes as individual modules. In this study, we develop an adaptive transceiver with channel state information(CSI) by taking into account the importance of video components and channel conditions. The design is more effective than the traditional ones. However, in practical systems, perfect CSI may not be available. Therefore, we compare the imperfect CSI case with existing schemes, and validate the effectiveness of our design through simulations and measured channels in terms of a better peak signal-to-noise ratio and a higher video structural similarity index.

Power control scheme for multiple antenna systems with space-time coding in Rayleigh fading channels

Two optimal power control （PC） schemes under the power constraint for space-time coded multiple input multiple output systems over the flat Rayleigh fading channel with the imperfect channel state information （CSI） are presented. One is based on the minimization of a bit error rate （BER）, and the other is based on the maximization of a fuzzy signal-to-noise ratio. In these schemes, different powers are allocated to individual transmit an- tennas rather than equal power in the conventional one. For the first scheme, the optimal PC procedure is developed. It is shown that the Lagrange multiplier for the constrained optimization in the power control does exist and is unique. A practical iterative algorithm based on Newton＇s method for finding the Lagrange multiplier is proposed. In the second scheme, some existing schemes are included, and a suboptimal PC procedure is developed by means of the asymptotic performance analysis. With this suboptimal scheme, a simple PC calculation formula is provided, and thus the calculation of the PC will be straightforward. Moreover, the suboptimal scheme has the BER performance close to the optimal scheme. Simulation results show that the two PC schemes can provide BER lower than the equal PC and antenna selection scheme under the imperfect CSI.

HIGH SNR SUM CAPACITY ANALYSIS OF BD MIMO BC SYSTEMS WITH IMPERFECT CSI

We investigate the sum capacity of Block Diagonalization precoding Multiple Input Mul-tiple Output Broadcast Channels(BD MIMO BC) with imperfect Channel State Information(CSI) at the base station.Since it is difficult to obtain the exact expression,a lower and an upper bounds of the sum capacity under Gaussian channel estimation errors are drived instead.Analyses show that the gap between two bounds is considerably tight at all Signal to Noise Ratio(SNR) region.From the lower bound of the sum capacity,we can see that the multiplexing gain tends to be zero at high SNR region,which indicates that the BD MIMO BC system with channel estimation errors is interference-limited at high SNR.

ROBUST OPTIMIZATION OF TRANSMIT/RECEIVE BEAMFORMER FOR MIMO DOWNLINK WITH IMPERFECT CSI AT BASE STATION

A robust scheme is proposed to jointly optimize transmit/receive beamformers for Mul-tiple Input Multiple Output(MIMO) downlinks where the available Channel State Information(CSI) at Base Station(BS)(CSIBS) is imperfect.The criterion is to minimize the sum Mean Square Error(sum-MSE) over all users under a constraint on the total transmit power,which is a non-convex and non-linear problem.Observing from the first order optimization condition that the optimal trans-mit/receive beamformers are mutually dependent,the transmit/receive beamformers for each user are updated iteratively until the sum-MSE is minimized.Simulation results indicate that the proposed scheme can effectively mitigate the system performance loss induced by imperfect CSIBS.

RIS辅助的MISO系统安全鲁棒波束赋形算法

为解决无线信道开放性导致的信息传输安全及信道估计误差等不确定性带来的系统传输性能恶化问题,该文提出一种存在用户窃听的可重构智能超表面(RIS)辅助多输入单输出(MISO)系统的Charnes-Cooper鲁棒波束赋形算法。针对窃听用户建立有界信道不确定性模型,并通过约束最大发射功率以及RIS相移,联合优化基站波束和RIS相移来最大化用户保密率。为求解该非凸问题,首先通过变量替换、Charnes-Cooper方法和S-procedure方法将其转换为凸优化问题,进而采用间接交替优化耦合变量来获得鲁棒波束赋形矩阵和RIS相移。仿真结果表明,该文提出的基于RIS的联合优化算法具有更好的用户保密率和鲁棒性。

大规模MIMO系统中功率分配的深度强化学习方法

对于最大化下行链路总和频谱效率优化问题,目前仍然缺乏针对多小区多用户大规模MIMO系统的研究,且通常未考虑上行信道状态信息的不完美.鉴于此,研究了上行信道状态信息不完美条件下的多小区多用户大规模MIMO系统下行链路总和频谱效率优化问题,以最大化下行链路总和频谱效率为目标,提出了深度Q网络和深度确定性策略梯度的两种功率分配方法.深度Q网络可解决通信系统中维度爆炸和缺乏泛化的问题,但Q-Learning算法仅适用于离散空间,必须量化传输功率.而深度确定性策略梯度是适用连续动作空间的算法,可解决由于量化功率带来的性能下降问题.仿真结果表明,与其他传统功率分配方法相比,所提方法可获得更优的总和频谱效率性能,而且时间复杂度要低得多.此外,深度确定性策略梯度方法在总和频谱效率性能和时间复杂度方面都优于深度Q网络.

卫星网络和高空平台网络频谱共存下的分布式鲁棒波束成形算法

面向由卫星网络和高空平台网络有机结合的星空融合网络,提出一种基于非完美信道状态信息的分布式鲁棒波束成形算法。首先,在卫星网络和高空平台网络分别采用多播技术和非正交多址技术服务多个用户的场景下,以最大化网络和速率为目标函数,并以满足各个用户速率需求为约束,建立卫星和高空平台发射功率受限为约束的优化问题。其次,在仅能获取用户非完美信道状态信息且仅能实现非完美连续干扰消除的情况下,采用S-procedure和连续凸逼近对非凸问题进行转化,并进一步提出基于拉格朗日对偶的分布式波束成形算法,以实现网络间的频谱共享。最后,计算机仿真表明所提分布式算法相比现有工作能以更低的信令开销获取更高的频谱效率。

非理想顺序干扰消除和信道状态信息下SWIPT-NOMA-CR网络中断性能

针对基于无线携能通信(SWIPT, simultaneous wireless information and power transfer)和非正交多址接入(NOMA, non-orthogonal multiple access)的认知中继(CR, cognitive relay)(SWIPT-NOMA-CR)网络,考虑非理想顺序干扰消除(SIC, successive interference cancellation)和信道状态信息(CSI, channel state information)实际情况,研究系统在采用理想、时间开关(TS, time switching)和功率分割(PS, power splitting)3种中继传输方案时次用户的中断性能。推导出次用户中断概率的解析表达式,并通过蒙特卡洛仿真验证理论推导的正确性。实验结果表明,非理想SIC和CSI会导致次用户的中断性能下降,相对于非理想CSI,非理想SIC给系统中断性能带来的损失更大。此外,用户采用PS中继传输方案的中断概率比采用TS方案低,当改变非理想SIC和CSI因子时,采用PS方案用户的中断概率差值比TS方案小,说明PS中继传输方案的可靠性优于TS方案。

大规模MIMO-NOMA双向中继认知系统物理层安全研究

针对基于中继辅助传输的认知无线电-非正交多址(CR-NOMA)系统中,频谱利用率低及安全性较差的缺点,提出将大规模多输入多输出(MIMO)技术应用到基于双向中继的CR-NOMA网络中,使两组认知非正交多址(NOMA)用户在双向中继的协助下交换信息.在不完全信道状态信息的约束下,推导出受发射功率、信道估计误差和天线数量影响的安全中断概率的闭合表达式.仿真结果表明,随着中继天线数量的增加,安全中断概率收敛到特定数值,同时可得到复杂度较低且安全性能最优天线数量.