Cooperative Covert Communication in Multi-Antenna Broadcast Channels

With the gradual popularization of 5G communications,the application of multi-antenna broadcasting technology has become widespread.Therefore,this study aims to investigate the wireless covert communication in the two-user cooperative multi-antenna broadcast channel.We focus on the issue that the deteriorated reliability and undetectability are mainly affected by the transmission power.To tackle this issue,we design a scheme based on beamforming to increase the reliability and undetectability of wireless covert communication in the multi-antenna broadcast channel.We first modeled and analyzed the cooperative multi-antenna broadcasting system,and put forward the target question.Then we use the SCA(successive convex approximation)algorithm to transform the target problem into a series of convex subproblems.Then the convex problems are solved and the covert channel capacity is calculated.In order to verify the effectiveness of the scheme,we conducted simulation verification.The simulation results show that the proposed beamforming scheme can effectively improve the reliability and undetectability of covert communication in multi-antenna broadcast channels.

Multi-Antenna Jammer Assisted Covert Communications in Data Collected IoT with NOMA

In this paper,we investigate covert communications in data collected IoT with NOMA,where the paired sensor nodes S_(m) and S_(n) transmit covert messages to a legitimate receiver(Bob)in the presence of a Warden(Willie).To confuse the detection at Willie,an extra multi-antenna friendly jammer(Jammer)has been employed to transmit artificial noise(AN)with random power.Based on the CSI of Willie is available or not at Jammer,three AN transmission schemes,including null-space artificial noise(NAN),transmit antenna selection(TAS),and zeroforcing beamforming(ZFB),are proposed.Furthermore,the closed-form expressions of expected minimum detection error probability(EMDEP)and joint connection outage probability(JCOP)are derived to measure covertness and reliability,respectively.Finally,the maximum effective covert rate(ECR)is obtained with a given covertness constraint.The numerical results show that ZFB scheme has the best maximum ECR in the case of the number of antennas satisfies N>2,and the same maximum ECR can be achieved in ZFB and NAN schemes with N=2.Moreover,TAS scheme also can improve the maximum ECR compared with the benchmark scheme(i.e.,signal-antenna jammer).In addition,a proper NOMA node pairing can further improve the maximum ECR.

Group-Based Successive Interference Cancellation for Multi-Antenna NOMA System with Error Propagation

Non-orthogonal multiple access(NOMA)is viewed as a key technique to improve the spectrum efficiency and solve the issue of massive connectivity.However,for power domain NOMA,the required overall transmit power should be increased rapidly with the increasing number of users in order to ensure that the signal-to-interference-plus-noise ratio reaches a predefined threshold.In addition,since the successive interference cancellation(SIC)is adopted,the error propagation would become more serious as the order of SIC increases.Aiming at minimizing the total transmit power and satisfying each user’s service requirement,this paper proposes a novel framework with group-based SIC for the deep integration between power domain NOMA and multi-antenna technology.Based on the proposed framework,a joint optimization of power control and equalizer design is investigated to minimize transmit power consumption for uplink multi-antenna NOMA system with error propagations.Based on the relationship between the equalizer and the transmit power coefficients,the original problem is transformed to a transmit power optimization problem,which is further addressed by a parallel iteration algorithm.It is shown by simulations that,in terms of the total power consumption,the proposed scheme outperforms the conventional OMA and the existing cluster-based NOMA schemes.

Spectrum and energy efficient multi-antenna spectrum sensing for green UAV communication

Unmanned Aerial Vehicle(UAV)communication is a promising technology that provides swift and flexible ondemand wireless connectivity for devices without infrastructure support.With recent developments in UAVs,spectrum and energy efficient green UAV communication has become crucial.To deal with this issue,Spectrum Sharing Policy(SSP)is introduced to support green UAV communication.Spectrum sensing in SSP must be carefully formulated to control interference to the primary users and ground communications.In this paper,we propose spectrum sensing for opportunistic spectrum access in green UAV communication to improve the spectrum utilization efficiency.Different from most existing works,we focus on the problem of spectrum sensing of randomly arriving primary signals in the presence of non-Gaussian noise/interference.We propose a novel and improved p-norm-based spectrum sensing scheme to improve the spectrum utilization efficiency in green UAV communication.Firstly,we construct the p-norm decision statistic based on the assumption that the random arrivals of signals follow a Poisson process.Then,we analyze and derive the approximate analytical expressions of the false-alarm and detection probabilities by utilizing the central limit theorem.Simulation results illustrate the validity and superiority of the proposed scheme when the primary signals are corrupted by additive non-Gaussian noise and arrive randomly during spectrum sensing in the green UAV communication.

Zero-forcing beamforming with receiver antenna selection in downlink multi-antenna multi-user system

A study on the zero-forcing beamforming （ZFBF） scheme with antenna selection at user terminals in downlink multi-antenna multi-user systems is presented. Simulation results show that the proposed ZFBF scheme with receiver antenna selection （ZFBF-AS） achieves considerable throughput improvement over the ZFBF scheme with single receiver antenna. The results also show that, with multi-user diversity, the ZFBF-AS scheme approaches the throughput performance of the ZFBF scheme using all receiver antennas （ZFBF-WO-AS） when the base station adopts semi-orthogonal user selection （SUS） algorithm, and achieves larger throughput when the base station adopts the Round-robin scheduling algorithm. Compared with ZFBF-WO-AS, the proposed ZFBF-AS scheme can reduce the cost of user equipments and the channel state information requirement at the transmitter （CSIT） as well as the multiuser scheduling complexity at the transmitter.

On selecting transmission mode for D2D transmitter in underlay cellular network with a multi-antenna base station

The Device-to-Device(D2D)communication underlaying cellular networks is considered in this study.The D2D transmitter in the D2D mode can directly transmit messages to a receiver,but it may interfere with the transmission of another cellular user who shares the same uplink channel.The transmitter can also operate in a cellular mode in which no interference to another cellular user occurs.We propose a mode selection scheme that aims to minimize the transmission power of the D2D transmitter subject to constraints on the minimum required data rate and maximum interference to other cellular users.The proposed scheme is based on bounds for transmission power and is less complex than the optimal scheme.Furthermore,it requires only a few statistics and does not need a fading channel distribution.The performance of the scheme is close to optimum when the number of Base Station(BS)antennas is large,and the mean absolute deviation of the fading terms is small.We verify this with numerical results of the Rician and Rayleigh fading channels by assuming that the BS antennas are independent.The simulation results for the two correlated BS antennas are presented herein.

Design of multi-antenna relaying for OFDM in impulsive noise environment

A low-complexity multi-antenna relaying scheme is proposed for Orthogonal Frequency Division Multiplexing (OFDM) in the presence of Class-A Impulsive Noise (IN). One way and two way relaying are considered. The signal is transmitted and received by two terminal nodes, each with a single antenna in two time phases. In the proposed design, the processing at the relay consists of Maximal-Ratio Combining (MRC) or Power-based Selection Combining (PSC) for receive combining, Amplify and Forward (AF) for power scaling, and Space Time Block Coding (STBC) for transmit diversity. Channel State Information (CSI), Discrete Fourier Transform (DFT), and Inverse Discrete Fourier Transform (IDFT) are not needed. The Selective Mapping (SLM) technique is used at the transmitter to reduce the Peak-to-Average Power Ratio (PAPR) of the OFDM signal. Then, at the receiver, the clipping technique is used to reduce the impulses that result from the impulsive noise. The proposed system reduces the complexity of the conventional system, which uses multi-relay with a single antenna. Simulation results show that the Bit Error Rate (BER) of the proposed scheme outperforms that of the conventional scheme due to the diversity inherent in the proposed scheme.

Adaptive Rate Control for Multi-Antenna Multicast in OFDM Systems

We propose two rate control schemes for multi-antenna multicast in OFDM systems, which aim to maximize the minimum average rate over all users in a multicast group. In our system, we do not require all multicast users to successfully recover the signals received on each subcarrier. In contrast, we allow certain loss for multicast users, such that the multicast transmission rate can be increased. We assume that the loss-repairing can be completed at upper protocol layers via advanced fountain codes. Following this principle, we formulate the rate control problem via beamforming in multi-antenna multicast to optimize the minimum achievable rate for all multicast users. While the computation complexity to solve for the optimal beamformer is prohibitively high, we propose a suboptimal iterative rate control scheme. Moreover, we modify the above optimization problem by selecting a ?xed proportion of users on each subcarrier. The beamformer searching process will then be performed only based on the selected users on each subcarrier, such that the complexity can be further reduced. We also solve this new problem with a low complexity approach. Theoretical analyses and simulation results show that our proposed two rate control schemes can have higher minimum average rate than the baseline scheme without rate control, while achieving low complexity.

A Study on The Multi-Antenna Geometrical Depolarization Channel Modeling

The traditional geometrical depolarization model that single transmitter to single receiver provides a simple method of polarization channel modeling. It can obtain the geometrical depolarization effect of each path if known the antenna configuration, the polarization field radiation pattern and the spatial distribution of scatters. With the development of communication technology, information transmission spectrum is more and more scarce. The original model provides only a single channel polarization state, so the information will be limited that the polarization state carries in the polarization modulation. The research is so significance that how to carries polarization modulation information by using multi-antenna polarization state. However, the present study shows that have no depolarization effect model for multi-antenna systems. In this paper, we propose a multi-antenna geometrical depolarization model. On the basis of a single antenna to calculate the depolarization effect of the model, and through simulation to analysis the main factors that influence the depolarization effect. This article provides a multi-antenna geometrical depolarization channel modeling that can applied to large-scale array antenna, and to some extent increase the speed of information transmission.

An SNR-Adaptive Relaying Algorithm for Multi-Antenna Cooperative Networks

Multiple-input multiple-output(MIMO) and cooperative communications have been attracted great attention for the improvements of communication capacity, power consumption, and transmission coverage. The conventional fixed relaying protocols, amplify-and-forward(AF) and decode-and-forward(DF), have their own advantages and disadvantages, i.e. AF performs better than DF for low signal-to-noise ratio(SNR) region, while the reverse is true for high SNR region. Therefore, this paper proposes an SNR-adaptive forward(SAF) relaying scheme obtaining the advantages of both AF and DF. Furthermore, the proposed SAF does not need to switch between AF and DF when SNR changes. The main idea is to adaptively derive the soft information at the cooperative relay nodes based on the information of the received signal and the SNR. Besides, based on the theoretical analysis and the simulation results, it is affirmed that the proposed SAF achieves superior performance than both AF and DF for all SNRs. Moreover, the performance gain would be improved with the increasing number of parallel cooperative relay nodes.

Energy Efficiency Analysis of Multi-Antenna Cellular Networks with Strategic Sleep Relay

Energy efficiency(EE) of cellular networks has attracted considerable attention recently. However, EE of relay-assisted cellular networks where the macro base stations(MBSs) are equipped with the multi-antenna has not been thoroughly addressed. This paper considered the downlink transmission of multi-antenna relay-assisted cellular networks, meanwhile, a strategic sleep scheme was used in relay stations(RSs), which dynamically adjusted the RS working mode according to whether the number of users serviced by the relay exceeds a given threshold. A geometric model was built to derive the coverage probability and mean achievable rate from the MBSs to user(UE), the MBS to RS, the RS to UE links and analyze the system EE. It is shown that the energy efficiency of cellular network with strategic sleep RS is slightly higher than that of cellular network with non-sleeping strategy. Furthermore, the MBS equipped with multi-antenna has better impact on energy efficiency and spectral efficiency than the MBS with single antenna.

Quad-channel broadband compact multi-antenna GNSS down-converter for high-reliability navigation

A high-reliability broadband high-linearity down-converter for multi-antenna global navigation satellite system(GNSS)receiver is presented in this paper.Based on direction-of-arrival estimation,the multi-antenna GNSS receiver can separate the GNSS signals from the interfering signals and suppress harmful broadband radio frequency interferences.To drive the off-chip 50Ω2 resistive load and meet the stringent requirements of linearity,a quad-channel down-converter with a broadband common-gate low-noise transcon-ductance amplifier,current-driven passive mixer and novel bridge mode transimpedance driving amplifier have been proposed to contruct the multi-antenna recelver.The operating frequency of this down-converter is from 1.15 to 1.65 GHz,covering all bands for global positioning system(GPS),Beidou navigation satellite system(BDS),global navigation satellite system(GLONASS)and Galileo.The measured results show that the proposed quad-channel down-converter achieves+38 dBm output 3rd order intercept point(OIP3)and+17 dBm OP1dB(output-referred 1 dB compression point),9.5 dB to 12.9 dB noise figure(NF)across the variable gain of 10 dB to 27 dB and approximately 47 dB channel isolation.

智能反射面辅助的多天线通信系统鲁棒安全资源分配算法

为了解决蜂窝通信系统中因窃听者、障碍物阻挡和信道不确定性导致安全性低和传输质量差的问题,该文提出一种智能反射面(IRS)辅助的多天线通信系统鲁棒安全资源分配算法。首先,考虑合法用户的安全速率约束、最大发射功率约束和IRS相移约束,基于有界信道不确定性,建立了一个联合优化基站主动波束、IRS被动波束的鲁棒资源分配问题。然后,利用S-程序、连续凸近似、交替优化和罚函数等方法对含参数摄动的原非凸问题进行转换,得到可直接求解的确定性凸优化问题。最后,提出一种基于迭代的鲁棒能效最大化算法。仿真结果表明,该文算法具有较好的能效和较强的鲁棒性。

无线光通信一对多发射天线研究进展

无线光通信是一种新兴的通信技术,具有高速、大容量和安全性好等优势。然而,传统的无线光通信系统存在着单对单通信模式限制,无法满足多用户同时通信的需求。无线光通信中光学天线起着发射和接收耦合光信号的作用,一对多点发射天线可以拓展无线光通信的应用。对国内外一点对多点光学天线的发展进行总结,介绍了一对多光学天线的基本原理。对目前现有的几种一对多光学天线设计方案进行讨论。最后对该领域的发展趋势和未来发展方向进行展望。

用于多波段的多模式频率可重构天线

为了应对频率可重构模式单一,尺寸偏大,工作频段较窄等问题,基于传统的微带缝隙天线,通过对其进行结构的改造,设计并实现了一种应用于C,S,X,Ku波段的多模式频率可重构微带缝隙天线。天线为叉型结构,分别在3个叉形枝节和微带线之间嵌入PIN二极管,通过控制二极管的导通状态,使天线具有4种不同的模式,分别对应于单频带、双频段、三频段和四频段。此天线尺寸为20mm×22mm,较传统缝隙天线体积减少了20%以上,实现了小型化。天线在工作频点处的最大增益可达5dBi,具有良好的辐射特性。

Combined adaptive beamforming with space-time block coding for multi-antenna communications

Aiming at the multi-antenna communication systems, a downlink transmit scheme combining adaptive beamforming （ABF） with space-time block coding （STBC） is first presented, which utilizes the maximization of the output mean signal-to-noise ratio （SNR） and the minimization of the symbol error rate （SER） upper bound of the three widely used modulations as the design criteria. Then, based on the moment generating function （MGF） and the Gauss-Chebyshev integration, a simple and accurate numerical method is presented to analyze the SER performance of the system with the new transmit scheme under the three commonly used modulations. Finally, computer simulation results demonstrate the effectiveness and superiority of the proposed strategy.

采用螺旋线实现高隔离度的车载多频宽带MIMO天线

为解决车载天线工作带宽窄和MIMO天线低频段隔离度低等问题,提出一种应用于车载通信系统的多频宽带高隔离度的MIMO天线,其工作频段为824~960 MHz和1710~6000 MHz,可覆盖民用移动通信的2G/3G/4G/5G和无线局域网/车联网等频段。单极子天线单元采用弯曲、开槽等诸多技术实现多频宽带,还通过添加接地枝节来降低天线高度和提高物理稳定性;在MIMO天线设计上采用螺旋线来提高天线单元之间的隔离度。实测结果表明,天线在工作频段内的反射系数小于-10 dB,隔离度小于-20 dB,低频段增益和辐射效率略低,中高频段的增益均大于4 dBi,最高达到7 dBi,效率均高于70%,最高可以达到96%。实测数据与仿真数据具有良好的一致性,所研制的天线可满足车载天线对多频段通信和高隔离度MIMO天线的技术要求,其结构和尺寸专为安装于汽车内部中控台背面而设计。

舰用雷达阵面在不同冲击环境下的响应分析

通过理论计算和有限元仿真,研究舰用雷达阵面在不同冲击环境下的响应。文中将冲击载荷作用下舰用雷达阵面的受力模型简化为基础激励的多自由度系统,通过对受力模型的边界模态进行虚拟约束的方法计算了不同冲击环境下的响应。结果表明:舰用雷达阵面响应基本不受冲击谱参数中谱加速度变化的影响,而谱位移和谱速度对舰用雷达阵面响应影响较大。分析结果可为冲击环境下舰用雷达阵面的响应分析和影响评估提供参考。

An overview of multi-antenna technologies for space-ground integrated networks

Multi-antenna technologies have already achieved a series of great successes in the development of information networks. For future space-ground integrated networks(SGINs), the traditional various kinds of separated information networks will converge to a whole fully connected information network to provide more flexible and reliable services on a world scale. Regarding their great successes in existing systems, multiantenna technologies will be of critical importance for the realization of SGINs and multi-antenna technologies are definitely one of the most important enabling technologies for future converged SGINs. In this article, a comprehensive overview on multi-antenna technologies is given. We first investigate multi-antenna technologies from a theoretical viewpoint. It is shown that we can understand multi-antenna technologies in a general and unified point of view. This fact has two-fold meanings. First, the research on multi-antennas can help us understand the relationships between different technologies e.g., OFDMA, CDMA, etc. On the other hand,multi-antenna technologies are easy to integrate into various information systems. Following that, we discuss in depth the potentials and challenges of the multi-antenna technologies on different platforms and in different applications case by case. More specifically, we investigate spaceborne multi-antenna technologies, airborne multi-antenna technologies, shipborne multi-antenna technologies, etc. Moreover, the combinations of multiantenna technologies with other advanced wireless technologies e.g., physical layer network coding, cooperative communication, etc., are also elaborated.

Multi-antenna synchronized global navigation satellite system receiver and its advantages in high-precision positioning applications

The multi-antenna synchronized global navi- gation satellite system receiver is a high precision, low cost, and widely used emerging receiver. Using this type of receiver, the satellite and receiver clock errors can be eliminated simultaneously by forming between antenna single-differences, which is equivalent to the conventional double-difference model. However, current multi-antenna synchronized global navigation satellite system receiver products have not fully realized their potential to achieve better accuracy, efficiency, and broader applications. This paper introduces the conceptual design and derivable products of multi-antenna synchronized global navigation satellite system receivers involving the aspects of attitude determination, multipath effect mitigation, phase center variation correction, and ground-based carrier phase wind- up calibration. Through case studies, the advantages of multi-antenna synchronized global navigation satellite system receivers in high-precision positioning applications are demonstrated.