Hybrid transmit antenna selection and maximal-ratio transmission systems

Maximal-ratio transmission systems with transmit antenna selection is investigated. According to the order statistics of channel fiat fading coefficients, the closed-form expressions axe derived for average SNR with any amount of RF chains and average BER with two RF chains, respectively. The algorithm for calculating the minimum of total transmit antennas is presented in terms of reduced RF chains. The method of quantizing transmit precoders is employed in this study to decrease feedback information. Simulation results demonstrate the superiority of the proposed systems under full and quantized transmit precoders. The SNR of the proposed systems has been less degraded by the quantization of transmit precoder than that of pure maximal-ratio transmission systems.

An Introduction to Transmit Antenna Selection in MIMO Wiretap Channels

This paper is a survey of transmit antenna selection-a low-complexity, energy-efficient method for improving physical layer security in multiple-input multiple-output wiretap channels. With this method, a single antenna out of multiple antennas is selected at the transmitter. We review a general analytical framework for analyzing exact and asymptotic secrecy of transmit antenna selection with receive maximal ratio combining, selection combining, or generalized selection combining. The analytical results prove that secrecy is significantly improved when the number of transmit antennas increases.

Transmit Antenna Selection in MIMO-OFDM System Based on CO-SFBC Schemes

A transmit antenna selection(TAS)multi-input multi-output orthogonal frequency-division multiplexing(MIMO-OFDM)system based on channel-orthogonalized space-frequency block coding(CO-SFBC)schemes was proposed for better performance.Firstly,the principles and criterions for designing CO-STBC/SFBC schemes with angle feedback were proposed,and then the effect of quantization for the feedback angle information within such schemes was discussed.Meanwhile,the TAS scheme was applied to the system to further improve the overall performance.Simulation results show that the combination of the proposed CO-STBC and TAS schemes can significantly improve the system performance,which is much larger than only applying them to systems individually.

Diversity order of decode-and-forward MIMO relaying with transmit antenna selection

This article analyzes the diversity order of several proposed schemes, where the transmit antenna selection （TAS） strategies are combined with low-complexity decode-and-forward （DF） protocols in the multiple-input multiple-output （MIMO） relaying scenario. Although antenna selection is a suboptimal form of beamforming, it enjoys the advantages of tractable optimization and low feedback overhead. Specifically, this article proposes schemes that combine TAS strategies with fixed decode-and-forward （FDF） and selection decode-and-forward （SDF） protocols. Following that, the asymptotic expressions of outage probabilities are derived and the diversity order of the proposed schemes analyzed. These kinds of combination of transmit antenna selection strategies and low-complexity decode-and-forward protocols can achieve partial diversity order in the MIMO relaying scenario. The numerical simulations verify the analysis.

Low-complexity transmit antenna selection algorithm for massive MIMO

Massive multiple input multiple output(MIMO)systems can increase capacity and reliability greatly.However,extremely high hardware costs and computational complexity lead to the demand for reasonable antenna selection.Aiming at the problem that the traditional antenna selection algorithm based on maximizing sum capacity has large complexity and worse bit error rate(BER)performance,a two-step selection algorithm is proposed,which selects a part of the antennas based on the norm-based antenna selection(NBS)firstly,and then selects the antenna based on maximizing capacity via convex optimization.The simulation results show that the improved algorithm has better BER performance than the traditional algorithms.At the same time,it reduces computational complexity greatly.

Closed-loop transmit diversity systems with hybrid antenna selection

The paper investigates closed-loop transmit diversity （CLTD） systems with antenna selection technique. The expected received signal-noise-ratio （RxSNR） of the proposed systems is analyzed and compared with CLTD systems. An algorithm is proposed for determining the number of increased transmit antennas in terms of a reduced RF chains without performance degradation. Since a feedback channel is bandwidth-limited, we present a method of quantizing transmit-weight vectors. Simulation results demonstrate advantage of the proposed systems with full and quantized feedback information. Quantized feedback has less effect on the proposed systems than CLTD systems.

Achieving Directionality and Transmit Diversity via Integrating Beam Pattern Scanning (BPS) Antenna Arrays and OFDM

In this paper, we introduce a novel merger of antenna arrays with scanning beam patterns, and Orthogonal Frequency Division Multiplexing (OFDM) systems. Controlled time varying phase shifts are applied to the antenna array elements mounted at the base station with beam patterns directed toward the desired user. This creates a small beam pattern movement called Beam Pattern Scanning (BPS). In rich scattering environments BPS creates a time varying environment leading to time diversity exploitable at the receiver enhances its probability-of-error performance. Here, we apply OFDM signals to BPS antenna arrays, and we achieve: (1) directionality, which supports Space Division Multiple Access (SDMA);and (2) a time diversity gain, which leads to high performance. We discuss the structure of the base station antenna array and the OFDM receiver that exploits time diversity. We also introduce the merger of BPS and multi-carrier OFDM (MC-OFDM) systems. In MC-OFDM each bit is transmitted over all sub-carriers after serial to parallel conversion. BPS/ MC-OFDM receiver exploits both time diversity inherent in BPS, and frequency diversity inherent in MC-OFDM transmission technique. Simulation results show high Probability-of-error performance is achie- vable via BPS/OFDM and BPS/MC-OFDM schemes comparing to the traditional OFDM and MC-OFDM, respectively. Simulations also reveal that MC-OFDM system as well as its merger with BPS is capable of mitigating large Peak-to-Average Ratio (PAPR) problem in traditional OFDM system. In addition, performance simulations with coded OFDM (COFDM) and coded MC-OFDM (MC-COFDM) and their merger with BPS are studied.

基于物联网的中波广播发射天线健康状态智能监测系统设计

中波发射天线,作为中波广播发射的核心设施,其地理位置远离发射机房,因此易受到各种天气和地质条件的影响,从而可能引发播出事故。为确保广播电视的安全播出,并保障其平稳、高效运行,我们引入了广播发射天线健康状态智能监测系统。该系统主要由天线垂直度监测、拉线拉力监测、拉线倾角监测以及上位机监测软件等四个核心组件构成。通过对各项数据的精准采集、高效处理,以及实时的在线监测与预警,本系统成功解决了对天线健康状态的实时监测问题,充分满足了发射天线的监测与预警需求。因此,该系统具有广阔的应用前景和重要的实用价值。

基于发射天线选择的修改转发协作D2D网络的物理层安全

为了进一步提升与蜂窝网络共享频谱资源的解码转发(decode-and-forward,DF)协作终端直通(device-to-device,D2D)网络的物理层安全(physical layer security,PLS)性能,提出了一种D2D发送端采用发射天线选择(transmit antenna selection,TAS)的修改转发(modify-and-forward,MF)协作D2D-蜂窝网络PLS模型。配备多根发射天线的D2D发送端采用TAS技术,选择使D2D发送端至MF中继节点链路信干噪比最大的天线发送信号;中继采用MF协议将解码得到的合法信息进行修改后再转发,以避免被动窃听者能够解码出此阶段发送的合法信息,从而改善了D2D网络的PLS性能。推导了MF协作D2D网络的安全中断概率、非零安全容量概率和渐近安全中断概率的解析表达式,并与DF协作D2D网络的PLS性能进行对比分析。数值计算与仿真结果表明,MF协作D2D网络的PLS性能优于DF协作D2D网络,并且增大D2D发送端的发射天线数量,可以增强D2D网络的PLS性能。

大环发射天线磁感应透地无线起爆系统透地性能分析

为在露天矿等起爆作业场景中实现大规模的透地无线起爆,研究在地上发射端采用大环发射天线的磁感应透地无线起爆系统。建立磁感应透地无线起爆中发射天线线圈与接收天线线圈的等效电路,基于等效电路建立大环形天线无线起爆透地磁感应强度模型,计算得到透地无线起爆磁感应强度阈值。仿真分析透地深度、发射天线匝数与半径、发射功率等因素对透地磁感应强度的影响。研究结果表明:透地无线起爆系统能实现对地下7.52m深处雷管的起爆,且可通过增加发射线圈匝数、适当降低发射线圈半径,以及提高发射功率的方式提高透地无线起爆系统的起爆深度。研究结论为大环形发射天线磁感应透地无线起爆系统的参数选取提供理论依据。

太赫兹多层平面透镜天线的分层制造技术研究

现代信息科技的飞速发展对雷达系统提出了更高的要求,太赫兹(THz)雷达凭借其特殊的电磁特性在航空航天军事应用方面有着广阔的应用前景。高增益天线作为雷达系统的关键组成部分,在太赫兹波段的研究正受到高度关注。当天线工作频段高达1.0THz左右时,适用于低频器件的常规加工方法往往难以满足设计需求,限制了其进一步应用。本文提出并设计了一种基于UV-LIGA工艺的太赫兹多层平面透镜天线的分层制造方法,为提高透镜区域厚度均匀性,在外缘添加了片内辅助阴极作为装配区,经验证,厚度均匀性提高了33.08%。开展阶梯式电流密度电铸试验,当电流密度按1.5A/dm2、2A/dm2、1.75A/dm2阶梯变化时得到的沉积层具有更低的结合强度和表面粗糙度。透镜天线经过电性能测试,其在0.79~1.03THz范围内取得了良好的增益效果,有望应用于航空航天机载平台以提高雷达系统的识别能力。

全金属Fabry-Perot谐振腔天线

为实现远距离微波无线能量传输,发射天线应具有耐受大功率、高增益、低损耗和结构简单等优点。针对以上需求,文章设计了一款全金属结构的Fabry-Perot谐振腔天线。整个天线包含全金属腔体,波导馈口和双层金属栅格覆盖层。覆盖层的尺寸为3λ_(0)×3λ_(0),λ_(0)为对应的工作波长。每一层金属栅格都包含9×9个单元。所设计的双层覆盖层可以看作是一种电磁带隙结构,通过优化双层金属栅格单元的厚度和间距,实现了工作频段的宽带化,仿真结果表明其在9.72GHz~10.3GHz之间实现了插入损耗小于3dB的宽频带传输特性。通过电磁带隙结构对馈源辐射出来的微波进行幅度和相位的修正实现增益的提高,仿真结果表明:不加载双层覆盖层时该天线的增益为9.7dBi,加上覆盖层之后增益提高到了17.76dBi。为了验证上述设计和仿真,加工制作了一款全金属结构Fabry-Perot谐振腔天线,实测结果表明:该谐振腔天线在10GHz实现了17.31dBi的高增益,同时在9.51GHz~11.42GHz之间获得了回波损耗大于10dB的阻抗带宽。

硬质探空落球数传系统天线设计方法

针对硬质探空落球高空惯性运动工况及落球内部有限安装空间下的无线传输需求,给出了适用于临近空间气象探测落球数传系统的天线设计方法。该方法采用中心对称曲折线振子天线技术方案,解决了在狭小空间内实现全向天线覆盖的难题。实验结果表明,该方法有效解决了落球在空中下落过程中由于姿态变化引起的信号起伏大从而影响无线信号可靠传输的问题。

中波广播发射天线的选型技术研究

目前许多中波转播台使用的发射天线有很多仍为上世纪七八十年代所建的拉线塔天线,使用年限久,安全隐患大,同时有些台站面临搬迁,为节省土地资源并提升发射天线综合利用率,计划将部分桅杆式拉线天线升级改造为自立塔天线。本文着重分析工作频率多、发射场区地理环境复杂、具有多座发射天线的中播转播台、在规划更换改造发射天线时,针对天线类型的选择和分布定位等需要考虑的技术因素进行统筹规划,可为其他中波台在改造更换发射天线提供参考。

无线通信基站电磁辐射缓解技术分析

文中围绕电磁辐射缓解技术开展了讨论,以某无线通信基站为研究对象,分析了相关技术的应用路径与实际效果。通过增加天线高度,调整VRP(垂直辐射图)与HRP(水平辐射图),降低发射器功率等形式,缓解了人体所承受的电磁辐射,以达到照射导出限值标准。同时,利用天线的美化处理,更好地推动了人与自然的和谐统一,保障了人们的生命安全。

过时CSI下全双工中继辅助D2D网络的物理层安全

中继辅助终端直通(devicetodevice,D2D)网络通过与蜂窝网络共享频谱提高D2D用户的频谱效率和蜂窝用户(cellular user,CU)的物理层安全性。为进一步改善其性能,可以在基站和D2D链路的中继节点采用天线选择以及在中继节点采用全双工技术。然而,由于存在反馈时延和移动性,用于蜂窝链路和所有D2D链路天线选择的信道状态信息(channelstateinformation,CSI)均可能是过时的,针对该场景下的物理层安全性和可靠性问题,提出一种主动窃听和过时CSI场景下基站和中继节点均采用发射天线选择的全双工中继辅助D2D网络安全模型,推导CU的中断概率、遍历容量、非零安全容量概率、安全中断概率、渐近安全中断概率的解析表达式。数值计算与仿真结果均表明,基站发射天线数、中继干扰天线数越多,CU的安全性能越好;过时的CSI会降低CU的中断性能和安全性能。

航空发动机旋转件遥测天线研究与实现

以航空发动机高速旋转件非接触信号传输技术为研究对象,依托Datatel射频遥测系统,制定出一种航空发动机旋转件参数总体测试方案,提出一种1.34 GHz~1.7 GHz的发射/接收天线设计方法。基于ANSYS HFSS建立封装后的发射天线模型和接收天线模型,分析S参数随封装介质厚度、损耗角正切及介电常数的变化规律,形成了一套遥测转/静子工程应用装置。实验室测试结果表明:S参数实测与仿真结果较为吻合;高速旋转台测试结果表明:该装置在转速≯20 000 r/min,轴向间距≯10 mm状态下,具备高可靠信号传输的能力;某型航空发动机压气机试车结果表明:该装置能可靠应用于航空发动机压气机转速≯20 000 r/min,装配轴向间距为2.37 mm的复杂工况条件。

自适应调制MIMO无线系统的物理层安全

针对主动窃听场景下单输入单输出(single-input single-output,SISO)自适应调制频谱效率低和物理层安全(physical layersecurity,PLS)性能差的问题,提出了一种多输入多输出(multiple-input multiple-output,MIMO)安全自适应调制(secure adaptive modulation,SAM)无线系统PLS模型。其设计思路是:通过在发送端采用发送天线选择(transmit antenna selection,TAS)、在合法接收端采用最大比合并(maximal ratio combining,MRC)的天线分集技术来提高主信道的信噪比,以改善频谱效率;同时,限制主动窃听者的误比特率,使之无法解调出主信道发送的机密信息,从而保证合法接收端的PLS。在平均发射功率和PLS的联合约束下,推导SAM-MIMO系统的最佳切换门限和频谱效率以及窃听者的平均误比特率的解析表达式。数值计算与仿真结果表明:与SAM-SISO系统相比,采用TAS/MRC技术的SAM系统既可以提高主信道的频谱效率,又可以确保对主动窃听者的PLS。

一种基于改进ResNet的发射天线智能选择算法

为满足移动用户数据传输的需求,大规模多输入多输出在5G通信系统中得到了广泛应用,在N-Nakagami衰落信道下,建立了移动多天线协作通信系统。为提高发射天线的选择准确率,提出一种基于改进ResNet的发射天线智能选择算法,可以获得更大的信道容量。改进的ResNet网络以残差结构为网络主体,利用VGG神经网络代替原始的卷积层。VGG神经网络提取信道状态数据的信息特征,大大减少了浅层计算参数;丢弃池化机制以保护信息特征;重新构建三个残差模块结构以增强特征信息提取,提高发射天线的选择准确率,获得信道容量更佳的天线。与传统的天线选择算法相比,所提出的发射天线智能选择算法的准确率提升至94.0%,具有较好的系统容量性能,且可以有效降低设备成本。

无线电中波广播发射技术与维护

广电建设事业的快速发展,使得无线广播技术应用水平得到切实提升,为实现理想化无线电中波广播应用模式,业界加大对中波广播发射技术以及维护方式的研究力度。该文将通过对广播发射台基本情况的介绍,对无线电中波广播发射技术及其原理进行深度性探讨,并会就其维护方式展开研究,旨在提升无线电中波广播发射质量,实现理想化中波广播维护模式。