室内多径信道的三维宽带多极化测量方法

针对室内多径信道的特点,提出了一种可对室内多径信道进行三维宽带多极化测量的方法,并设计制作了三维宽带多极化测量系统,利用该系统对典型室内环境的多径信道进行了测量。测量系统的发射端和接收端天线阵列各由一组虚拟的多极化天线阵列构成,多径信道的频域响应由矢量网络分析仪测量得到。利用此系统对典型室内环境中多径信道进行的三维多极化测量结果表明,不同极化方式的电磁波在相同多径环境中的传播特性有明显差异。在不同的测量位置,包括直射和非直射的多径条件下,不同极化的多径信道之间相关系数都很低,证明可以利用不同极化方式多径信道的不相关在室内环境中构建极化分集的MIMO系统。     

基于网络分析仪的UWB频域测试

超宽带通信技术(UWB)在未来室内无线多媒体接入中有着广阔的应用前景,研究超宽带室内信道测量技术不仅有利于室内通信系统性能分析,而且有利于加速超宽带通信在民用和商用上的进程。本文在典型的办公楼室内环境下,使用矢量网络分析仪分别在LOS和NLOS场景中进行UWB信道频域测量,并用LABVIEW软件对测试数据进行拟合处理,分析计算后得到的信道参数。信道参数表明,由于室内环境复杂产生的通信阻塞效应,使NLOS场景中信道衰减比LOS场景中更大。在小尺度频域测量中,实测波形很好的反应UWB在室内传播的多径现象,并可以看出多径呈簇,相对于NLOS场景,LOS场景中多径数较少,而且多径能量损耗较小。结果表明,通过频域测试得到的信道参数满足实际信道建模,多径衰落特性与实测统计特性相符,从而验证了测试方法以及数据处理的正确性。     

MIMO-RFID系统反向识别距离研究

超高频(UHF)射频识别系统(RFID)读取可靠性受多径信道制约,而多天线分集技术(MIMO)被认为能有效提高其链路可靠性。不同于一般的无线通信系统,UHF RFID反向链路是两个多径信道的级联,本文基于最大比合并(MRC)准则,分阅读器单站和双站天线情形,导出了Nakagami-m多径信道下单天线(SISO)与多天线(MIMO)RFID系统反向识别距离(RIR)均值的解析表达式,并通过数值仿真和实际测试研究了相关因素对RIR均值的影响。实验结果表明:MIMO技术能有效提高多径信道下UHF RFID系统的反向识别距离,并且阵列天线数越多、信道相关系数越小、信道衰落参数m越大,RIR均值将越高。     

无线紫外光MIMO湍流信道中BCOSTBC编码研究

针对在准确估计信道情况下无线紫外光MIMO湍流信道中如何有效地获得全分集增益这一问题。首先研究了无线紫外光通信的传输特性,然后研究了MIMO信道以及影响紫外光通信的主要因素。最后,采用比特补码式正交空时码(BCOSTBC)编码,推导出在弱湍流情况下直视(LOS)和非直视(NLOS)的误码率公式。实验结果表明,采用编码后1×2、2×1和2×2系统的误码率性能在LOS和NLOS情况下分别约改善了3、6和9 d B。增加光电探测器数目可以提高分集增益,有益于系统性能的改善;其中,2×2系统需要的发射功率最小,传输的距离更远,数据传输速率更大,误码率更低;在NLOS条件下通过小角度收发仰角能够改善系统的误码率性能。     

无差错多路切换

在多信道无线中继系统中，保护信道可以对多径衰落时的频率分集提供对抗措施，本文讨论了应用于大容量无线数字系统中无损伤切换系统的要求，提出了设计导则，最后给出室内测量的结果。     

5G TM 信号无线信道测量平台研究与实现

为了研究第五代移动通信（5G）系统无线信道，获得准确的5G无线信道特性和信道模型，提出了一种基于5G新空口（NR）测试模式（TM）信号的无线信道测量平台。开展了TM无线信道测量平台的总体架构及测量信号接收处理算法设计，并基于软件无线电设备和高性能计算设备搭建测量平台。针对功率谱平坦度、峰均功率比和相关性等指标，对多种TM信号的测量性能进行评估。根据性能评估结果，选择适合作为测量波形的TM信号。采用射频馈线直连、多径信道模拟和静态空口实测3种方法对TM无线信道测量平台进行验证，该平台不仅可以实现准确的信道测量，同时能够对矢量幅度误差和误比特率等传输性能进行测试。     

相关无线光MIMO系统的信道容量

空间相关性是制约无线光多输入多输出(MIMO)系统性能的主要因素之一。结合OOK调制技术,建立了相关无线光MIMO系统的信道模型,推导了不同相关机制下无线光MIMO系统的平均信道容量的解析式,分析了其中断性能。采用仿真实验分析了对数正态衰落信道中,空间相关性对均匀圆阵光MIMO系统的平均信道容量和中断信道容量的影响。结果表明,空间相关性的存在使得无线光MIMO系统的平均信道容量减小,中断概率增大;同时完全相关对于系统性能的影响较部分相关而言更为严重。     

基于直接序列扩频的WSN通信信道均衡算法

对无线传感器网络（WSN）通信信道进行均衡设计,抑制无线传感器节点之间的码间干扰,改善通信质量。提出一种基于直接序列扩频的WSN通信信道均衡算法。进行了WSN的信道模型设计,为了降低信道输出的稳态误差,采用时间反转镜为匹配滤波方法,进行多径信道的码间干扰滤波,设计自相关匹配滤波器,通过直接序列扩频方法实现WSN通信的信道均衡。仿真结果表明,采用该算法进行WSN的通信信道均衡设计,发射信号沿各个路径到达接收机的信号分量得到准确分离,信号的多径分量得到无误码接收,通信信道均衡效果较好,通信误比特率低于传统方法,改善了WSN通信质量,展示了较好的应用价值。     

非视距环境下Massive MIMO信道的构建与分析

随着下一代移动通信研究的深入,Massive MIMO 技术已成为业界研究的热点。针对 Massive MIMO 系统特有的天线体积大、信道近场非平稳的特性,构建出较真实的信道模型,该模型适用于 Massive MIMO非视距、瑞利平坦衰落环境。在系统仿真中,基站侧采用128根线形排列的天线,基站天线到信道散射体的导向矩阵由精确的波程差来确定,得到发射端相关矩阵,并结合Kronecker模型构建信道。结合不同的预编码方法和散射体分布情况,对比分析了其对 Massive MIMO信道容量的影响。该信道的构建与分析能更准确地反映信道特性,具有较强的理论价值和实践意义。     

隧道中无线电波多径传播特性及仿真

隧道中无线电波多径传播非常严重,通信质量急剧下降。多径传播特性的研究对隧道内无线通信系统的设计具有重要的意义。通过分析和研究隧道中多径传播的衰减和时延特性,建立了多径信道的衰减和时延模型,给出了单频信号、窄带信号和宽带信号多径衰落的统计特性,并对多径信号的合成进行了仿真,为抗衰落技术的应用打下了基础。     

2.6 GHz频段走廊环境下MIMO信道特性的研究

本文采用高密度8×29MIMO 天线,在2.6 GHz 和20 MHz 带宽情况下测量获得走廊环境下的信道特性。在信道测量时采用了 RUSK 信道探测器来获得高分辨率的测量数据。测量的实际场景选择了典型的办公走廊和半开放式的走廊场景。本文重点分析在不同天线极化方式下的信道时延扩展和信道相关性,同时也分析了不同场景下的天线交叉极化功率比和角度扩展。     

Neutralizing interferences in two‐hop amplify‐and‐forward MIMO relay systems

In this paper, we present the interference neutralization technique for two‐hop multiple‐input multiple‐output (MIMO) relay systems. It enables multiple MIMO transmitters (sources) to simultaneously transmit independent data streams to their MIMO receivers (destinations) without mutual interferences, thereby improving spectral efficiency of the systems. To neutralize the mutual interferences using multiple amplify‐and‐forward (AF) MIMO relays, we establish the sufficient condition for the antenna configuration in the MIMO relay networks, and provide a filter design technique for the AF MIMO relays. The proposed method increases sum rates of the systems linearly with the number of transmitters participating in simultaneous transmission. To improve the sum rates further, this method is combined with transmit power allocation using the water‐filling algorithm. In addition, it is shown that by employing the minimum number of relays required to meet the sufficient condition, the system cost for the proposed method can be reduced without compromising the sum rate performance severely. Finally, simulation results successfully demonstrate that by exploiting radio resources such as frequency and time efficiently, the proposed method achieves a higher sum rate than the existing techniques based on interference avoidance. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Multiple-antenna communication systems: an emerging technology

A recent development in wireless communications is the application of multiple-input multiple-output (MIMO) systems to radio communications via use of multiple antennas. In order to investigate the technologys potential, an experimental MIMO system containing two four-element antenna arrays (4x4) has been developed at the University of Alberta. The system is used to obtain MIMO channel measurements in a typical indoor office environment in the ISM band (902-928 MHz). Measurement campaigns have been performed using different antenna spacings and two different types of antenna: half-wavelength (lambda/2) centre-fed dipoles and dual-polarized patches. The measurements are used to calculate channel capacities for an indoor 4x4 MIMO system. The measurements confirm the high capacity potential of a MIMO channel, with ergodic capacity of approximately 21 bits per channel use available with either antenna type at a signal-to-noise ratio of 20 dB if the antenna element separation is lambda/2 or larger. An introduction to basic MIMO theory, a discussion of the University of Alberta wireless MIMO testbed, and observations regarding the measured indoor MIMO channel are presented in the paper.     

DC-DC变换器的差模传导干扰耦合通道建模分析

为了实现对电力电子装置差模传导干扰的系统化分析和预测,提出了一种基于系统辨识的方法,描述差模传导干扰耦合通道的特性。以Buck变换器为研究对象,在MOSFET元件漏源极之间加入伪随机信号(PRBS)作为系统输入信号,取电源侧的差模干扰作为输出信号,由提取的数据用最小二乘法辨识出耦合通道的系统模型。结果表明,由耦合通道模型预测的波形和实验波形时域波形吻合性较好,频域特性成分较一致。应用建立的模型通过测量MOSFET元件漏源极之间干扰电压为输入,即可预测电源侧传导干扰,所需测试电量较少,可得到较好的效果。     

MIMO技术研究及空时编码在电力线通信中的应用

M IMO系统可以大幅度提高无线信道的容量和质量,降低系统成本。多天线技术与编码技术以及OFDM技术相结合,能更大幅度提高信道的容量和可靠性。文章介绍的编码技术包括空时格型码和空时分组码。由于电力线信道的特殊性,其衰落特性类似于多天线无线信道,M IMO中的天线选择算法以及空时编码技术都可以应用到电力线通信中。可以把三相电力线当作天线阵子来使用,并把编码技术应用其中,从而提高电力线通信的信道质量。     

宽带电力线载波MIMO系统干扰消除预编码方法

随着电力线载波通信在电力系统中的广泛应用,宽带多输入多输出系统会有共信道干扰,此干扰是除了异步脉冲噪声和周期脉冲外影响电力线载波宽带MIMO系统最大的因素。针对此问题,利用多输入多输出信道的状态信息,在发送端采用块对角化的方法消除信道间的干扰,从而提高宽带电力线载波系统的容量,同时降低了系统的误比特率。通过仿真结果和分析可以表明,所提的块对角化的预编码方法有效地消除了共信道干扰,提高了信干噪比,从而提高了系统的最大互信息并降低了系统的误比特性能。     

Blind MIMO equalization with optimum delay using independent component analysis

Blind space–time equalization of multiuser time‐dispersive digital communication channels consists of recovering the users' simultaneously transmitted data free from the interference caused by each other and the propagation effects, without using training sequences. In scenarios composed of mutually independent non‐Gaussian i.i.d. users' signals, independent component analysis (ICA) techniques based on higher‐order statistics can be employed to refine the performance of conventional linear detectors, as recently shown in a code division multiple access environment (Signal Process 2002; 82 :417–431). This paper extends these results to the more general multi‐input multi‐output (MIMO) channel model, with the minimum mean square error (MMSE) as conventional equalization criterion. The time diversity introduced by the wideband multipath channel enables a reduction of the computational complexity of the ICA post‐processing stage while further improving performance. In addition, the ICA‐based detector can be tuned to extract each user's signal at the delay which provides the best MMSE. Experiments in a variety of simulation conditions demonstrate the benefits of ICA‐assisted MIMO equalization. Copyright © 2004 John Wiley & Sons, Ltd.     

A novel hybrid fix‐LLL lattice reduction algorithm for MIMO detection system

Lenstra–Lenstra–Lovász (LLL) is an effective lattice reduction algorithm for multiple‐input multiple‐output (MIMO) systems, which was considered to achieve full diversity in the MIMO fading channel. In the LLL algorithm, size reduction is performed for pairs of consecutive basis vectors, and the concern of numerical stability is raised. However, the whole complexity of the LLL algorithm is of polynomial order, and its characteristics of the convergence perform poor in MIMO system. In this paper, a variant version, named the novel hybrid algorithm, which combines both fix measurement and round measurement, is proposed. By modifying the iteration criterion and choosing proper values of the parameters, the algorithm has a large probability to skip the size reduction and cause a faster convergence, It means in one algorithm iteration the LLL potential can be reduced as much as possible. Also, the performance bound derived by the proximity factor shows that the hybrid LLL has a minor performance loss compared to the LLL algorithm. As a direct consequence, in simulation results, the hybrid LLL algorithm can make a better compromise between the rate of convergence, complexity of the algorithm, and algorithmic performance. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

MIMO systems with antenna selection

Multiple-input-multiple-output (MIMO) wireless systems are those that have multiple antenna elements at both the transmitter and receiver. They were first investigated by computer simulations in the 1980s. Since that time, interest in MIMO systems has exploded. They are now being used for third-generation cellular systems (W-CDMA) and are discussed for future high-performance modes of the highly successful IEEE 802.11 standard for wireless local area networks. MIMO-related topics also occupy a considerable part of today's academic communications research. The multiple antennas in MIMO systems can be exploited in two different ways. One is the creation of a highly effective antenna diversity system; the other is the use of the multiple antennas for the transmission of several parallel data streams to increase the capacity of the system. This article presented an overview of MIMO systems with antenna selection. The transmitter, the receiver, or both use only the signals from a subset of the available antennas. This allows considerable reductions in the hardware expense.