无线接入信道损耗特性分析

小尺度衰落中的瑞利衰落和莱斯衰落是2种最为常见的无线接入信道衰落。从工程设计角度出发,重点分析了莱斯和瑞利信道条件下的2个重要指标——衰落深度和衰落速度,推导了相应的计算公式,特别是莱斯和瑞利信道条件下的衰落中值进行分析和计算。给出了在瑞利和不同莱斯因子条件下的PSK误码性能,为进行多径衰落无线接入信道的系统工程设计提供了参考。     

On Unbounded Path-Loss Models: Effects of Singularity on Wireless Network Performance

This paper addresses the following question: how reliable is it to use the unbounded path-loss model G(d) = d^?α, where α is the path-loss exponent, to model the decay of transmitted signal power in wireless networks? G(d) is a good approximation for the path-loss in wireless communications for large values of d but is not valid for small values of d due to the singularity at 0. This model is often used along with a random uniform node distribution, even though in a group of uniformly distributed nodes some may be arbitrarily close to one another. The unbounded path-loss model is compared to a more realistic bounded path-loss model, and it is shown that the effect of the singularity on the total network interference level is significant and cannot be disregarded when nodes are uniformly distributed. A phase transition phenomenon occurring in the interference behavior is analyzed in detail. Several performance metrics are also examined by using the computed interference distributions. In particular, the effects of the singularity at 0 on bit error rate, packet success probability and wireless channel capacity are analyzed.     

无线信道空域特性的实验研究

随着移动通信技术的发展,特别是智能天线技术的引入,提出了无线信道的空域(或角域)特性的问题.本文介绍了信道空域特性的一些实验研究方法和近年来这方面的最新研究成果,包括一些实验结果和理论分析,并给出了详细而有条理的引文来源,希望能够说明个人通信环境下空域传播特性研究的重要性和存在的主要问题.同时文中还提出了一种新的测量思路,以克服实验中遇到的困难.     

无线信道中的电波传播

分析了信号在无线信道中传输时所经受的两种衰落,介绍了主要的无线传播模型,在此基础上提出了对抗衰落的措施。     

A New Approach for Performance Evaluation of TCP over Interference-Limited Wireless Channels over Interference Wireless Channels

A new metric for performance evaluation of transport control protocol(TCP) overwireless channels based on the interference-limited characteristics of code division multipleaddress(CDMA) system is proposed.According to the new metric,the performance of TCP over CDMAcorrelated channel for different protocol parameters and different versions is investigated.The resultsshow that appropriate selection of protocol parameters and packet error rate(PER) operation point canimprove significantly the capacity of packet-switched CDMA-based network.     

无线中继传感网络中异向散射信道的路径损耗特性

使用点渗流网格建模无线传播信道,使用酒徒行走模型建模电磁波在传感信道中的传播过程。酒徒经过k步后,得到某个扇区内取向角均匀分布的随机游走的平均行走距离。在此基础上,得到随机射线在传播空间给定位置的概率分布,最后使用随机射线方法得到了放大传送模式下传感网络的路径损耗模型。该模型中出现指数为1.75的距离r的对数函数形式,以及距离的线性项,该项作为新模型的修正项。     

Rateless Coding for Wireless Relay Channels

We propose a novel coding framework for wireless relay channels based on rateless codes, which allows for a natural extension to multiple antenna and multiple relay settings. The relaying protocol is half-duplex, and relays independently choose when to collaborate, if at all. With a simulated fountain code based implementation of this framework, we show that the use of rateless codes is both robust and efficient when the channel state information is not available at the transmitters     

Linear-Complexity Models for Wireless MAC-to-MAC Channels

Wireless local area networks suffer from frequent bit-errors that result in Medium Access Control (MAC) layer packet drops. Bandwidth and media quality constraints of real-time applications necessitate analysis and modeling at the “MAC-to-MAC wireless channel”. In this paper, we propose and evaluate stochastic models for the 802.11b MAC-to-MAC bit-error process. We propose an Entropy Normalized Kullback-Leibler (ENK) measure to accurately evaluate the performance of the models. We employ this measure to demonstrate that the traditional full-state Markov chains of order-10 and order-9 are required for accurate representation of the channel at 2 and 5.5 Mbps, respectively. However, the complexity of this modeling paradigm increases exponentially with respect to the order. For many real-time and non-real-time applications, which require (or could benefit significantly from) accurate modeling, the high complexity of full-state high-order Markov models makes them impractical or virtually ineffective. Thus, we propose two new linear-complexity models, which we refer to as the short-term energy model (SEM) and the zero-crossing model (ZCM). These models, which constitute the most important contribution of this paper, constrain the complexity to increase linearly with the model order. We illustrate that the linear-complexity models, while yielding orders of magnitude reduction in complexity, provide a performance comparable to that of the exponential complexity full-state models. Within the linear-complexity context, we illustrate that the zero-crossing model perform better than its short-term energy counterpart. Finally, for varying window sizes and due to its low complexity, we show that the zero-crossing model can be adapted in real-time. Such an adaptive model provides accurate channel modeling and characterization for rate adaptive applications.Syed Ali Khayam received the B.S. degree in computer systems engineering from National University of Sciences and Technology (NUST) Pakistan in 1999. He secured the Pakistan Higher Education Commission M.S./Ph.D. scholarship to pursue post graduate studies at Michigan State University (MSU). He completed his M.S. in Electrical Engineering from MSU in 2003. He is currently a Ph.D. candidate in the Department of Electrical and Computer Engineering at MSU. He also worked at Communications Enabling Technologies where he led a design team which realized various modules of a Voice-over-IP system-on-chip. His research interests include statistical analysis and modeling of computer (and in particular wireless) networks, network security, cross-layer protocol design, real-time multimedia communications over IP-based networks, and VLSI chip design.Hayder Radha received the B.S. degree (with honors) from Michigan State University (MSU) in 1984, the M.S. degree from Purdue University in 1986, and the Ph.M. and Ph.D. degrees from Columbia University in 1991 and 1993 (all in electrical engineering). He joined MSU in 2000 as Associate Professor in the Department of Electrical and Computer Engineering. Between 1996 and 2000, Dr. Radha worked at Philips Research USA where he initiated the Internet Video project and led a team of researchers working on scalable video coding and streaming algorithms. Dr. Radha is a Philips Research Fellow. Prior to working at Philips, Hayder Radha was a Distinguished Member of Technical Staff at Bell Labs where he worked between 1986 and 1996 in the areas of digital communications, signal/image processing, and broadband multimedia. His research interests include image and video coding, wireless technology, multimedia communications and networking. He has more than 20 patents in these areas. Dr. Radha served as Co-Chair and Editor of the ATM and LAN Video Coding Experts Group of the ITU-T in 1994–1996.     

Multihop Diversity in Wireless Relaying Channels

Multihop Diversity in Wireless Relaying Channels This paper presents theoretical characterizations and analysis for the physical layer of multihop wireless communications channels. Four channel models are considered and developed: the decoded relaying multihop channel; the amplified relaying multihop channel; the decoded relaying multihop diversity channel; and the amplified relaying multihop diversity channel. Two classifications are discussed: decoded relaying versus amplified relaying; and multihop channels versus multihop diversity channels. The channel models are compared, through analysis and simulations, with the “singlehop” (direct transmission) reference channel on the basis of signal-to-noise ratio, probability of outage, probability of error, and optimal power allocation. Each of the four channel models is shown to outperform the singlehop reference channel under the condition that the set of intermediate relaying terminals is selected intelligently. Multihop diversity channels are shown to outperform multihop channels. Amplified relaying is shown to outperform decoded relaying despite noise propagation. This is attributed to the fact that amplified relaying does not suffer from the error propagation which limits the performance of decoded relaying channels to that of their weakest link.     

随机桥过程研究短程无线信道的空时特性

使用随机桥过程的样本建模短程无线信道中多径分量的传播轨迹。由随机桥过程的样本构造出基本随机变量,在一定的映射规则下由基本随机变量的样本得到反映无线信道空时特性的多径时延、多径信号抽头增益、多径信号的波达方向等参量。使用随机桥过程的特例布朗桥过程,分别对散射体均匀分布的信道传播环境和有约束的无线信道传播环境的空时特性进行仿真分析。仿真结果表明,在这两种传播环境中,多径分量的波达方向在仰角和水平角维度上均存在一定的局部偏好性,不满足均匀分布的假设。在仰角-水平角-多径分量到达时延这3个自由度的空间中,多径分量的分布表现出一定的规律性。     

Joint Power Minimization in Wireless Relay Channels

Energy-constrained multihop wireless links are considered, where the total power consumption is minimized under given requirements on the end-to-end bit error rate (BER). As multihop transmissions are known to be able to save transmission energy in a wireless environment, we study the optimal power scheduling schemes over intermediate hops when the source- relays-destination link can be modeled as cascaded binary symmetric channels. The problem is formulated with an end- to-end BER constraint, and the resulting power consumption is compared with that of the individual link requirement strategy where each hop assigns power under a per-link BER constraint. Results show that the proposed joint power scheduling strategy can achieve a maximum power reduction factor of M in an M-hop route.     

基于无线信道预测的自适应调制

该文研究了在平坦Rayleigh衰落信道下,借助于无线信道预测对一个基于非编码的MQAM自适应调制进行优化设计的问题。主要是通过采用无偏二阶估计的方法去研究一个已知的预测误差方差对最优化传输特性的影响。推导出基于预测的信噪比和预测误差方差的数据速率的最优解,以此对数据速率进行调整,使得频谱效率在误比特率的约束条件下达到最大化。通过仿真给出的数值解表明它能更好地将链路自适应地快速调整到信道的真实条件,提高整个系统的性能。     

TCP在无线衰落信道下的性能研究

本文在分析无线TCP原理的基础之上,讨论了各种提高无线链路TCP性能的方法,并对其优缺点进行了分析和总结.最后给出无线环境下TCP改进的基本原则,并初步探讨了进一步改进的方向.     

无线信道密钥生成技术综述

无线信道密钥生成技术作为物理层安全领域的关键技术之一,不需要密钥分发设施,而是利用无线信道的性质在合法通信双方之间共享相同的密钥,用于后续加密手段中,达到信息论意义上的安全.针对无线信道密钥生成技术,从评价标准、步骤、不同条件和场景下的无线信道密钥生成技术进行了综述,并对无线信道密钥生成的应用实现以及未来研究方向进行了...     

无线局域网信道特性的研究

无线信道是整个现代数字无线移动通信研究的基础,从电磁波传播方式、无线信道对传输信号的影响以及等效低通信道的时变冲激响应等几个方面对无线信道的特性进行了研究。结果表明,信号通过无线信道传播时,会产生各种形式的衰落,衰落对无线移动通信系统传输性能的影响是很大的,在实际中应设法消除。     

无线衰落信道的Markov模型研究

高速移动数据通信是目前通信的发展热点之一 ,而当数据传输速率较高时 ,无线信道中相邻数据分组之间的相关性不容忽视 ,更接近这种记忆信道的一种模型是Markov模型。本文研究了瑞利衰落信道的一阶Markov模型。结果表明 ,采用一阶的Markov信道模型已经足以得到令人满意的效果 ,没有必要采用复杂的高阶模型 ,而且利用该模型可以简化对高层协议性能的研究。     

复杂信道条件下WSDM的可行性分析及解决方法

针对无线信道统计复用(WSDM)技术,本文分析了其在复杂信道条件下的可行性。首先,基于无线信道的时变特性以及信道中存在的噪声,理论分析说明了信道混合矩阵的条件数是影响信号有效分离的关键因素,仿真结果表明,当信道混合矩阵的条件数大于门限值10时,信号分离效果较差,无法实现信道复用。其次,在复杂恶劣的信道环境中,为了实现信道复用,本文从增设接收天线角度给出了解决方法,同时,对于如何快速选取一组有效的天线,本文提出BHC算法进行快速有效选择,从而大大降低了信号分离算法的复杂度,使WSDM技术更加实用。     

Block-Differential Modulation Over Doubly Selective Wireless Fading Channels

Block-Differential Modulation Over Doubly Selective Wireless Fading Channels Differential encoding is known to simplify receiver implementation because it bypasses channel estimation. However, over rapidly fading wireless channels, extra transceiver modules are necessary to enable differential transmission. Relying on a basis-expansion model for time- and frequency-selective (doubly selective) channels, we derive such a generalized block-differential (BD) codex and prove that it achieves maximum Doppler and multipath diversity gains, while affording low-complexity maximum-likelihood decoding. We further show that existing BD systems over frequency-selective or time-selective channels follow as special cases of our novel system. Simulations using the widely accepted Jakes model corroborate our theoretical analysis.     

Stochastic Differential Equation Theory Applied to Wireless Channels

Modeling wireless channels is essential to wireless communication systems. An autoregressive (AR) process of order one for wireless channel has long been assumed, but without a rigorous mathematical/physical basis. In this paper, we derive a first-order stochastic AR model for a flat stationary wireless channel, which comes from stochastic differential equation (SDE) theory concerning the nature of multipath fading channels. The resulting AR model describes more of the origin of multipath fading channels than previous AR models, and it can efficiently model and generate Rayleigh-distributed stationary fading channels. The Markovian property of the AR model is inherited through the SDE approach.     

28 GHz MIMO无线信道特性分析与研究

基于室内视距(Line-of-Sight,LOS)和非视距(Non-Line-of-Sight,NLOS)无线信道测量数据,研究了28 GHz多输入多输出(Multiple-Input Multiple-Output,MIMO)信道参数和容量特性.具体地说,分析了莱斯K因子、时延扩展、出发角和到达角的角度扩展等信道参数,研究了MIMO信道容量及空间相关性对容量的影响.结果表明:莱斯K因子、时延扩展以及角度扩展值取决于测量环境及场景;LOS条件下时延扩展的累积分布函数(Cumulative Distribution Function,CDF)曲线与正态分布拟合优于NLOS条件下的数据;MIMO天线空间相关性越大信道容量越小.本文结果可为28 GHz无线通信系统设计提供有用信息.