Shaping the power spectrum of UWB radio-frequency signals

科学家对宇宙爆炸遗留的微波背景辐射提出质疑来源：教育部科技发展中心发布时间： 2006-09-12 点击数：225美国科学家在2006年9月1日的《Astrophysical Journal》上发表文章，表明一些本该在微波背景中存在阴影的宇宙空间中并未发现阴影，从而对宇宙微波背景辐射是表明宇宙起源于大爆炸的证据这一观点提出了质疑。

美国阿拉巴马大学（UAH）的科学家们应用最新精确的宇宙微波辐射测量技术研究，结果表明，临近银河系的很多星系团不存在阴影效应。

UAH研究小组首席科学家，物理学教授Richard Lieu博士通过应用NASA的威尔金森微波各向异性探针（WMAP）探测到的数据分析了宇宙中31个星系团在宇宙微波辐射中是否存在阴影。

“这些阴影早在多年前就被预言存在，”Lieu博士表示。

“它们是唯一直接确定我们到宇宙微波背景辐射原点距离的方法，如果你能在背景上观察到阴影，这表明辐射来源于星系团的后方，但是如果你无法在相应星系团的背景上观察到阴影，那一定有什么问题。

在我们所观察的31个星系团中，有的存在阴影，而有的却没有。

”如果传统宇宙大爆炸理论是准确的，并且我们所观测到的背景辐射确实是从宇宙最遥远的边际传播到地球的话，那么这些靠近我们所处银河系的发出X射线的巨大星系团理应全部在背景辐射中产生阴影。

观测的结果显示，大约有四分之一被预言存在阴影效应的星系团确实存在阴影，这和在整个天际随机观测到阴影的几率大致相当。

Lieu博士表示：“这说明或者微波背景并非来自于星系团后方，它并不能作为宇宙大爆炸理论的依据，或者发生了其它事情造成这一现象，其中一个可能是，这些大的星系团本身就是微波辐射源，它们通过自身的某一部分—也许是内部的结构，或者是外部的光环状构造来辐射出微波。

”Lieu博士又表示：“根据我们对已知的辐射源和星系团周围光环的研究，我们并不认为会有这样的辐射产生，很难想象数个不同的星系团会同时发射出和宇宙微波背景辐射频率，强度均一致的微波。

面向钻孔救援的UWB雷达回波信息处理关键问题研究进展随着现代社会的不断发展，人类对于应对各种突发事故的能力也越来越重要。

救援行动在紧急情况下的及时性与准确性必须得到保证，因此，对于面向钻孔救援的UWB（Ultra-Wideband，超宽带）雷达回波信息处理关键问题进行研究成为了当前学术界的热点。

本文将就该领域的研究进展进行探讨。

一、UWB雷达的原理与优势UWB雷达是一种利用非常窄的脉冲信号进行测量的雷达系统。

相较于传统雷达，UWB雷达具有以下优势：1. 分辨率高：UWB雷达能够提供极高的时间分辨率，可以准确测量目标的位置、速度等参数；2. 抗干扰：UWB雷达的宽带信号具有较强的穿透力，可以穿过建筑物、土壤等障碍物，减小环境对回波信号的影响；3. 多目标定位能力：由于UWB雷达的高时空分辨率，可以同时探测和定位多个目标。

二、UWB雷达在钻孔救援中的应用钻孔救援是指在灾难发生后，通过地下钻孔进行救援行动。

UWB 雷达由于其特殊的优势，在此过程中扮演着重要的角色：1. 地下目标探测：UWB雷达能够穿透地表，实时监测地下救援区域的情况，探测被困人员的位置，为救援人员提供重要信息；2. 钻孔导航：根据UWB雷达的回波信息，可以为钻孔操作提供导航指引，确保钻孔的准确性和有效性；3. 人员定位与监测：通过UWB雷达，可以实时监测被困人员的移动情况，提供精准的人员定位，保证救援行动的安全性。

三、面向钻孔救援的UWB雷达回波信息处理关键问题钻孔救援的UWB雷达回波信息处理面临以下几个关键问题：1. 回波信号的提取与处理：如何使用合适的算法从UWB雷达接收到的信号中提取目标的回波信号，并将其与杂波信号进行区分；2. 目标参数的估计与重构：根据提取到的回波信号，如何准确地估计目标的位置、速度等参数，并进行目标形状与结构的重构；3. 多目标分离与跟踪：在复杂的环境下，如何对多个目标的回波信号进行分离和跟踪，保证救援行动的准确性和及时性；4. 数据传输与可视化：如何将处理过的回波信息传输给救援人员，并进行直观、清晰的可视化，提供实时有效的救援指导。

超宽带雷达生命探测技术研究赵尤信1， 姚海飞1，2， 李佳慧3， 彭然1， 李璕1（1. 煤炭科学技术研究院有限公司 矿山智能通风事业部，北京　100013；2. 中国矿业大学（北京） 应急管理与安全工程学院，北京　100083；3. 华北科技学院 建筑工程学院，河北 廊坊　065201）摘要：超宽带（UWB ）雷达生命探测技术具有功耗低、穿透性好、保密性高等优点，有利于提高灾后受困人员的生存率。

系统总结了UWB 雷达生命探测技术的国内外研究进展及现状。

根据发射信号形式不同，将UWB 雷达生命探测技术分为连续波雷达生命探测技术和脉冲波雷达生命探测技术，分别介绍了2种探测技术的原理与应用优势。

基于连续波雷达生命探测技术和脉冲波雷达生命探测技术的各自特点，从探测信号发射、回波信号预处理、生命信号提取与分析3个角度，分析了UWB 雷达生命探测关键技术，总结了3种关键技术的研究现状。

对UWB 雷达生命探测技术的研究进行展望：突破生命探测仪收发机硬件性能，提升发射信号带宽，优化射频功率放大技术，以增大穿墙探测距离；综合利用多种特征提取方法和智能模式分类方法，以及人工智能、大数据、云计算等新一代信息技术，提高目标识别的精确度；研制基于多输入多输出雷达的人体目标辨识与定位装备和高精度分布式组网全极化UWB 雷达生命探测仪，提升探测结果维度。

关键词：灾后救援；生命探测；超宽带雷达探测；连续波雷达；脉冲波雷达；生命信号提取中图分类号：TD67 文献标志码：AResearch on ultra wideband radar life detection technologyZHAO Youxin 1, YAO Haifei 1,2, LI Jiahui 3, PENG Ran 1, LI Xun 1(1. Mine Intelligent Ventilation Division, CCTEG China Coal Research Institute, Beijing 100013, China ；2. School of Emergency Management and Safety Engineering, China University of Mining and Technology-Beijing,Beijing 100083, China ； 3. Architectural Engineering College, North China University of Science and Technology,Langfang 065201, China)Abstract : Ultra wideband (UWB) radar life detection technology has the advantages of low power consumption, good penetration, and high confidentiality. It is beneficial for improving the survival rate of trapped personnel after disasters. This paper systematically summarizes the research progress and current status of UWB radar life detection technology both domestically and internationally. According to the different forms of transmitted signals, UWB radar life detection technology is divided into continuous wave radar life detection technology and pulse wave radar life detection technology. The principles and application advantages of the two detection technologies are introduced respectively. Based on the respective features of continuous wave radar life detection technology and pulse wave radar life detection technology, this paper analyzes the key technologies of UWB radar life detection from three perspectives: detection signal transmission, echo signal preprocessing, and life signal extraction and analysis, and summarizes the research status of the three key technologies. The paper proposes prospects for the research on UWB radar life detection technology. The technology breaks through the收稿日期：2023-07-03；修回日期：2023-09-14；责任编辑：李明。

史上⾸次！美国加州⼤学河滨分校创造出室温下的电⼦液体导读近⽇，美国加州⼤学河滨分校的物理学家们通过强⼤的激光脉冲轰击超薄的半导体“三明治”，创造出了⾸个室温条件下的“电⼦液体”。

背景太赫兹波，是指频率范围在 100GHz 到 10THz 之间，波长介于微波和红外线之间的电磁波，对于⼈眼来说是不可见的。

（图⽚来源：维基百科）虽然微波与红外线的应⽤都已⾮常成熟，但是太赫兹波却是⼈类迄今为⽌了解最少、开发最少的⼀个波段，因此也被称为“太赫兹空⽩”。

然⽽，这⼀空⽩却蕴藏着巨⼤潜⼒。

太赫兹波具有穿透性强、安全性⾼、定向性好、带宽⾼、时间与空间分辨率⾼等技术优势。

因此，太赫兹技术可应⽤于成像、存储、通信、雷达、电⼦对抗、电磁武器、天⽂学、医学、安全检测、⽆损检测等多个领域。

太赫兹安检成像⽰意图（图⽚来源于⽹络）⽤太赫兹技术对⼀本合上的书中的书页内容进⾏成像（图⽚来源：Barmak Heshmat）太赫兹通信系统（图⽚来源：荷兰内梅亨⼤学）⽤太赫兹频段电磁脉冲切换计算机存储单元的存储状态（图⽚来源：莫斯科物理技术学院）然⽽，⽬前影响太赫兹技术发展的主要原因就是：缺少稳定有效的太赫兹发射源与探测器。

创新今天，笔者要为⼤家介绍⼀项新成果，它将为⾸个⾼效实⽤的太赫兹波⽣成与检测设备的开发开辟道路。

近⽇，美国加州⼤学河滨分校的物理学家们通过强⼤的激光脉冲轰击超薄的半导体“三明治”，创造出了⾸个室温条件下的“电⼦液体”。

这项研究有望带来应⽤于外太空通信、癌症检测、安全检测等领域的太赫兹设备。

在超薄材料组成的器件中，电⼦与空⽳凝结成类似于液态⽔的液滴。

（图⽚来源：加州⼤学河滨分校）2⽉4⽇，加州⼤学河滨分校的物理学家们将他们的成果在线发表在《⾃然光⼦学》期刊上。

加州⼤学河滨分校物理系副教授、量⼦材料光电⼦学实验室主任 Nathaniel Gabor 是科研团队的领头⼈。

论⽂的其他合著者还包括实验室成员 Trevor Arp 与 Dennis Pleskot，以及物理与天⽂学副教授 Vivek Aji。

2008年3月Journal on Communications March 2008 第29卷第3期通信学报V ol.29No.3基于认知无线电的超宽带系统中窄带干扰抑制技术周刘蕾1，朱洪波1，张乃通2（1. 南京邮电大学通信与信息工程学院，江苏南京210003；2.哈尔滨工业大学电子与信息技术研究院，黑龙江哈尔滨 150001）摘要：基于认知无线电的思想，在满足联邦通信委员会（FCC）频谱限制的基础上，提出一种能避开多个无线电台工作频段的UWB脉冲波形设计算法，从而达到抑制窄带干扰的目的。

仿真结果表明，提出的脉冲比通常使用的Scholtz脉冲的性能更优，抗干扰能力更强。

且此方法不需要在整个频段内降低UWB脉冲的功率谱密度，为提高UWB脉冲发射功率，增大UWB系统的通信距离，提供了一种灵活易行的方案。

关键词：认知超宽带无线电；频谱感知；脉冲波形设计；干扰抑制中图分类号：TN929.5 文献标识码：A 文章编号：1000-436X(2008)03-0135-06Narrowband interference suppression in UWB systembased on cognitive radio theoryZHOU Liu-lei1, ZHU Hong-bo1, ZHANG Nai-tong2(1. College of Telecommunications & Information Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210003, China;2. School of Electronic and Information Technology, Harbin Institute of Technology, Harbin 150001,China)Abstract: A novel adaptive UWB pulse shaping algorithm was presented for producing the expected spectral notches right in the frequency band occupied by the nearby wireless devices. Simulation results show that the proposed UWB waveform has a better single-link BER performance in AWGN channel, and stronger anti-jamming abilities than other conventional waveforms such as Scholtz’s monocycle, etc. Besides, the power spectral density of UWB pulse does not need to be reduced over the whole frequency band. Therefore, it is possible to expand the communication range of UWB systems by increasing the transmitted power of UWB pulse.Key words: cognitive ultra wideband; spectrum sensing; pulse waveform shaping; interference suppression1引言超宽带（UWB，ultra-wideband）技术正在成为无线通信领域的一个研究热点。

一种改进的高斯-拉普拉斯金字塔互感器红外图像增强算法范晓狄;万文略;郑银【期刊名称】《电力科技与环保》【年(卷),期】2024(40)2【摘要】互感器为电力系统中不可或缺的重要设备之一。

然而由于采集到互感器红外图像受到不同的强噪声以及设备特性等因素影响,可能导致互感器无法正常识别,因此,互感器图像的清晰程度尤为重要。

采用不同算法对图像进行灰度化对比试验,根据图像效果,选择加权平均法对互感器红外图像进行灰度化;针对红外图像强噪声、模糊等问题,通过采用均值、高斯、中值以及双边滤波等不同算法对互感器红外图像进行去噪对比实验,比选出峰值信噪比(peak signal to noise ratio,PSNR)值较高的双边滤波作为互感器去噪处理算法,在此基础上,为提高图像对比度,提出了一种改进的高斯-拉普拉斯金字塔图像增强算法,并通过PyCharm实验平台进行直方图、对比度(Contrast)评价指标的对照实验。

实验结果表明:电流互感器Contrast 值为100.6886,比原图像增强算法Contrast值提高了19.9087;电压互感器Contrast值为86.1501,比原图像增强算法Contrast值提高了21.8088,验证了该方法的有效性。

【总页数】9页(P198-206)【作者】范晓狄;万文略;郑银【作者单位】重庆理工大学电气与电子工程学院;贵州电网有限责任公司遵义供电局【正文语种】中文【中图分类】TK011【相关文献】1.一种改进的红外图像增强算法及其在FPGA上的实现2.一种改进的红外图像增强算法3.基于高斯金字塔和拉普拉斯金字塔融合的图像对比度增强算法研究4.基于高斯-拉普拉斯金字塔的DR图像增强改进算法研究5.基于高斯-拉普拉斯滤波的增强局部对比度红外小目标检测算法因版权原因，仅展示原文概要，查看原文内容请购买。

uwb定位物理原理英文回答：UWB (Ultra-Wideband) positioning is a technology that uses radio waves to determine the precise location of an object or person. It operates by transmitting short-duration, low-power pulses across a wide frequency range. These pulses can penetrate obstacles such as walls and furniture and reflect off objects, allowing for accurate positioning even in complex indoor environments.The physical principle behind UWB positioning is based on the time of flight (ToF) measurement. By measuring the time it takes for the UWB signal to travel from the transmitter to the receiver, the distance between the two can be calculated. This is done by comparing the time stamp of the transmitted signal with the time stamp of the received signal. The difference in time between the two timestamps directly corresponds to the distance traveled by the signal.To improve the accuracy of UWB positioning, multiple antennas are often used. By using multiple antennas, the system can determine the angle of arrival (AoA) of the signal, which further enhances the positioning accuracy. This is similar to how our ears help us determine the direction from which a sound is coming.UWB positioning can be used in various applications, such as asset tracking, indoor navigation, and even in healthcare for monitoring patients. For example, in a warehouse, UWB can be used to track the location ofinventory in real-time, making it easier to locate specific items. In a hospital, UWB can be used to track the movement of patients and staff, ensuring their safety and providing efficient care.中文回答：UWB（超宽带）定位是一种利用无线电波来确定物体或人的精确位置的技术。

uwb脉冲重复频率
脉冲重复频率（PRF）是指雷达系统中发射脉冲的频率。

对于超宽带（UWB）雷达系统来说，脉冲重复频率通常是非常高的，可以达到几千赫兹甚至更高。

这种高的脉冲重复频率可以提供更高的分辨率和目标探测能力。

从技术角度来看，UWB雷达系统的脉冲重复频率取决于系统设计和应用需求。

通常情况下，UWB雷达系统会以毫秒甚至微秒级的时间间隔发射脉冲，以实现对目标的高分辨率探测和精准测距。

此外，脉冲重复频率也受到雷达系统工作频率、脉冲宽度、目标距离和速度等因素的影响。

在设计UWB雷达系统时，工程师需要综合考虑这些因素，以确定最佳的脉冲重复频率，以满足特定应用场景下的性能需求。

除了技术层面，从应用角度来看，高脉冲重复频率可以提高雷达系统对目标的探测精度和抗干扰能力。

在无线通信、地质勘探、医疗影像等领域，UWB雷达系统的高脉冲重复频率也可以实现更精准的测量和成像。

总的来说，UWB雷达系统的脉冲重复频率是一个重要的参数，它直接影响着雷达系统的性能和应用效果。

通过合理设计和选择脉冲重复频率，可以实现更高的探测精度和应用价值。

Ultra-wideband radio technology:overview and future researchWalter Hirt *IBM Research,Zurich Research Laboratory,CH-8803Ru¨schlikon,Switzerland Received 26February 2002;accepted 26February 2002AbstractThe emergence of commercial wireless devices based on ultra-wideband radio technology (UWB-RT)is widely awaited and anticipated.UWB-RT is not only applicable to communications,imaging and ranging,it also promises to alleviate the problem of increasingly scarce spectrum resources while enabling new wireless applications and business opportunities.These prospects have caught the early attention of the technology-providing wireless industry and,more recently,that of the radio regulatory authorities.Moreover,the technical challenges and problems to be solved when conceiving and deploying UWB radio systems have spurred a growing interest within the wireless research community.This paper discusses the key characteristics and capabilities of UWB-RT and indicates where one expects to exploit them in applications.A brief overview of the current status of UWB-RT is provided and directions for future research are discussed.It is proposed to explore and develop this new technology in the context of ‘wireless systems beyond 3G’and within a forum of sufficient international breadth to facilitate regulatory and standardization frameworks with global support.q 2002Elsevier Science B.V.All rights reserved.Keywords:Ultra-wideband radio technology;Wireless systems;Data communication;UWB;UWB-RT1.IntroductionThe emerging modern version of ultra-wideband radio technology (UWB-RT)is built on a long history of technological advancements based on the underlying principles and characteristics of wideband radio signals;a comprehensive account of the historical developments and principles of UWB-RT can be found in references [1,2].1Given the potential of UWB-RT for covert communication and ranging systems as well as the lack of appropriate regulatory guidelines regarding spectrum usage,the development and use of systems based on UWB-RT have thus far been mainly the privilege of US military and government agencies.However,the recent initiative taken by the Federal Communications Com-mission (FCC)in the US to regulate the legal use of UWB radio devices have not only induced growing commercialization activities but also similar regulatory and research efforts in other geographies,notably inEurope [3–5].2For example,CEPT study groups are currently investigating how to regulate the commercial use of UWB radio devices within the spectrum range 1–40GHz such that they can coexist with other radio services.However,neither the FCC nor the CEPT will ultimately provide the functional standards for UWB radio systems.This important task can only be tackled by the pertinent industry and appropriate standard bodies after the necessary regulatory framework has been laid and based on—preferably broadly supported—market needs and technical requirements.The recent regulatory efforts and the significant techno-logical advances made by several US-based pioneering developers of UWB-RT have spurred a growing interest within the wireless industry as well as within academicand*Tel.:þ41-1-724-8477;fax:þ41-1-724-8955.E-mail address:hir@ (W.Hirt).1Lists of patents,papers and books related to UWB-RT at /CDROM/Welcome.html .2FCC/Part 15permits operation of certain radio frequency devices without a license or need for frequency coordination;it also seeks to ensure a low probability that unlicensed devices will cause harmful interference to other spectrum users.Part 15.109rules subject unintentional radiators (devices not intentionally transmitting a telecommunication signal)to a set of limits.For example,for frequencies .960MHz the electrical field strength at 3m distance from the source is not to exceed 500m V/m (rms)when measured in a 1MHz bandwidth.Specific limits for UWB devices are currently being prepared and on February 14,2002,the FCC announced a First Report and Order to permit operation of certain types of UWB devices (/Bureaus/Engineering_Technology/News_Releases/2002/nret0203.html).other research institutions.The mainly classified nature of the early development efforts and the lack of legal spectrum regulations and limits explain the fact that widespread commercial interest in UWB-RT emerges only now.In this respect,the deployment of UWB-RT appears to follow a process similar to that observed during the commercializa-tion of classical spread-spectrum communication systems [6].3Thus,given the present status of UWB-RT it appears appropriate to call for the inclusion of UWB-RT on the agenda of any forum contemplating the future of wireless systems,particularly those considering‘wireless systems beyond3G’.We consider the latter notion to include (infrastructure-based)wide area cellular systems as well as local(ad hoc)networks for specific environments,e.g.self-organized network topologies and supporting systems capable of accessing cellular networks.A suitable podium for a comprehensive treatment of the technical issues associated with designing these next-generation systems is provided by the recently established Wireless World Research Forum(WWRF).4The WWRF aims to identify and promote research areas as well as technical and societal trends for mobile and wireless systems for the‘wireless world’that could become operational within a decade’s time.The WWRF’s list of proposed research tasks covers the multiple technical and operational aspects of future wireless systems,including the exploration of systems based on UWB-RT[7].Although the technological basis of UWB-RT is apparently well understood and developed today,it is generally recognized that efficient realization and widespread commercial deployment and application of this new technology still hinges on several significant regulatory and technical challenges.These problems must be resolved before the very promising benefits of UWB-RT can possibly be consumed in practice.Thus,it appears both timely and sensible to attempt this by dealing with the corresponding regulatory and technical issues as well as standardization questions on a global scale.Proponents of UWB-RT promise a broad array of new or improved(short-range)wireless devices and radio services that could provide enormous progress in the areas of public safety as well as for home and business applications.5It has been proposed that the FCC’s Part15rules be amended such that the imposed power limits(maximal electricalfield strength at a defined distance)are also applicable to intentional emissions from an UWB radio device[3].2It is claimed that,ideally,UWB devices could operate over the entire spectrum,including the bands reserved for other radio services without degrading their quality of operation. Although this assertion has been maintained by only certain proponents,the very question concerning the degree to which UWB devices can potentially cause harmful inter-ference in the receivers of other radio services—notably the Global Positioning System(GPS)—has become the primary focus of regulatory procedures[8].The resolution of these and other interference issues(e.g.cumulative impact of many UWB radio sources)require complex technical investigations and assessments;in addition,it is equally challenging to reconcile the various competing business interests with legitimate security concerns.For the purpose of this paper,we shall assume that the regulatory issues will eventually be resolved—preferably on a global scale.The FCC has proposed a definition of UWB radio signals similar to that of the OSD/DARPA UWB radar review panel [3],i.e.that the fractional bandwidth—the ratio between the signal’s bandwidth and center frequency—be greater than 0.25(25%)or the signal occupy at least1.5GHz of the spectrum.The bandwidth is measured at the upper and lower cutoff points(210dB),f H and f L,respectively,and the center frequency,f C,is defined as the average of these cutoff points,i.e.f C¼ðf Hþf LÞ=2:It is an open issue whether this definition should be applied only to UWB devices emitting pulsed signals of low duty cycle,where the bandwidth is inversely related to the width of the pulses. Clearly,other technical approaches can be employed to produce UWB radio signals,and it will be important to include these alternative methods in any future investi-gations of UWB-RT[9,10].However,for the sake of brevity and objectivity,this paper focuses on UWB signals as characterized earlier and in Section2,where potential applications are discussed.Section3gives a brief overview of the status of UWB-RT and indicates directions of possible future research,emphasizing the desirability of a regulatory and standardization framework with global support;conclusions are drawn in Section4.2.Key characteristics and applications of UWB-RTThis paper deals with UWB devices that transmit sequences of information carrying pulses of very short duration(e.g.0.1–2ns).These pulses are widely spaced such that the waveform’s duty cycle is up to several orders less than unity(e.g.1/10–1/1000).There are two principal methods to generate pulsed UWB signals.With thefirst method,the pulses are emitted as so-called baseband pulses, which in their purest form require spectra starting at very3Further notice of inquiry and notice of proposed rulemaking(in theMatter of Authorization of Spread Spectrum and Other WidebandEmissions not presently provided for in the FCC Rules and Regulations),Docket No.81-413,Federal Communications Commission,Release-Number:FCC84-169,May21,1984;Adopted April26,1984.4Wireless World Research Forum(WWRF)at http://www..5Partial list of companies and organizations actively developing orpromoting UWB-RT(alphabetical order).(a)Aetherwire and Location,Inc.():localizers;(b)Lawrence Livermore NationalLaboratory():micro-power radar;(c)MultispectralSolutions,Inc.():communication,radar,location;(d)Pulse,LINK,Inc.():wirelesshome networking;(e)Time Domain,Corp.(http://www.time-domain.com):communication,radar,location;(f)UWB Working Group(UWBWG;):industry consortium;(g)XtremeSpectrum,Inc.():communication.W.Hirt/Computer Communications26(2003)46–5247low frequency(nearly DC;e.g.(e)in footnote5).The second method emits envelope-shaped‘pulses’in the form of several sinusoidal cycles(e.g.(c)in footnote5).In systems that use thefirst approach,control of the signal’s center frequency,f C,and large emission bandwidth,f H2f L, is intimately coupled to the actual shape of the single pulse emitted from the antenna.The second approach offers a more independent adjustment of the signal’s center frequency and—typically somewhat smaller—bandwidth. Furthermore,whereas the antenna is generally a more important spectral-shaping element in a system based on the first approach,the higher frequencies used by the second method tend to reduce the signal’s ability to penetrate materials.In any case,independent of the method of signal generation,the following are some of the benefits and characteristics claimed for practical systems based on UWB-RT[3]:5†Extremely low power spectral density(PSD).Average power levels in the order of millionths of a Watt(m W) and excessive signal bandwidth yield power spectral densities in the order of several tens of nW/MHz.†Spectrum reuse.Potential reuse of scarce spectrum resources by overlaying UWB emissions of extremely low power spectral densities on already assigned spectral bands.†Robust performance under multipath conditions.The short pulses potentially allow differentially delayed multipath components to be distinguished at the receiver with the benefit that a reduced fading margin may be applied in a system’s link budget analysis.†Multiuser communication.The application of sequence-coded access methods to pulsed and inherently low-duty-cycle UWB signals could enable very densely populated multiuser systems with high immunity to interference.†High-resolution position location and tracking or radar sensing.The large signal bandwidth yields a distance resolution between communicating devices or a radar-sensing accuracy within a few centimeters.The inherently good receiver robustness in environments subject to multipath propagation and the fact that pulsed wideband signals are ideal for ranging applications enable one to conceive mobile short-range radio devices for the indoor environment that support(high-performance)digital data transmission as well as precise location determination and tracking.Therefore,it appears realistic to envisage certain future short-range wireless devices featuring scal-able data communication combined with precise location tracking of mobile terminals.Achieving location awareness in ad hoc networks as required in Ref.[11]could be greatly facilitated by the availability of wireless devices offering precise location-tracking functions that support efficient multihop routing mechanisms.The ultimate benefits that UWB-RT could bring to ad hoc networking stem from the ability to couple location tracking with(high-performance)data transmission.As pulse-based UWB devices typically operate with a single transmitted pulse waveform in all modes,they offer a high degree offlexibility in terms of data rate selection and transmission range.The physical(PHY) and medium access control(MAC)layers of UWB radio devices are thus particularly suited for implementations based on software-defined radio principles.Changes in data rate and/or transmission range can be made,for example,by simply changing the transmitter’s(average)pulse repetition frequency(PRF),possibly in combination with adjusting the number of information bits carried by a single pulse.This inherentflexibility of UWB radio devices is illustrated in Fig.1,which shows results computed for an ideal free-space channel and a receiver that is subject only to additive white Gaussian noise.Thefigure compares UWB systems using antipodal signaling(APS)combined with pulse position modulation(PPM)with direct-sequence spread-spectrum (DSSS)systems using binary phase shift keying(BPSK). Clearly,to achieve the same data rate,BPSK-DSSS tends to require chip rates that are significantly higher than the PRF of a corresponding APS/PPM UWB system.6UWB-RT potentially enables implementation of wireless platforms that support a variety of operating modes including data transmission,precision positioning and tracking,radar sensing or even a combination thereof. Thus,a wide range of novel wireless applications become possible,such as:†Wireless personal area networks(WPANs)and wireless local area networks(WLANs)with integrated position location and tracking capabilities,†multiuser ad hoc(self-organized)networking with location-aware routing support,†high-rate wireless home networking(multimedia access and distribution;wireless connection of displays),†alternate high-rate access into cellular network infra-structure(‘hot spot’scenario),†personnel and asset tracking(RF tagging),particularly in indoor environments,†public safety applications,including motion detection in disaster situations,†collision avoidance and proximity sensors for motor vehicles.Expected key applications for UWB radio devices are data communication and position location and tracking, particularly in the areas of short-range systems(WPAN, WLAN)and ad hoc networking.The home and single-office/small business(SOHO)environments will presumably become primary target markets for systems that support link 6Details on the system model are given in Fig.1,where the average power limit of0.3mW is the result of the assumed4GHz bandwidth and the FCC/Part15.109limit on the emissions of unintentional radiators.For frequencies.960MHz this limit is500m V/m at3m distance,measured in a1MHz bandwidth(PSD at the source:241.3dBm/MHz;see Ref.[3]and footnote2).W.Hirt/Computer Communications26(2003)46–52 48distances of between 10and 100m.UWB systems covering much larger distances will mainly be reserved for exempt systems operated by military and government entities.For example,field tests of long-range UWB surface wave transceivers designed for the US Navy for non-line-of-sight video transmission over up to 60nautical miles have been reported ((c)in footnote 5).3.Current state of UWB-RT and future research directionsThe US-based developers of UWB-RT have already achieved a rather advanced level in the design of PHY functions and,to a somewhat lesser degree,the MAC and higher-layer functions required to support the application scenarios described earlier.5In fact,it must be acknowl-edged that a few pioneering individuals and companies have collectively generated an impressive amount of intellectual property and complete concept or prototype systems that have proved to a reasonable degree the practical feasibility and benefits of UWB-RT [1,2].1,5However,a large gapexists between the current level of the base technology and the ultimately desirable state of widely available and highly integrated,cost/power efficient,standardized systems and applications,e.g.for integration into cell phones,personal digital assistants,laptops,and other mobile devices.A major task will be to achieve user-friendly coexistence and cooperation (e.g.handover)between existing and new systems alike,the WWRF is striving to provide an appropriate podium particularly in this area.43.1.System level issuesShort-range wireless systems based on narrow-band carrier modulation are often inadequate or incapable of providing sufficiently accurate information about a mobile terminal’s location to support location-aware applications or routing;on the other hand,there is a growing need for these capabilities [11–14].Fig.2is a rather speculative view of how devices based on UWB-RT can potentially outperform conventional radio devices both in achievable spatial capacity—measured in terms of aggregate data rate per unit area or (Kb/s)/m 2[15]—and locationprecision.parison of UWB and DSSS radio systems in terms of required average power vs.chip (pulse)rate to maintain a bit error rate (BER)of P b <1025over the free-space channel (range r ¼250m)in the presence of additive white Gaussian noise.With M -ary modulation,M ¼2m ;m ¼1;2;3;…;a pulse represents m bits,where the first bit encodes the polarity of the pulse.When m $2,the remaining m 21bits define one of L ¼M =2¼2m 21possible pulse positions within a chip interval (T C ).For M ¼2ðL ¼1Þthis hybrid modulation reduces to simple antipodal signaling (APS),whereas M $4(L $2)results in a combination of APS and L -ary PPM (APS/PPM).The transmitter may repeat each pulse chip N times to achieve an (ideal)signal processing gain G P ¼N at the receiver.The bit rate over the channel is thus R b ¼m =T S ¼ðm =N ÞR C ;N $1;where R C is the chip (pulse)rate,also called the PRF.There is a choice of the parameters m ,N ,and R C to achieve some given data rate,R b .For example,the four systems with parameters N l m ¼1l 6;1l 1;10l 6;and 10l 1achieve R b ¼10MB =s with R C ¼10=6;10,100/6,and 100MC/s,respectively.Also shown are the results for binary phase-shift keyed (BPSK),direct-sequence spread spectrum (DSSS)systems with processing gains G P ¼N ¼100ð20dB Þand 1000(30dB),respectively.BPSK-DSSS systems are modeled by letting the pulse width be equal to the chip duration ðt P ¼T C Þ;setting the carrier frequency f carrier ðDSSS Þ¼f peak ðUWB Þ;and assuming a spreading sequence of length N .Note that the BPSK-DSSS system with 20dB processing gain ðN ¼100Þrequires a chip rate of 1GC/s (!)to achieve a data rate of 10MB/s.W.Hirt /Computer Communications 26(2003)46–5249Whereas ‘spatial capacity’can be a sensible metric to compare different systems,it should be noted that this measure is relatively sensitive to changes in the assumed coverage area,e.g.the spatial capacity quadruples when the coverage radius is halved.Thus,it remains an objective of ongoing as well as future research to determine the practical limits of achievable spatial capacity.Many open questions exist in the areas of system scalability (large number of UWB devices operating in a given area),mutual interference between similar and dissimilar devices,required and achievable level of quality of service (QoS),to name a few.Concerning localization,it will be necessary to determine the actually required level of accuracy for any given application and whether this level of quality can be maintained under varying channel and network load conditions.Direction estimation methods may be worth developing to enhance the basic distance measurement methods;ultimately,effective methods for two-and three-dimensional location tracking capabilities need to be developed.In ad hoc networking,the role and efficiency of the MAC function in a highly loaded network has to be assessed.Even if UWB-RT promises to deal well with the basic requirements of data communication and location tracking,practical and workable solutions that combine the benefits of both modes of operation have to be defined and evaluated.For example,aiming at high-rate data in combination with precision location capabilities may not always be the most sensible approach to pursue.Instead,it may be more practical to trade range for performance and thus support location-aware applications over much greater distances at a reduced location precision and in combination with low-rate data transmission.3.2.Deployment and user scenariosThe choices for possible deployment and user scenarios when considering UWB systems for the enterprise and the consumer markets are abundant.It is thus imperative to consider carefully the all-important scenarios from which the key system requirements should be derived.In particular,the requirements relevant to the PHY and MAC layer functions must be clearly identified,e.g.link range,data rate,location precision,battery burden,level of adaptability to channel conditions,multiuser scalability,to name a few.Following this path,relevant research topics appear to be (i)definition of typical deployment environ-ments (may be limited by regulatory restrictions),(ii)identification of realistic user and application scenarios where the use of UWB-RT appears to be a definite asset compared to conventional solutions (e.g.data mode combined with position location and tracking)and (iii)deduction of the technical PHY and MAC requirements that can enable the selected scenarios.3.3.UWB radio channel and physical layerA variety of modulation and sequence coding techniques as well as corresponding methods for signal detection and processing have been proposed or used in experimental versions of UWB radio devices.5Naturally,not all of these techniques are equally applicable under different practical operating conditions.It is necessary to assess the merits and drawbacks of the various known as well as new approaches by subjecting them to different usage scenarios and propagation environments.For example,it is not clear whether methods that average a large number of pulsestoFig.2.A speculative comparison of UWB radio devices and conventional short-range wireless systems in terms of achievable spatial capacity,measured as the maximal aggregate data rate of N active devices per unit area (Kb/s)/m 2,maximal transmission range and average location error [12–14].The notation ‘IEEE802.11b (3£11Mb/s)’means that three ðN ¼3ÞIEEE802.11b devices communicate simultaneously with three different access points,each at a data rate of 11Mb/s over a distance of 100m.Although rarely possible in practice,it is assumed that the specified maximal ranges and data rates are achieved simultaneously by all devices.Each of the various options for UWB-RT assumes that N active devices transmit at the indicated data rate by using some multiple access scheme (e.g.N ¼6;data rate:50Mb/s,range:10m,[15]).W.Hirt /Computer Communications 26(2003)46–5250recover a bit of information will demonstrate sufficiently robust performance in situations of high relative velocity between transmitter and receiver platforms.In addition, although UWB systems feature a certain inherent robustness to multipath effects,they are not entirely immune to them. For example,in situations where there is an excessive ratio of link distance(d)to antenna height,the time difference between the line-of-sight and the reflected signal com-ponents can be substantially shorter than the duration of a pulse.This may result in signal losses according to the familiar(d/d0)n attenuation model with n<4;where d0is the reference distance.Extreme signal propagation situ-ations can also be observed in indoor environments where the numerous multipath components associated with each transmitted pulse result in propagation delay profiles that last tens and even hundreds of nanoseconds[16].The potential intersymbol interference caused by these not uncommon situations will severely limit the maximally achievable data rate of a system(small PRF)unless an effective method can be found that mitigates these effects.A further aspect not entirely understood today relates to the deteriorating effects of in-band interference in UWB receivers that originate from other radio signals, be they in near-or far-field proximity.The problem of nearby interference is not only one of academic interest, considering that UWB devices might be integrated into mobile platforms that make simultaneous use of a variety of other radios.Thus,the very advantage that UWB devices emit an extremely low PSD—as a result of the excessive signal bandwidth—potentially yields increased susceptibility to noise and interference in the UWB receiver.Similar effects may occur in areas with a large concentration of active UWB devices;this raises questions concerning harmful compound effects of multipath propagation and cross-device interference phenomena.Further topics related to UWB channel and PHY issues offering research potential are:†issues related to implementing the PHY of UWB radio devices,e.g.—signal propagation,channel modeling and esti-mation,—adaptive modulation methods and receiver archi-tectures,—dynamic rate adaptation in response to channel quality variations,—achievable single-user data rate and aggregate data rate per unit area(spatial capacity),—channel coding and error correction strategies,†characteristics of UWB antennas(e.g.in proximity of objects and the human body),†coexistence and integration of UWB radio devices with existing(short-range)wireless systems.3.4.Packet routing in ad hoc networks and medium access controlA key application for UWB devices is expected to be in the area of ad hoc and self-organized wireless networks based on multiuser communication and multihop routing capabilities[11].In this area,subjects that offer significant research potential are(i)definition of MAC functions to support ad hoc network architectures(e.g.location-based routing),(ii)influence of cooperative routing and associated protocols on the network load,(iii)investigation of multiple access schemes for UWB radio devices such as code division multiple access(CDMA)and(iv)methods to determine location information(e.g.MAC frame that supports applications using data communication and ran-ging).3.5.Regulation and standardization of UWB-RTLike any other wireless technology with a potential for widespread deployment,the eventual success of UWB-RT will depend greatly on the availability of suitable and timely PHY and MAC standards—in compliance with the rules imposed by regulatory authorities and backed by a represen-tative part of the industry.Thus,broadly supported PHY and MAC standards will be a prerequisite for successful deployment.Fig.3illustrates that the regulatory framework and standardized PHY and MAC functions are also key building blocks for systems based on UWB-RT.Although one can argue over the degree to which the need for standardization depends on the intended application,the currently observed emergence of UWB-RT should be considered a unique opportunity to develop and standardize PHY and MAC functions suitable for short-range wireless systems that combine data communication and positioning capabilities.In fact, these combined capabilities are poorly supported by conventional narrow-band systems,which certain standardization efforts are already trying to improve[14, 17].For example,the IEEE P802.15ALT PHYStudy Fig.3.The regulatory framework and(broadly supported)standardized PHY and MAC functions will also be the key building blocks of a system based on UWB-RT.W.Hirt/Computer Communications26(2003)46–5251。