NETEX UWB test results

The goal of the Defense Advanced Research Projects Agency's (DARPA) Networking in Extreme Environments (NETEX) program is to create a wireless networking technology for the military user that enables robust connectivity in harsh environments and support its integration into new and emerging sensor and communication systems. Phase 1, resulted in a thorough understanding of the effects of ultra wide band (UWB) system operation on existing military spectrum users based on modeling, simulation, and measurements. In order to accomplish this task, the DARPA Advanced Technology Office (ATO) procured a set of UWB emitters and broadband antennas to use as interference sources and contracted with the Naval Air Warfare Center Aircraft Division (NAWC AD) Electromagnetic Environmental Effects (E/sup 3/) Division to provide candidate victim systems from the existing (legacy) US naval aircraft and shipboard inventory for testing. Testing was conducted on seventeen legacy systems during October 2002 through March 2003. The purpose of this paper is to provide a brief overview of the results of these tests. This paper will provide a brief discussion of the UWB emissions as described by the US Federal Communications Commission (FCC) and describe the generic UWB emitter used for these tests. It will then provide a discussion of the results as they apply to the purpose of the NETEX program.     

RFI suppression for ultra wideband radar

An estimate-and-subtract algorithm is presented for the real-time digital suppression of radio frequency interference (RFI) in ultrawideband (UWB) synthetic aperture radar (SAR) systems used for foliage- and ground-penetrating imaging. The algorithm separately processes fixed- and variable-frequency interferers. Excision of estimated targets greatly reduces bias in RFI estimates, thereby reducing target energy loss and sidelobe levels in SAR imagery. Performance is demonstrated on data collected with the Army Research Laboratory's UWB rail SAR.     

Short-distance ultra wideband radars

The possibility of ultrawideband (UWB) radar usage in various fields for remote measuring the object's motion at short distance is considered. Application of UWB radar in medicine for remote measuring of patient's heart activity and respiration is shown. The measuring method is described and practical results of tests are cited. The opportunity of radar application in other areas is described.     

UWB radar for patient monitoring

During the last few years the Moscow Aviation Institute (Russia) and the Industrial Technology Research Institute (Taiwan) have worked jointly on the development of ultrawideband (UWB) medical radars for remote and contactiess monitoring of patients in hospitals. Preliminary results of these works were published in [1]. As of the present, several radars have been produced and tested in real conditions in hospitals in Russia and Taiwan. Some results of these tests are given.     

The UWB (impulse) radar caper or `punishment of the innocent'

The author describes his experiences chairing a panel to review ultrawideband (UWB), or impulse, radar. The panel's report pointed out the fallacies in the proposals of the extremists pushing the rapid development of such a radar, noted the very good work of the real contributors, and made several recommendations. Pressure from the extremists led to an investigation by the Inspector General of the US Department of Defense of the panel and its members. That investigation found no basis for the allegations and concluded that the panel's report was credible and the panel balanced     

Doppler visibility of coherent ultrawideband random noise radar systems

Random noise radar has recently been used in a variety of imaging and surveillance applications. These systems can be made phase coherent using the technique of heterodyne correlation. Phase coherence has been exploited to measure Doppler and thereby the velocity of moving targets. The Doppler visibility, i.e., the ability to extract Doppler information over the inherent clutter spectra, is constrained by system parameters, especially the phase noise generated by microwave components. Our paper proposes a new phase noise model for the heterodyne mixer as applicable for ultrawideband (UWB) random noise radar and for the local oscillator in the time domain. The Doppler spectra are simulated by including phase noise contamination effects and compared with our previous experimental results. A genetic algorithm (GA) optimization routine is applied to synthesize the effects of a variety of parameter combinations to derive a suitable empirical formula for estimating the Doppler visibility in dB. According to the phase noise analysis and the simulation results, the Doppler visibility of UWB random noise radar depends primarily on the following parameters: 1) the local oscillator (LO) drive level of the receiver heterodyne mixer, 2) the saturation current in the receiver heterodyne mixer, 3) the bandwidth of the transmit noise source, and 4) the target velocity. Other parameters such as the carrier frequency of the receiver LO and the loaded quality factor of the LO have a small effect over the range of applicability of the model and are therefore neglected in the model formulation. The Doppler visibility curves generated from this formula match the simulation results very well over the applicable parameter range within 1 dB. Our model may therefore be used to quickly estimate the Doppler visibility of random UWB noise radars for trade-off analysis     

Multipath and ground clutter analysis for a UWB noise radar

An ultrawideband (UWB) random-noise radar operating in the 1-2 GHz frequency band has been developed and field-tested up to a 200 m range at the Environmental Remote Sensing Laboratory (ERSL) of the University of Nebraska. A unique heterodyne correlation technique based on a delayed transmitted waveform using a photonic delay line has been used to inject coherence within this system. The performance of this radar in the presence of ground reflections is investigated analytically and experimentally, and the mitigating effects of UWB waveform on multipath-induced interference are analyzed. In addition, the ground clutter statistics, in a look-down mode, are theoretically established and experimentally verified. The performance of this radar in detecting clutter embedded targets with small radar cross section (RCS) is also experimentally examined.     

Thinned spectrum ultrawideband waveforms using stepped-frequencypolyphase codes

An ultrawideband (UWB) radar can interfere with external RF sources because of the mutual occupancy of the same frequency band. A stepped-frequency polyphase code (SFPC) waveform is proposed as a generic UWB waveform whose interference with the external RF sources is significantly reduced. The subpulses of the individual stepped-frequency (SF) pulses are phase coded using small phase perturbations. This results in a waveform which places nulls at the frequency locations of the external RF sources. Because the phase perturbations are small, a mismatched filter which uses the unperturbed pulses (no phase modulation) as a reference signal results in a simple receiver design and a small mismatch loss on receive. Furthermore, the proposed methodology also has application to narrowband or wideband radars     

FOPEN SAR imaging using UWB step-frequency and random noisewaveforms

The detection and identification of targets obscured by foliage have been topics of great interest. Several synthetic aperture radar (SAR) experiments have demonstrated promising images of terrain and man-made objects obscured by dense foliage, by using either linear frequency modulation (LFM) or step-frequency waveforms. We present here the methodology and results of a comparative study on foliage penetration (FOPEN) SAR imaging using ultrawideband (UWB) step-frequency and random noise waveforms. A statistical-physical foliage transmission model is developed for simulation applications. The foliage obscuring pattern is analyzed by means of the technique of paired echoes. The results of the comparative study demonstrates the ability of a UHF band UWB random noise radar to be used as a FOPEN SAR. Advantages of the random noise radar system include covert detection and immunity to radio frequency interference (RFI)     

Receiver operating characteristics for the coherent UWB randomnoise radar

An ultrawideband (UWB) random-noise radar operating in the 1-2 GHz frequency band has been developed and held-tested at a 200 m range at the University of Nebraska. A unique heterodyne correlation technique based on a delayed transmitted waveform using a photonic delay line has been used to inject coherence within this system. The performance of this radar, assuming a point target, has been investigated from a statistical point of view by developing the theoretical basis for the system's receiver operating characteristics (ROC). Explicit analytical expressions for the joint probability density function (pdf) of the in-phase (I) and quadrature (Q) components of the receiver output have been derived under the assumption that the input signals are partially correlated Gaussian processes. The pdf and the complementary cumulative distribution function (cdf) for the envelope of the receiver output are also derived. These expressions are used to relate the probability of detection (P_d) to the probability of false alarm (P_f ) for different numbers of integrated samples, and the results are analyzed     

P-3 ultra-wideband SAR: description and examples

Under the Advanced Research Projects Agency (ARPA)/ASTO sponsorship, through a contract from the Naval Air Warfare Center (NAWC), the Environmental Research Institute of Michigan (ERIM) has developed an ultrawideband (UWB) very high frequency (VHF)/ultrahigh frequency (UHF) fully polarimetric airborne synthetic aperture radar (SAR) for studying the detection of foliage-obscured objects. The radar is installed in the NAWC P-3 testbed aircraft and takes advantage of existing ERIM-built multimode, fully-polarimetric X/L/C-band SAR hardware. This paper describes the radar and presents some examples of its capabilities including polarimetric imagery and two-pass interferometric surface height estimates     

脉冲超宽带信号测量性能分析

超宽带技术是一项新兴的无线通信技术,具有极其广阔的发展前景,但目前仅用于室内短距离通信,少见用于航天测控系统。为了将超宽带技术应用于测控系统中,以模糊函数为工具,对脉冲超宽带信号的测量性能进行分析。首先推导矩形脉冲串信号和载波调制矩形脉冲串信号的模糊函数,并对其模糊特性进行仿真分析。在此基础上,主要针对用于测控系统的伪码调制脉冲超宽带信号,利用其模糊函数分析其测距测速性能。结果表明:该超宽带信号具有良好的测距测速性能,其最大无模糊距离为1个伪码周期,最大无模糊多普勒频率为脉冲重复频率的倒数;单脉冲宽度越窄,其测距性能越好而测速性能越差。     

UWB radar detection of targets in foliage using alpha-stableclutter models

We address the problem of detection of targets obscured by a forest canopy using an ultrawideband (UWB) radar. The forest clutter observed in the radar imagery is a highly impulsive random process that is more accurately modeled with the recently proposed class of alpha-stable processes as compared with Gaussian, Weibull, and K-distribution models. With this more accurate model, segmentation is performed on the imagery into forest and clear regions. Further, a region-adaptive symmetric alpha stable (SαS) constant false-alarm rate (CFAR) detector is introduced and its performance is compared with the Weibull and Gaussian CFAR detectors. The results on real data show that the SαS CFAR performs better than the Weibull and Gaussian CFAR detectors in detecting obscured targets     

ECCM capabilities of an ultrawideband bandlimited random noise imaging radar

Investigated here is high-resolution imaging of targets in noisy or unfriendly radar environments through a simulation analysis of the ultrawideband (UWB) continuous-wave (CW) bandlimited random noise waveform. The linear FM chirp signal was selected as a benchmark radar waveform for comparison purposes. Simulation of the recovery of various types of target reflectivity functions (TRFs) for these waveforms were performed and analyzed. In addition, electronic counter-countermeasure (ECCM) capabilities for both types of systems were investigated. The results are compared using the error between the interference (jamming)-free recovered TRF and the recovered TRF under noisy conditions as a function of the signal-to-interference/jamming ratio (SIR/SJR). Our analysis shows that noise waveforms possess better jamming immunity (of the order of 5-10 dB improvement over the linear FM chirp) due to the unique radar correlation processing in the receiver.     

Prescreening during image formation for ultrawideband radar

Standard radar image formation techniques waste computational resources by full resolving all areas of the scene, even regions of benign clutter. We introduce a multiscale prescreener algorithm that runs as part of the image formation processing step for ultrawideband (UWB) synthetic aperture radar (SAR) systems. The prescreener processes intermediate radar data generated by a quadtree backprojection image former. As the quadtree algorithm iterates, it is resolving increasingly finer subpatches of the scene. After each quadtree stage, the prescreener makes an estimate of the signal-to-background ratio of each subpatch and applies a constant false alarm rate (CFAR) detector to decide which ones might contain a target of interest. Whenever the prescreener determines that a subpatch is not near a detection, it cues the image former to terminate further processing of that subpatch. Using a small database of UWB radar field data, we demonstrate that the prescreener is able to decrease the overall computational load of the image formation process. We also show that the new multiscale prescreener method produces fewer false alarms than the conventional two-parameter CFAR prescreener applied to the completely formed image     

Proposed UWB radar terminology

The term ultra-wideband (UWB) [which was formally defined by DARPA in 1990], for classifying an emerging technology in the field of radar and radio communications is synonymous with the following terms: baseband; video pulse; nonsinusoidal; carrierfree (carrierless); impulse; time-domain; super-resolution; ultra-high resolution; stealthy; spread spectrum; Rayleigh spectrum. The paper lists the terminologies that may be used for the emerging technology of UWB radar.     

Ultra-wideband impulse radar-an overview of the principles

Over the past decade, extensive research work has been carried out to develop the ultra-wideband (UWB) technology for radar applications, and to resolve the practical challenges in implementing an efficient UWB radar system. In this paper, we present an overview of the basic principles of UWB impulse radar. The focus is on the principles of UWB signal generation, impulse radiation, waveform design, pulse compression, range-velocity resolution (ambiguity function), array beamforming, and radar-target signature     

Ultra wideband technology for aircraft wireless intercommunications systems (AWICS) design

Current intercommunications system (ICS) designs for military, multicrew aircraft utilize lengthy, encumbering cords to physically attach the crewmember's helmet or headset to a distributed audio intercom system. Typical ICS long-cords are approximately 100 feet in length and allow crewmembers to maintain communications as they move about the aircraft while performing their mission duties. These cords also allow crewmembers to maintain communications with the aircraft when disembarked, as when they are controlling aircraft during engine start-up. Unfortunately, the current wired topology significantly reduces mission effectiveness, impedes crewmember movement, and greatly increases the crewmember's risk of injury. These drawbacks are more pronounced onboard military rotary winged aircraft (helicopters) where several crewmembers have been injured or killed during emergencies requiring the aircraft to ditch at sea. During ditching, crewmembers often became entangled in their lengthy ICS cord, preventing or delaying aircraft egress. This paper discusses the development of an aircraft wireless intercommunications system (AWICS) which utilizes ultra wideband (UWB) technology to address mission requirements for these multicrew, military aircraft. UWB offers unique advantages in this application - multipath mitigation, low probability of detection, low probability of interference to onboard legacy systems, and high throughput in a multiuser environment.     

基于PSWF 的TH-PPM超宽带系统优化设计与仿真

在分析PSWF脉冲的最佳时域能量聚集性和频谱灵活可控性的基础上,提出了满足FCC(FederalCommunications Commission)频谱掩膜要求的UWB脉冲波形优化设计方法,并将该方法应用于多进制TH-PPM超宽带系统中,理论计算了基于PSWF脉冲的多进制PPM-UWB系统的符号差错率公式。与高斯脉冲进行比较,采用Systemview可视化仿真平台进行了仿真。仿真结果表明,基于PSWF脉冲的UWB系统符号差错率性能要明显优于Gauss脉冲。在给定SER的前提下,使用PSWF脉冲的UWB系统能够容纳更多的用户。     

航天器交会对接模拟系统逼近过程自抗扰控制

航天器交会对接地面模拟系统用于研究航天器交会对接过程的动力学、导航与控制等方面的相关问题。模拟器通过气浮轴承悬浮在大理石平台上来模拟太空的无摩擦微重力环境。通常情况下要保证大理石平台足够水平,由于实际平台不可能完全水平,模拟器的重力分量会使模拟器产生下滑现象,这种现象对大型地面模拟器设备尤为严重。针对模拟器的逼近过程设计了轨迹规划。为了减小测量信号噪声的影响,采用跟踪微分器(TD)对整个逼近过程中的测量信号进行滤波。针对逼近过程中模拟器存在下滑力等干扰问题设计控制器,通过扩张状态观测器(ESO)实时估计干扰量,进而对干扰量进行补偿。对模拟器冷喷气推力系统制定了推力器分配策略,采用脉冲宽度调制(PWM)技术实现对推力的近似等效。提出的控制方法应用于航天器交会对接地面模拟系统,实验结果表明所提出的控制方法能有效消除下滑力等干扰的影响。