超宽带雷达信号处理技术和实验研究

针对探测空中目标的超宽带(UWB)/冲激雷达,本文讨论了UWB/冲激雷达的信号处理技术,主要是信号检测和目标特性分析,首先讨论了目标检测技术,提出了用小波变换和高阶谱估计技术在变换域内进行检测的算法;其次讨论了目标特性分析技术,采用了高阶谱估计,提出了一种时域双谱估计算法,它可精确估计复杂形体目标的局部散射中心的分布.最后,结合作者等人研制的冲激雷达实验系统,对上述信号处理方法进行了实验研究,验证了上述信号处理方法的有效性。     

Performance evaluation of non‐Gaussian channel estimation techniques on ultrawideband impulse radio channels

We study the problem of adaptive channel estimation for a multipath channel on an ultrawideband (UWB) impulse radio (IR) system. The purpose of the work is to demonstrate that the statistical characteristics of the UWB‐IR environment are strongly non‐Gaussian and that as a result, non‐Gaussian signal processing techniques are both efficient and powerful in a UWB‐IR environment. The multipath channel estimation problem has been chosen as an illustrative example because UWB‐IR systems often operate in complex multipath environments. We study both blind and training‐based estimation techniques and demonstrate that even simple non‐Gaussian strategies can achieve significant performance improvement when compared to more common second‐order estimation techniques. Copyright © 2006 John Wiley & Sons, Ltd.     

Coexistence Between Ultra-Wideband Radio and Narrow-Band Wireless LAN Communication Systems—Part I: Modeling and Measurement of UWB Radio Signals in Frequency and Time

The correct modeling and measurement of ultra-wideband (UWB) radio signal are a critical issue to evaluate the electromagnetic (EM) emission of any communication system based on this technology. In this paper (Part I), UWB radio communication systems based on impulse radio (IR) and multiband orthogonal frequency division multiplex (MB-OFDM) technologies are characterized by simulations and experiments in both frequency and time domains. The EM characteristics of UWB radio are measured by different methods (conducted and radiative) and in different environments (anechoic and reverberation chambers).      

基于延迟锁相环的到达时间估计算法

超宽带脉冲信号具有高时间分辨能力,能达到厘米级的定位精度。目前,脉冲超宽带测距定位系统中普遍采用基于能量检测的非相关到达时间(TOA)估计算法的性能通常受限于阈值门限和估计偏差。该文在原先锁相环方案基础之上引入延时迟支路和衰减因子,提出了一种易于实现的基于延迟锁相环的TOA估计算法。通过在迟支路中设置不同的衰减因子,仿真结果表明,在IEEE802.15.4a4种信道模型CM1~CM4中,新算法均能有效提升测距定位精度,即缩短了首达路径与锁相环稳态锁定点之间的时差,其估计偏差最低可降至原有方案的1/10。     

TH-CDMA-PPM with Noncoherent Detection for Low Rate WPAN

Ultra wideband (UWB) impulse radio (IR) is a prospective transmission technology for low-rate indoor communications, as described in the physical-layer proposals for IEEE 802.15.4a wireless personal area networks (WPAN). Time hopping (TH) code division multiple access (CDMA) is considered as an access scheme' for multiuser UWB-IR systems. The TH- CDMA system widely addressed in the literature adopts binary phase-shift keying (BPSK) with coherent detection, which requires accurate channel estimation and thus increasing the implementation complexity. In this correspondence, we suggest using TH-CDMA-PPM (pulse position modulation) with non-coherent detection to simplify the receiver structure. The influence of different combinations of TH and CDMA processing gains on error performance of the new scheme is analyzed and numerical results are presented for illustration.     

超宽带雷达生命信号频率检测的Cramer-Rao下界

该文基于脉冲超宽带顺序信号模型和极大似然准则,结合Fisher信息矩阵和Cramer-Rao矩阵不等式,分析了UWB生命信号参数估计的泛化Cramer-Rao下界(CRLB)。根据等效时间采样原理,采用正弦位移函数近似生命微动信号,推导出了修正的UWB生命信号频率检测CRLB公式。仿真结果表明,增大观测时间、发射脉冲带宽以及系统信噪比可提高UWB雷达生命信号频率检测的精度。心跳信号检测比呼吸信号要求更高。     

Principles of space-time array processing for ultrawide-bandimpulse radar and radio communications

The emerging ultrawide-band (UWB) impulse technology has found numerous applications in the commercial as well as the military sector. The rapid technological advances have made it possible to implement (cost-effective, short-range) impulse radar and impulse-radio communication and localization systems. Array beamforming and space-time processing techniques promise further advancement in the operational capabilities of impulse radar and impulse-radio communications to achieve long-range coverage, high capacity and interference-free quality of reception. We introduce a realistic signal model for UWB impulse waveforms and develop the principles of space-time array processing based on the signal model. A space-time resolution function (STRF), a space-frequency distribution function (SFDF) and a monopulse-tracking signal are derived for impulse waveforms received by a self-steering array beamforming system. The directivity peak-power pattern and energy pattern of the beamformer are also derived. Computer plots of the STRF, SFDF and the beam patterns are obtained. The directivity beam patterns of impulse waveforms are sidelobe-free and, therefore, there is no need for sidelobe suppression via amplitude weighting of the array elements. Also, the resolution angle for the beam patterns is derived as a decreasing function of array size and frequency bandwidth. Electronic beamsteering based on slope processing of monopulse waveforms is described     

UWB Echo Signal Detection With Ultra-Low Rate Sampling Based on Compressed Sensing

A major challenge in ultra-wide-band (UWB) signal processing is the requirement for very high sampling rate. The recently emerging compressed sensing (CS) theory makes processing UWB signal at a low sampling rate possible if the signal has a sparse representation in a certain space. Based on the CS theory, a system for sampling UWB echo signal at a rate much lower than Nyquist rate and performing signal detection is proposed in this paper. First, an approach of constructing basis functions according to matching rules is proposed to achieve sparse signal representation because the sparse representation of signal is the most important precondition for the use of CS theory. Second, based on the matching basis functions and using analog-to-information converter, a UWB signal detection system is designed in the framework of the CS theory. With this system, a UWB signal, such as a linear frequency-modulated signal in radar system, can be sampled at about 10% of Nyquist rate, but still can be reconstructed and detected with overwhelming probability. The simulation results show that the proposed method is effective for sampling and detecting UWB signal directly even without a very high-frequency analog-to-digital converter.     

Multiuser detection of time-hopping PPM UWB system in the presence of multipath fading

Ultra-wideband (UWB) impulse radio (IR) systems are currently being considered for several applications due to their attractive features that include low-power carrierless and ample multipath diversity. Among the various modulation and multiple-access schemes, time-hopping (TH) pulse position modulation (PPM) is a popular technique in application. Most past works rely on strict power control and perform single-user detection (matched filtering) on the desired signal. This paper aims to apply multiuser detection techniques in binary PPM (BPPM) UWB IR multiple-access systems. Moreover, we consider frequency-selective multipath fading channels to account for the wireless cellular environment. A class of linear multiuser detectors (LMDs) is applied to extract the information bits while eliminating multiuser interference (MUI) in the presence of multipath fading. Simulation results are provided to compare the performance of different LMDs.     

具有窄带干扰抑制能力的新型修正非线性chirp超宽带脉冲研究

超宽带（UWB）信号极宽的带宽使超宽带系统不可避免地与其频带内已有的窄带系统产生干扰。本文针对超宽带系统提出了两种新型的具有窄带干扰（NBI）抑制能力的修正非线性chirp超宽带波形。这两种波形基于窄脉冲超宽带的通信方式设计,其能量可以在时间上均匀分布,从而避免了高峰值功率的问题。此外这两种设计方法对有用信号没有损失,只需要对波形进行时域处理即可改变相应的频域特性。仿真结果和理论分析显示,基于这两种超宽带波形的直接序列扩频二进制相移键控超宽带（DS-BPSK UWB）系统,在抑制窄带干扰方面极大优于采用传统线性chirp波形的超宽带系统。      

超宽带冲激脉冲正交解调接收机系统反射校正算法及其实现

基于超宽带冲激脉冲的信号特征,提出了超宽带正交解调接收机系统中脉冲信号的反射模型与校正算法。通过时域瞬态传输线模型、信号流图模型分析,指出整个系统可等效为一个延时滤波网络。最后提出了拟合该等效延时滤波网络,求解其补偿网络的具体校正算法。在实际系统目标探测的外场试验中,也验证了模型分析与校正算法的正确性和有效性。     

An ultrawideband system architecture for tag based wireless sensor networks

With the latest improvements in device size, power consumption, and communications, sensor networks are becoming increasingly more popular. There has also been a great increase in the popularity of commercial applications based on ultrawideband (UWB). Impulse radio (IR) based UWB technology utilizes noise-like signal, has potentially low complexity and low cost, is resistant to severe multipath, and has very good time domain resolution allowing for location and tracking applications. In this paper, the architecture and performance of a noncoherent low complexity UWB impulse radio based transceiver designed for low data rate, low cost sensor network applications is presented. The UWB-IR transmitter is based on a delay locked loop (DLL) and UWB monocycle pulse generator. The UWB-IR receiver utilises a noncoherent, energy detection based approach, which makes it largely independent of the shape of the transmit waveform and robust to multipath channels. The test circuits are designed for 0.35 /spl mu/m SiGe BiCMOS technology. This paper presents system simulations results as well as the performance of key functional blocks of the designed UWB application specific integrated circuit (ASIC) transceiver architecture. The simulated power consumption of UWB-IR transceiver circuits is 136 mW with 100% duty cycle with a 3.3 V power supply.     

基于协同阵的超宽带MIMO成像阵列优化设计方法

在多输入多输出（Multiple-Input Multiple-Output, MIMO）雷达成像系统中,天线阵列配置是系统设计的一个关键问题,影响到成像质量、参数估计和目标检测等。阵列的拓扑结构、阵元数量及发射信号的形式等都会影响阵列设计的结果,合理的阵列设计有利于简化系统结构并降低信号处理的复杂度。与传统窄带分析有所不同,在超宽带条件下天线阵列表现出一些新的性质,可以用于实现阵列的稀疏化。本文推导了超宽带多输入多输出阵列角分辨率和旁瓣、栅瓣水平的计算式,提出了一种针对步进频率信号体制的超宽带多输入多输出阵列优化设计方法,仿真数据处理结果验证了本文方法的有效性。      

Residue number system assisted fast frequency-hopped synchronous ultra-wideband spread-spectrum multiple-access: a design alternative to impulse radio

Ultra-wideband (UWB) systems having a bandwidth on the order of gigahertz have received wide attention both in the US and in Europe. The family of UWB systems may communicate either, by generating ultra-wideband signals or with the aid of innovatively combining conventional narrowband, wideband, or broadband signals. At the time of writing, UWB systems have only been implemented using ultra-wideband signals, such as those known from impulse radio systems. Hence, in this paper, UWB systems using narrowband signals are explored as a design alternative, which are based on the well-known family of frequency-hopping (FH) spread-spectrum multiple-access techniques. In the proposed UWB system, FH is implemented using multistage frequency-hopping multiple access (MS/UWB FHMA). We highlight the principles of the synchronous MS/UWB FHMA communication system, investigate the associated spectrum assignment, and the residue number system (RNS) based FH strategy: detection of the received signal can be achieved with the aid of existing fast FH signal detection schemes. Our study shows that the RNS assisted FH strategy is capable of efficiently dividing the huge number of users supported by the synchronous MS/UWB FHMA system into a number of reduced-size user groups, where the multiuser interference only affects the users within the same group. Since the number of users in each group is only a small fraction of the total number of users supported by the synchronous MS/UWB FHMA system, advanced multiuser detection algorithms can be employed for achieving near-single-user performance at an acceptable complexity. Our results show that MS/UWB FHMA is capable of supporting an extremely high number of users, while employing relatively simple receivers.     

Underwater acoustic sensor networks: Target size detection and performance analysis

Underwater acoustic sensor network consists of a variable number of sensors and vehicles that are deployed to perform collaborative monitoring tasks over a given area. Scalability concern suggests a hierarchical organization of underwater sensor networks with the lowest level in the hierarchy being a cluster. In this paper, we show that an ultra-wide band (UWB) channel can be used for underwater channel modeling and propose a maximum-likelihood (ML) estimation algorithm for underwater target size detection using collaborative signal processing within a cluster in underwater acoustic sensor networks. Theoretical analysis demonstrates that our underwater sensor network can tremendously reduce the variance of target size estimation. We show that our ML estimator is unbiased and the variance of parameter estimation matches the Cramer–Rao lower bound. Simulations further validate these theoretical results.     

基于OFDM信号的外辐射源雷达杂波信道估计

基于正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)信号调制特性的外辐射源雷达杂波信道状态信息估计方法,针对OFDM外辐射源雷达探测存在的问题,提出了基于信号特性的处理方法。针对该体制雷达中纯净的直达波信号获取问题,提出基于模糊函数的方法提取导频的周期信息,从而得到导频的位置信息,然后,利用导频信息得到杂波信道脉冲响应信息估计。相比常规的处理方法,文中方法能够在参考信号包含多径时得到正确的杂波信道状态信息。     

基于功率合成的超宽带冲击雷达研究

用电路合成和空间合成技术，将多个数干伏、纳秒级、超宽带脉冲源合成为兆瓦级高功率脉冲源；文中设计了一套由功率合成的全固态脉冲发射机、超宽带平面喇叭收发天线阵、正交解调采样接收机、主控计算机四大部分组成的冲击体制雷达目标探测系统，介绍了系统的工作原理；给出了实际系统目标探测的外场试验相关试验结果，验证了系统的可行性以及信号处理算法的正确性和有效性，为高功率冲击体制雷达技术的发展奠定了一定的实践基础。     

Non‐Data‐Aided Weighted Non‐Coherent Receiver for IR‐UWB PPM Signals

This letter proposes an energy‐detection‐based non‐data‐aided weighted non‐coherent receiver (NDA‐WNCR) scheme for impulse radio ultra‐wideband (IR‐UWB) pulse‐position modulated signals. Compared to the conventional WNCR, the optimal weights of the proposed NDA‐WNCR are tremendously simplified as the maximum eigenvector of the IR‐UWB signal energy sample autocorrelation matrix. The NDA‐WNCR serves to blindly obtain the optimal weights and entirely circumvent the transmission of training symbols or channel estimation in practice. Analysis and simulation results verify that the bit error rate (BER) performance of the NDA‐WNCR closely approaches the ideal BER of the conventional WNCRs.     

UWB Impulse Radio Receiver Based on Single Bit Quantization

Impulse Radio (IR) modulation is perceived to be a practical means of exploiting the multi-gigahertz bandwidth available for UWB links. However, the RMS delay spreading of indoor channels relative to the transmitted pulse width is typically very large such that several hundred signal samples are required to be quantized and processed for each received pulse. To realize a relatively low power low-complexity receiver of satisfactory performance in low signal to noise ratio environments, signal sampling based on single bit quantization is proposed which is readily realizable at gigahertz rates with modest power consumption. In this paper, the architecture and performance of a coherent IR receiver based on single bit quantization will be analyzed from the perspectives of Rake receiver processing, channel estimation and signal detection. This paper demonstrates that single bit quantization results in a modest manageable performance penalty relative to linear multi-bit sampling. This penalty is readily justifiable in light of the significant reduction in overall receiver complexity.     

基于PCA与EMD的超宽带雷达生命信号检测算法

 本文分析了脉冲超宽带(UWB)生命信号模型,提出了基于主元分析(PCA)和经验模态分解(EMD)的非接触生命信号检测方法.根据UWB信号杂波与生命目标回波特点,结合PCA去除杂波.提取适当的主元特征向量序列曲线上峰值所对应的时延,估计目标距离信息.采用EMD分解目标回波序列为有限个固有模态函数(IMF)分量,在时域上重构平滑生命特征曲线,且其在高信噪比下可实现心跳与呼吸信号的分离.实验研究表明该方法简单有效,能同时提供生命信号的频域和时域波形位置信息,且重构得到的生命信号较符合实际信号时变、非平稳特性.