An Effective Timing Synchronization Scheme for DHTR UWB Receivers

In performing short-distance, high-data-rate wireless communications using ultra-wideband (UWB) systems, it is necessary to reduce the average transmission power and ensure a fixed synchronization error between the transmitter and receiver ends. Furthermore, to reduce multipath interference, the UWB system should be sometimes implemented using a rake receiver. However, for such receivers, the delay time and attenuation loss over each transmitted route must be known in advance. In the present study, the complexity of rake receivers with a large number of “fingers” is reduced by means of a delay-hopped transmitted-reference (DHTR) scheme, in which the delayed signal is correlated with the original signal; thereby avoiding the need for a separate template signal. The synchronization performance of the proposed DHTR receiver is analyzed both theoretically and numerically. An effective timing synchronization scheme, designated as “parallel signal acquisition with shared looped delay-line” (PS-SLD), is then proposed. The simulation results show that for multipath environments with a single user, the proposed synchronization scheme achieves a higher detection probability and a lower normalized mean square error (MSE) than the traditional timing dirty templates (TDT) algorithm.     

UWB for multi-gigabit/s communications beyond 60 GHz

The recently allocated 71–76 GHz and 81–86 GHz bands provide an opportunity for realizing Line Of Sight (LOS) links for directional point-to-point “last mile” applications. An efficient use of this spectrum may allow wireless to finally “catch up” with wires, leading to systems such as “multi-Gigabit wireless Ethernet,” and “wireless fiber.” However, the transmission at such a frequency range is characterized by several additional challenges compared to lower frequency bands, from both technological and propagation point of view, which makes difficult to use them efficiently. In this scenario, IR (Impulse Radio) UWB (Ultra Wide Band) technology might offer some more degrees of freedom for the design of a highly integrated and low cost transceiver. This work has at its core the design and BER (Bit Error Rate) performance evaluation of an IR-UWB architecture based on an 85 GHz up-conversion stage of train of Gaussian pulses having duration lower than 1 ns. Finally, we compare performance of this architecture with the ones of a more traditional continuous wave communications system with FSK (Frequency Shift Keying) modulation. Simulation results show that BER performance, in presence of RF non-linearities, for an IR-UWB transceiver architecture operating at 85 GHz (with same data rate and bandwidth) are better than a coherent BFSK scheme working in a similar scenario. Finally, some conclusions are reported, pointing out the UWB antenna design and the future works related to the modeling of the channel at frequencies beyond 60 GHz and the implementation of the test bed.     

A 0.65-to-1.4 nJ/Burst 3-to-10 GHz UWB All-Digital TX in 90 nm CMOS for IEEE 802.15.4a

We propose an all-digital UWB transmitter architecture that exploits the low duty cycle of impulse-radio UWB to achieve ultra-low power consumption. The design supports the IEEE 802.15.4a standard and is demonstrated for its mandatory mode. A digitally controlled oscillator produces the RF carrier between 3 and 10 GHz. It is embedded in a phase-aligned frequency-locked loop that starts up in 2 ns and thus exploits the signal duty cycle that can be as low as 3%. A fully dynamic modulator shapes the BPSK symbols in discrete steps at the 499.2 MHz chip rate as required by the standard. The transmitter can operate in any 499.2 MHz band of the standard between 3.1 and 10 GHz, and the generated signal fulfills the emission spectral mask. The jitter accumulation over a burst is below 6 ps_RMS, which is within specifications. The transmitter was realized in a 1 V 90 nm digital CMOS technology, and its power consumption drawn from a 1 V supply is from 0.65 mW at 3.1 GHz to 1.4 mW at 10 GHz for a 1 Mb/s data rate.     

All-digital low-power CMOS pulse generator for UWB system

An all-digital CMOS ultra-wideband (UWB) pulse generator which complies with FCC regulations is presented. The proposed pulse generator generates a single UWB pulse satisfying FCC regulations without any filtering. The average power consumption of the whole circuit is 15.4 mW and 675 /spl mu/W at the pulse repetition frequency of 500 and 1 MHz, respectively.     

Model-Based Multichannel Compressive Sampling with Ultra-Low Sampling Rate

The emerging compressive sampling (CS) theory makes processing ultra-wide-band (UWB) signal at a low sampling rate possible if the underlying signal has a sparse representation in a certain basis. The feasibility of model based compressive sampling for ultra-wide-band (UWB) signal is investigated. In this paper, a multichannel compressive sampling architecture is developed to capture UWB signal at a rate much lower than Nyquist rate. The proposed framework considers sub-Nyquist sampling stream of delayed and weighted versions of a known signal with finite support in time domain. A basis function is constructed to realize sparse signal representation. To reduce the hardware cost, a segmented architecture is suggested. In addition, a joint signal recovery algorithm is presented. Experimental results indicate that, with this system, a UWB signal sampled at about 4% of Nyquist rate still can be recovered with overwhelming probability.     

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.     

An efficient FPGA-based implementation of UWB radar system for through-wall imaging

The work presented in this paper aims to develop a low-cost ultra-wideband (UWB) radar system that has the capability to image through the wall of a human target. The proposed radar system relies heavily on a field-programmable gate array (FPGA) platform. The Xilinx FPGA Kintex-7 (KC705) board is employed to integrate the main functionalities of the radar system, such as the generation and acquisition of a UWB signal. The generated signal is a monocycle signal, which has an ultra-wide bandwidth. Due to the UWB nature of this signal, the radar system achieves better penetration ability, as well as high imaging resolution. However, the major challenge of a UWB radar system lies in the stage of digitization, as it requires a high sampling rate analog-to-digital converter (ADC). In fact, such a chip is very expensive. Hence, to reach a high sampling resolution using a low-cost and low-speed ADC, an efficient sampling strategy is implemented. In contrast to other UWB sampling methods, which require a hardware delay line chip, the new sampling scheme depends only on the FPGA firmware to realize a combination of real-time and equivalent-time sampling, which provides better jitter performance. Finally, to demonstrate the imaging capability, experimental tests are conducted in an indoor environment while human targets are located in different places. The measurement results revealed that the proposed radar system has the ability to provide 2D images that accurately determine the location of the target.     

基于光纤XPM光学生成UWB信号的方法

提出了一种基于色散位移光纤(DSF)的交叉相位调制(XPM)效应的超宽带(UWB)光学生成方法。该方法首先利用DSF的XPM效应实现高功率的高斯泵浦光对低功率的直流探测光的交叉相位调制,然后利用光纤布拉格光栅(FBG)对探测光进行鉴频,实现相位调制到强度调制的转换,从而获得单周期UWB信号。利用光子仿真软件对方案进行了仿真实验,得到了中心频率分别为7GHz和6.95GHz、相对带宽分别为143%和145%的UWB信号,验证了所提方法的可行性。同时,研究了输入信号脉冲宽度、FBG的反射率、鉴频器的类型对产生的单周期UWB脉冲信号波形和频谱的影响。仿真实验的结果表明,该方案对输入信号脉冲宽度不是过宽的情况下具有良好的容忍度,光学高斯带通滤波器、波分复用器和FBG等光滤波器均可作为鉴频器,采用FBG优点是可通过改变反射率灵活地调整产生的UWB脉冲信号的波形。     

超宽带载波包络调制及其频谱相关解调

针对超宽带载波包络调制的频谱特性,提出新颖的正交梳状频谱相关解调方法,将超宽带脉冲信号的处理从时域扩展到了频域。阐述了该解调方式的基本原理和设计思路,推导了正交梳状频谱的载波选择原则。对系统性能的分析和仿真证明了频域相关解调的方法有着和时域解调相同的误码率性能。该方法接收机结构简单、成本低,可由全数字电路实现,便于采用其它数字信号处理技术进一步提高系统性能。     

基于PCA和DCT的雷达人体动作识别

无载波超宽带雷达人体动作识别系统的关键优势在于无载波超宽带雷达具有极高的分辨率,能够捕获人体的细微动作变化,并且对于室内复杂环境具有很强的抗干扰能力。但是由于无载波超宽带雷达信号不含载波信息,本身能量集中于极窄的波形内,并且发射信号与回波相关性弱,因此传统的提取信号特征的方法不再适用。针对这一问题,首次搭建无载波超宽带雷达人体动作识别系统,并提出一种新颖的基于主成分分析法（PCA）和离散余弦变换（DCT）相结合的无载波超宽带雷达人体动作识别方法,同时利用改进的网格搜索算法优化支持向量机的参数并验证该方法的优越性。最后,基于实测数据在Matlab平台上进行仿真,对实测的10种不同类型的人体动作进行分类识别,实验结果显示,该方法具有很高的识别率,针对不同的方案识别率均能达到99%以上,对小训练样本具有很强的鲁棒性。     

Power-efficient switching-based CMOS UWB transmitters for UWB communications and Radar systems

This paper presents a new carrier-based ultra-wideband (UWB) transmitter architecture. The new UWB transmitter implements a double-stage switching to enhance RF-power efficiency, reduce dc-power consumption, and increase switching speed and isolation, while reducing circuit complexity. In addition, this paper also demonstrates a new carrier-based UWB transmitting module implemented using a 0.18-/spl mu/m CMOS integrated pulse generator-switch chip. The design of a UWB sub-nanosecond-switching 0.18-/spl mu/m CMOS single-pole single-throw (SPST) switch, operating from 0.45 MHz to 15 GHz, is discussed. The design of a 0.18-/spl mu/m CMOS tunable impulse generator is also presented. The edge-compression phenomenon of the impulse signal controlling the SPST switch, which makes the generated UWB signal narrower than the impulse, is described. Measurement results show that the generated UWB signal can vary from 2 V peak-to-peak with 3-dB 4-ns pulsewidth to 1 V with 0.5 ns, covering 10-dB signal bandwidths from 0.5 to 4 GHz, respectively. The generated UWB signal can be tuned to cover the entire UWB frequency range of 3.1-10.6 GHz. The sidelobe suppression in the measured spectrums is more than 15 dB. The entire CMOS module works under a 1.8-V supply voltage and consumes less than 1 mA of dc current. The proposed carrier-based UWB transmitter and the demonstrated module provide an attractive means for UWB signal generation for both UWB communications and radar applications.     

Effect of multipath channel models to the recovery algorithms on compressed sensing in UWB channel estimation

Multipath arrivals in an Ultra-WideBand (UWB) channel have a long time intervals between clusters and rays where the signal takes on zero or negligible values. It is precisely the signal sparsity of the impulse response of the UWB channel that is exploited in this work aiming at UWB channel estimation based on Compressed Sensing (CS). However, these multipath arrivals mainly depend on the channel environments that generate different sparse levels (low-sparse or high-sparse) of the UWB channels. According to this basis, we have analyzed the two most basic recovery algorithms, one based on linear programming Basis Pursuit (BP), another using greedy method Orthogonal Matching Pursuit (OMP), and chosen the best recovery algorithm which are suitable to the sparse level for each type of channel environment. Besides, the results of this work is an open topic for further research aimed at creating a optimal algorithm specially for application of CS based UWB systems.     

单载波UWB系统中OOK调制电路设计与实现

设计并实现了一种基于单载波UWB（Ultra-wide Band）通信系统中OOK（On-off Keying）调制电路，电路通过UWB极窄脉冲控制BJ]r振荡器的导通或截止来实现UWB信号对载波的调制，将UWB信号的中心频率搬移到FCC开放频段（3．1GHz-10．6GHz）。通过对实际电路的测试，得出当UWB脉冲重复速率为310MHz时，可以实现载波对UWB信号稳定、高效的调制，结果证明此电路是一种非常有效的调制电路。     

基于SOA增益饱和效应生成UWB信号的研究

光纤传输超宽带信号(UWB over fiber)的提出解决了UWB传输距离短的问题,成为国内外研究的热点课题,如何在光域中生成UWB是该系统的关键技术之一。对称形UWB(doublet)与常用的单周期高斯脉冲信号(monocycle)相比,在低频部分的功率谱密度较低,在UWB系统中有更好的性能。为此提出了利用半导体光放大器(SOA)的增益饱和效应生成对称形UWB信号的方法,并进行了仿真实验,得到了符合美国联邦通信委员会(FCC)标准的中心频率为8.3GHz,相对带宽约为142%的对称形UWB信号,验证了该方法的可行性。     

高速超宽带脉冲检测电路的设计

在介绍了一种基于TH-PPM调制方式的并行检测接收机方案的基础上,结合UWB脉冲信号的时域特征提出并实现了一种结构简单、性能稳定的脉冲能量检测电路.实验结果表明该电路可在100Mb/s的高传输速率情况下取得较好的超宽带信号检测效果.     

一种新型UWB信号的抗干扰性能研究

着眼于抗干扰通信的军事应用研究,通过对UWB MC-DS-CDMA的分析改进,得到了一种新型应用于超短波的UWB信号,分析了该信号的抗干扰性能,并与UWB MC-DS-CDMA信号进行了比较,然后使用安捷伦公司的ADS仿真软件进行了仿真验证,得出了该新型UWB信号具有极强的抗干扰性能的结论。     

All-digital reverse modulation architecture based carrier recoveryimplementation for GMSK and compatible FQPSK

A carrier recovery circuit implementation with an all-digital reverse modulation approach for coherent detection in the GSM/GMSK system as well as the GMSK compatible improved efficiency cross-correlated FQPSK system is presented. The proposed carrier recovery implementation utilizes all-digital reverse modulation circuit in a feedback loop to remove the modulated signal from the received intermediate frequency (IF) signal and to estimate the phase error of this carrier signal using a phase-locked loop (PLL). The digital reverse modulation approach avoids the multipliers required in an analog reverse modulation design, so that it can be implemented in a single chip FPGA. Hardware implementation of the coherent detection demonstrates that cross-correlated FQPSK is completely compatible with GMSK in the system performance and the receiver structure for GSM. Experimental performance evaluations show that the proposed carrier recovery circuit provides a Bit Error Rate (BER) performance within 0.3 dB in a non-linearly amplified channel corrupted by additive white Gaussian noise (AWCN) as compared with the simulated performance of the GSM/GMSK system     

On the performance of ultra-wide-band signals in Gaussian noise anddense multipath

An ultra-wide-band (UWB) signal is characterized by a radiated spectrum with a very wide bandwidth around a relatively low center frequency. In this paper, we study the reduced fading margin property of UWB signals. To evaluate the fading margin, we compare the performance of UWB signals in an environment with only additive white Gaussian noise (AWGN) versus the performance of UWB signals in a dense multipath environment with AWGN. The assumption here is that the presence of multipath causes a small increase in the signal-to-noise ratio required to achieve reasonable levels of bit error rate. A numerical example confirms this assumption, more specifically, the example shows that to achieve a bit error rate equal to 10^-5, we require about 13.5 dB in the AWGN case and about 15 dB in the multipath case, resulting in a fading margin of just 1.5 dB. This small fading margin can be understood by the ability of the UWB signal to resolve the dense multipath     

On the robustness of ultra-wide bandwidth signals in densemultipath environments

The results of an ultra-wide bandwidth (UWB) signal propagation experiment, using bandwidth in excess of 1 GHz, performed in a typical modern office building are presented. The robustness of the UWB signal in multipath is quantified through cumulative distribution functions of the signal quality in various locations of the building. The results show that an UWB signal does not suffer multipath fading