UWB Multiple Access Communication System

Recently, the emerging Ultra-Wideband (UWB) impulse technology has found numerous applications in the civil as well as the military sectors. In this paper, an UWB multi-user communication system is studied. In a previous work, two systems (DS–CDMA–UWB and Gegenbauer–UWB) were compared in a rather simple case: only two users were considered, and a perfect synchronization between each receiver and transmitter for the two users was assumed. In the present paper, a more general case is studied. Different synchronous (different users detected at the same time or with constant delays) and asynchronous (each user transmitting independantly of other) scenarios are introduced. The interferences between users are also taken into account (for two users and more). Two systems are described and analyzed and their performance in terms of Bit Error Rate (BER), synchronization errors and users interference is studied by simulation. The first system, which is only based on orthogonal UWB waveforms called Modified Gegenbauer functions (MGF), gives a satisfactory multi-user detection in the synchronous case only. The second one uses an hybrid coding technique: an UWB orthogonal coding is associated to a spread spectrum DS–CDMA (Direct Sequence Code Division Multiple Access) technique (in fact a combination of the two systems sudied in the previous work). This allows an efficient multi-user detection in the asynchronous case.     

超宽带多址通信信号的功率谱分析

超宽带(UWB)多址通信是继CDMA技术之后迅速发展的一种宽带传输技术.本文在介绍了各种UWB通信调制方式后,针对产生的UWB多址信号,分析了信号特征,结合数学模型,以简明方式分析了TM-UWB与DSC-UWB多址通信信号的功率谱密度分布,它是UWB通信系统设计与用户干扰分析的基础.     

多用户检测在超宽带无线通信中的应用

在超宽带(UWB)通信系统中多址干扰是限制系统性能的重要原因,为了有效抑制多址干扰,本文将多用户检测技术应用于超宽带多用户通信系统中。通过分析信号特征,给出了应用在UWB系统中的几种次最佳多用户检测器的结构,考虑到实际UWB系统需要接收机有较低的复杂度,又提出了一种特别针对UWB系统的类最小均方差(MMSE)检测器并分析了其性能。在UWB室内信道环境下的仿真表明,采用本文提出的多用户检测器可以取得明显优于传统接收机的系统性能。     

Reduced-complexity UWB time-reversal techniques and experimental results

This paper presents a reduced-complexity time reversal technique for ultra-wideband (UWB) communications. Time reversal takes advantage of rich scattering environments to achieve signal focusing via transmitter-side processing, which enables the use of simple receivers. The goal of this paper is to demonstrate a UWB time reversal system architecture based on experimental results and practical pulse waveform, taking into account some practical constraints, and to show feasibility of UWB time reversal. Pre-decorrelating in addition to time reversal processing is considered for a downlink multiuser configuration. Multiple transmit antennas are employed to improve the performance.     

Multiple ultra-wideband signal sources exploiting XPM in SFRL

A novel scheme for all-optical broadcast ultra-wideband (UWB) monocycle pulses generation based on cross-phase modulation (XPM) in semiconductor fiber ring laser (SFRL) is proposed, in which three UWB positive or negative monocycle pulses can be generated simultaneously. A comprehensive broad-band dynamic model for this kind of all-optical broadcast UWB monocycle sources is established, which is further applied to numerically analyze the impacts of injection current of semiconductor optical amplifier (SOA), the power and wavelength of the signal light on the performance of the UWB positive monocycle pulses with higher power spectral density. The results show that the spectra of the UWB positive and negative monocycle pulses generated by this scheme match the Federal Communications Commission (FCC) definition quite well. Three UWB positive monocycle pulses with better performance can be obtained when the power of signal light is at a high level, and three other UWB positive monocycle pulses with good tolerance to both the injection current of the SOA and the wavelength of the signal light can be obtained. In addition, the powers of the lasing light coupled into the SFRL should not be strong to obtain three UWB positive monocycle pulses with better performance.     

Multiple Access Performance of Balanced UWB Transmitted-Reference Systems in Multipath

Recently, a novel balanced transmitted-reference (TR) system has been proposed for UWB communications. This TR system is capable of properly eliminating the inter-pulse interference (IPI) between the reference and data pulses in a single user multipath environment. In this paper, we investigate its multiple access (MA) performance by evaluating the second- order moments of noise and interference terms. The analytical framework developed here can also be used to accurately evaluate the MA performance of conventional TR system. It is shown that the proposed balanced TR system can achieve comparable MA capacity as conventional TR, while operating at higher information rate. On the other hand, given a target information rate, the balanced TR system in conjunction with M-ary signaling offers higher MA capacity than conventional TR system. The performance results suggest there exists a trade-off between the inter-pulse distance, thus the achievable information rate, and the MA capacity.     

Noncoherent Ultra-Wideband (De)Modulation

Ultra-wideband (UWB) radios have received increasing attention recently for their potential to overlay legacy systems, their low-power consumption and low-complexity implementation. Because of the pulsed or duty-cycled nature of the ultra-short transmitted waveforms, timing synchronization and channel estimation pose major, and often conflicting, challenges and requirements. In order to address (or in fact bypass) both tasks, we design and test noncoherent UWB (de)modulation schemes, which remain operational even without timing and channel information. Relying on integrate-and-dump operations of what we term "dirty templates," we first derive a maximum likelihood (ML) optimal noncoherent UWB demodulator. We further establish a conditional ML demodulator with lower complexity. Analysis and simulations show that both can also be applied after (possibly imperfect) timing acquisition. Under the assumption of perfect timing, our noncoherent UWB scheme reduces to a differential UWB system. Our approach can also be adapted to a transmitted reference (TR) UWB system. We show that the resultant robust-to-timing TR (RTTR) approach considerably improves performance of the original TR system in the presence of timing offsets or residual timing acquisition errors     

On the performance of using multiple transmit and receive antennas in pulse-based ultrawideband systems

This paper presents an analytical expression for the signal-to-noise ratio (SNR) of the pulse position modulated (PPM) signal in an ultrawideband (UWB) channel with multiple transmit and receive antennas. A generalized fading channel model that can capture the cluster property and the highly dense multipath effect of the UWB channel is considered. Through simulations, it is demonstrated that the derived analytical model can accurately estimate the mean and variance properties of the pulse-based UWB signals in a frequency-selective fading channel. Furthermore, the authors investigate to what extent the performance of the PPM-based UWB system can be further enhanced by exploiting the advantage of multiple transmit antennas or receive antennas. Numerical results show that using multiple transmit antennas in the UWB channel can improve the system performance in the manner of reducing signal variations. However, because of already possessing rich diversity inherently in the UWB channel, using multiple transmit antennas does not provide diversity gain in the strict sense [i.e., improving the slope of bit error rate (BER) versus SNR] but can possibly reduce the required fingers of the RAKE receiver for the UWB channel. Furthermore, because multiple receive antennas can provide higher antenna array combining gain, the multiple receive antennas technique can be used to improve the coverage performance for the UWB system, which is crucial for a UWB system due to the low transmission power operation.     

DTR-DS-BPSK超宽带通信系统的同步算法研究

分析了采用差分传输参考(differential transmitted reference)-直接序列扩频-二进制移相键控(DTR-DS-BPSK)方案的超宽带(ultra-wideband,UWB)通信系统的原理及其实现方案,在此基础上,提出了一种适用于DTR-DS-BPSK UWB通信系统的同步方案,并利用Matlab对该方案在室外环境下的捕获性能进行了仿真,从而为室外环境下超宽带通信系统的相关设计提供了依据.     

Performance analysis of an over-sampling multi-channel equalization for a multi-band uwb system

This paper proposes an over-sampling multi-channel equalizer per sub-band for multi-band ultra-wideband (UWB) system and compares its performance with conventional RAKE receiver when operating in practical UWB channel models. Three transmission modes have been considered, and inter-symbol interference (ISI) is found to be inherent to certain transmission modes due to the large UWB channel delay spreads. Through detailed analytical and simulation studies, the proposed over-sampled minimum mean square error (MMSE) equalizer is shown to be able to handle ISI under any channel conditions or transmission modes, with an acceptable BER. In addition, the rich multipath diversity of the UWB channels is harnessed by the over-sampling scheme, for output SNR improvement. Over-sampling is done in the expense of an increase in system complexity     

基于Turbo编码的超宽带系统性能分析

为了降低严重的时间弥散影响,提出了一种Turbo信道编码方案引入超宽带系统中,分析和仿真了在不同无线室内环境下基于Turho编码的超宽带系统的误比特率性能。无线室内环境是由IEEE802．15．3a提出的修正的SV信道模型。为了降低迭代译码的复杂度,采用了LOG-MAP算法。仿真结果表明,相比于无编码的系统,具有Turbo编码的超宽带系统在不同无线室内环境下提供了可观的编码增益,随着迭代次数的增加,超宽带系统的性能得到了改善。     

Smart UWB System Based on STC and TR Techniques for BER Performance Enhancement and Interference Rejection

In this research, a novel smart UWB system is introduced. The proposed system is based on using an adaptive maximum ratio combining (MRC) Rake receiver. The proposed adaptive Rake receiver uses Genetic algorithm (GA) to adaptively select the delays of the fingers of the Rake receiver depending on the channel impulse response. It adaptively selects the delays that will allow the Rake receiver to capture most of the energy in the multipath components with minimum complexity. This adaptive Rake receiver is referred to as a GA Rake. The adaptive GA Rake is applied to a single-input single-output and space time coding (STC) multi-input single-output UWB systems. The performance of those systems using a GA Rake is compared to their performance when using a conventional MRC-Rake receiver and showed a great enhancement in performance with less receiver complexity. Also, in this paper, the smart UWB system using STC is modified by using the time reversal (TR) pre-coding technique. The modified system is referred to as a TR smart UWB system. This modification leads to more enhancements in performance and more reduction in receiver complexity over the smart UWB system. Moreover, this paper also shows the ability a TR smart UWB system in combating interference from other UWB systems.     

The effects of the human body on UWB signal propagation in an indoor environment

Ultra-wideband (UWB) communication systems are investigated for their ability to operate in dense multipath environments. While a great deal of time and effort has been spent characterizing both the indoor and outdoor UWB channels, the effects of human body interaction with a close proximity UWB antenna remains unexplored. Measurements of a commercially available UWB antenna performance in an anechoic chamber and in various indoor multipath environments were conducted. Comparisons of these measurement results indicate that while the human body creates a deep (23.6 dB) in a light multipath environment, this is drastically reduced (6.8 dB) in a dense multipath environment.     

基于多天线辅助估计的高精度UWB快速捕获算法研究

本文提出了一种基于多天线辅助估计的UWB(超宽带)快速捕获算法,利用UWB信号的循环平稳特性,将接收信号与它自身延迟一个信息位产生的模板相关,应用最大似然方法就可得到一个粗略的同步时间估计,在充分利用线性天线阵空间分集增益的情况下,这种估计相当准确。在此基础上继续进行精确同步,直到捕获任一符号位的第一帧第一个到达脉冲。文中采用流图法给出了本算法平均捕获时间的闭式解。理论分析和计算机模拟表明,该算法与同等硬件复杂程度和同等捕获精度的其他捕获方法相比可明显地缩短平均捕获时间。     

A Single Input-Multiple Output Time Reversal UWB Communication System

Time reversal is a promising technique for the improvement of UWB communication systems. Intersymbol interference (ISI) limits the system performance in such wireless systems. This paper presents a general ISI analysis for time reversal UWB communication systems. The time reversal UWB system gives good performance for rates below the coherence bandwidth but at higher data rates the performance of the system is limited by intersymbol interference and bit error rate saturates even for high signal-to-noise ratio. To mitigate the ISI effects, a single input/multiple output (SIMO) time reversal UWB system is used and its performance is analyzed. It is shown that by using a SIMO TR transceiver, ISI reduces and the system capacity increases. Transmitted signal power at SIMO time reversal decreases, therefore in low data rate SISO performance is better than SIMO, But in high rate scenario, SIMO TR suppresses the ISI better than the SISO TR and its performance is better than SISO TR. It is possible to compensate the reduced power by using a receiver with more sensitivity.     

Multiple access interference and multipath interference analysis of orthogonal complementary code‐based ultra‐wideband systems over multipath channels

In order to alleviate multiple access interference and multipath interference of ultra‐wideband (UWB) system, we propose the orthogonal complementary code (OCC)‐based direct‐sequence UWB system and offset‐stacking (OS)‐UWB system. OCC has perfect partial autocorrelation and cross‐correlation characteristics. With the application of OCC in UWB system, we can obtain better performance in multiple access interference and multipath interference. The proposed OS‐UWB structure can also achieve variable data rate transmission because of its innovative OS spreading technique. Theoretical analysis and simulation results show that the proposed UWB system can achieve excellent performance and outperform the unitary code‐based direct‐sequence UWB system. Copyright © 2013 John Wiley & Sons, Ltd.     

基于容错决策树的UWB辅助惯性定位方法

针对惯性导航系统误差随时间累积和超宽带(UWB)定位受到非视距问题、多径效应和人体影响出现粗大误差的问题,提出了一种基于容错决策树的UWB辅助人员室内惯性定位方法。该方法提出并采用陀螺仪高精度分段拟合误差补偿模型,抑制惯性导航误差漂移;同时在UWB辅助人员室内惯性定位的基础上,构建惯性导航与UWB单点定位数据共同作用的容错决策树判定模型,剔除UWB定位的粗大误差因子,进而对惯性导航和UWB的参数应用扩展卡尔曼滤波,实现UWB辅助增强惯性定位。根据实验验证表明,在复杂狭窄巷道环境,该方法将距离均方误差占路线长度的比例从6.02%提升到0.76%;在常规方正室内环境,该方法将最大误差占路线长度的比例从2.207%提升到0.635%。实现了长时间的连续可靠定位,具有较强的工程应用价值。     

正交Hermite脉冲的超宽带的多用户通信

正交Hermite脉冲被提出用于超宽带无线通信。该文提出新方法用于超宽带通信的多用户传输系统。通过同时传输多个正交Hermie脉冲,超宽带多用户传输系统可以获得好的性能特征。该文还提出了正交Hermite脉冲应用于UWB的DS-CDMA系统以同时支持更多的用户通信。     

基于超宽带阵列与里程计的多机器人相对定位

精准的相对定位是实现多机器人协作与编队控制的关键。在弱全球定位系统(GPS)的室内环境中，视觉或激光雷达(LiDAR)通过特征匹配的方式确定机器人间相对位置，但在非视距环境下难以工作。针对这一问题，该文提出一种基于多超宽带(UWB)节点的移动机器人相对定位方法。首先，利用每个机器人携带的多个UWB节点构成UWB阵列，通过非线性优化实现移动机器人间相对姿态估计。为进一步提升估计精度，利用里程计对非线性优化结果进行约束，通过图优化算法对滑动窗口内的相对位姿与里程计进行优化，保证了算法的实时性。然而，图优化过程中难以确定相对位姿估计的误差，对定位结果影响较大。因此，利用粒子滤波融合里程计和滑动窗口优化后的相对位姿，进一步提升相对姿态估计的精度。实验结果表明，该方法在12×6 m的室内环境中，能够达到0.312 m的平均定位误差以及4.903°平均角度误差，且具有良好的实时性。     

低频UWB SAR的冲击响应函数

提取系统的冲击响应函数(impulse response function,IRF)是测量雷达系统性能指标的前提,IRF来自理想点目标的雷达图像。对于低频超宽带合成孔径雷达(ultra wide band synthetic aperture radar,UWB SAR),参考点目标的电磁散射特性是频率和方位角的函数,不满足理想点目标的散射特性要求。本文从IRF的定义出发,结合低频UWBSAR系统处理模型,利用二维数字聚焦方法消除杂波的影响,同时利用低频电磁散射数值建模的方法计算参考点目标的电磁散射特性,最后给出了计算系统IRF的方法。