Effect of Channel Estimation Error on Time Reversal UWB Communication System

In this paper, effects of channel estimation error on time reversal (TR) UWB systems are investigated. In time reversal, a signal is prefiltered by using a time reversed complex conjugate of the channel impulse response as a transmitter prefilter. To investigate the effect of channel estimation error, an error function is added to TR-UWB prefilter. Analytical and simulation results show that channel estimation error degrade the performance. The signal-to-interference plus noise ratio decreases with increasing error variance. It is shown that the channel performance is degraded about 0.5 dB in CM1 and 1.3 dB in CM4 channel.     

Performance Analysis of Time Reversal UWB Communication with Non-coherent Energy Detector

Non-coherent receivers, such as energy detectors (ED), are the simplest and the most practical alternatives to coherent receivers for low-rate and low-complexity applications in ultra-wideband (UWB) systems. However, these advantages are achieved at the expense of non-negligible performance degradation. One solution to improve the performance is to make use of time reversal (TR) technique. In this study, the performance of TR technique with non-coherent ED is analyzed in UWB systems. First, we derive an approximate analytical formula for the error probability of TR-ED which is based on tapped-delay line (TDL) channel model. Next, we theoretically and by simulations analyze the optimum integration interval which maximizes the performance of TR-ED. The results show that TR technique, by reducing the integration interval, considerably improves the performance compared to the conventional ED scheme.     

空时编码在单天线UWB通信系统中的应用

超宽带(UWB)适用于基带多用户通信、战场无线通信和高数据率多媒体业务等通信系统,其数据传输速率高、功耗低、多径分辨能力强。但超宽带脉冲信号时域支撑区极窄,信道为密集多径,将空时编码技术引入超宽带通信系统,能够提升无线通信系统的信道容量与抗误比特率性能。在对UWB空时分组编码系统模型性能理论分析的基础上,对空时分组码在单天线UWB系统应用方案与UWB空时分层码方案进进行了简要介绍,利用Matlab对IEEEUWB信道模型进行仿真,提出了空时编码在UWB通讯技术中应用后提升短距高速率无线通信的性能的结论 。     

一种低复杂度超宽带通信系统

超宽带通信系统首先要解决的问题是降低系统的功耗和硬件的复杂度。在研究基于TR技术的超宽带通信系统的基础上,提出一种降低ADC实现复杂性的方法,同时对ADC和AGC联合设计,降低超宽带通信系统实现的复杂性。仿真的结果表明,提出的ADC实现方法和传统的2 b ADC的性能相当,但复杂度降低;在前导序列时间内AGC能完成信号的合理放大,使之满足信号的接收解调需要,而在信息数据解调期间不用调整AGC的增益。     

Detection by Time Reversal: Single Antenna

This paper studies the binary hypothesis test of detecting the presence or absence of a target in a highly cluttered environment by using time reversal. In time reversal, the backscatter of a signal transmitted into a scattering environment is recorded, delayed, energy normalized, and retransmitted through the medium. We consider two versions of the test-target channel frequency response assumed known or unknown-and, for each version, contrast two approaches: conventional detection (where no time reversal occurs) and time reversal detection. This leads to four alternative formulations for which we derive the optimal detector and the generalized likelihood ratio test, when the target channel frequency response is known or unknown, respectively. We derive analytical expressions for the error probabilities and the threshold for all detectors, with the exception of the time reversal generalized likelihood ratio test. Experiments with real-world electromagnetic data for two channels (free space with a target immersed in 20 scatterers and a duct channel) confirm the analytical results and show that time reversal detection provides significant gains over conventional detection. This gain is explained by the empirical distribution or type of the target channel frequency response-richer scattering channels induce types with heavier tails and larger time reversal detection gains     

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.     

Enhanced Secure Error Correction Code Schemes in Time Reversal UWB Systems

In this paper, secure channel coding schemes based on turbo codes are suggested for time reversal ultra wideband (TR-UWB) systems. Turbo code has the capability of error correction near Shannon’s limit. Adding security to turbo code is an attractive idea since it could reduce the overall processing cost of providing secure coded data and enjoys the advantages of high-speed encryption and decryption with high security, smaller encoder and decoder size and greater efficiency. The proposed turbo code schemes are labeled as follows: secure puncturing rate, secure frame length, and secure interleaving. Using these scenarios, secure turbo code is defined in a way that the redundant information used for error correction is not pre-determined by the nature of the error correction part of the algorithm but it can be chosen arbitrarily out of the whole set of possible strings. The lower bound of bit error probability for secure turbo code schemes in AWGN and TR-UWB systems are evaluated. Analytical and simulation results show secure turbo code performance is very satisfying. Various crypto-analytical attacks are investigated against these schemes. Based on this analysis, secure turbo code structures changed during the encryption procedure to increase the complexity of linear and differential cryptanalysis. It is seen that the performance of conventional turbo code and random frame length with Poisson distribution are the same. Comparing these schemes shows, secure interleaving approach has the best performance and secure puncturing rate the worst, but the latter provides the most security. The enhanced security of UWB, due to rich multipath nature of UWB channel, could be exploited. Due to space-time focusing property of time reversal UWB, there is an environmental confidentiality (or spatial security), which is additional security for secure turbo code in this system. Using secure turbo code, it is possible to increase the transmission range of UWB systems.     

单频信号对TH-PPM UWB通信最佳干扰分析

介绍了单频信号对TH-PPM UWB通信设备造成最佳干扰的理论分析,得出最佳干扰频率,并在AWGN信道下,用计算机仿真验证了该干扰频率的最佳性以及对UWB通信所产生的干扰效果。     

超宽带无线通信系统的一种新的接收机结构

本文提出了超宽带(UWB)无线通信系统的一种新的接收机结构及其相应的算法。这种接收机可以使用天线阵，然后对脉冲序列相关器的输出进行加权处理，从而增强了通信系统对多用户干扰(MUI)的抑制能力。计算机仿真结果说明，不管是用于脉位调制(PPM)还是脉幅调制(PAM)系统中，这种接收机的性能都优于常规的接收机。     

时间反转水声通信系统的优化设计与仿真

针对现有时间反转(Time Reversal,TR)水声通信存在的传输波形能量聚集性低和难以准确跟踪信道特性变化的问题,从脉冲波形设计和接收解调方案2个方面入手,对TR水声通信系统进行了优化设计。利用具有最佳时频能量聚集性的椭圆球面波函数(Prolate Spheroidal Wave Functions,PSWF),设计了TR水声通信的传输波形,提出了基于接收参考的时间反转传输方案。仿真结果表明,该方法在改善调制信号功率谱密度的同时,有效地提高了系统在水声信道下的误码率性能。     

On the Use of Uniform Circular Arrays for Characterizing UWB Time Reversal

Time reversal (TR) is a promising technique for the improvement of future telecommunication systems. A better understanding of this phenomenon requires deeper investigation of real propagation channels. This paper presents a new scheme to characterize the space-time focusing characteristics of time reversal. The originality of this technique relies on the use of a virtual Uniform Circular Array, which allows to simply derive the space-time focusing characteristics of the channel. An extensive ultrawideband (UWB) propagation experiment is reported, and the method is applied to the experimental data. Different focusing parameters are computed in different configurations. In particular, the paper shows that the delay spread parameter is inappropriate to study time focusing, and a new parameter characterizing the maximum symbol rate is introduced. In a UWB single-input single-output (SISO) configuration, time reversal increases the power of the strongest path by up to 10 dB and the total received power by up to 5 dB. Our analysis shows that when the received signal is appropriately focused in time, the data rate can be increased by a factor of three. The received signal is also focused in space, and the average size of the focus area is approximately $3lambda$ , where $lambda$ is the wavelength of the central frequency. We observed that the focusing spot is larger than the ideal case and is often directed inline with the transmitter direction. At $9lambda$ away from the target, the received signal is attenuated by up to 10 dB in a non line-of-sight environment, which demonstrates the high focusing capabilities of the TR-UWB scheme.      

超宽带通信系统的同步捕获算法研究

描述了UWB通信系统的信号和信道模型,重点讨论了传统非传输参考(TR)和传输参考体制下的超宽带通信系统的同步捕获问题,总结比较了这两种体制的主要同步方法,最后阐明了超宽带同步研究中的主要问题及其研究方向,从而为超宽带同步捕获的研究提供一定的参考.     

超宽带通信中的天线技术

超宽带（UItra-wide Bandwidth,UWB）短距离无线通信是近几年来的一个热门课题。UWB技术具有高保密性、低功耗等一系列特点,在众多领域都有很好的应用前景。UWB天线作为其中的一项关键技术,也得到了广泛的研究。本文就超宽带中的天线技术作一个简单介绍以便更深的了解超宽带系统。     

时间反转技术在无线通信抗干扰中的应用

时间反转技术是一种空间信道匹配新技术,具有空间及时间聚焦特性,在克服码间干扰、共道干扰和多址干扰等方面具有独特的优势.本文简要介绍了时间反转技术的基本概念及其空间和时间聚焦特性,通过与一些传统抗干扰技术的对比分析,总结了时间反转技术在无线通信抗干扰中的应用及研究进展,同时指出了今后的研究方向.     

被动时反镜在水声通信中的应用研究

被动时反镜（PTRM）技术具有时间压缩性能,在水下通信中,PTRM技术能实现多径信号的重组,既实现了多径信号能量的聚焦,又抑制了码间干扰。将PTRM技术应用于多径扩展严重的浅水水声通信系统中,在对声信道没有任何先验知识的情况下与声信道自动匹配,实现自适应聚焦。仿真结果表明：PTRM可以良好地重组多径扩展,拟制码间干扰,减小误码率,提高通信质量。     

UWB无线视频传输系统的设计实现

UWB无线视频传输系统具有传输速率高、频谱利用率高等特点,能够很好地满足家庭等对带宽有较高需求的局域无线应用场合,因而倍受业界关注。提出一种UWB无线视频传输系统的设计实现方案,经过测试验证,该设计方案可行。通过该方案能够加速UWB技术的转换实现,特别适用于点对点高速传输的应用场合,可以为超宽带无线通信技术的标准化和产业化提供有力支撑。     

认知超宽带无线通信系统的结构模型

阐述了认知超宽带(CUWB)无线通信系统的基本工作原理,描述了其认知过程,给出了简化的系统认知循环处理模型,并在此基础上设计出了系统的结构框架。然后,对CUWB系统的核心功能与关键技术进行了详细分析。     

基于可重构天线的时间反演安全通信方法

方向图可重构天线可以选择信号传播的空间信道,而时间反演技术可以回溯信号的传播路径(空间聚焦特点)。因此,文中将时间反演技术和方向图可重构天线技术结合可以产生多个具有不同截获位置的信号。将信息分别调制到这些信号上,可以改善信息传播的安全性。文中,利用MATLAB所构建的电磁仿真模型模拟室内空间环境,对这一方法进行了仿真研究。     

Secrecy Capacity Achievable Time Reversal Pre-filter in MISO Communication System and the Unequal Secrecy Protection Application

Wireless Personal Communications - Classical time reversal (TR) pre-filtering has been considered as one of the key physical layer security techniques for wireless communication applications in the...