超宽带跳时扩频调制技术研究

简要介绍了超宽带无线通信中PPM、PAM、OOK及BPSK二进制跳时扩频调制技术的实现原理,给出了高斯信道环境下多用户系统的误码率性能,并对其发送信号的功率谱及在高斯信道下的误码率性能进行了仿真,最后指出,TH-BPSK易实现且具有较好的性能。     

基于小波分组调制的多码多载波跳频通信系统分析

介绍了一种将多码调制、小波分组调制以及跳频技术相结合的高效通信方式——小波分组多码多载波跳频通信系统.推导了系统在Nakagami-m衰落信道下的误码性能,给出了用户数、小波分组类型、小波分组滤波器长度以及跳频点数与系统性能之间的关系.理论分析与数值计算表明:增加小波分组滤波器长度可以有效降低系统误码率,但不同小波分组类型对系统性能的影响不大;跳频技术的引入不仅增加了系统的安全性,同时也可有效降低多址干扰对系统性能的影响,提高了系统的可靠性.     

移动无线多媒体通信中的多载波调制技术

无线通信的发展方向是提供灵活的、无缝的、高质量的多媒体业务。为适应这种业务发展,无线通信系统需要满足多媒体业务对宽带高速率的更高要求。多载波调制技术能有效地提高频谱利用率,对于宽带高速无线传输系统性能的改善具有重要的意义。OFDM技术是高频谱利用率的多载波调制技术,在多径衰落信道中传输宽带高速数据时其性能有很强的鲁棒性。小波包调制则是一种采用了新的正交变换方法的多载波调制技术。通过对基于DFT的OFDM技术和小波包调制进行比较,小波包的优越性能有益于多载波调制性能的改进。     

基于小波变换/小波包变换的多载波调制技术

小波/小波包在通信系统中的应用是近年来一个新的研究领域,而基于小波/小波包变换的多载波调制技术是其中一大研究热点。由于小波/小波包基函数具有良好的正交性与时频局域性等特点,基于小波/小波包变换的多载波调制技术,能够有效地提高通信系统性能。本文介绍了当前几种主要的基于小波/小波包变换的多载波调制方案,分析了这些方案的性能特点及发展趋势,并与其他方案进行了比较。     

采用跳时调制的超宽带冲激无线电技术及其在通信对抗中的应用

论述超宽带冲激无线电通信系统基本原理，分析使其具有巨大军事应用潜力的冲激脉冲和跳时调制这两项关键技术，并结合该项通信新技术的特点阐述了它在通信对抗中的应用。     

跳时脉幅脉位混合调制超宽带通信性能研究

针对目前超宽带通信调制方式误码率高的问题，提出正交脉冲脉幅脉位混合调制（OAPPM）改善系统性能的方法。OAPPM调制方式是把信息调制在信号的位置和幅度上，接收端利用最佳检测器进行接收。文中分析了TH—OAPPMUWB系统的信道容量和误符号率并进行了仿真。结果表明：该方法与传统的PPM和PAM相比，降低了误符号率和系统复杂度，较好地改善了UWB通信系统性能。     

超宽带系统的调制技术

目前一种新的无线通信技术引起了人们的广泛关注,这就是所谓的超宽带(UWB,Ultra WideBand)技术,它被认为是未来五年电信热门技术之一。本文主要介绍了UWB信号的各种调制技术,包括数据调制和多址调制,其中重点介绍了PPM(Pulse Position Modulation,脉冲位置调制)及TH-PPM(Time-Hopping PPM,跳时PPM),最后简要分析比较了IEEE 802．15．3a标准的两大提案——DS-UWB和MB-OFDM。     

基于小波包函数调制的跳频小波包分多址通信系统

本文提出了一种跳频小波包分多址（FH－WPDMA）通信系统模型,分析讨论了该系统在多经衰落时变信道下采用判决反馈均衡的接收性能,采用空间分集接收,可显著降低系统的误码率。该系统易于支持多速率话音和数据业务,具有频谱利用率高,抗窄带干扰能力强和保密性等优点。     

UWB-新型宽带无线接入技术

本文主要介绍了超宽带(UWB)无线通信技术的起源、概念及其基本工作原理,并总结了UWB的性能特点,对UWB的局限性也作了简单的介绍。     

采用跳时调制的超宽带冲激无线电技术及其在通信对抗中的应用

论述超宽带冲激无线电通信系统基本原理 ,分析使其具有巨大军事应用潜力的冲激脉冲和跳时调制这两项关键技术 ,并结合该项通信新技术的特点阐述了它在通信对抗中的应用     

Multiple access for UWB impulse radio with pseudochaotic time hopping

Pseudochaotic time hopping (PCTH) is a previously proposed encoding/modulation scheme for ultra-wideband (UWB) impulse radio. PCTH exploits concepts from symbolic dynamics to generate aperiodic spreading sequences, resulting in a noise-like spectrum. We present a multiple-access technique suitable for the PCTH scheme. In particular, we provide an analytical expression of the bit-error rate performance as a function of the number of users and validate it by simulation.     

A new noncoherent UWB impulse radio receiver

This letter analyzes the implementation issues related to coherent receivers for UWB impulse radio with a special emphasis on timing and jitter problems. We propose a new jitter tolerant receiver design that is easy to implement. Analytical BER analysis and simulations verify that the performance of the proposed receiver is comparable to that of a correlator-based receiver that includes jitter. The new design is a promising candidate for low-cost low-power UWB IR receiver implementations.     

一种适用于超宽带的MRC-PRC判决反馈滤波器

针对超宽带无线通信系统提出了一种MRC—PRC判决反馈滤波器。对于系统的信干噪比以及误比特率性能进行了理论分析,并给出了计算机仿真验证结果。结果表明跟传统的MRC-PRC相比,MRC-PRC-DFF能获得3dB的信千噪比增益;此外,MRC-PRC—DFF跟性能优越的MMSE—PRC相比,系统的复杂度大大降低。     

脉冲超宽带技术在航天测控系统中的应用

针对当前航天测控系统安全性不足的问题,将脉冲超宽带技术应用于航天测控系统中,构建了一种新的脉冲超宽带测控体制。建立了基本的脉冲超宽带测控信号模型,对脉冲超宽带测控系统的性能和传输链路进行了分析。给出了脉冲超宽带测控系统结构框图,介绍了系统工作过程。针对并行信号捕获方法资源消耗大的不足,提出了两步并行捕获方法。分析表明,脉冲超宽带技术可用于航天测控系统中,完成测距测速和数据传输任务。脉冲超宽带测控系统可有效提高测控系统的隐蔽性和抗干扰能力,同时提高测距精度。在信号捕获方面,与并行捕获方法相比,两步并行捕获方法的硬件资源消耗得到大大降低,同时还可保证较快的捕获速度,但会产生一定的信噪比损失。     

脉冲超宽带测控信号时延精密跟踪方法

脉冲超宽带测控新体制可有效提高测控系统的安全性能,且具有潜在的高精度测距能力.为了实现其高精度测距功能,提出了一种基于延迟锁定环路的脉冲超宽带测控信号时延精密跟踪方法.该方法在传统伪码跟踪环的基础上进行改进,利用基于非相干积分的非线性反馈环路对接收信号的脉冲相位进行精密跟踪.理论分析和仿真结果表明,该延迟锁定环路可以完成对脉冲超宽带测控信号的时延精密跟踪.与直扩测控信号相比,在相同条件下,脉冲超宽带测控信号的时延跟踪相对误差更大,但由于脉冲宽度很窄,在一定载噪比条件下,其测量精度仍可达厘米量级甚至更高.     

Performance evaluation of impulse radio UWB systems with pulse-based polarity randomization

In this paper, the performance of a binary phase shift keyed random time-hopping impulse radio system with pulse-based polarity randomization is analyzed. The effects of interframe interference and multiple-access interference on the performance of a generic Rake receiver are investigated for asynchronous systems in frequency-selective environments. A key step is to model the asynchronous system as a chip-synchronous system with uniformly distributed timing jitter for the transmitted pulses of interfering users. This model allows the analytical technique developed for the synchronous case to be extended to the asynchronous case and allows the derivation of closed-form equations for the bit error probability in various Rake receiver architectures. It is shown that a Gaussian approximation can be used for both multiple-access and interframe interference as long as the number of frames per symbols is large (typically, at least 5), whereas there is no minimum requirement for the number of users for the equations to hold. It is observed that under many circumstances, the chip-synchronous case shows a worse bit error probability performance than the asynchronous case; the amount of the difference depends on the autocorrelation function of the ultra-wideband pulse and the signal-to-interference-plus-noise-ratio of the system. Simulations studies support the approximate analysis.     

Equivalent system model and equalization of differential impulse radio UWB systems

A discrete-time equivalent system model is derived for differential and transmitted reference (TR) ultra-wideband (UWB) impulse radio (IR) systems, operating under heavy intersymbol-interference (ISI) caused by multipath propagation. In the systems discussed, data is transmitted using differential modulation on a frame-level, i.e., among UWB pulses. Multiple pulses (frames) are used to convey a single bit. Time hopping and amplitude codes are applied for multi user communications, employing a receiver front-end that consists of a bank of pulse-pair correlators. It is shown that these UWB systems are accurately modeled by second-order discrete-time Volterra systems. This proposed nonlinear equivalent system model is the basis for developing optimal and suboptimal receivers for differential UWB communications systems under ISI. As an example, we describe a maximum likelihood sequence detector with decision feedback, to be applied at the output of the receiver front-end sampled at symbol rate, and an adaptive inverse modeling equalizer. Both methods significantly increase the robustness in presence of multipath interference at tractable complexity.     

Rapid search algorithms for code acquisition in UWB impulse radio communications

Ultrawideband (UWB) impulse radio is an emerging technology suitable for high-rate tactical wireless communications. One of the crucial challenges for a connecting station remains the initial code acquisition, in a hostile propagation environment (e.g., urban combat). In this paper, we address the coarse acquisition of pseudonoise (PN) codes and propose algorithms for speeding up the acquisition process and/or reducing the complexity of the acquisition algorithm itself. Also, in the case of energy detection, we show that the front-end sampling rate may be reduced. An in-depth analysis, supported by simulations in the presence of multipath is presented, and the results discussed.     

Direction finding receiver for UWB impulse radio signal in multipath environment

In this paper, we propose a direction finding (DF) receiver for ultra wideband impulse radio (UWB‐IR) signal in a realistic multipath environment. The receiver uses an array of antenna, where each antenna is connected to a proposed propagation‐delay estimation structure. The advantage of the proposed structure is that it outputs a trapezoidal signal whose amplitude reflects the propagation delay and thus relaxes the sampling rate requirement of the analog‐to‐digital‐converter (ADC). The angle‐of‐arrival (AOA) is estimated from the vector of propagation delays measured with respect to reference antenna. Because these estimated delays contain outliers, we propose a simple AOA estimation algorithm based on minimum fractional‐distance search. Experimental results based on simulation show that the proposed DF receiver achieves better performance compared with the minimum ?₁‐ and ?₂‐based (least‐squares based) distance search. Copyright © 2010 John Wiley & Sons, Ltd.     

Multiple access capacity of UWB m-ary impulse radio systems with antenna array

In this paper, the multiple access capacity of an Mary pulse position modulation (PPM) impulse radio (IR) system with antenna array is analyzed in dense multipath environments. An antenna array with Rake receivers is used to capture the signal energy from multipaths. Multiple access performance of the system is evaluated in terms of number of supported users for a given bit error rate and bit transmission rate with different number of antenna elements and selected paths. Numerical results show that the multiple access capacity of an M-ary IR system can be improved significantly by increasing the number of antenna elements and/or by adding more paths coherently at the receiver.