基于多径条件的TH-PPM UWB RAKE接收机性能分析

用半理论的方式对TH-PPM多径信道下A-Rake、S-Rake和P-Rake的BER性能进行分析。A-Rake做为一种理想的接收机,对系统的复杂性要求较高,而在实际的Rake接收机设计中,S-Rake和P-Rake的性能与支路数有关,S-Rake要优于P-Rake。P-Rake与S-Rake的性能差距随着支路数的增加而减小。在对系统的复杂性要求较高的情况下,可直接采用P-Rake接收机。     

基于TH-PPM-UWB多径信道下的Rake接收机性能分析

超宽带信号在无线信道中传播会产生严重的衰落和多径干扰等问题,而在抗多径干扰方面采用Rake接收机的方式是一种行之有效的手段.利用IEEE802.15.3a标准信道模型,采用TH-PPM调制方式对信道冲激响应的特性进行了分析,并对标准信道模型下的A-Rake,P-Rake和S-Rake三种接收机模型在不同的支路下的BER进行了对比分析.从仿真结果可以得出A-Rake为理想接收机性能最佳,相同支路下S-Rake接收机的性能要优于P-Rake接收机,但是随着支路数的增加两者的性能差距也越来越小.     

60 GHz芯片间无线互连系统中的Rake接收性能

在60 GHz芯片间无线互连信道中存在着多径干扰问题,采用Rake接收是提高系统性能的重要手段。针对脉冲超宽带( IR-UWB)的芯片间无线互连系统,分析了多径信道下Rake接收机的误码性能。在IEEE 802.15.3 c信道模型基础上,对不同分支数以及不同合并方案下的选择Rake ( S-Rake)和部分Rake(P-Rake)接收机误码性能进行了研究。仿真结果表明采用支路数为2的P-Rake在数据速率为10 Gb/s时仍具有良好的抗多径性能,这为芯片间无线互连系统的Rake接收方案提供了技术参考。     

多径信道PAM-TH-MA系统性能分析

超宽带(UWB)通信具有数据速率高、功率谱密度低、定位精度高以及抗多径能力强等优点,通过重复利用频谱,可解决频谱拥挤不堪的问题,已成为无线通信领域研究的热点。本文针对PAM-TH-MA系统在多径信道下的抗噪性能进行研究,并比较了分别采用S-Rake和P-Rake接收机时的性能。仿真结果表明,采用S-Rake接收机时的系统性能优于P-Rake接收机。     

基于Rake接收机的UWB通信系统性能分析

针对无码间干扰的TH-PPM-UWB通信系统,分析了该系统在IEEE UWB室内多径信道模型下采用Rake接收机时的系统性能,仿真了不同结构Rake接收机的误码率,结果表明,总体上SRake的性能要优于PRake,且两种接收机的性能随着叉指数目的增加都有明显的改善。     

基于平衡Gold码的TH-UWB系统性能分析

针对有码间干扰的跳时脉冲脉位调制超宽带(PPM-TH-UWB)通信系统,为了在不增加系统复杂度的前提下,提高系统抗码间干扰的性能,研究了基于平衡Gold码的Rake接收机的性能,并在IEEE 15.3a UWB信道下对采用平衡Gold码作为跳时序列的Rake接收机和采用传统伪随机序列的Rake接收机的误比特率进行计算机仿真比较,结果表明:采用平衡Gold码作为跳时序列,Rake接收机得到明显改善,而且码间干扰越严重,性能提升越显著。     

DS-UWB系统中二种抑制窄带干扰的多天线接收机

直接序列扩频超宽带(DS-UWB)系统采用窄脉冲和扩频技术能够与其它无线电系统共存,但是,在进行系统设计时,必须对同频段系统的干扰加以抑制.文中在存在窄带干扰的情况下,提出一种自适应多天线Rake接收机,通过自适应调整天线合并权向量来抑制窄带干扰对系统的影响,并通过仿真实验与现有抑制窄带干扰接收机进行比较.理论分析与仿真结果表明,该接收机具有较好的环境鲁棒性,并且能够一定程度上抑制窄带系统对DS-UWB系统的干扰,保证系统接收性能.     

超宽带系统中基于认知的Rake接收机设计

直接序列扩频超宽带（DS-UWB,directed．spread．spectrum ultra wide band）系统采用窄脉冲和扩频技术进行通信,由于带宽很宽,有可能与同频段窄带系统共存。当存在窄带干扰时,最优接收机为采用MMSE准则的Rake接收机,而不存在窄带干扰时,MRC合并算法Rake接收机为最优接收机。由...     

脉冲超宽带在AWGN中的误码率性能分析

针对跳时超宽带(TH-UWB)和直接序列超宽带(DS-UWB)在加性高斯白噪声干扰下(AWGN)的误码率性能进行了分析,并对超宽带信号脉冲位置调制(PPM)和脉冲幅度调制(PAM)的误码率做了比较。通过理论分析和软件仿真,结果说明在加性高斯白噪声干扰下,对于TH-UWB调制和DS-UWB调制,PAM的误码率性能都优于PPM,并在此基础上给出了几种方法来提高超宽带脉冲信号抗加性高斯白噪声的能力。     

扩频通信系统中Rake接收性能仿真研究

在扩频通信中,Rake接收是抵抗多径衰落的有效方法。本文首先介绍无线移动通信的信道特性,然后对Rake接收的基本原理和接收机结构进行详细描述,并对Rake接收性能进行了仿真比较。仿真结果表明,在多径信道条件下,Rake接收方式能很好的改善接收系统误码性能;采用GOLD序列扩频比m序列扩频方式时,Rake接收方法性能提高的更明显。     

UWB多址技术的研究

UWB技术不需载波,能直接调制脉冲信号,产生带宽高达几GHZ的窄脉冲波形,其带宽远远大于目前任何商业无线通信技术所占用的带宽.超宽带系统的成功,很大程度上依赖于有效的多址技术的发展.主要研究内容是超宽带无线通信系统中的多址技术.通过计算机仿真的方法,比较了TH-UWB和DS-UWB两种多址方式的多址性能,得出DS-UWB无论是用户容量还是误比特率都要优于TH-UWB.     

Frequency-Domain Turbo Equalization and Multiuser Detection for DS-UWB Systems

One of the major challenges in direct sequence-ultra wideband (DS-UWB) receiver design is intersymbol interference (ISI). Several equalization schemes to eliminate ISI in DS-UWB systems have been proposed in the literature. It was shown that frequency-domain (FD) equalization techniques can offer better trade off between performance and complexity compared to timedomain equalization schemes for DS-UWB systems on highly dispersive channels. In this paper, we derive low-complexity FD minimum mean square error turbo equalization schemes for single-user binary phase shift keying (BPSK) and quaternary bi-orthogonal keying (4BOK) DS-UWB systems. For multiuser DS-UWB systems, we combine FD turbo equalization schemes with soft interference cancelation to obtain multiuser FD turbo detectors. The bit error rate performance gain due to turbo detection is shown to be significant, particularly for multiuser DS-UWB systems.     

一种较低复杂度的UWB信道自适应均衡技术

针对多用户UWB信道存在的符号间干扰和用户间干扰问题,提出了一种用于DS-UWB/TH-UWB接收机的较少复杂度的自适应均衡技术及相应算法,并与传统算法在复杂性和性能方面进行了比较。研究结果表明所提出的算法在运算量上远小于单独使用RLS算法,在输出误差的收敛上远快于单独使用LMS算法。     

Bit Error Rate of TH-BPSK UWB Receivers in Multiuser Interference

It is well known that the Gaussian distribution is not an accurate model for approximating the probability density function (PDF) of the multiple access interference (MAI) in time-hopping UWB (TH-UWB) systems. An exact theoretical model which explains the key features of the PDF of the MAI in TH-UWB systems is discussed. These features, which can be precisely anticipated by the proposed model include impulses, singularities, and the tail behaviour in the distribution of the MAI. The model reveals in quantitative terms why a Gaussian approximation for the MAI in TH-UWB systems is highly imprecise even in an environment with a large number of independent interferers. Based on the model obtained for the PDF of the MAI and exploiting the maximum a posteriori (MAP) receiver design rule, the optimal attainable BER performance of binary TH-UWB receivers in additive white Gaussian noise channels is numerically determined. The performances of some recently proposed UWB receivers are benchmarked against the optimal performance showing that some of them achieve near-optimal performance.     

超混沌序列对DS-UWB多址性能的改善

利用Roessler超混沌系统构造了一种新的超混沌序列,分析了序列的相关特性,并将其应用于直接序列超宽带（DS—UWB）系统中,以提高它的误码性能。建立了DS-UWB通信系统的模型,以超混沌序列作地址码对高斯白噪声信道中多用户DS—UWB系统误码率进行了分析,并将其与m序列作地址码时的相应性能进行了比较。由分析和仿真可知,构造的新的超混沌序列能较好地改善DS-UWB的多址性能。     

空时码在DS-UWB系统的应用研究

直接序列超宽带(DS-UWB)通信技术是无线通信中的一个非常有发展前途的技术.为克服无线传输中多径衰落效应,针对DS-UWB系统,提出了一种将空时编码和Rake接收结合的方案,并进行性能分析和仿真.该方案建立在码片波形,使系统不仅获得空间分集,同时获得多径分集.仿真结果表明,基于这种方案的多天线系统的性能明显优于单天线系统.     

存在CDMA干扰时超宽带系统性能分析

超宽带系统信号功率很低,并且占用很宽的频段,系统需要与其它窄带系统共存.因此,在进行系统设计时,必须考虑窄带干扰信号对超宽带系统性能的影响.文中采用特征函数的方法精确分析了多径信道环境下,存在CDMA信号干扰时直接序列超宽带系统的性能,推导得到系统的误码率公式;最后,在基于IEEE 802.15.3a推荐的多径信道环境下进行系统仿真和数值分析,结果表明,文中方法得到的系统性能与仿真结果基本吻合,能够较准确估计系统在存在CDMA窄带信号干扰时的性能.     

Equalization for DS-UWB Systems—Part I: BPSK Modulation

Ultra-wideband wireless transmission has attracted considerable attention both in academia and industry. For high-rate and short-range transmission, direct sequence based ultra-wideband (DS-UWB) systems are a strong contender for consumer market applications. Due to the large transmission bandwidth, the UWB channel is characterized by a long root-mean-square delay spread and the RAKE receiver cannot always overcome the resulting intersymbol interference. We therefore study equalization for DS-UWB systems. This paper is comprised of two parts. In this first part, we consider DS-UWB with binary phase-shift keying (BPSK) modulation, which is the mandatory transmission mode for DS-UWB systems promoted by the UWB Forum industry alliance. We derive matched filter bounds for optimum equalization taking into account practical constraints like receiver filtering, sampling, and the number of RAKE fingers when RAKE preprocessing is applied at the receiver. Our results show that chip-rate sampling is sufficient for close-to-optimum performance. For analysis of suboptimum equalization strategies we further study the distribution of the zeros of the channel transfer function including RAKE combining. Our findings suggest that linear equalization is well suited for the lower data rate modes of DS-UWB systems, whereas nonlinear equalization is preferable for high-data rate modes. Moreover, we devise equalization schemes with widely linear processing, which improve performance while not increasing equalizer complexity. Simulation and numerical results confirm the significance of our analysis and equalizer designs and show that low-complexity (widely) linear and nonlinear equalizers perform close to the pertinent matched filter bound limit.     

MMSE multipath diversity combining for multi-access TH-UWB in the presence of NBI

The performance of asynchronous time-hopping ultra-wideband (TH-UWB) multiple access spread spectrum is analytically investigated in a UWB realistic multipath channel and in the presence of narrowband interference (NBI). In particular, an interference suppression receiver for TH-UWB wireless systems is proposed. It consists of selecting the first strongest multipath components using an appropriate Rake receiver with the path diversity combining being based on the minimum mean square error criterion. Pulse position modulation and pulse amplitude modulation schemes are considered. The expressions of the signal-to-interference and noise ratio at the output of the selective Rake combiner, the system multi-access data rate as well as the conditional bit error rate are also derived. The impact of different parameters, such as the number of selected dominant paths, the NBI power as well as the time hopping sequence code on the system performance are studied. Results reveal that the proposed receiver can almost completely eliminate the effect of NBI.