【作者】 郑霖；

【导师】 欧阳缮；

【作者基本信息】 西安电子科技大学 ， 信息与通信工程， 2007， 博士

【摘要】 无线脉冲超宽带（IR-UWB）通信系统利用极高的带宽和很低的发射功率满足近距离范围上大容量通信以及精确定位的要求。但有别于传统无线系统采用连续载波调制的通信体制,IR-UWB采用基带脉冲波形来承载信息。因为在实际无线环境下脉冲信号传播受到传播路径衰落快、密集多径、延迟扩展相对较长,以及多用户干扰等多方面的影响,传统信号检测和处理方法受到了极大的挑战。本论文主要从IR-UWB信号的检测和多用户信号处理算法两个方面进行了研究,力图结合脉冲接收信号的特征,获得简单高效的IR-UWB多用户信号检测方法。论文的主要工作和结果概括如下:1.根据脉冲调制方式,分析了IR-UWB多址系统下的解调性能。提出了一种通过求解干扰信号方差来计算多用户下误码性能的简单方法;进一步,在考虑实际超宽带多径衰落的条件下,通过理论分析,获得了相干检测和Rake分集检测的多址误码性能表达式,并通过仿真验证了其正确性。通过理论分析和仿真实验说明了在多用户UWB信道中,检测性能受多径幅值衰落和延迟扩展长度影响的规律;2.针对脉冲接收信号能量较集中,通过时域加窗可获较高的E_b/N₀特征,提出了一种基于最小四阶矩（LMF）准则的多用户检测方法。理论分析了当前常用HOS盲多用户检测准则的收敛性,通过直接求Hessian矩阵的方法,在有噪条件下推导出了检测准则的Hessian矩阵。分析了LMF准则的解相关性和收敛性。在多径CDMA通信系统中,对LMF准则的最小二乘推演,得到了更具快速收敛性的RLS-LMF算法;3.根据脉冲扩频信号的非交叠特性,提出了一种简化脉冲多用户检测的框架,称为免多径约束框架。在此框架下常规多用户检测方法不再需要多径码矩阵的约束运算,这使很多在AWGN信道下的高效检测方法,如Kalman算法等,能够直接应用在多径IR-UWB检测中,简化了运算,提高了性能。将自适应LMF检测做最小二乘推演,得到类AWGN信道下的MF-RLS-LMF算法,比多径RLS-LMF具有更低的计算复杂度;4.针对发送参考脉冲UWB（TR-UWB）通信方式,提出了一种改进的多用户信号检测方法。不仅利用了参考信号模板信息,而且利用其参考符号信息。采用用户伪随机码调制参考脉冲,通过模拟LMS反馈迭代获得最优的检测模板。这种方法实际是利用了用户多径信号的统计独立性,作为其特征波形来减小相关干扰的影响;5.针对低速（LDR）大用户容量通信要求,采用一种直接序列扩频的间隔脉冲调制方式,提出了具有低复杂度的高性能低速大容量多用户检测算法。算法同样利用了间隔脉冲信号不交叠的特性,避免了多径码矩阵约束带来的计算复杂性,根据接收用户脉冲波形存在延迟扩展独立性和扩频独立性的特征,得到具备均衡能力的双插值多用户检测接收机形式。性能分析和仿真证明了这种算法在NLOS环境下较好的检测性能。更多还原

【Abstract】 Both large capacity and precise ranging are persuing goals in IR-UWB communication systems. Extremely high bandwidth, and very low-bound transmit power is the fundamental characteristics for reaching this expective performance. IR-UWB carries information on base-band impulse while traditional wireless system on continuous carry modulation. The traditional signal detection and processing method are confronted with a significant handle in practice due to several drawbacks of the impulse transmission, such as rapid path fading, density multipath, long delay spread, and multiuser interference. In view of problems mentioned above, IR-UWB gains importance in its own right. This thesis concentrates on the signal detection and the multiuser signal processing. It tries the best to take advantages of the received impulse signal to obtain simple and effective policies of multiuser detection. The main contribution is concluded as follows:1. The demodulation performances are analyzed for IR-UWB multi-access system. The thesis provides a simple approach to compute bit-error-rate （BER） in multiuser environment. Furthermore, considering the multipath fading channel in UWB, the expression on multi-access BER performance of coherent detection and Rake division detection are concluded and verified via simulation. Through analysis and experiments in multiuser UWB channel, we find the internal relation between the detection performance and the channel factors, including the fading of the multipath components and the length of the delay spread;2. We propose a least mean fourth （LMF） based multiuser detection criterion, which has the outstanding decorrelation capability at high SNR environment. By time-domain window filtering, the high E_b/N₀ can be obtained for the concentrative energy in impulse signal. The thesis analyzed the convergence of different high-order statistics （HOS） based blind multiuser detection criterions. The Hessian matrix is derived in noise environment, and furthermore, is used to analyze and prove the decorrelation and convergence of LMF criterion. In multuser CDMA system, the least square method is adopted to construct a RLS-LMF algorithm with faster convergence in multipath channel;3. In view of the non-overlap characteristics of impulse spreading signa, we propose a framework, called "multipath-free", for simplifying multiuser detection. Under this framework, the code matrix in the common multipath constrain is not necessary for multiuser detection. That makes many efficient detection approach in AWGN channel, for example, Kalman algorithm, could be directly applied in the impulse radio system. No doubt, it simplifies the algorithms and boosts the proformance. Moreover, least-square derivation is implemented in adaptive LMF detection and the MF-RLS-LMF algorithm is obtained. It has lower complexity than multipath RLS-LMF proposed above;4. A modified TR-UWB signal and detection are proposed for suppressing the multiuser interference. The approach not only uses the information in the reference signal template, but also the reference symbol information. It modulates the reference impulse by user pseudo-random code, and uses analog LMS feedback to obtain the optimal detection template. This approach, in fact, takes advantage of the statistics independence of multipath signal to construct an effective signature to lessen the correlative interference.5. For low data rate and large user capacity IR-UWB communicaiotn, we propose a multiuser detection algorithm with high performance and low computation complexity. The algorithm adopts an interval-guarded impulse modulation with direct sequence spread. Due to the non-overlap characteristics of impulse spreading signal, the multipath-free framework is applied in the proposed dual-interpolating multiuser detector. The effective equalization is applied in the algorithm at the same time. The analysis and simulation verify the efficiency of the proposed algorithm even in the NLOS channel.更多还原