【作者】 杨志华；

【导师】 张乃通； 张钦宇；

【作者基本信息】 哈尔滨工业大学 ， 信息与通信工程， 2010， 博士

【摘要】 随着网络对社会的影响越来越广泛和深刻,高速率、高质量及多业务模式特征的无线网络已成为信息获取的重要手段。脉冲超宽带(Impulse Radio Ultra-Wide Bandwidth,IR-UWB)通信技术所具有的大带宽、无载波和低功率谱密度特性,有利于降低系统复杂性,实现多业务功能一体化,提高系统容量和实现较好的电磁兼容等,成为中短距离数据应用领域无线个域网络(Wireless Personal Area Network, WPAN)最具竞争力的无线技术之一。WPAN的典型应用之一是室内的短距离通信。室内UWB无线通信系统的信道环境相对于室外以及传统连续波通信系统来说更为复杂,主要体现为密集多径引起的较大时延扩展。这一点给IR-UWB系统的接收机设计带来了较高的复杂度,尤其是以RAKE接收机为代表的相干系统和Tansmitted Reference(TR)系统,而UWB非相干能量检测(Energy Detection,ED)系统由于相对简单而受到了广泛关注。针对密集多径衰落信道的基本特征,本文研究UWB ED系统的平均性能指标计算和接收前端优化设计两个问题。通过对接收机检测窗口内信噪比的统计特性的描述,给出系统平均比特错误概率指标和平均捕获性能指标的闭合表达式,并针对分组传输模式给出包捕获性能的评价指标,从而完整的建立起UWB ED分组业务系统在室内多径衰落信道下系统性能评估的理论框架。同时,为了提高UWB ED系统的性能,本文研究ED系统接收前端的优化设计问题,主要针对检测窗口的选择、判决门限电平的设计以及高性能的信号捕获算法,为UWB ED系统的工程优化提供一定的算法基础,以拓展UWB ED系统的应用范围。论文研究的内容包括:第一,ED系统及信道模型简介。与连续波系统不同,IR-UWB(Impulse Radio, IR)系统采用窄脉冲体制,不需要载波调制,因此接收机端可以省去锁相环,中频等环节,降低了系统的复杂性。对于ED系统,接收机结构减少了相关器,相比于RAKE接收机和TR系统占用的系统软硬件资源更少。鉴于UWB信号的脉冲形式,有必要介绍与之相对应的两种调制方式,同时针对室内密集多径信道环境,给出信道冲激响应的数学模型,以便于后续分析。第二,UWB ED系统平均比特错误概率指标计算问题的研究。由于大量的多径信号分量随机到达接收机,使得固定时间窗口内信噪比为随机变量,其统计特性求解困难,从而影响到系统平均比特错误概率指标的计算。本部分内容针对低速率(无符号间干扰)和高速率(具有符号间干扰)两种情况,以簇生点过程对信道建模,给出了两种情况下系统平均比特错误概率的闭合表达式。同时,推导出了系统符号传输速率和比特错误概率二者之间的定量关系,并通过仿真给出了以门限优化和窗口长度选择为手段的平均比特错误概率性能的上界。第三,ED系统平均捕获性能指标计算问题的研究。对于UWB系统,密集多径分量和巨大的搜索空间导致信号捕获的目标,手段及性能评估方法都与传统连续波系统有所不同,主要体现在捕获命中集推导、搜索策略的选择以及平均捕获性能指标的计算三个方面,其中最后一个方面包含了前面两部分内容。本节以第二部分获得的平均比特错误概率入手,给出捕获命中集的闭合解,以Markov链模型推导出串行搜索策略下的平均捕获性能指标的表达式,包括平均捕获时间和特定时间内捕获概率两项常用指标。同时,针对UWB ED系统的典型业务模式(分组传输),给出了分组捕获概率的闭合表达式,为UWB ED系统应用的拓展奠定了理论基础。第四,UWB ED接收前端优化方法的研究。首先研究了ED接收机检测窗口的最优长度问题,同时对判决门限电平进行了优化设计。针对判决统计量服从的卡方分布难于闭合求解,给出了以高斯分布近似该统计量,并以最小二乘多项式拟合的最佳门限求解方法,在保持了一定性能的基础上降低了系统工程优化上的复杂度。同时,针对ED接收机捕获信号时需要同时对检测窗口长度和需要估计的定时相位进行二维搜索的特点,给出了以遗传算法为基础,结合信噪比实时估计的搜索算法,在上述两项捕获性能指标上均优于现有搜索策略,丰富了UWB信号的捕获方法。更多还原

【Abstract】 With the wide and profound influence on society, wireless network of high speed and super quality become important approach to access information. As one technology of carrierless and huge bandwidth, Impulsed radio Ultra-Wide Bandwidth (IR-UWB) presents most potential competence for short-distance data transimission, such as wireless personal area network (WPAN), due to its large capacity and good electromagnetic compatibility.The typical application of WPAN is short distance communication indoor. Contrasted to outdoor system and traditional carrier system, UWB system indoor experience compicated environment where dense multipath components lead to large delay spread. This makes the system design difficult, especially in coherent system of RAKE receiver and in noncoherent Transmitted Reference (TR) system. However, energy detection (ED) system suffers less for its principle and simple structure. Considering the basic characteristics of multipath fading channel (MFC) indoor, this dissertation focuses on two problems of UWB ED system, averaged criterion of system performance and performance optimization. By describing the stastics characteristic of signal power to noise ratio (SNR) in detection window of receiver, we derive the closed form of averaged bit error probability and the criterion of acquisition performance of sytem. Moreover, the packet acquisition performance of UWB packet transmission system is evaluated by the criterion proposed here with a complete analytical framework of UWB ED system performance in MFC. Besides, to improve the UWB system performance, the optimization design of receiver scheme, including selection on detection window, determination on threshold of decision and signal acquisition algorithm, is investigated for the engineering implements of UWB ED system. The main content consist of :I. The ED system and channel model. Different with the sine carrier system, IR-UWB system employs the short pulse to carry information. Therefore a lot of components of receiver, such as phase-locking loop and medium-frequency, are not necessary. Moreover, for ED system, the receiver has not correlator which is indispensable in RAKE and TR system and thus has more simple structure. And two modulations corresponding to the pulse format are introduced followed by the channel model indoor.II. The investigation on the averaged criterion of BEP (Bit Error Probability) of UWB ED system. Since many MPCs arrive the detection window of receiver randomly, the statistic of SNR of window is difficult to describe which is critical for the derivation on averaged BEP. In this dissertation, the averaged BEPs are derived in closed form based on the channel model described by clustered point process, respectively on two conditions of low data rate (without Inter symbol Interference, ISI ) and high data rate (with ISI). In addition, the qualitative relation between data rate and BEP is given and the averaged BEP bounds are demonstrated by simulation in term of optimization on threshold and integral length.III. The investigation on the averaged criterion of acquisition performance of UWB ED system. Due to the dense MPCs and huge search space, the objects, approachs and evaluations of the signal acquisition in UWB ED system are different from traditional sine system. This embodies the three terms of derivation on HIT set, design of search strategy and averaged criterion of acquisition performance. Based on the averaged BEP given, the HIT set is obtained in closed form and subsequently the expressions of mean acquisition time and the acquisition probability in certain interval are derived with serial search strategy via the model of Markov process. Moreover, the probability of packet acquisition of UWB packet transmission system is defined and given in closed form for the UWB applications in the future.IV. The approaches of optimization on UWB ED receiver scheme. First, the optimal length of detection window and the optimal threshold of data detection are investigated and designed. Gaussian distribution is employed for approximation since chi-square distribution of statistic of decision variable is hardly expressed in closed form. Based on this approximation, the polynomial fitting of least square is used for the solution of optimal threshold of decision, which does not improve the complex of engineering of system implements. Moreover, considering the feature of two-dimension search on parameters of signal acquisition, the acquisition scheme based on genetic algorithm combined with SNR estimation is proposed for signal acquisition. The results show that the proposed algorithm performs better than general search strategy.更多还原