【作者】 孟繁宇；

【导师】 顾学迈；

【作者基本信息】 哈尔滨工业大学 ， 信息与通信工程， 2011， 博士

【摘要】 进入21世纪以来,随着无线通信技术和网络技术的发展,信息传播无论从速度还是广度上都有了质的飞跃。人们希望可以不受时间和空间的限制,自由流畅地进行信息的传递交流。低速无线个域网正是未来多域异构的无线网络的重要组成部分之一,它不仅可以有效地解决最后1米的无线接入问题,而且能够在个人空间范围内为用户提供丰富业务类型的无线连接,随时随地的为用户提供信息传输、协同和处理。低速无线个域网不但要求传输技术能够适应复杂的室内无线环境,具有较高的抗频率选择性衰落和抗干扰能力,较大的系统容量,还必须具有低功耗和低复杂度的特点。Chirp扩频技术具有良好的抗干扰能力和较高的带宽利用率,该技术既不采用伪随机码作为扩频码,也没有跳频图样,而是利用chirp信号的匹配滤波和脉冲压缩特性来进行扩频通信,因此又兼顾了低复杂度和低功耗的特点,非常适合于低速无线个域网的通信要求。因此在低速无线个域网中采用chirp扩频技术作为物理层传输方案以提高系统性能是一项十分重要的研究课题。在这样的背景下,本文对chirp扩频技术应用于低速无线个域网的相关技术进行深入研究,主要研究内容包括以下几方面:首先,本文研究了低速无线个域网中chirp扩频传输模型。针对低速无线个域网的网络环境特点以及对传输技术的特别要求,本文首先分析chirp扩频信号的匹配滤波和脉冲压缩特性,并比较了基于BOK的调制方案与混合调制方案在低速无线个域网环境下的性能优劣以及时域交叠问题所带来的影响。分析表明,虽然基于BOK的调制方案直接应用于低速无线个域网通信仍有不完善之处,但是在考虑复杂度,抗干扰特性和系统容量等多种因素之后将其作为一种优选方案,为本文在低速无线个域网中应用chirp扩频技术的研究工作奠定了基础。其次,本文研究了基于最优信号组的M进制chirp扩频调制。针对基于BOK的chirp扩频调制方案无法为低速无线个域网提供较高的链路容量的问题,提出一种对数据进行M进制编码并利用多个chirp信号对其进行对应传输的调制方案。针对多chirp信号的互相关性所导致的系统误码率性能下降问题,本文对chirp信号的选取进行了最优化设计。通过分别使用线性chirp信号和组合chirp信号构建最优信号组,在适度增加系统复杂度的前提下,可以为低速无线个域网提供较高的链路容量。第三,本文研究了基于匹配信号变换的chirp干扰抑制方法。在2.4GHz的无线频段中,由于存在多种无线传输体制使得相互间的干扰不可避免,而其中对chirp扩频影响最严重的是chirp干扰。针对现有的干扰抑制方法都无法有效抑制这种干扰的问题,本文提出一种结合匹配信号变换在chirp率域上进行处理的方法。该方法不但考虑chirp干扰信号chirp率与有用信号chirp率不同的一般情况,还针对干扰信号chirp率与有用信号chirp率相同的特殊情况提出了针对性解决方案。理论分析和仿真验证都证明了采用基于匹配信号变换的干扰抑制方法可以有效保证系统不受到chirp干扰信号的影响。最后,本文研究了chirp扩频多址干扰抑制方法。针对现有的基于chirp扩频的多址系统中抑制多址干扰的方法或复杂度过高或效果不佳等问题,本文提出了一种联合chirp率和信号出现相位构建多址信号基的方法,该方法能够在多址chirp信号相邻很近的情况下,依靠初始相位的不同来保证多址信号间的正交性,从而可以在有限的信号带宽内容纳更多的多址chirp信号。同时,本文还比较了几种典型非线性chirp信号的互相关特性,提出一种利用sin chirp信号构建多址信号基的多址接入方法抑制混合调制方案中的多址干扰,该方法在固定信号带宽和信号持续时间内为不同多址用户分配具有不同周期的sin chirp信号来实现多址接入。两种方法虽然基于不同的调制方案,但是在多址信号基的构建上都能够做到简单易实现,并且对多址干扰都有较好的抑制效果。更多还原

【Abstract】 The tremendous advancement in wireless communication and networking technologies has raised a significant number of major qualitative breakthroughs in improving the speed and scale of information dissemination, since the beginning of the 21st century. The fundamental goal of a communication system is to convey information smoothly without the constraints in time and space. Low-rate wireless personal area network(LR-WPAN) is an essential component of the future multi-domain heterogeneous wireless network. It can not only resolve the last mile access problem, but also can provide wireless connections to various services in personal operating space, which supports on-demand information transmission, coordination and processing. LR-WPAN requires the signaling techniques to adapt to the complicated indoor wireless environment, with robust performance in frequency selective fading channels, low power consumption, and low complexity. Chirp spread spectrum technique is equipped with good anti-interference ability and high bandwidth efficiency. Furthermore, it utilizes chirp signal matched filter and pulse compression features in spread spectrum communications, instead of using pseudo-random code as spreading code, without the requiremnent of frequency hopping pattern. Therefore, chirp spread spectrum technique is power efficient with low complexity, which makes it a very competitive candidate in LR-WPAN. Chirp spread spectrum in LR-WPAN has attraced a significant number of research attentions in recent years.As the background stands, this dissertation conducts an in-depth study on chirp spread spectrum technique for LR-WPAN communication:First, the chirp spread spectrum transmission model in LR-WPAN is investigated. According to the characteristics and transmission requirements of LR-WPAN, this work analyzes the properties of chirp signal in matched filtering and pulse compression characteristics. The dissertation also compares the performance of the BOK modulation shceme and the mixed modulation scheme in LR-WPAN, as well as the effects of chirp signal overlapping in time domain. Analysis indicates that although there is much to be desired, BOK modulation scheme is still the best choice for chirp spread spectrum in view of complexity, capacaity and system performance.Second, the M-ary chirp modulation scheme is studied based on the optimal chirp signal set. BOK modulation scheme fails to provide high link capacity for LR-WPAN, A new modulation scheme is proposed to improve the link capacity, where data is encoded by M-ray and transmitted by several chirp signals respectively. This work optimizes the design of chirp signal selection in order to improve the system BER performance degradation problem resulting from the cross correlation of multi-signal. The optimal signal set, constructed with liner chirp signal and combined chirp signal, can provide higher link capacity for LR-WPAN without significant increase in system complexity.Third, the chirp interference suppression method based on matched signal transform is sutided. Due to the coexistence of various wireless transmission system in 2.4G ISM band, interference is inevitable. Chirp interference has the most severe impact on chirp spread spectrum system, with no efficient and effective solution yet. This dissertation proposes a chirp inteference suppression method based on matched signal transfom. This method not only considers general case where the chirp rate of chirp interference signal is different from the useful one, but also provides solution for the special case where the interference and the useful signals share the same chirp rate. Theory analysis and simulation verification both prove that, by using this method, the system is not interfered by chirp interference.Last, this work studies the muti-access interference suppression methods for chirp spread system. A bivariate chirp method is proposed, which makes use of both chirp rate and intinal phase to construct the multi-access signal base. When the chirp rate differences are small, this method ensures the orthogonality of multi-user signals by distinguishing different initinal phases, so that more chirp signals can be contained in limited signal bandwidth. Meanwhile, a novel method is also proposed with non-linear chirp signal to enhance the multiple access capacity of a mixed chirp modulation communication system. This method makes use of the characteristics of sin chirp signal to suppress the multi-access interference. Both methods are easy to realize and have good performance to suppress multi-access interference. Although based on different modulation schemes, both methods have good performance for multi-access interference suppression and are suitable for expanding for mulit-user systems.更多还原