【作者】 孟宏伟；

【导师】 王树勋；

【作者基本信息】 吉林大学 ， 通信与信息系统， 2007， 硕士

【摘要】 本文以超宽带(UWB)无线通信理论为基础,分析了UWB信号以及信道的特点,研究了适合超宽带的测距与定位方式,主要针对超宽带定位中的信号时延估计和角度估计算法作了深入研究。首先,分析了超宽带各种定位技术的优缺点,从理论上论证了适合UWB的测距和定位方式。理论表明:基于场强测量的定位精度不高;基于TOA和AOA的定位可以充分发挥UWB信号带宽宽的优点,提高定位精度;基于AOA的定位需要使用阵列天线,不适合在室内多径密集的环境下定位。然后,在基于时间估计的超宽带定位中,指出了传统相关算法中多径分辨率低的缺点,引入了基于MUSIC算法的高分辨率的时延估计算法。提出了一种频域下MUSIC算法,该算法在接收端加入了相关器,利用相关器估计出的粗时延,缩小了MUSIC算法中谱峰搜索的范围,降低了算法的复杂度。仿真结果表明,在信号通过相关器后,信噪比增大,时延估计准确性比一般MUSIC算法高。提出了两种通过信道解卷积来估计多径信号时延的算法,分别把高阶累积量和维纳滤波引入到了超宽带时延估计算法中。在信道解卷积后,利用维纳滤波器的思想,导出了最小均方误差准则下的信道解卷积滤波器响应函数,进一步提高了频域下MUSIC算法的性能,仿真结果也表明了其相对于一般解卷积的优势。另外,在加性高斯白噪声情况下,信道解卷积后的数学表达式与谐波信号相同,利用谐波信号估计中高阶累积量的方法来抑制高斯噪声,降低了时延估计的误差。最后,在超宽带信号的角度估计中,通过一个超宽带雷达信号模型,提出了信号到达角度与阵列踪迹信号正负峰值连线斜率之间的定量关系。推导了在此信号模型下的阵列空时处理方法,给出了系统的空时分辨率函数、空间频率分布函数,算出了峰值功率和能量表达式并给出仿真结果。分析了系统的时间分辨率和角度分辨率,与信号参数、阵列天线的尺寸、阵元间距和频率带宽之间的关系。更多还原

【Abstract】 Ultra-wideband (UWB) radios have relative bandwidths larger than 20% or absolute bandwidths of more than 500 MHz. Such wide bandwidths offer a wealth of advantages for both communications and radar applications. In both cases, a large bandwidth improves reliability, as the signal contains different frequency components, which increases the probability that at least some of them can go through or around obstacles. Furthermore, a large absolute bandwidth offers high resolution radars with improved ranging accuracy. For communications, both large relative and large absolute bandwidth alleviate small-scale fading; furthermore, spreading information over a very large bandwidth decreases the power spectral density, thus reducing interference to other systems, effecting spectrum overlay with legacy radio services, and lowering the probability of interception.UWB radars have been of long-standing interest, as they have been used in military applications for several decades. Emerging applications of UWB are foreseen for sensor networks as well. Such networks combine low to medium rate communications with positioning capabilities. UWB signaling is especially suitable in this context because it allows centimeter accuracy in ringing, as well as low-power and low-cost implementation so communication systems. These new possibilities have also been recognized by the IEEE, which has set up a new standardization group 802.15.4a for the creation of a new physical layer for low data rate communications combined with positioning capabilities; UWB technology is a leading candidate for this standard.In this article, we concentrate on the different methods for UWB position system. Position system can be divided into three main categories: time-of-arrival (TOA), direction/angle-of-arrival (D/AOA), and receive-signal-strength (RSS) based systems. Depending on the positioning technique, the AOA technique measures the angles between a given node and a number of reference nodes to estimate the location information, while the RSS and TOA based approaches estimate the distance between nodes by measuring the energy and the travel timeof the received signal, respectively. This paper investigates each approach from the viewpoint of a UWB position system.The RSS method relies on a path-loss model, the distance between two nodes can be calculated by measuring the energy of the received signal at the reference node. This distance-based technique requires at least three reference nodes to determine the 2-D location of a given node, using the well-known triangulation approach. To determine the distance from RSS measurements, the characteristics of the channel must be known. Therefore, RSS-based positioning algorithms are very sensitive to the estimation of those parameters. It’s position accuracy is depends on the channel parameters and the distance between the two nodes. Therefore, the unique characteristic of a UWB signal, namely the very large bandwidth, is not exploited to increase the best achievable accuracy. In such cases, RSS measurements can be used in conjunction with hybrid scheme with time delay measurements to improve the location estimation accuracy.Time-based positioning techniques rely on measurements of travel times of signals between nodes. If two nodes have a common clock, the node receiving the signal can determine the time of arrival (TOA) of the incoming signal that is time-stamped by the reference node. If there is no synchronization between a given node and the reference nodes, but there is synchronization among the reference nodes, the time-difference-of-arrival (TDOA) technique can be employed. In this case, the TDOA of two signals traveling between the given node and two reference nodes is estimated, which determines the location of the node on a hyperbola, with foci at the two reference nodes. Again a third reference node is needed for localization. Unlike RSS-based techniques, the accuracy of a time-based approach can be improved by increasing the SNR or the effective signal bandwidth. For example, with a receive UWB pulse of 1.5GHz bandwidth, an accuracy of less than an inch can be obtained at SNR=0 dB.An AOA-based positioning technique involves measuring angles of the target node seen by reference nodes, which are done by means of antenna arrays. The AOA approach is not suited to UWB inside positioning for the following reasons. First using of antenna arrays increases the system cost, annulling the mainadvantage of a UWB radio equipped with low-cost. More importantly, due to the large bandwidth of a UWB signal, the number of paths may be very large, especially in indoor environments. Therefore, accurate angel estimation becomes very challenging due to scattering from objects in the environment. But the AOA-based positioning technique can be used as impulse radar outside for the military. So the array beamforming and space-time processing techniques promise further advancement in the operational capabilities of impulse radar and impulse-ratio communications to achieve long-range coverage, high capacity, and high location accuracy.The main work and content are summed up as follow:The thesis mainly consists of six chapters.The sense of this paper is described in chapter 1. Introduce the development of UWB communication techniques, especially figure out the advantages of positioning using UWB.In Chapter 2, the characteristics of UWB signal and UWB channel model is introduced. The UWB pulse is very narrow in time domain and so wide in the frequency domain, the bandwidth exceeded several GHz. The IEEE 802.15.4a UWB channel model is simulated.Chapter 3 analyzes the time-of-arrival (TOA), angle-of-arrival (AOA), and receive-signal-strength (RSS) based position systems, investigates each approach from the viewpoint of UWB position system, and derives the CRLB of TOA estimation achieved by the ML estimator for AWGN channel.Chapter 4 mainly studies the time delay estimation algorithm using in TOA-based location system. Conventional correlation approaches of time delay estimation causes the ambiguity of detecting the first path because of the dense multipath environment. MUSIC algorithm is proposed instead of the correlation approaches. Propose an improved the F-MUSIC algorithm. A correlator is used to find out the coarse timedelay and enhance the SNR. This method reduces the rearching range of MUSIC pseudospectrum maxmum value. The simulation results show that the improved MUSIC algorithm achieves better probability of multipath resolvability, and smaller variance of estimation erros than other MUSICalgorithm.Use the channel deconvolution to estimate the multipath timedealy and propose two methods. In the first method the time delay estimation was transformed to complex harmonic frequency estimation. Use the fourth-order statistic method to eliminate the AWGN. If the noise is not AWGN, the second method uses the Weiner deconvolution to reduce the erros of estimation results. The simulation results show that these two methods is effectively than other deconvolution.Chapter 5 introduces a realistic signal model for UWB impulse waveforms and develops the principles of space-time array processing for AOA based on the UWB signal. A space-time resolution functions, a space-frequency distribution functions, and a tracking signal are derived for impulse waveforms received by a self-steering array beamforming system. The resolution angel for the beam patterns is derived as a decreasing function of array size and frequency bandwidth. Electronic beamsteering based on slope processing of tracking waveform is described too.Chapter 6 mainly talks about the application of UWB location system in the market. Combining the wireless sensor network, propose a wireless location scheme for lunar roving vehicle.更多还原