常见手机定位方法概述(A-13).doc

晏潇 2801305017洁 2805105026渝 2805105001常见手机定位方法概述【摘要】：本文简要介绍了常见的手机定位算法的原理，并详细地介谷歌地球所使用的E-OTD技术的实现过程。最后，本文还对这些方法的共同原理进行了总结。 关键词：手机定位 E-OTD 总结1. 常用手机定位方法1.1到达时间TOA(Time of Arrival)定位TOA技术原理:先测量出从移动台发出的信号到达基站i的时间，那么就可以得到移动台与基站i之间的距离(其中，c=3x108m/s，指电磁波在空气中的传播速度) 于是，在利用到达时间进行定位的方法中，移动台位置坐标和定位基站位置坐标之间存在如下关系： 从上式可以看出，移动台的轨迹为一个以基站i为圆心，以它们之间的距离为半径的圆，只要我们能够得到移动台发出的信号分别到达3个不同定位基站的时间，就能确定3个这样的圆，它们的交点就是移动台所在的位置，通过联立求解方程组就能得到移动台的位置坐标，其原理图如图（1-1）： 图1-1 到达时间TOA(Time of Arrival)定位原理TOA技术要求定位基站在时间上精确同步，否则定位精度将大大降低。当基站间存在1微秒的误差时，距离上会产生300米的误差。1.2到达角AOA(Angle of Arrival)定位到达角方法也称为到达方向方法(DOA，Direction Of Arrival)，简称DOA/AOA方法，是利用多天线阵元来测量移动台发出的信号的到达角，一个DOA测量值使目标移动台的位置必然处于以该测得的DOA画出的一条直线上，如果我们从两处不同位置上的两个天线上测得至少两个DOA值，那么目标移动台的位置就一定处于从这两个天线处发出的两条直线的交点上，在通常情况下，利用多个测的DOA值来提供冗余信息可以达到提高定位精度的目的。下图显示了利用3个天线阵来对目标移动台进行定位的原理： 图1-2 到达角AOA(如Angle of Arrival)定位原理令移动台的位置为（x，y），第个基站的位置为，基站通过阵列天线测出移动台来波信号的入射角，则基站和移动台连线的直线方程可以写为： 通过两个或两个以上的基站，就可得到一组方程组，他们的交点即为待定移动台的位置。这种方法不会产生二义性，因为两条直线只能交于一点。1.3到达时间差TDOA(Time Difference of Arrival)定位到达时间差TDOA方法是通过测量目标移动台发出的信号到达多个接收基站的时间差来对目标移动台进行定位的方法，即各接收基站对来自同一移动台的信号作到达时间TOA的测量，然后将各TOA值传送到定位处理中心，中心根据TOA求出各基站间的TDOA并计算出目标的位置坐标。到达时间差TDOA定位技术的基本原理是一组TDOA测量值确定一对双曲线，该双曲线以参与该TDOA测量的两个接收基站为焦点，需要定位的目标移动台就在这对双曲线的某一条分支上，因此，通过求由两组TDAO值确定的两对双曲线的交点就可以得到移动用户的精确位置，其原理图如下图所示: 图 2-3到达时间差TDOA(Time Difference of Arrival)定位原理设基站A、B间距离为b，M(x，y)为移动台的位置，移动台发射的信号到达A、B的时间分别为，由此得到同一信号到达两个基站的时间差为：相应的距离差为：由此可列出以A，B为焦点双曲线方程，移动台在双曲线的一支上：上式是一个典型的双曲线方程，焦点为A、B，并且确定了到达时间差为t的移动台位置M(x，y)的轨迹。如果同时存在3个基站A、B、C，目标移动台在同一时刻发出的信号到达这三个基站的时间分别为。这样就可以获得两个时间差：，于是可以确定类似(2.8)式的两组双曲线方程，联立求解两组双曲线的交点即为目标移动台所在位置M(x，y)。 图2-4 3个基站进行TDOA定位示意图1.4增强观测时间差定位E-OTDE-OTD定位方法也是利用对信号传播时间差的估计来计算移动台位置的方法，与TDOA以方法不同的是，E-OTD使用下行链路信号来估计两个或多个基站到达移动台的时间差，由移动台测量得到的基站间信号的到达时间差称为移动台观测时间差(OTD)，当基站完全同步时，假设信号都是沿着直射路径到达移动台，根据OTD就可以估计出两个基站与移动台距离的差值。完全由于两个基站与移动台距离的差值引起的时间差称为地理位置时间差(GTD)，此时OTD=GTD，当基站间无法实现精确同步时，两个基站间的时钟差(RTD)就会给OTD带来附加的时延差，此时GTD=OTD一RTD，当我们获得三个以上基站相互间的RTD和OTD后，就可以利用双曲线定位方法求出移动台的位置。这一点和到达时间差TDOA方法完全相同，就不再叙述了。1.5混合定位方法通过把以上介绍的定位方法结合起来，即采用混合定位方法来得到比仅使用一种定位方法更高的定位精度的目的。2. 定位方法原理总结几何角度看，确定空间的一个点，可以由三个或三个以上的曲面或曲线在三维空间内相交而得出。手机定位方法的基本原理就是通过对一些数据的测量，根据算法得出手机所在曲面或曲线的多个方程，然后联立这些方程，得出手机的位置。参 考 文 献【1】基于WCDMA蜂窝网络移动台定位技术的研究 常翠芝 武汉大学【2】基于网络的移动通信系统移动台定位技术研究 董海 电子科技大学【3】GSM手机定位技术研究 朗亚东 吴娟 A Brief Introduction to Common Mobile Phone Location Determination TechnologyAbstract：This paper gives a brief introduction to the algorithm and implementation of common mobile phone location determination technology and carefully examines the E-OTD method used by Google Earth. Finally, this paper summarizes the principle behind all these methods.Key words: mobile phone location determination technology E-OTD summary1.1TOAThe time-of-arrival (TOA) system determines the mobile phone position based on the intersection of the distance (or range) circles (Fig. 1). Since the propagation time of the radio wave is directly proportional to its Traversed range, multiplying the speed of light to the time obtains the range from the mobile phone to the communicating base station. Two range measurements provide an ambiguous fix and three measurements determine a unique position. The same principle is used by GPS, where the circle becomes the sphere in space and the fourth measurement is required to solve the receiver-clock bias for a three-dimensional solution. The bias is caused by the unsynchronized clocks between the receiver and the satellite. Similarly, for terrestrial-based systems, it also requires precisely synchronized clocks for all transmitters and receivers Otherwise, a 1- s timing error could lead to a 300-m position error.Math presentation: Fig.1. Location Determination by time of arrival (TOA). 1.2 AOAThe angle-of-arrival (AOA) system determines the mobile phone position based on triangulation (Fig. 2). It is also called direction of arrival in some literature. The intersection of two directional lines of bearing defines a unique position, each formed by a radial from a base station to the mobile phone in a two-dimensional space. This technique requires a minimum of two stations (or one pair) to determine a position. If available, more than one pair can be used in practice. Because directional antennas or antenna arrays are required, it is difficult to realize AOA at the mobile phoneMath presentation: Fig.2. Location determination by angle of arrival (AOA)1.3 TDOAThe time-difference-of-arrival (TDOA) system determines the mobile phone position based on trilateration (Fig. 3). This system uses time difference measurements rather than absolute time measurements as TOA does. It is often referred to as the hyperbolic system because the time difference is converted to a constant distance difference to two base stations (as foci) to define a hyperbolic curve. The intersection of two hyperbolas determines the position. Therefore, it utilizes two pairs of base stations (at least three for the two-dimensional case as shown in Fig. 3) for positioning. The accuracy of the system is a function of the relative base station geometric locations.Math presentation: Fig.3. Location determination by time difference of arrival (TDOA).1.4 E-OTDE-OTD is a TDOA positioning method based on the OTD, but it works on the receiver end. The MS measures relative time of arrival of the signals (bursts) from several BTS (Base Transceiver Stations). The position of the MS is determined by trilateration (Fig. 4). There are three basic timing quantities associated with this method:1) Observed Time Difference (OTD) is the time interval observed by an MS between the receptions of signals (bursts) from two different Base Transceiver Stations (BTS). If we denote t1 as the moment that a burst from the BTS 1 is received and t2 as the moment that a burst from the BTS 2 is received, the OTD value is the time difference i.e., OTD =t1-t2. 2) Real-Time Difference (RTD) is the relative synchronization interval in the network between two BTS. If we denote t3 as the moment that the BTS 1 sends a burst and t4 as the moment that the BTS 2 sends a burst, the RTD value is the difference of these moments, i.e., RTD=t3-t4 . If the BTS transmit exactly at the same moment, the difference is zero, i.e., RTD =0. 3) Geometric-Time Difference (GTD) is the time interval measured at the MS between bursts from two BTS due to geometry. These quantities are related by GTD= OTD RTD. Since the MS knows OTD, and RTD can be measured by an additional location measurement unit (LMU) in the infrastructure, we can calculate GTD as shown in the above equation. A constant GTD value between two BTS defines a hyperbola. Intersection of two hyperbolas determines the location of the MS.Since the E-OTD method is only the use of TDOA on the user end. The math presentation is the same as TDOA. Fig.4. Location determination by E-OTD1.5 Combined WaysBy using a combination of the methods introduced above, a higher level of accuracy can be obtained .And the way to combine these methods is decided according to specific application.2. The princ