Research On Hybrid Location Technology Based On WCDMA Networks

The United States Federal Communications Commission ( FCC ) issued the E-911mandate since 1996, mobile location service has been developing rapidly and mobile location technology is concerned by more and more people. Now we are stepping into the third generation of mobile communication. It will bring about more superior quality of voice, the more colorful multimedia services and the more added values. The most importance is location-based services will be a necessary feature of 3G. Besides providing location information for consumers, mobile location technology plays an important role in other areas, such as network optimization and resource management, intelligent transportation systems. As for many people pay attention to themselves own security and the convenience of location-based services, more and more people will need it. As a result, the research on location services has been a hot point.Mobile location technology uses wireless signals between the base station and mobile terminal to calculate some characteristics of MS'signals, such as Time of Arrival (TOA) and Time Difference of Arrival (TDOA), Angle of Arrival (AOA). And then we can use these characteristics to calculate MS's location. According to the position of location estimated, position subject and adopting different equipment, the location systems can be divided into mobile-based location system, network-based location system, mobile assisted location system, GPS assisted location system. If adopting mobile-based location system or GPS assisted location system, we have to modify the mobile station properly and add the essential software and hardware equipments. If adopting network-based location system, we only need appropriate modifications for the existing cellular network. This paper researches on network-based positioning technology.In the cellular network, the main location methods are: TOA location method, TDOA location method, AOA location method, and hybrid location methods. Because the influence of Gaussian noise and non-line-of-sight propagation and multi-path spread and so on, location values of measurements attained from methods inevitably have errors, which results in decline of location accuracy. A single location technology only uses one of these characteristics to determine MS'location, so it has its limited character. And hybrid location can use these measured values as many as possible and mostly make use of advantages of these location methods to improve location accuracy of the MS'location. As soon as smart antenna technique is used in 3G, utilizing base station to estimate angle of signal arrival is possible. TDOA method is relatively easy to realize in the cellular network, and can relatively reach high accuracy. TDOA method is also one of the most promising and popular location techniques in the cellular wireless communication system. TDOA/AOA Hybrid location method use the characteristics of TDOA and AOA measurements to estimate MS'location, which can obtain better location accuracy than a single location method. At the present time, there are a lot of literatures adopting different methods and ways to study the hybrid location technology and arithmetic, and these literatures have proved that adopting hybrid location method can gain more accurate location than adopting a single location. This paper researches on hybrid location technology based on WCDMA network. The main job of this paper as follows:In chapter one, the research background and significance of this paper are stated. And then location methods in the cellular wireless network and location technology are discussed. Several typical methods are introduced and the main reasons of influencing location accuracy are comprehensively analyzed in the cellular network. At last domestic and foreign research actuality in wireless location technologies and the development trend of location services are studied and summarized.In chapter two, the process of location in the WCDMA system and functions of kinds of location units are systemically discussed. Several location methods are detailedly introduced and compared. The principle of the IPDL technology is stated. The advantages of technology achieve location in the WCDMA networks are discussed.Three basic location algorithms of TDOA method are introduced in detail in chapter three: Chan algorithm, Taylor series expansion algorithm, Fang algorithm. This paper analyzes Channel environments and evaluation index of position precision, and carries on emulation to the three algorithms under Gauss of noises and T1P1 mobile channel environments. The simulation result shows that: the location precision of Chan algorithm is the best when channel environment is Gauss distribution; and it will drop under the circumstance of NLOS, worse than Taylor series expansion algorithm. Taylor algorithm can be suitable for various channel environments, but it is necessary to need initial position to ensure restrain. Fang algorithm is the simplest algorithm, only uses the information of three base stations to estimate MS'location. The location precision of Fang algorithm is the worst in various channel environments.In chapter four, this paper firstly introduces the principle of smart antenna. Smart antenna can achieve better precision on AOA. Secondly three basic algorithms are stated, they are Capon algorithm, MUSIC algorithm, ESPRIT algorithm. This paper compares these algorithms in different signal to noise ratio, the different number of array element and snapshots. The simulation result shows: with increasing of signal to noise ratio, the number of array element and snapshots, the performance of these algorithms is improved. The performance of MUSIC algorithm is best, Capon algorithm is worst.In the last chapter, this paper mainly researches on TDOA/AOA hybrid location algorithm. First, an improved algorithm based Chan algorithm and a hybrid location algorithm based on Taylor series expansion algorithm are studied. An improved Chan algorithm is extended to solve hybrid TDOA/AOA location equations by adding AOA information into Chan algorithm, and then makes use of twice least-square algorithm to estimate MS'location. When the measuring value of AOA is exacter, the improved Chan algorithm can have better location precision than Chan algorithm. A hybrid location algorithm based on Taylor series expansion method is that adopts Taylor series to expand the nonlinear equation at the target initial estimating point and neglects quadratic item and other items which are upward quadratic. And then it turns the nonlinear equation into linear equation and adopts least-square algorithm to estimate the offset used to correct the target location that is estimated. It needs repeated iteration. When the offset is smaller than a certain threshold value, we obtain superior estimation of MS'location. The simulation result shows that the performance of hybrid location method based on Taylor series expansion is better than Taylor algorithm. Taking the strong influence of NLOS into account, this paper researches on an iterative method. It can correct TDOA measuring value. In order to reduce the impact of NLOS error, this method adds loose variable into hybrid location equations and uses loose variable obtained from loose variable equation to renew the equations, makes TDOA measuring value closer to true value via repeated iteration. By setting a threshold value, we can obtain an exacter value of MS'location when the margin of these loose variables lowers the threshold value. The simulation result shows the performance of this algorithm is better than the two algorithms above. Not only do we think about the error of NLOS, but also we think about the error of AOA measuring value. We present a new algorithm. It uses Kalman filter to obtain the estimated value of AOA and makes use of loose variable to mitigate the error of TDOA measuring value. It only needs once WLS to estimate MS'location for once iteration, so the computational complexity of this algorithm is lower compared to the algorithm above. The simulation result shows the performance of this algorithm is better than the algorithms above when the error of AOA measuring value exceeds a certain value.