Research Of Cellular Network Wireless Location Ways Based On Hybrid Location Methods

Wireless position location has brought our considerableattention over the past few years due to the United States FederalCommunications Commission's(FCC) 1996 E-911(Emergency call '911')report and order. Wireless location is one of the personal services,which is developing with the advancement of the mobile communications.Location in the cellular systems is one of the basic ways to implementwireless location, the advantage of this method is that we needn'trequire any modifications to the MS, thus customer's advantage willbe ensured.In these days, commonly technologies studied include signalattenuation location technology, angle of arrival (AOA) locationtechnology, time of arrival (TOA) location technology, and timedifference of arrival (TDOA) location technology. But , in thedifferent channel and network environment, TDOA, TOA, AOA and signalattenuation have the different error statistics characteristic andthey adopt different positioning calculation ways, so the functionsof these basic location technologies are not same, there is not anytechnology can show a best function in the different channel andnetwork environment. This is to say, a single location technologyhas its limited character. Therefore, how to make full use of thebeneficial electric wave characteristic provided by network and usethe excellence of the above various location ways to improve theposition precision for MS, it is a topic that is worthy of thoroughresearch . Hybrid location technology is a kind of technology thatblends different characteristic to estimate MS's position. At thepresent time, there has been a lot of literatures adopt differentmethods and ways to study the hybrid location technology andarithmetic, and these literatures have proved that adopting hybridlocation way can gain more accurate location function than adoptinga single location.The TDOA technology is one of the most promising position locationtechnologies for cellular wireless communication systems, which canprovide accurate position location information using the existingcellular infrastructure. In new generation mobile communicationsystem, along with the extensive application of the intelligenceantenna array, the electric wave's AOA measure value will be checkedaccurately and effectively in the base station. Had the accuratemeasured value of AOA, using TDOA/ AOA hybrid location way can gainmore accurate location performance than using a single TDOA location.This thesis discussed the algorithm of TDOA/ AOA hybrid locationmethods of Taylor series deeply. Taylor series expansion method hasbeen widely used in solving nonlinear equations for its high accuracyand good robustness. But the performance of Taylor algorithm dependshighly on the initial estimation. The choice of the initial estimationfor Taylor series expansion affects greatly about the location result,if the initial estimation is not being good chosen, the calculateway will convergent hardly. But in actual application,the initialestimation is very difficult to be assured, this also limits thelocation precision's improvement of the Taylor series expansion way.Therefore, we can initially location the measure data through a kindof algorithm ,and think location result as the initial value of Taylorseries expansion method, then make use of the Taylor seriesexpansion method to calculate the location result. This thesis adoptsa new method based on the Least-Square to estimate the initial value,and then subscribers' position can be estimated by Taylor seriesexpansion method. After estimating the initial position of the target,it will assure that the calculation way is not unconvergent for thegreat error to the true location.The core idea of the TDOA/AOA hybrid location method of Taylorseries expansion which is based on the Least-Square is: first, weadopt Taylor series to expand the nonlinear equation at the targetinitial estimate point, and neglect quadratic item and other itemswhich are upward quadratic, turn the nonlinear equation into linearequation, and adopt least squares method to estimate the offset;And then, we make use of the offset that has been estimated to correctthe target location that is estimated, and keep it iterative, makethe estimated target position approach the true position, thus getsuperior estimate of the target position. Through the simulationanalysis of chapter 5 ,we can see that this method is valid, andthis method can get more accurate location function.The main jobs of this thesis as follows:Chapter 1 is the introduction part, this chapter introduced theresearch background of the thesis first, then gave the concept andsummary of wireless location , and systemically discussed theactuality ,development status and application foreground of wirelesslocation.The cellular network wireless location methods were concretelydiscussed in chapter 2,and several typical location methods wereintroduced deeply, then detailedly discussed all kinds of factorsthat need to be thought when a location technology being selected andthe application of the cellular network wireless location technology.Based on the analysis to the main factors that influence the cellularnetwork location precision, the ways and measurements that canfarther improve the location performance were made certain. Severalmain evaluation indexes provide foundation for the simulationanalysis.The hybrid location technology to estimate the MS's position wasdiscussed in chapter 3. This chapter concretely expatiated on theprinciples ,location precision and some existing algorithm of TDOAand AOA location methods,and introduced principle and characteristicof TDOA/AOA hybrid location method. This chapter showed two kinds ofTDOA/AOA hybrid location methods: Chan algorithm and Kalman filteralgorithm. The results of these two algorithm show that adoptinghybrid location way can gain more accurate location function thanadopting a single location.This thesis introduced a kind of TDOA/AOA hybrid locationmethod—TDOA/AOA hybrid location method of Taylor series expansion ,which is based on the Least-Square. This method locates the target(MS) with method of Taylor series expansion, and estimates MS'sinitial position with the Least-Square method. The location model andoperation process of this algorithm was researched and discussed indetail in chapter 4. Meanwhile, the flow chart of this algorithm wasgiven.In the last chapter, the algorithm—TDOA/AOA hybrid locationmethod of Taylor series expansion based on the Least-Square, wassimulated and analyzed in the laboratory on a computer. The locationprecision of this algorithm was influenced by these factors: TDOAstandard deviation, AOA standard deviation, the numbers of basestations which join the location and the distance between the MS andserveing BS. Compared with other location methods, this method cangain more accurate location performance, so it is a kind of validmethod.