Investigation Of Mobile Station Location In Cellular Network

In cellular envirorunents, because of the influence of several adverse factors,such as muItipath, non-line-of sight propagation, noise, interference and channelfrequency characteristics, radio statistics measuremenis like TDOA, TOA and AOArelated to mobile position, the performance of location algorithms mny besignificantly degraded and the position estimation of MS is inevitably biased.Therefore, in order to focus on the core problem of mobile location accuracyimprovement, this thesis aims at TDOA location techniques, and investigates thefollowing cellular netWork based location techniques: performance analysis of basicTDOA location algorithIns, hybrid location algorithIns, mobile position estimationtechniques based on data fusion, and high accuracy location techniques to mitigatethe influence of NLOS. Besides, the key techniques and relative problems ofWCDMA network mobile location are analyzed and discussed.,First of all, the mathematical model of TDOA hyperbolic equations isestablished, the advantages and disadvanages of sevcral TDOA location algoritlunsare analyzed in detail, based on the simulation in different channel environrnents,location perfOrmance of several major algorithIns are evaluated. It is shown byanalysis that Chan's algorithIn is the most suitable one When channel environment isrelatively good, otherwise Taylor series expansion method is more aPpropriate.Secondly, based on the limitations of single location technique and thecharacteristics of Chan and AOA algorithIns, a hybrid TDOA/AOA and aTOA/AOA location algorithIn are proposed, and the corresponding CarBtheoretical bounds of these algorithms are derived. Simulation under differentenvironments shows that, if the accuracy of AOA measurement delivered by the.serving BS is relatively high, better performance can be obtained. Besides, WhenTOA location method is aPplied, the relative position between the MS and theserving BS, the relationship betWeen the location performance and the nUmber ofTOA measurements are studied. Then a dynarnic location algorithm is proposed,which firstly estimates the distance between MS and serving BS through an initialMS position estdriation, then chooses TOA measurements, and finally determinesthe weighted factors of WLS algorithm, thus resulting an improved location performance.Thirdly, the data fusion model proposed by Kleine-Ostmann for mobile position estimation is investigated in great detail. Based on this model, an enhanced data fusion model combining the AOA and signal strength is proposed, and a model for the fusion of TDOA location algorithms is also proposed. The fusion rules of these models are analyzed and their effectiveness to improve the location performance is demonstrated by simulation. Besides, in case that the prior information about channel environment is unknown, in order to fuse location results obtained by different location algorithms to get more accurate and reliable location results, two location fusion methods which depend on the location results weighted by location distance residual are proposed, the feasibility of this algorithm fusion methods are demonstrated by simulation under two environment conditions.Fourthly, based on the analysis to TDOA/TOA measurement errors, an accurate location algorithm is proposed. In order to reduce the adverse influence of NLOS error to location performance, this algorithm firstly makes initial mobile position estimation by mean TDOA/TOA measurements, then estimates NLOS error within TDOA/TOA measurements by parameters of TIP 1 channel model, smoothes and reconstructs TDOA/TOA measurements, and finally utilizes two step WLS computation. The application of this algorithm under different cellular environments is also discussed and its effectiveness is demonstrated by simulation results.Finally, the basic location method, location method implementation, network architecture, signaling protocol and interface, and location procedures of WCDMA network mobile l...