Research On Radio Location For Mobile Station In CDMA Cellular System

With the development of the Third Generation (3G) mobile communication systems andthe release of the Emergent 911 (E911) call in USA, cellular radio location technic for theMobile Station (MS) has been broadly focused more and more. Because the service canprovide the position information about MS, the location technology plays an important rolein many fields, such as network optimization, entertainment, emergency rescue andcountry security etc. Location in cellular system also faced many challenges for thecomplexities of the radio transfer channels. The key issue emphasized by internationalfields in MS location is how to improve the location accuracy.CDMA cellular system which will hold the balance in the future market is one of theimportant standards composed of the 3G mobile communications. Different users aredivided to improve the utilization ratio of the resources by Pseudonoise Sequence (PNSequence) which has a wide frequency band. Then, different users share the samefrequency at the same time. The aim of this paper is to improve MS location accuracy inCDMA cellular system from the research on the CRLB of parameters estimation, the timedelay estimation in Multiple Path environments and Multiple Access Environments,position estimation in NLOS environments in passive way.Firstly, the way to expand the research and the contents of this paper are ascertaineddefinitely based on theory analysis and data. The basic location technics are describedshortly. Then, the performance comparision among these technics are providedqualitatively. The characteristics of the CDMA cellular radio network are analysizeddetailedly. The error sources of location are brought forward. The international anddomestic present studies on cellular radio location are reviewed. According to thoseanalyses, the paper ascertains the way to study.Secondly, the lower bounds of some important parameters estimation are given. TheCRLB of time delay estimation in Multiple Path environments and Multiple AccessEnvironments, the CRLB of location estimation in NLOS environments are deduced in thispaper. Some conclusions are achieved by discussing the physical implications of theseCRLB. Simulation experiments clarify the physical implications ulteriorly. Theperformances of the new algorithms proposed in this paper are compared with theappropriate CRLB.Thirdly, two new algorithms of time delay estimation are proposed in the paper. Onedelay estimator which has a super resolvability is used in Multiple Path environmentswhen the ratio of bit energy and noise power density (E_b/N₀)is low. When the delaybetween two propagation path is lower than a chip cycle and E_b/N₀dB, the estimationerror of this algorithm is around five samples. The performance of this method which isclosed to CRLB is better than conventional algorithm and MUSIC. The other delay estimator is used in Multiple Access environments when the spread codes are longsequences. When the interfered users are 7 and E_b/N₀=15dB, the estimation error of thisalgorithm is lower than two samples. The performance of this method which is closed toCRLB is better than conventional algorithm. The time delay estimation is the parametersent to the location algorithm. So the accuracy of time delay estimation will seriouslyimpact the accuracy of location estimations. MAI and MPI are the most important factorsthat reduce the accuracy of location estimation. These two algorithms proved by thesimulated data and practical data can mitigate the interferences, and improve the locationaccuracy.Fourthly, a fast location method and NLOS constrained location estimator are proposed.The fast location algorithm works in iterative way. The time delay estimation at every timesent to the method are taken as new information to improve the location accuracy. Whenthe iterative numbers are 100, the method is convergent and has good location accuracy. Inthe regard of NLOS problems, a combined detection location algorithm and a nonlinearoptimization location method are proposed to resolve this problem. When the noise poweris -15dB and the number of BSs which has LOS path (the other BSs which participate thelocation have NLOS path) are more than 3 (normalized value), the location error ofcombined detection location method is lower than１. The performance of the algorithmwhich is closed to CRLB is better than PiChun method which is a classical NLOSconstrained method. When the max NLOS propagation error is 6 (normalized value) andthe number of BSs that have NLOS path is more than 2 (normalized value), the locationerror of nonlinear location method is lower than 5 (normalized value). The performance ofthe algorithm is better than PiChun method.Fifthly, a MS passive location trials system is set up for IS-95/cdma2000 1x cellularnetwork. The composing theories and flames are discussed. The performances of somenew algorithms proposed in this paper are also detected by this MS location test system.The location results and analysis of trials are provided. The validity of this algorithm isproved by the practical data.At last, the conclusions and expectations are presented in the last part of this paper. Thecreative views and the short comings are induced. The way to study the MS location andthe objective of the future research are discussed.