Research On Time Delay Estimation Oriented To UE Position Location In LTE

Location based services (LBS) have in-depth in all areas of life, in the face of increasingrequirements for location services, long time evolution (LTE) has made new protocols andreference signal assisting localization. Having low requirements for environment and equipment,location technique based on time delay parameters has been one of the main location techniquesin LTE. Time delay estimation (TDE) is the precondition of accurate position location, thereforeresearches on TDE in LTE will be of great significance, which will both benefit the publicthrough location based services and support safeguarding national security and social stability innon-cooperative position location.This thesis conducts a research on improving time delay estimation performance in LTEposition location considering influencing factors in real application environments. The work inthis thesis can be summarized as follows:Firstly, this thesis summarizes overseas and domestic research status of TDE and points outthe inadequacy of TDE in LTE networks. Based on the analysis of position reference signalarchitecture, this thesis dissects the main influencing factors on TDE: sampling rate, frequencyoffset, multipath and interference through modeling and simulation, which lays a foundation onthe research afterwards.Secondly, aimed at TDE in AWGN channel and considering definition and anti-noiseperformance of TDE, the thesis proposes a hierarchic TDE algorithm and derives the CRLB.Taking advantage of signal architecture, the integer TDE is processed through time delay searchwith a step of half CP utilizing the self-correlation of position reference signal in time domain.The fractional TDE is estimated with LMMSE estimation of frequency domain signal phaseoffset of subcarriers used by position location. The final estimation can be derived from the twoabove TDE results. Theoretical and simulation results show that the proposed algorithm achieveshigh performance near CRLB, which can eliminate the side beam caused by direct match filterand break the TDE definition bound limited by sampling rate.Thirdly, aimed at TDE in multipath channel and considering the multipath componentaliasing affect on first arrival path (FAP) TDE, this thesis proposes a TDE algorithm based onFastICA. Through transforming received signal into frequency domain, the TDE problem can besolved by frequency estimation of mixed multiple single frequency signals by using FastICA toseparate multiple paths. Taking advantages of prior multipath information and revised whiteningprocess, the proposed algorithm revises the problem of output disorder and vulnerability aboutnoise of multipath TDE using FastICA. Simulation results show that the proposed algorithm has better multipath separation performance than traditional subspace method based on eigen valuedecomposition.Fourthly, aimed at TDE under the environment with interference, considering the mutualinterference of position location signals, this thesis proposes a grouped joint TDE algorithm. Inorder to jointly estimate the location signals with mutual interferences, the proposed algorithmsorts and group these signals according to their power and conducts joint TDE inside a group anduses SIC among groups so as to suppress interference level and keep low calculation complexity.Simulation results show that the proposed algorithm can lower the error propagation in SIC andachieve better TDE performance, which combines successive interference cancellation (SIC)with maximum likelihood estimation.