Design And Implementation Of Positioning Receiver Tracking Algorithm For Mobile Networks

Global Navigation Satellite System(GNSS)provides accurate location information for outdoor activities.However,the positioning performance is limited in indoor environment.With the development of mobile networks and terminals,location based services(LB S)has become a research hotspot for mobile network applications.The indoor positioning technology based on terrestrial mobile network has received much attention,which has the characteristics of low deployment cost,strong signal penetration and no ionospheric interference.TC-OFDM(Time&Code Division-Orthogonal Frequency Division Multiplexing)system is a wide-area indoor and outdoor seamless positioning system based on mobile networks,which can achieve meter-level positioning accuracy.This paper studies tracking loop algorithm of TC-OFDM positioning receiver for mobile network on the TC-OFDM system development platform.The tracking loop mainly includes carrier loop and code loop.Under weak signal conditions,the existing carrier loop has large estimation error of residual carrier frequency,which limits the tracking sensitivity of the receiver.In complex indoor environment,the positioning signal amplitude is prone to violent fluctuations in a short time period,resulting in instability or even loss of lock of the code loop.According to the above problems,the tracking loop algorithm of TC-OFDM positioning receiver has been improved.The main research contents and results are as follows:1.According to the problem that residual carrier fr-equency estimation error is large under weak signal conditions,a multi-parameter maximum likelihood estimation(MLE)joint with Kalman filter(KF)carrier tracking algorithm is proposed.MLE is utilized to replace the existing carrier discriminator and phase discriminator.The signal amplitude,residual carrier frequency and carrier phase are used as MLE estimation parameters.The efficient Lemenberg-Marquardt(LM)algorithm is adopted to solve the MLE.KF is applied to improve the estimation accuracy of MLE calculation results.The simulation results show that compared with carrier tracking algorithm based on frequency-locked loop(FLL)and phase-locked loop(PLL),and EKF-based carrier tracking algorithm,the proposed carrier tracking algorithm can effectively improve the residual carnier frequency estimation accuracy and earier tracking sensitivity.2.According to the problem that large fluctuation of positioning signal amplitude prone to cause the code loop to lose lock in the complex indoor environment,a joint estimation algorithm of signal amplitude and code phase difference based on Extended Kalman Filter(EKF)is proposed.The signal amplitude and code phase difference are used as state vector in the algorithm.The signal amplitude and code phase difference estimation values are used to adjust the observed noise covariance matrix in real time,and EKF is utilized to construct a closed code tracking loop.The simulation results show that the algorithm takes advantage of the statistical properties of signal amplitude,overcomes the shortcomings of the traditional DLL and EKF without amplitude estimation,and effectively improves the robustness of the tracking loop of TC-OFDM positioning receiver.3.The above proposed algorithms are tested on the hardware receiver platform.After testing,the improved tracking loop algorithm can track the xweak signal with the carrier-to-noise ratio(CNR)of 24dB-Hz,which effectively improves the tracking sensitivity of the existing positioning receiver and enhances the robustness of the tracking loop.In summary,the proposed carrier tracking algorithm and code tracking algorithm optimize the tracking loop performance of the existing TC-OFDM positioning receiver.The optimized tracking loop algorithm improves the receiver tracking sensitivity under weak signal conditions and the robustness of the tracking loop when the signal amplitude occur violent fluctuations in a short period of time.