Suppression Of Near-far Effect In TC-OFDM Indoor Positioning System Based On VTL And SIC

The demand of IOT brought by 5G has greatly promoted the development of indoor positioning technology.Facing the rapid increase of communication base stations,the integration of communication and navigation is the development trend of indoor and outdoor positioning in the future.With the ultra-dense networking of 5G,the relative displacement between the base station and the receiver increases.In indoor environment,the distance between positioning base stations is small,indoor obstacles are complex and random,and it is difficult to predict the signal strength when positioning signals arrive at the receiver.In TC-OFDM positioning system,the near-far effect caused by incomplete orthogonality of ranging codes is more obvious in indoor environment,which leads to the decrease of positioning accuracy and limits the normal working range of the receiver.Therefore,it has important theoretical significance and practical application value to study the suppression of near-far effect in indoor TC-OFDM positioning system.In this paper,the near-far interference in indoor TC-OFDM positioning system is analyzed,and its suppression technology is studied.In order to reduce the influence of near-far effect on indoor TC-OFDM positioning system,and improve the positioning accuracy and available range of the positioning system.This paper focuses on the application of vector tracking algorithm(VTL)and interference cancellation algorithm in the suppression of near-far effect in indoor TC-OFDM positioning system.The main research contents and achievements of this paper are as follows:1.The causes of near-far effect in indoor TC-OFDM positioning system are analyzed.The influence of near-far effect on indoor TC-OFDM positioning system is analyzed from two aspects of acquisition and tracking.A hardware-in-the-loop algorithm simulation test platform based on matlab and USRP is designed for subsequent algorithm verification.2.A hybrid vector tracking loop based on pseudo-range residual detection is proposed,which improves the integrity of the vector tracking receiver and reduces the tracking error of the weak positioning signal loop and the positioning error of the receiver under the near-far effect.Firstly,the VTL is modeled according to the characteristics of indoor TC-OFDM positioning system,and the signal processing of vector tracking loop is designed based on EKF recursive algorithm,and the carrier-to-noise ratio(CNR)estimation methods used in vector tracking algorithm are compared and analyzed.In order to solve the problem of error diffusion in VTL,a hybrid-VTL based on pseudo-range residual detection is proposed,which not only reduces the computation of vector tracking algorithm,but also isolates single-channel faults.3.A serial interference cancellation(SIC)algorithm based on adaptive filtering is proposed,which reduces the parameter estimation error of interference reconstructed signal and improves the performance of SIC.To solve the problem that the number of visible positioning signals in the "near boundary" of near-far effect of indoor positioning base station is small,this paper studies the effectiveness of SIC algorithm in suppressing near-far effect in indoor TC-OFDM positioning system,and analyzes the influence of reconstructed signal amplitude estimation on the performance of SIC algorithm.In view of the large error of amplitude parameter estimation in time-varying positioning received signals,this paper proposes a SIC algorithm based on adaptive filtering,which improves the accuracy of amplitude parameter estimation in reconstructed signals and reduces the cancellation residual caused by interference cancellation.To sum up,this paper mainly proposes a hybrid-VTL based on pseudo-range residual detection and a SIC algorithm based on adaptive filtering,which respectively suppress cross-correlation interference in different interference areas with near-far effect.The tracking stability of weak signals is improved by vector tracking algorithm,and the near boundary of TC-OFDM positioning receiver interfered by far-near effect is reduced by interference cancellation algorithm.