| With the growing demand for location services,Global Navigation Satellite Systems(GNSS)such as Beidou and GPS have been able to meet the needs of outdoor positioning,but cannot provide high-precision location services in indoor environments.The Time&Code DivisionOrthogonal Frequency Division Multiplexing(TC-OFDM)system proposed by Beijing University of Posts and Telecommunications reuses requency resources and base stations by fusing positioning signals and 5G wireless network,which realizing indoor and outdoor high-precision seamless coverage of positioning signals.This article focuses on intermittent sigals tracking for positioning reviver of TC-OFDM system.The tracking loop includes carrier loop and code loop.Carrier loop is easily affected by dynamic error and needs a long time to converge.Code loop is susceptible to noise error with the changing of CNR.This article mainly launches the research and engineering practice of the following technical contents:1.In response to the issues of carrier loop discussed above,this article proposes a carrier intermittent tracking algorithm based on Mamdani fuzzy control,which adopts a dual-input-signal-output fuzzy controller and takes the phase difference from phase detector and frequency difference from frequency detector as inputs.The output adjusts carrier NCO after filtering by the second-order Jaffe-Rechtin filter.Simulation results show that the algorithm can shorten at least 250ms for convergence time of carrier loop when tracking intermittent signals,and can greatly improve the tracking accuracy in dynamic environments.2.In response to the issues of code loop discussed above,this article proposes a CNR estimation method that is not affected by message bit and applies the mothed to adaptive code tracking loop.The TC-OFDM positioning receiver acquires long-term coherent integrations results by accumulating 1ms coherent integrations results.This article analyzes and compensates the attenuation caused by the accumulation.The simulation results of the entire tracking loop proposed by this article show that it can improve the accuracy and robustness of intermittent signal tracking,and the loop ranging error is less than 1m.3.The intermittent signals tracking loop proposed in this article is implemented on TC-OFDM receiver of FPGA+ARM architecture,and its performance is verified in different environments.The results show that the tracking loop proposed by this article has higher tracking sensitivity and can better cope with the degradation of CNR.The receiver that using the intermittent tracking loop proposed in this article can track all positioning signals stably and achieve sub-meter positioning accuracy by average error of 0.764m,it’s much better than 3.997m of open loop and 2.189m of second-order FLL-assisted third-order PLL. |
