Research And Implementation Of Carrier Tracking Loop And Multipath Mitigation Algorithm For TC-OFDM Location Receiver

In indoor complex environments,the quality of Global Positioning System(GPS),Beidou and other satellite signals is poor and the performance of most receiver drops dramatically or even fails.The Time&Code Division-Orthogonal Frequency Division Multiplexing(TC-OFDM)system multiplexes mobile communication network resources and uses mobile communication network base station to realize network construction,which can achieve wide-area high-precision indoor and outdoor seamless location information service.In this thesis,a carrier tracking algorithm based on adaptive weight adjustment and a short multipath mitigation algorithm are proposed to solve the problems encountered in the development of TC-OFDM receiver tracking loop,such as slow convergence speed and loop instability of carrier tracking loop and low tracking accuracy under multipath interference.Specific research contents are as follows:1.According to the problems that slow convergen ce speed of receiver carrier loop and loop instability caused by indoor signal power instantaneous large changes,a carrier tracking algorithm based on adaptive weight adjustment is proposed.The frequency error and phase error is utilized to construct the adaptive weight adjustment algorithm.The algorithm adaptively adjust the influence of the frequency and phase discrimination value on the loop,so that the loop can complete the frequency traction under large frequency error and simultaneously realize the fast phase convergence under small frequency error.The loop filter based on Kalman filter can quickly respond to the instantaneous large change of signal power.The simulation results show that the algorithm can reduce the carrier convergence time by 16%compared with the frequency-locked loop assisted phase-locked loop based on weight adjustment,and the loop has higher stability in the case that signal power changes dramatically in an instant.2.According to the problem that the tracking accuracy of code tracking loop is degraded due to multipath interference in indoor environment,a modified short multipath insensitive strobe discriminator(MSMISD)is proposed.In order to suppress the movement of the zero position of the phase discrimination value,the delay correlation value is constructed and the inverse multipath compensation factor is designed in MSMISD.Ensure that the local replica pseudo code is highly synchronization with the direct signal,which can reduce the tracking error.The simulation results show that the MSMISD algorithm has better anti-multipath performance than the strobe discriminator with 0.2 chip spacing between Early and Late correlator in the short multipath environment.3.The TC-OFDM system positioning receiver verification platform is built by FPGA+ARM architecture.The verification results show that the proposed carrier tracking algorithm can track the signal with a carrier-to-noise ratio of 25dB-Hz.Compared with frequency-locked loop assisted phase-locked loop based on weight adjustment,the carrier convergence time is reduced by 15%and the loop has higher stability when the signal power is instantaneously attenuated by 10 dB;under the short multipath of 0.05 chip delay,the proposed short multipath mitigation algorithm is compared with the strobe discriminator with 0.2 chip spacing between Early and Late correlator,the mean of the time difference of arrival(TDOA)error is reduced by 0.0181 chips,and the TDOA standard deviation is reduced by 0.0043 chips.