Research On Long Code Direct Acquisition And Channel Equalization In Satellite Navigation Signal Quality Monitoring System

Signal acquisition and channel equalization are two important processes for GNSS signal quality monitoring system.The signal quality monitoring system needs to monitor the Beidou military code signal or public signal such as L2 C signal.Long code direct acquisition technology can be used to capture long code signal.Research on long code direct acquisition is of great importance to the signal quality monitoring system.In general,the channel characteristics of the received signal are not ideal,resulting in the signal transmitted to the receiving end does not coincide with the signal received by the antenna.The channel characteristic is studied and the channel equalization algorithm is designed to restore the received signal to the real state,which can ensure the correctness of the signal quality monitoring results.Therefore,the study of long code direct acquisition and channel equalization are of great significance to the signal quality monitoring system.This paper studier the three aspects of long code direct acquisition,channel time domain equalization and channel frequency domain equalization.The main work is as follows:(1)This paper studies the direct acquisition algorithm of long code signal,compares the mean method and the extended replication overlap method,and proposes an improved algorithm based on the mean method.The improved algorithm does not need to pad zero after received signal,and uses the two local pseudo codes to correlate with the received signal respectively,and selects the lager acquisition statistics.The improved algorithm has higher acquisition probability than the mean value method when the false alarm probability is the same.(2)Adjust the phase characteristics of the ideal channel,which is still a linear phase after adjustment.After the phase adjustment,the unit impulse responses of the ideal channel are mainly distributed at the lower order.After adjusting the phase characteristics of the ideal channel,the time domain equalization LMS,RLS algorithm and the least squares fitting method of frequency domain equalization can be applied well.(3)The non-ideal channel time domain equalization is studied.The LMS and RLS algorithm are used to equalize the non-ideal channel.The LMS algorithm and the RLS algorithm can converge after a period of time,and the output of the signal through the equalizer is close to that of the ideal channel.(4)The non-ideal channel frequency domain equalization is studied.The frequency characteristic of the ideal equalizer is obtained by ideal channel frequency characteristic and non-ideal frequency characteristic.The least squares algorithm is used to obtain the real equalizer.The output of the equalizer is similar to that of the ideal channel.Then,the ideal equalizer is subjected to discrete Flourier transform,and the two time sequences which concentrate most of energy are used to construct FIR filters.FIR filters then cascade delay units to form sub equalizers,which are connected in parallel to obtain the real equalizer.The simulation results show that the equalizer output signal and the ideal channel output is basically the same and its computation complexity is less than least square fitting method.In the GNSS signal quality monitoring system,the improved average method can be used to capture the long code signal directly.Besides,the time domain or frequency domain equalization algorithm can be applied to correct the non-ideal channel,which can reduce the adverse effects of the channel non-ideal characteristics.