High-sensitivity Technology Research On Baseband Signal Processing Of Beidou Navigation Receiver

With the development of BeiDou Navigation Satellite System,its application field has become more and more wide and has covered many aspects of people's life.In some complex environments,such as urban canyons,tunnels,dense foliage and indoor spaces,the strength of satellite signals is attenuated greatly and the design of traditional receiver cannot meet navigation requirements.Therefore,high-sensitivity receiver design has become an important issue.The structure characteristics of BeiDou signals are very different from traditional GPS signals,so signal process technologies of traditional GPS receivers cannot be directly used for BeiDou signals.Hence,it has great theoretical significance and application reference value to carry out research of BeiDou high-sensitivity receivers.In order to sovle problems of high-sensitivity signal processing in BeiDou receiver,three key technologies in baseband signal process are researched including signal acquisition,signal synchronization and signal tracking.Several signal process algorithms suitable for BeiDou signals are designed and are verified using simulation tests.In addition,a BeiDou receiver hardware system is designed and is carried out to test these algorithms.The main work includes the following aspects.First,siganl acquisition technologies for BeiDou signals are researched.Based on analyzing the structure characteristics of BeiDou signals,the problem that frequent bit transitions result in attenuation of the traditional one-millisecond coherent integration is modeled and analyzed.A novel BeiDou signal acquisition algorithm based on block matching filters and FFT is proposed.With this method,the code phase and carrier frequency can be estimated by parallel search and the influence of bit transitions is eliminated.After analysis,this algorithm improves signal processing efficiency and speed compared with the traditional algorithm and the signal gain is same.A simulation system of BeiDou intermediate frequency signal is designed and carried out to verify the availability of the proposed algorithm.It also provides support for verifications of relevant signal process algorithms.Secondly,weak siganl acquisition technologies are researched.There are more frequent bit transitions in BeiDou signals compared with GPS signals and the transitions limit the integration time.In order to improve acquisition sensitivity for BeiDou weak signals and resolve the problem,a novel BeiDou weak signal acquisition algorithm based on zero-padding and differential correlation is proposed to weaken the effect of NH code and realize 1 ms correlation.Furthermore,a novel BeiDou weak signal acquisition algorithm based on modified differential correlation is proposed.In the proposed algorithm,the differential operation is moved from the post-correlator stage to the intermediate frequency samples to weaken the influence of data bit reversions.Code phase and carrier frequency are estimated by one-dimensional search using FFT.Finally,Monte Carlo simulations are conducted to analyze the performance of the proposed algorithm.Thirdly,weak siganl bit synchronization technologies are researched.Because of the structure characteristics of BeiDou signals,signal bit synchronization algorithms in traditional GPS receivers cannot be used for BeiDou signals.A novel BeiDou weak signal bit synchronization based on grouping and bit matching is proposed to weaken the effect of NH code.In weak signal environments,the signal to noise ratio(SNR)is very low and the tracking frequency deviation is large,causing that the traditional bit synchronization algorithm is failed.In order to realize bit synchronization for BeiDou weak signals with large frequency deviation,a bit synchronization algorithm based on differential coherent and maximum likelihood is proposed.Differential coherent operations are used to remove the effect of frequency deviation and NH code.Monte Carlo simulations are conducted to analyze the detection performance of the proposed algorithm.Forthly,the research of the beidou weak signal tracking algorithms is carried out.Signal tracking quality is influenced by thermal noise and dynamic stress which also limits the extension of the integration time.Assist of inertial information and structure optimization of tracking loop are often used to reduce the tracking error.Therefore,an optimal filtering algorithm after assist of inertial information is designed.The inertial information is used to remove the dynamic stress and the Kalman filter is used to obtain a better loop tracking quality.In order to solve the problem that the VDLL + VFLL tracking structure is difficult to be realized,a vector loop control method is designed.It can realize tracking of carrier phase and it is easy to be realized on actual hardware system.A test platform consists of satellite navigation system and inertial navigation system is designed to verify the algorithms.Finally,a BeiDou navigation receiver system is designed on a DSP+FPGA platform and a comprehensive test system is constructed.Based on BeiDou real signals and simulated siganls,weak signal tests,static tests and vehicular tests are carried out to verify algorithms above respectively.The test results show that these algorithms can effectively improve the sensitivity performance of BeiDou navigation receiver and enhance the adaptability of BeiDou receiver in weak signal environment.