Research On The Tracking Method Of AltBOC Signal

With the rapid development of the global satellite navigation system(GNSS),many signal modulation methods have been used to improve the performance of the GNSS system and utilize frequency resources in a reasonable way.As one of the derivative signals of binary offset carrier(BOC)signal,alternate binary offset carrier(AltBOC)signal maintains code tracking accuracy and is excellent in anti-multipath and anti-noise performance.Moreover,the upper and lower sidebands of AltBOC signal are equipped with two orthogonal signal,which make it possible to reuse the multiplexing of four signals at two frequencies.A constant envelope modulation of AltBOC signal can also be achieved by introducing intermodulation components.The E5 signal of the Galileo navigation system has adopted constant-envelope AltBOC(15,10)modulation.With the extensive application of the AltBOC signal,it is important to research the tracking method of the AltBOC signal.Signal tracking is an important prerequisite for navigation message demodulation,processing doppler frequency shift,and obtaining the pseudo-distance measurement.The paper takes the AltBOC signal as the key object,researching the mainstream tracking method,considers the design of the AltBOC signal tracking method based on extended kalman filter method(EKF),and proposing the tracking method based on liner quadratic guassian method.The performances of EKF and LQG methods are compared with the dual-BPSK tracking(DBT)which is a widely recognized tracking method.The main research contents of this paper are as follows:(1)Firstly,the paper studies the structure and characteristic of several typical modulated signals that mainly include BPSK,BOC and AltBOC signal.The paper analyzes the performance of the AltBOC signal from three aspects: power spectrum density,auto-correlation function and code tracking accuracy.The Galileo E5 signal modulated by AltBOC(15,10)is simulated.Understanding the structure of modulation signal is the basis of signal tracking loop design.(2)This paper analyzes the carrier loop and code loop and explores the current mainstream AltBOC signal tracking method.Firstly,the phase/frequency locked loop(PLL/FLL)and delay locked loop(DLL)have been introduced.This paper mainly studies the DBT tracking method and analyzes the performance of carrier loop discrimination,the sub-carrier loop discrimination and code loop discrimination.(3)By establishing a system model based on the EKF tracking method of AltBOC,the paper proposes the LQG tracking method,which has conducted and established themeasurement model and state model.The advantages and disadvantages of two modeling methods which include carrier tracking loop auxiliary code tracking loop are analyzed.The AltBOC signal tracking method based on extended Kalman filter is designed and an in-depth analysis of the principle of LQG regulator is given.The optimal control problem is explored.The method of obtaining state feedback matrix is studied and the design method of parameter matrix in quadratic performance index function is discussed.In summary,this paper designs the AltBOC signal tracking method based on LQG regulator.(4)Employing the simulation data and the actual data have verified the feasibility of the LQG method and the EKF methods.Besides,the DBT method,which uses traditional loop discriminators,is used to compare and analyze the tracking performance of these three methods.In order to compare and analyze the tracking performance in a real environment when the carrier noise ratio(CNR)changes in a short time,the dynamic Galileo E5 signal data was collected by using the navigation signal collection equipment and the experimental car.In order to evaluate the performance of each tracking method in the carrier frequency ramp environment,the MATLAB tool is used to generate the simulation data of the frequency slope scenario.The experiment shows that the LQG method can be tracked steadily when the EKF method and the DBT method cannot lock the carrier loop and the sub-carrier loop in the CNR jump condition.At that time,the DBT method also cannot lock the code loop.The mean and variance of the LQG method code phase error estimated are less than the EKF method to several orders of magnitude.By way of simulation,the carrier phase and code phase error variance of LQG method less than the DBT method to several orders magnitude.The advantages of LQG method are quite significant.With the extensive application of AltBOC signal and other BOC derivative signals in GNSS system,research into the AltBOC signal tracking method may be offers a reference for other derivative BOC signal tracking methods.Meanwhile,the LQG tracking method proposed in the paper provides a reference for improving the performance of signal tracking loop.