Research On Multiplexing And Processing Methods For New Generation GNSS Signals

With the rapid development of global navigation satellite system(GNSS)and its extensive and intensive applications,the demand of position,navigation and timing(PNT)service performance to different users has become more refining.Therefore,in the new generation of GNSS,the diversified PNT services demand bring about new requirements for the signal design and processing method.To be specific,firstly,it is necessary to select the modulation signal with optimal ranging performance for GNSS application.Secondly,it is essential that the signals which have arbitrary chip waveform values,more than one frequency points,arbitrary signal component number and arbitrary power and phase schemes are multiplexed into one signal with constant envelope,so it can be broadcasted through one radio link.Thirdly,it is needed to realize unambiguous tracking of the new navigation signals and to improve the tracking robustness while retaining the unique advantages of the new signals.Fourthly,it is necessary to improve the signal acquisition performance in complex environment while reducing the computation complexity.Because the present methods cannot meet these requirements completely,this dissertation focuses on the in-depth research on these key issues and the main achievements are as follows.1.For the problem that the present GNSS signal code time delay estimation error assessment methods are not systematic and comprehensive enough,the code tracking loop can be divided into four types according to whether the receiving mode is matched or the processing is coherent.Under the assumed condition that code delay estimation error is very small,this dissertation deduces expressions of code delay estimation error for non-coherent processing under non-matched receiving model,and analyzes the relationship with other three types.In the meantime,it solves the assessment based on the Ziv-Zakai bound(ZZB)when the code time delay estimation error cannot meet the assumed condition.Those two together constitute a complete code time delay estimation error assessment method,which has very high universality,and it can provide important theoretical guide for signal design and receiver development.2.For the problem that the current dual-frequency multiplexing methods can only be used for the bipolar signals with particular constraints of initial power and phase,this dissertation proposes an efficiency optimized multiplexing method for both bipolar signals and multi-level coded symbol(MCS)signals.This method can meet the requirements of signals multiplexing problem with arbitrary frequency points number,arbitrary signal waveform modulation and arbitrary initial power and phase,in which it can choose any subcarrier according to the specific need during multi-frequency multiplexing.Therefore,it is very universal and flexible.Both of the current typical single frequency bipolar multiplexing methods and dual-frequency bipolar multiplexing methods respectively can be seen as the necessary condition and the particular cases of this method.For the signal multiplexing problem of Beidou system in transition stage and global Beidou system,this method can offer a good multiplexing solution.3.For the problem that the present unambiguous tracking methods of the binary offset carrier(BOC)class signals cannot be applied to MCS signals,this dissertation uses pseudo correlation function(PCF)to design a general unambiguous tracking method for MCS signals.Under the framework of the same receiver loop,the proposed method can get one peak narrow correlation function for any MCS signals and eliminate tracking ambiguity,meanwhile it keeps the advantages of the MCS signals and simplifies the receiver design.As a particular case of the MCS signals,it also applies to the BOC class signals.Compared with traditional methods such as BPSK-Like,this method only needs to add one local reference signal,and its complexity is nearly the same as that of the sub-carrier phase cancellation(SCPC)method which is designed for the BOC class signals.4.For the question that the searching range of Doppler frequency is large under high-dynamic environment and the coherent integration time of the new modulation signals is limited by secondary code in the low carrier to noise ratio(CNR)environment,this dissertation respectively proposes an acquisition method based on partial matched filters compensated by FFT(PMF-FFT)and a joint acquisition method based on spreading code and secondary code.With respect to the PMF-FFT acquisition method,this dissertation discusses the selecting criterion of matching filter parameters and then analyzes computation amount and acquisition performance.With respect to the joint acquisition method,this dissertation presents a solution algorithm for the characteristic code of secondary code and analyzes computation amount and acquisition performance.Theoretical analysis and experimental result show that the two methods are appropriate for the GNSS signals acquisition in corresponding complex environments.