Research On Receiving And Pulse Shape Techniques For GNSS Signals

With the advent of the new global navigation satellite system (GNSS), theunambiguous acquisition and tracking for the binary offset carrier modulation (BOC) andthe pulse shape design of the navigation signal are two hot issues.The autocorrelation function (ACF) of navigation signal affects the performance ofthe GNSS system. Due to the split spectrum of BOC signals, they have been proposed toimprove the measurement precision, enhance robustness against multipath and guaranteethe coexistence and compatibility with different systems. However, the autocorrelationfunction (ACF) of the BOC signals has multi peaks which may bring about ambiguity intraditional code tracking loop. Mitigating or eliminating the ambiguity effectively forBOC signals acquisition and tracking is the prerequisite for exerting the inherent highaccuracy and anti-multipath advantages of BOC signals. The pulse shape determines theACF and power spectral density of the navigation signal which affects ranging accuracyand anti-multipath interference performance, so it is also the key part of the system. Maincontents about the two issues are as follows.(1) An effective method of suppressing the sub-peak and mitigating ambiguity isproposed for Cosine phased BOC (CosBOC) signals. One particular symbol of the localauxiliary signal is derived in this thesis. The main idea is to use the cross-correlationfunction of the received cosine-phased BOC signal with the specifically designed localauxiliary signal to counterbalance the undesired side peaks of the received cosine-phasedBOC autocorrelation function, the final correlation function has only two small positiveside peaks and the amplitude ratio of the main and side peak increases significantly, thencombing with the classical Bump Jump (BJ) technique to distinguish the main peak andthe two small residuary peaks effictively. Simulations show that at the cost of somedegradation of detection probability in the acquisition phase the proposed method is betterthan the traditional BJ method in mitigating the ambiguity, as the modulation orderincreases the improvement is more obvious. The SNR of the proposed method atprobability of the main peak tracking as0.9is4dB lower than that of the BJ method.Even under multipath interference the proposed method is also higher in the main peak tracking probability than the BJ method.(2) One kind of sufficient condition of the local reference waveform for the pseudocorrelation function (PCF) method is proposed. The mathematical expressions of the PCFmethod are derived, and the performances when the parameters of the local referencepulse shape are different are analysed. Simulations show that the PCF method isunambiguous, as the width factor of the local reference signal increases the trackingaccuracy gradually increases. The accuracy of the PCF method is close to the traditionalacquisition under the assumption that no false acquisition occurs when the width factor is1and the C/N0is larger than30dB-Hz. And the method is better than the traditionalmethod in mitigating the middle and long multipath interferences, the multipath errorenvelopes are zero when the multipath delay is larger than0.3chip.(3) Research shows that the additions of the ACFs of SinBOC (1,1) orMBOC(6,1,1/11) and the absolute value of their ACFs are unambiguous. An unambiguoustracking technique which substitutes the combination of the correlation outputs and theabsolute value of the correlation outputs for the correlation outputs in the coherentEarly-minus-Late architecture loop is proposed. The technique can completely removesthe side-peaks from the ACF of SinBOC (1,1) and MBOC(6,1,1/11) while still keepingthe sharp main-peak, which maintains the tracking accuracy and anti-multipath propertiesof the BOC modulation. The performances are better than the BOC-PRN coherent method.(4) According to the demand of navigation signal, the thesis analyses thepracticability that the prolate spheroidal wave functions (PSWF) which are concentrated inthe time domain and maximized energy in the specified bandwidth as a new kind ofnavigation signal pulse shape. The ACF and power spectral density of the pulse shape aregiven. Then the navigation performances of the PSWF pulse shape and BOC pulse shapewith the same code rate and bandwidth constraints are compared. The results show thatwithin the appropriate bandwidth the PSWF pulse shape is better than the band-limitedBOC in code tracking precision and anti-multipath interference on the whole.