Research On The Key Technologies Of Modernization Signal Design For LEO Navagation-enhanced GNSS

As technology of Global Navigation Satellite Systems(GNSS)becames more mature,satellite navigation enters the era of Multi-Constellation.However,due to vulnerabilities and limitations of GNSS based on MEO and GEO satellites,anti-jamming performance and usability have been challenged,and the precision point position(PPP)convergence time is too long,which restricts the further application and expansion of GNSS.The conception on the basis of LEO constellations for navigation-augmented GNSS has been investigated and explored recently due to higher floor power and rapid spatial geometric changes,which can improve the anti-jamming performance and decrease PPP convergence time.The LEO enhanced GNSS will become the new trend of future satellite navigation,which brings the new opportunity to satellite navigation signal design.This article takes LEO enhanced GNSS as the research background and explores the modernization signal design for anti-jamming and compatibility performance degradation from massive signal and high dynamic reception complexity.There are five research results as follows:(1)By the new features from the dynamic phase and extended waveform period in the subcarrier,a dynamic phase subcarrier modulation model has been proposed in the paper.The model takes multiple code delays as the subcarrier period and dynamically adjusts the subcarrier phase,which can reshape the autocorrelation function(ACF)and power spectral density(PSD)by directly designing the subcarrier and improve signal performance.The linear phase and frequency subcarrier modulation signals based on the model have the superior performance potential and design flexibility,and offer the foundation for the specific signal design later.(2)For the anti-jamming and compatibility performance degradation from massive navigation-enhanced signals,a binary offset carrier based on periodic offset subcarrier(BOC-POS)has been proposed in the paper.The subcarrier phase of BOC-POS modulations is periodically linear with the time-multiplexed method.Meanwhile,the improved MBOC modulations based on periodic offset subcarrier(MBOC-POS)using the low order BOC-POS signal has been constructed in the paper.The BOC-POS modulation has improved anti-interference performance and compatibility while giving consideration to code tracking and multipath mitigation performance.The BOC-POS modulation can be received by using traditional BOC receotion methods.The analysis and performance evaluation show that the anti-matching spectrum interference quality factor of BOC-POS(1,1,Δφ)increases 42% than BOCs(1,1),37% for MBOC-POS modulation with the filter bandwidth of 14 MHz.And the compatibility increases by1～2d B.(3)For the anti-jamming and compatibility performance degradation from massive navigation-enhanced signals,a binary offset chirp carrier modulation(BOCC)has been proposed in the paper.The subcarrier frequency of BOCC modulation is periodically linear.Meanwhile,the evolution of multiplexed binary offset chirp carrier(MBOCC)and alternative binary offset chirp carrier(Alt BOCC)based on lower order BOCC signal have been carried out.The BOCC modulation has the rectangular power spectral density and roll-off characteristics,and obviously superior anti-interference performance.In addition,the side pearks of autocorrection function of BOCC modulation is smaller than BOC signals,which is convenient to robust reception.After analysis and evaluation,it can be seen that the anti-match interference quality factor of BOCC(0.5,1,1,1ms)increase 71% than BOCs(1,1),70.8% for QMBOCC(6,1,4/33,0.5,1,1ms).And the compatibility of low order BOCC signal increases 1～2d B.(4)For the unambiguous reception of BOCC modulations,a double estimation tracking scheme based on chirp delay locked loops(CDLL)has been proposed in the paper.The scheme takes the binary chirp subcarrier alone by CDLL for unambiguous reception,and the tracking process and theoretical tracking accuracy are described in the paper.In addition,the Monte Carlo simulation results show that the double estimation tracking scheme based on CDLL can track the BOCC signal unbiased,and the simulation tracking performance is similar to the theoretical performance.Meanwhile,the anti-interference performance of low order BOCC signal can improve2 d B comparing with the corresponding BOCs signal,especially under the higher C/N0,which can prove the superior anti-interference performance of BOCC modulations.The tracking method based on CDLL is convenient to practical application.(5)For the high reception complexity in the dynamic condition,the chirp signal modulated by pseudo-noise code(chirp-PC)is applied in LEO enhanced GNSS,which can reduce the acquisition complexity and improve the sensitivity due to the couple of code delay and Doppler frequency.Meanwhile,in order to relieve the delay estimation bias of chirp-PC signal,a comnibation tracking scheme of open and closed loops based on chirp phase locked loops(CPLL)has been proposed in the paper.The scheme can uncouple time delay and Doppler frequency by tracking the chirp signal with open loops for unbiased reception.And the theoretical tracking error has been presented in the paper.It can be known by simulation experiments that the Doppler search numbers of chirp-PC(0.25,2,1ms)can reduce by 81% than the corresponding BPSK signal.In addition,the acquisition sensibility of chirp-PC(0.25,2,1ms)can increase 1.8d B under the same detection probability.Meanwhile,chirp-PC signal can be tracked unbiased by the comnibation tracking scheme of open and closed loops,and the carrier and code phase tracking errors are similar to the BPSK signal with corresponding spreading code rate.