Study On C Band Satellite Navigation Signal Architecture

Satellite navigation system is one of the most rapid developments for information technology in the world today.Currently,on account of GPS,Galileo,GLONASS and China's Beidou satellite navigation systems coexisting in L-band and spectrum of more and more navigation service signals overlaping seriously lead to intensified interinterference of signals.So the search for new navigation service bands will be very necessary.C-band between 5010 MHz and 5030 MHz is divided for the downlink signals of navigation services in the World Radio Conference 2000.ESA has researched the signal system,space and related ground stations and user terminals of C-band.China has fallen behind United States about satellite navigation systems in L-band,so the signal system has a lot of limitations.In view of this,we need to pre-study C-band in order to seize first mover advantage and use patents to protect the interests of BeiDou in the future.It may also provide technical reference for top-level design of China's own satellite navigation system and international coordination navigation systems.This paper relies on BeiDou special issue "GNSS L / S / C-band compatibility analysis".The thesis analyzes signal performance and compatibility techniques.Based on these analyses,we study the related signal system technology and propose a series of new design results.In this paper,the performance of the C-band and filter algorithm of performance improvement,compatibility assessment technology and applications,the research of navigation message design and signal modulation are studied in depth.The main content and results include the following four aspects:(1)The signal propagation properties and signal tracking performance are compared between C-band and L1-band so that we design the associated signal system.The coordinate conversion and time conversion between different navigation systems in order to provide a reference for interoperability of inter-system are comprehensively analyzed.Because of the Divided Difference Filter is after the first iteration,the system state already contains measurement noise information.Therefore the state estimation and measurement noise statistics are no longer orthogonal,resulting in affecting the accuracy.For the problem,this thesis proposes a new filtering algorithm-state augmentation based iterated divided difference filtering.The results show that attenuation of free-space loss,the troposphere,raindrops,clouds and mists are greater than L1 band due to increased carrier frequency of C-band.But the attenuation of ionosphere is less than L1 band for C-band.In addition,PLL tracking performance is poor in C-band,but its phase multipath performance is better and DLL tracking performance is identical.The new filtering algorithm let measurement noise information augment to the system state.It can ensure that the state estimation and measurement noise statistics are orthogonal and therefore improve the filter accuracy of nonlinear Gaussian system.(2)By analyzing the influence of the interference signal to receiver,calculation formula of degradation of effective carrier-power-to-noise density ratio based on spectral separation coefficient and code tracking sensitivity coefficient are deduced.It can be used to evaluate the compatibility in band.The compatibility assessments between navigation signals of the C-band and radio astronomy or microwave landing system are studied.Based on theoretical methods,compatibility simulations for typical signals of L-band are made.The results show that the interoperability modulation of L-band-Multiplexing binary offset carrier(Multiplexed Binary Offset Carrier,MBOC)moved to the C-band will cause greater inter-band signal interference.And when Binary Coded Symbol(BCS)modulation sequence based on Minimum Shift Keying pulse-MSK-BCS([1,-1,1,-1,1,-1,1,-1,1,1],1)is as the interoperable modulation scheme,it can reduce inter-band interference to some extent.The current modulation schemes are unable to meet all the strict out band compatibility requirements,and only MSK-BCS(7)[-1,1,1,1],1(8)can meet the requirements.But the modulation has poor properties for other performances;therefore we need to study much better modulation for C-band.(3)The navigation message structure for C-band is designed and coding and decoding technology principles of LDPC and FEC are introduced.In full consideration of phase-locked loop tracking error and the bit error rate to meet the threshold,the best compromise solution of the data channel and pilot channel power ratio and the message rate is selected.The results show that,the navigation message of C-band broadcast not only general navigation information but also the navigation message digital signature authentication,new keys,as well as correction of zenith tropospheric delay data and zenith wet delay data when with a view to the C-band performance.The best compromise proposal is that data channel and the pilot channel power ratio 50/50,and bit rate 50 bps which can meet the tracking and data demodulation.(4)The principles of rectangular modulation waveform and sinusoidal modulation waveform are introduced for L-band.GMSK and PSWF as candidate modulation waveforms for C-band are briefly theoretical analyzed.Aim at the drawback of erroneous locking resulted by autocorrelation sidelobes very close to the amplitude of the main lobe for current existing sequence MSK-BCS([1,-1,1,-1,1,-1,1,-1,1,1],1),an improved modulation sequence is proposed.The modulation sequence with the existing typical modulation schemes are compared and analyzed and simulation results show that the new modulation has a better autocorrelation,multipath,code tracking,in band compatibility,as well as meeting stringent out band compatibility for C-band.The key technology and innovation of this thesis is mainly reflected in the following aspects:(1)Taking the presence of state estimation problem of nonlinear system and Gaussian noise for navigation systems,the low estimation accuracy and the slow convergence of filter output error of the traditional extended Kalman filter,and state estimation and measurement noise statistics are no longer orthogonal after one iteration thus affecting the accuracy into account,a new filtering algorithm-state augmentation based iterated divided difference filtering is proposed.The algorithm will augment measure noise information to the system state and ensure that the state estimation and measurement noise are statistical orthogonal,then,it improves the filtering accuracy of nonlinear Gaussian system.(2)Aim at the problem of the effect of the data rate and the power allocation of the receiver data channel and pilot channel on the tracking and data demodulation,under consideration phase-locked loop tracking error and bit error rate meeting the threshold,the best compromise choice about data channel and pilot channel power ratio and message rates is proposed.Based on it,tracking and demodulation performance can be realized at the same time.(3)Aim at the drawback of erroneous locking resulted by autocorrelation sidelobes very close to the amplitude of the main lobe for current existing sequence MSK-BCS([1,-1,1,-1,1,-1,1,-1,1,1],1),an improved modulation sequence is proposed.Simulation analysises show that the modulation sequence has good autocorrelation,multipath,code tracking,in band compatibility,and can meet stringent out band compatibility.It can be used as a candidate modulation for C-band.