Research On The Key Techniques Of Compass-M1 Civilian Software Receiver

Receiver is one of the three segments of satellite navigation system whose responsibility is to detect and receive satellite navigation signal together with observations extraction and positioning calculation.SDR ( Software Defined Radio) is the ultimate goal of radio development who has the merits of open in hardware, reprogrammabality in software and compatibility in function.Centering with the principle,stucuture,realization pattern and key techniques of Compass-M1 civilian software receiver,the thesis made a thoroughly research on its main structure design,signal collection,PN(Pseudo Noise)code acquisition and tracking,carrier tracking and multipath mitigation techniques and gained a feasible plan of Compass-M1 software receiver realization.The main works are as follows:The modulation principle,power density funtions and autocorrelation functions of MBOC(6,1,1/11)(-Multiplexed Binary Offset Carrier) and AltBOC(15,10)-(Alternate Binary Offset Carrier) modulations were investigated respectively based on that of BOC(Binary Offset Carrier)modulation and the four-BPSK(Binary Phase Shift Keying) multiplex character of AltBOC(15,10) is derived,which is the premise to design Compass-M1 civilian software receiver.The structure of double bands Compass-M1 civilian software receiver was designed based on SDR concept and the A/D converter was selected which is capable of direct radio frequency bandpass sampling for Compass-M1 civilian software receiver.The principle of bandpass sampling was derived and bandpass sampling pattern was analysed.The method and process of selecting the minmum sampling frequency for double bands Compass-M1 civilian software receiver when adopting direct bandpass sampling without aliasing was proposed.In view of long PN code acuqisition by software,the thesis proposed a method called FFT-based frequency complement parrallel search which can finish two-dimension search of code phase and Doppler frequency by only FFT-transforming of the incoming signal once to shorten the satellite navigation signal acquisition processure.The single side band processing pattern of AltBOC(15,10) was chosen to simplify receiver design,lower power consumption and facilitate multimode receiver design and the Tong algorithm was select as the software receiver acquisition decision strategy.To eliminate the threat of ambiguous acquisition and tracking of MBOC(6,1,1/11) signal,the FFT-based acquisition circuit and noncoherent DLL discriminators were modified for MBOC(6,1,1/11) signal by ASPeCT(Autocorrelation Side-Peak Cancellation Technique).The method of unifying ASPeCT-based DLL discriminators was derived and the RMS(Root Mean Squre) of EMLP(Ealy Minus Late Power) and DP(Dot Product) discriminators were analyzed.The mathematical model of multipath was established and the multipath error envelops of EMLP and DP DLL discriminators for BOC(1,1) and single side band AltBOC(15,10) caused by one multipath whose amplitude is half of that of the direct path were derived.The principle and limits of narrow correlator were analyzed.The MEDLL(Multipath Estimating Delay Lock Loop) technique was selected to allieviate the multipath effect for Compass-M1 software receiver and a LS(Least Square)-based realization method of MEDLL was brought forward which is effective in perfomance and simple in realization.Based on the performance of second order PLL(Phase Lock Loop) on dynamic and total phase viberation in different CNR(Carrier to Noise Ratio) and dynamic stress situations,a pilot based pure PLL was decided as the carrier tracking loop of Compass-M1 software receiver.To take advantage of the tracking accuracy and dynamic performance of pure PLL,a bandwidth adjustable PLL structure was proposed whose principle and digital diagram were derived.