A Study Of Compass B1C Band QMBOC Modulated Signal Tracking Technology

The new generation Compass navigation system has adopted quadrature multiplexed binary offset carrier(QMBOC)modulated signal for its B1C pilot channel which modulated the BOC(1,1)and BOC(6,1)components in two branches in-phase quadrature with each other.This signal has a similar auto-correlation property with the GPS L1 C signal with a multi-peak auto-correlation function.In order to achieve an unambiguous and anti-multipath tracking for QMBOC signal,this dissertation obtains the following results based on the existing research results and the signal structure of QMBOC signal modulation:1.The signal structure of B1C signal is deeply researched in this work.We mainly focus on the modulation method of the B1C data and pilot channels,and the property of the time domain and frequency domain of the QMBOC signal including the time domain implement and the ACF of the QMBOC signal.2.The match receiver is researched in this work.The principle of QMBOC match receiver is analyzed,and the corresponding schematic diagram is also given.The probability of ambiguous acquisition and tracking is analyzed in detail.The Cramer-rao bound of tracking error under noise condition is given,and the tracking error under multipath is also analyzed.3.The principle of double estimator is adopted for QMBOC signal processing,this method regards the ranging code and the subcarrier as two independent components,and the multi-correlators structure is employed to generate a two dimensional cross-correlation function with the received signal.Based on the result of the 2-D CCF,two delay lock loops(DLL)are used to tracking the ranging code and subcarrier respectively,a precious tracking result can also be obtained combining the two dimensional tracking results.Then a strobe double estimator is proposed to further improve the anti-multipath performance of the double estimator.The local replica of the ranging code is replaced with a strobe waveform.A sharper and narrower discrimination function can be obtained by cross-correlation operation with the received signal.In this way,the anti-multipath performance of the double estimator is improved.Finally the anti-multipath and anti-noise performances are verified by computer simulation.4.The principle of double phase estimator is adopted for QMBOC signal processing,this method also regards the ranging code and the subcarrier as two independent components.The ranging code is locked with a DLL,however,considering the effect of the front-end filtering,the received square sinusoidal signal can be distorted and more approaching a sinusoidal signal.Therefore,this method proposes to adopt a phase lock loop to estimate the subcarrier to further improve the tracking accuracy of the subcarrier.The anti-multipath and anti-noise performances are verified by computer simulation.5.Considering the complexity of the double estimator and double phase estimator,this dissertation proposes a local replica designing method based on least square method.Because the pilot and data are modulated on the in-phase quadrature with each other,thus these two components can be distinguished and processed individually.Therefore,this dissertation proposes to employs the least square method to deduct the local replica referring to the ideal discrimination function.In this work,the local replicas for the in-phase and quadrature-phase components are designed respectively,and the outputs of the cross-correlation are weighted combined to fully exploit the signal power of the QMBOC signal.An unambiguous and anti-multipath discrimination function can be obtained.The anti-multipath and anti-noise performances of the proposed method are verified by computer simulation.6.In degraded signal environment,the receiver can lose lock of the signal if the receiver only process the pilot channel.In order to further improve the accuracy and robustness of B1C signal tracking,the B1C data and pilot channels are proposed to be combined with or without the sign recovery mechanism.The early minus late(EML)and EML power discriminator are employed for the data/pilot combining strategies,and the corresponding tracking accuracy is analyzed in theory.The computer simulation is finally performed to verify the correctness of the theoretical analysis.The result shows,the proposed data/pilot combining tracking methods can improve the B1C signal tracking robustness significantly.The result also shows the EML discriminator based on the non-coherent combination strategy obtains the best tracking accuracy and robustness.Finally,the conclusion is given at the end of this dissertation in combination with the research results,and the future research direction and prospect are also given.