Constant-envelope Transmission And Multipath Mitigation For Modern Satellite Navigation Signals

Signal modernization is an important milestone in the development of Global Navigation Satellite Service(GNSS). The application fields of GNSS expand rapidly since GPS claimed the Full Operational Capability(FOC), which have far exceeded the signal service capability designed in 1970 s. It directly motivates the modern GNSS signal theory represented by GPS modernization and Galileo programs. Modern signals adopt new signal design features such as advanced forward error correction(FEC), data/pilot separation, binary offset carrier(BOC) modulation, and thus significantly improved the military and civil services. But meanwhile, they also introduce new challenges for both the transmitters and receivers that process modern signals.The spectrum allocation for satellite navigation has been over crowded. Modern signals must share the spectrum with traditional service signals that already have huge user group, and they trend to use multiple spreading codes. All these increase the number of codes that must be broadcasted on satellites. In order to reduce the satellite complexity and improve the signal quality, the multiple spreading codes must be modulated into constant envelope. However, classic constant-envelope modulation techniques cannot provide satisfying problems in GNSS systems.This paper studies the optimum constant-envelope transmission problem with specified phase/power constraints systematically. Classic binary signal transmission problems have optimum numerical phase look-up table, but the results have no analytical description on the individual items of the constant-envelope baseband signal. As a result, the compatibility and receiving algorithms can only be validated by numerical simulations. This paper proposes a novel inversion algorithm that converts any phase look-up table into an analytical baseband signal, and solves the problem for the lack of theoretical analysis. For typical three-code multiplexing problems, the existence non-exclusiveness of the optimum solution is discussed. The binary signal is further extended into multi-level signals and the phase-optimized constant-envelope transmission(POCET) algorithm is generalized as MPOCET for multi-level signals. Alt BOC is derived independently by MPOCET. The result shows that sub-carriers with higher efficiency will not improve the efficiency of Alt BOC.Based on the MPOCET theory, the B1 and B3 bands of Compass system is discussed with two modulation solutions. The Dual QPSK modulation multiplexes two QPSK signals with π/4 phase shift and achieves the optimum 85.36 efficiency. It can combine the traditional QPSK(10) and the new BOC(15, 2.5) signals on B3 band. UAlt BOC modulation combines a QPSK signal and two in-phase BPSK signals, which can solve the backward compatibility problem for signals with different carriers on B1 band.Modern signals can improve the navigation performance such as measurement accuracy, etc. The proposal of advanced model and multi-frequency signals has decreased the ephemeris error and ionosphere error. But multipath remains a major error source for navigation accuracy even in the modernized GNSS error budget. This paper first studies the code correlation reference waveform(CCRW) multipath mitigation algorithms for BPSK(n) signals significantly. The theoretical limitation of linear reference waveform, the generalized description of non-linear waveform and optimum waveform design for specified bandwidth are discussed. The false alarm problem caused by distorted correlation peak under limited bandwidth is improved for MEDLL technique. The field test results show that the design can achieve the theoretical limitation of multipath mitigation for BPSK(n) signals.BOC modulation is an efficient spectrum separation technique for modern signals. BOC signals tend to have larger Gabor bandwidth, thus provide better measurement accuracy. However, the ambiguity feature of BOC correlation function makes the traditional multipath mitigation algorithms for BPSK signals hard to implement. This paper studies the most complicated multipath mitigation problems for CBOC and high-order BOC signals. The proposed joint multipath mitigation algorithm first employs CCRW on pilot and data channels individually, then the two channels are combined non-coherently to eliminate the BOC(6,1) components. In this way the optimum multipath mitigation performance can be achieved. High-order BOC signals are first converted into BPSK-like signals by QBOC technique, then multipath is mitigation by Strobe technique designed for BPSK signals. The bandwidth and parameter design problems are also discussed. Simulations show that the combination of QBOC and Strobe can eliminate multipath efficiently without ambiguity.At last, the research work of the dissertation is summarized and reviewed. The major achievement of this dissertation has already been implemented in the related GNSS program of China.