全球衛星導航系統BOC(1,1)訊號無混淆追蹤之研究

Abstract

In the next generation of Global Navigation Satellite System (GNSS), modernized GPS and Galileo will adopt variations of the Multiplexed Binary Offset Carrier (MBOC) modulation such as time-multiplexed binary offset carrier (TMBOC) and composite binary offset carrier (CBOC) modulations to achieve improved tracking properties and spectrum separation. The MBOC power spectrum density (PSD) is created by linear combination of BOC(1,1) and BOC(6,1) PSDs, and BOC(6,1) plays an important role to increase the power of high frequency component. Compared with the binary phase shift keying (BPSK) signals, such new signal structures have some properties. In the frequency domain, the subcarrier modulation causes the only main lobe to be split into two symmetric lobes on the sides of the central frequency. In the time domain, the multi-peak of the autocorrelation gives rise to a potential threat of signal tracking. Typically, it usually uses the BOC(1,1) receiver to receive the incoming MBOC or BOC(1,1) signal due to their similar properties and low hardware complexity. A GNSS receiver employs a code tracking loop such as a delay lock loop for keeping track of the code phase of a specific code. An important ingredient in the delay lock loop is the discriminator which is responsible for the generation of the error signal for code tracking. The early-minus-late discriminator which is used in receiving legacy GNSS signals cannot be directly applied to the reception of MBOC or BOC(1,1) signals due to the side peak issues. In the dissertation, the ambiguity in BOC(1,1) signal tracking is addressed. The objective is to design a receiver that is ambiguity-free. To achieve the goal, different types of correlators and various methods in combining correlator outputs are investigated. In particular, the coupling effects of different correlators are analyzed and the optimization approach is adopted to seek for the synergistic integration of the correlators for ambiguity-free discrimination without sacrificing tracking and multipath performances. The resulting designs are compared with other existing methods in terms of multipath mitigation, code tracking error, and implementation complexity. Besides the software simulation, the hardware implementation of the GNSS BOC(1,1) receiver with the proposed scheme is realized by a DSP/FPGA development board. Finally, the GIOVE-B signal transmitted by the Galileo experimental satellite is received in real time to validate the performance of the proposed scheme.