Chun Yang, Andrey Soloviev, Ananth Vadlamani, QuNav; Joung C. Ha, AFRL/RYWN

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Abstract:

The binary offset carrier (BOC) modulation was initially developed for easy sharing of spectrum between GPS modernization signals and legacy binary phase shift keying (BPSK)-modulated signals in the same band. It is now adopted by all GNSS constellations as a BOC signal has a larger Gabor bandwidth, producing better ranging (accuracy and multipath) performance. However, general BOC signal acquisition and tracking encounters the problem of multiple peaks (less an issue for MBOC, though), and many methods have been proposed to address this issue. A simple method to avoid such an ambiguity is to extract the upper and lower sidebands of the split spectrum of a BOC signal, treat them separately as a BPSK signal each, and then combine the results so as to recover the reduced sideband signal strength. Coherent combining is more gainful than the noncoherent counterpart particularly when the incoming signal is weak and/or when a strong interference signal is present. In this paper, a long coherent combining and integration (LCCI) scheme is presented, which enables standalone acquisition of a BOC signal without external aiding from a network or an inertial navigation system (INS) under combined narrowband and matched spectral interference signals. The LCCI scheme burns through the strong interference via building up the desired signal while averaging out noise and interference. To build up the desired signal, it makes use of all information resources available (e.g., L1 and L2, upper and lower sidebands, odd and even chips, and/or I and Q components) and applies coherent combining and long coherent integration, followed by non-coherent accumulation if necessary. Issues and enabling techniques are presented in this paper. The LCCI scheme is implemented on a software defined receiver (SDR) platform consisting of FPGA and ARM. Results of real-time demo with input RF signals generated by a Spirent GPS Simulator are described in the paper.