Optimum Semicodeless Carrier-Phase Tracking of L2

This paper discusses the performance of various codeless and semicodeless techniques used to obtain the carrier phase of the GPS L2 signal without knowledge of the encrypted Anti-Spoofing (AS) Y-code. Four known techniques have been published in the past: squaring, cross-correlation, P-code aided L2 squaring, and Z-tracking. All these techniques perform significantly worse than an ideal phase lock loop. Five new techniques are presented in this paper: (1) code-aided L2 Costas loop with W-bit integrate and dump arm filtering, (2) P-code aided L1, L2 cross-correlation, (3) soft decision Z-tracking, (4) optimum L2 demodulation motivated by maximum a posteriori (MAP) estimation theory, and (5) linear approximation of the MAP approach. The first three are modifications of existing techniques, with improved performance. Techniques 4 and 5 are optimum and near-optimum techniques based on statistical estimation theory, and provide the best performance in squaring loss and mean time to cycle slip.