| 摘要 |
<p>A global position system receiver recovers the L1 and L2 carriers, the C/A-code measurements and the L1 and L2 P-code measurements by (a) producing an estimate of the L1 carrier phase angle and synchronizing a locally generated C/A-code with the L1 signal using an L1 delay lock loop and controlling, based on the locally generated C/A code, an L1 P-code generator that produces a synchronized version of the P-code; (b) initializing an L2 P-code generator based on the phase of the P-code generated by the L1 P-code generator; (c) determining, for the L2 signal, an estimate of signal power that is adjusted to compensate for noise; (d) determining an L2 carrier phase angle; (e) tracking the L2 P-code by adjusting an L2 P-code generator until the estimate of signal power is maximized. The GPS receiver also resolves a 1/2 cycle ambiguity in tracking the L2 P-code by comparing demodulated L1 P-code bits and L2 P-code bits. If the bits do not match in the majority of instances, the receiver determines that it is tracking the L2 P-code with 1/2 cycle error and adjusts its estimate of the P-code phase accordingly. The receiver thus tracks the L2 P-code and carrier independently of the L1 signal, with the exception of the resolution of the 1/2 cycle ambiguity. Accordingly, the receiver can determine the reliability of the L2 signal by determining a carrier-to-noise ratio.</p> |
