| 摘要 |
A Global Positioning System (GPS) commercial receiver includes programmable logic that utilizes P-code modulated L1 and L2 GPS signals to derive estimates of in-phase and quadrature-phase components of both L1 and L2 signals, a programmable processor that calculates pseudoranges and pseudo-Doppler phases, and derives navigation solutions. In processing received L1 and L2 signals encrypted by an unknown W-code, a received comple L1 signal is multiplied by a locally-generated replica of the P-code, and integrated over a tim period having a duration that is approximately the same as the bit duration of the W-code. The received complex L2 signal is multiplied by a replica of the P-code, integrated, and latched to account for L2 signal delay relative to L1. In-phase components of the integrated signals are weighted proportionally to L1 and L2 signal amplitude, and the weighted sum is compared to zero and its magnitude is compared to a predefined threshold. Simultaneously, the integrated complex L2 signal is added to, or subtracted from a previously accumulated complex L2 signal in accordance with a sign of the weighted sum, and on condition that the magnitude of the weighted sum exceeds the predefined threshold. A resulting complex accumulated L2 signal comprises near-ML estimates of desired L2 amplitude and pseudo- Doppler phase. |
