| 摘要 |
A GPS receiver comprises a first order code tracking loop 202 and a second order carrier AFC tracking loop 204. Lock detection 208 compares signal-to-noise ratios (SNRs) averaged (summed, integrated) over various times (periods) with respective thresholds for both fast and slow lock detection. Fast lock is good for moving receivers, slow lock is better for low CNO (carrier-to-noise ration, CNR) and gives better probability of detection and probability of false alarms. A primary tracking loop (302, fig. 3) has a fixed wide bandwidth, and a secondary loop has a narrow variable bandwidth which is based on signal strength. If one loop loses lock, it can restart the other (312). The secondary loop may use data stripping, but not the primary loop. SNR is calculated and converted to CNO 210 using tables (pages 15-17). |
