| 摘要 |
A system and method is provided that searches for the frequency and phase of a CDMA transmission in an iterative manner. With its automatic frequency control (AFC) disabled, the receiving system performs a coarse search for the transmitter's CDMA phase at a nominal receiving frequency. When the coarse phase is obtained, the AFC is invoked with a large-range pull-in, to obtain an initial, coarse frequency that is likely to be closer to the transmitter's frequency than the initial nominal frequency. At this coarse frequency, the receiving system repeats its search for the transmitter's CDMA phase, starting at the previously determined coarse phase. Because this second phase determination is conducted in the presence of less frequency error, it provides for a more accurate phase determination. The AFC is again invoked, but with a small-range pull-in, to obtain a finer frequency determination. Because the finer frequency determination is conducted in the presence of less phase error, a substantial improvement in the accuracy and precision of the frequency determination can be achieved. To achieve this more accurate phase and frequency determination within the same time duration as a conventional acquisition process, the initial coarse phase determination is conducted using a rapid, albeit less accurate, process than the conventional phase determination.
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