High sensitivity GLONASS/GPS automatic frequency control

摘要

Updates to an AFC loop can be performed to provide high-sensitivity tracking. A 20 ms update interval and PDI=10 ms is used for every other update. A setting is used for each update between the 20 ms updates. Notably, the setting uses PDI=5 ms. The setting can include first, second, and third cross-dot pairs associated with a first bit, a second bit, and a cross-bit boundary between the first and second bits, respectively. A sum of these pairs can be scaled down when the signal strength is below a predetermined threshold. In another embodiment, the setting can include a first cross-dot pair associated with a first bit and a second cross-dot pair associated with a second bit. A sum of these pairs can also be scaled down when signal strength is below a predetermined threshold.

主权项

1. A method of providing automatic frequency control (AFC) tracking for reception of GLONASS signals, the method comprising:
determining whether a channel signal to noise ratio (CNo) exceeds a threshold; when the CNo exceeds the threshold, performing pull-in using a first series of predetection integration (PDI) periods (PDIs) with activated decision-directed flips (DDFs) until a N ms boundary of a GLONASS data bit is found, wherein N is a positive integer, and wherein the activated DDFs selectively adjust polarities of cross-dot pairs generated based on the PDIs; and using a receiver, performing updates to an AFC loop, wherein performing includes:
using a N ms update interval and PDI=(N/2)ms for every other update; andusing a setting for an update between N ms updates, the setting using PDI=(N/4)ms.