Fine frequency estimation for GPS receivers
A GPS receiver designed for indoor operation must have an operation mode with equivalent noise bandwidth on the order of 10 Hz in the acquisition stage. This requires current systems to perform large numbers of code/frequency search combinations which is extremely time-consuming. Due to these large searches, the tracking stage often must include a preliminary fine frequency process for refining the carrier frequency determination before tracking initiates. An alternative is to provide for a more precise signal acquisition, however, correlation becomes corrupted if the signal fragment is larger than 20 ms. Correlation is required due to the Doppler shifting and clock inaccuracies. The precision of the carrier frequency must be within 50 Hz. We have validated that four solutions are obtainable from the patent equations which greatly reduce the uncertainty of fine frequency offset. Additionally, precision can be observed by limiting the amount of noise associated with the carrier frequency. This allows for reduction in the computational burdens of the receiver and removing the acquisition stage from the ranging receiver.