Patent ID: 7224950

Claim:
A method for estimating reference frequency drift in an uninitialized navigation receiver from a local oscillator in a cellular telephone handset operating in standby mode, the method comprising the steps of: associating a cellular telephone handset subject to standby mode operation in which a base station provides 20-msec bursts of frequency reference information about every 700-msec, with a navigation receiver requiring initialization; during said standby mode operation, sampling said 20-msec bursts of frequency reference information from a base-station; running a numeric controlled oscillator (NCO) at a nominal frequency; periodically adjusting said NCO with samples obtained in the step of sampling such that said base station provides a basis for accurate frequency measurement through a series of updates that coincide with said 20-msec bursts of frequency reference information; correlating both in-phase and quadrature-phase outputs of said NCO; computing a navigation receiver reference frequency drift estimate from information derived in the step of correlating; and using said drift estimate to improve initialization performance in said navigation receiver by reducing local oscillator frequency uncertainty.