Flat model software compensated crystal oscillator for GPS receiver

A method of compensating the initial search by a digital signal processor for carrier frequency lock in software for frequency errors caused by operating temperature instabilities in a crystal oscillator in a GPS receiver, comprising:

• installing a flat software correction model in a particular GPS receiver such that a single static frequency-offset value is included for an entire operating temperature spectrum, and a confidence value, sigma, is attached to various sub-ranges of said operating temperature spectrum to indicate a variance in said offset value;
• initializing said flat software correction model once during the manufacture of a particular GPS receiver with frequency-versus-temperature data provided by a manufacturer of a local crystal reference oscillator (TCXO);
• thereafter during operation, reading a current operating temperature with a temperature sensor (TSO) and using it as an index to select a corresponding static frequency-offset (A0) and sigma values from said flat software correction model that represent how much offset to use and how wide a frequency search should be made by navigation software given the frequency uncertainties expected at a particular TCXO operating temperature;
• using said static frequency-offset (A0) and sigma values to initialize said navigation software in a cold start radio spectrum search to find GPS satellite transmissions and obtain a first position fix;
• and
• updating selected entries in said software correction model in run time with information derived from precise time and frequency information that becomes available from said particular GPS receiver after it produces user position fixes and locks onto GPS system time and can accurately gauge any frequency errors of said TCXO at certain operating temperatures then read by said TSO;
• wherein, the actual frequency of operation of said TCXO is not corrected, and only where-to-search for GPS satellite transmissions in a down-converted radio spectrum is affected;
• and
• wherein, each said updating improves future time-to-first-fix (TTFF) delays from a cold start of the GPS receiver.