| US 7,570,208 B2 | ||
| Unassisted indoor GPS receiver | ||
| Chi-Shin Wang, Half Moon Bay, Calif. (US); Zongde Qiu, Shishi (China); Shridhara A. Kudrethaya, Cupertino, Calif. (US); and Jun Mo, San Jose, Calif. (US) | ||
| Assigned to SiRF Technology, Inc., San Jose, Calif. (US) | ||
| Filed on Dec. 29, 2005, as Appl. No. 11/324,144. | ||
| Prior Publication US 2007/0152878 A1, Jul. 05, 2007 | ||
| Int. Cl. G01S 5/14 (2006.01); H04B 1/16 (2006.01) | ||
| U.S. Cl. 342—357.15 [455/343.2] | 48 Claims |
| 1. A method for operating a satellite-based navigational receiver under weak signal conditions, comprising:
switching the receiver between a sleep state with a portion of the satellite-based navigation receiver powered down and a
wake-up state where the receiver has access to first ephemeris data;
predicting first position information for an at least one satellite using polynomial extrapolation based upon at least the
first ephemeris data;
acquiring at least one satellite signal during the wake-up state using at least the predicted first position information,
if the receiver is unable to acquire the at least one satellite signal during the wake up state, switching the receiver to
the sleep state and reattempting to reacquire the at least one satellite signal after a predetermined period using at least
the predicted first position information; and
attempting to collect second ephemeris data from the at least one satellite signal acquired during the wake-up state.
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