Magellan Files for Patent Providing More Reliable GPS Positioning
Magellan’s parent company, Thales, has filed a patent for “Asynchronous assisted GPS position determination”. Basically what all of this boils down to is that they are seeking a patent on a technology that will allow more accurate GPS positioning when the traditional GPS signal becomes unreliable. More specifically:
A method of and computer system for assisting GPS position determination is described. Ephemeris and updated almanac information for a GPS satellite is received over a datalink. Based on the received updated almanac information and GPS parity algorithms, data bits of the GPS signal are reconstructed. Based on the current time, the reconstructed data bits are synchronized with the time of reception of a GPS signal from a satellite currently in view. The reconstructed data bits are subtracted from the received GPS signal at the synchronized time. A coherent integration of the received GPS signal over the time period corresponding to the reconstructed data bits is performed to obtain a GPS pseudo-range measurement. The GPS receiver position is determined using the generated, synchronized pseudo-range measurement and the ephemeris information received over the datalink.
The primary function of this patent is to:
A method of assisting GPS position determination comprising: receiving ephemeris information for a GPS satellite over a datalink; receiving updated almanac information for a GPS satellite over a datalink; based on the received updated almanac information and GPS parity algorithms, reconstructing data bits of the GPS signal; based on the current time, synchronizing the reconstructed data bits with the time of reception of a GPS signal from a satellite currently in view; subtracting the reconstructed data bits from the received GPS signal at the synchronized time; coherently integrating the received GPS signal over the time period corresponding to the reconstructed data bits to obtain a GPS pseudo-range measurement; and determining the GPS receiver position using the generated, synchronized pseudo-range measurement and the ephemeris information received over the datalink.
Which overcomes the following limitations (in part):
 Disadvantageously, in order to determine position, the GPS receiver must spend a significant amount of time to collect sufficient satellite data. At the same time, the GPS receiver decoding the satellite data requires a stronger GPS satellite signal than is required for position determination when satellite and time information are already known. Assisted-GPS (A-GPS) as a concept has gained significant popularity recently in light of stringent time to first fix (TTFF), i.e., first position determination, and sensitivity requirements of United States Federal Communications Commission (FCC) E-911 regulations. The E-911 regulations require wireless devices being used for emergency calls to report, among other things, the telephone number, location of the tower receiving the emergency call, and location information, e.g. latitude and longitude of the calling device to within 50 to 100 meters, of the wireless device. Problematically, wireless devices may be used in locations where there is no unobstructed satellite view, e.g. inside buildings or under tree cover, and consequently providing accurate location information responsive to the E-911 regulations is impossible.
 A typical A-GPS service using a wireless link provides a GPS receiver with an information signal for determining the GPS receiver’s approximate position, time synchronization mark, satellite ephemerides, and satellite Dopplers. Different A-GPS services may omit some of these parameters. The A-GPS service provided information allows a GPS receiver to perform a “hot” fix without requiring time to be spent on searching for the satellite Doppler and collecting ephemeris information.
 Another important use of the assistance signal, i.e. the signal providing the above-described additional information, is to provide the GPS information bits in real-time to a GPS receiver. By receiving the information bits over a wireless link, a GPS receiver can perform longer than 20 millisecond (ms) coherent accumulation of the GPS signal and thereby increase the receiver sensitivity and allow performance of “in-door”, i.e. obstructed, position determination satisfying the E-911 regulations.