Stand-Alone High-Sensitivity GPS Receiver

The GPS technology has been widely used in various application fields. In recent personal navigation systems such as US E911, a GPS receiver is incorporated in a cellular phone. The conventional stand-alone GPS receivers with an RF sensitivity of approximately -140dBm are insufficient for indoor use because the GPS signal is substantially attenuated inside a building or the like. So it is expected to improve the sensitivity of GPS receivers. To achieve a high sensitivity, various technologies including the well-known Assisted GPS (AGPS) have been proposed so far. The conventional AGPS has achieved approximately -150dBm of receiver sensitivity, by transferring the assistance information from a cellular network server to the GPS receiver. Therefore, the AGPS is surely available for indoor applications, but its sensitivity is not yet enough everywhere indoors. And the AGPS method requires a dedicated infrastructure and its positioning service is not available outside of its service area. We have developed a prototype stand-alone high-sensitivity GPS receiver that requires no assistance information. The developed receiver effectively uses the self-retrieved information such as the clock deviation, time, position and orbital data in order to obtain a high sensitivity. Our stand-alone high-sensitivity GPS receiver has achieved a sensitivity of -161dBm, which is improved more than 20dB compared with the conventional stand-alone GPS receivers. Further, it is superior to the conventional high-sensitivity AGPS receivers. We have confirmed that our stand-alone high-sensitivity GPS receiver achieves high positioning performance in various poor receiving environments.