Effect of Kinematics and Interference on Assisted GPS (AGPS)

The E-911 mandate from the Federal Communications Commission (FCC) requires a mobile 911 caller location to be established for 67 percent of calls to within 50 meters, and 95 percent of calls to within 150 meters for wireless handset-based solutions. To meet the E-911 requirement, a GPS receiver can be incorporated into mobile phones which use frequency modulated (FM) signals for communications. The incorporation of GPS into a cellular handset means that a potential jammer will be operating nearby at the cellular frequency. A second concern is that mobile phone users will be using their phones while they are driving, during which user dynamics increase the Doppler search range in the acquisition process. They also limit the duration of the pre-detection integration time since the Doppler varies quickly for high user dynamics. The focus of this paper is to investigate Assisted GPS (AGPS) receiver performance from two perspectives. The first is to evaluate the acquisition capabilities of an AGPS receiver in vehicular dynamic conditions. The second is to investigate the effect of various Radio Frequency Interference (RFI) effects on AGPS acquisition and tracking performance. A SiRFLoc evaluation kit is used to investigate AGPS receiver performance. Tests are conducted using a hardware simulator and results are analyzed in terms of Time-To-First-Fix (TTFF) and position accuracy. In dynamic mode, it was found that with increasing velocity, a decrease in position accuracy was seen for both AGPS and HS receivers. Three types of in-band interference were analyzed: Continuous Wave (CW), Amplitude Modulated (AM) and FM. It was found that an AGPS receiver was able to tolerate 5 to 10 dB more interference power than a High Sensitivity (HS) receiver and 10 to 15 dB more than a conventional receiver in acquisition mode. Both AGPS and HS had similar performance while tracking. In all RFI cases, all the receivers were able to tolerate more interference while tracking than in acquisition.