The performance of a Doppler-aided GPS receiver is analyzed. It is shown that Doppler aiding increases the receiver's robustness to interference and jamming. This is achieved by narrowing the noise bandwidth of the carrier-tracking loop using an external estimate of the Doppler shift of the GPS signal. The Doppler estimate is computed using an inertial navigation system and is incorporated into the carrier-tracking loop in a feed-forward fashion. The minimum achievable loop bandwidth is a function of phase noise on the receiver oscillator, satellite clock phase noise, and the quality of the external Doppler estimate. Using the criterion for loss of lock of 15 deg phase jitter, it is shown analytically that for an unaided receiver, loss of lock occurs at a signal power equal to approximately 26 dB-Hz. With Doppler aiding and a nominal-quality receiver clock, an additional 4 dB-Hz margin can be achieved, allowing signals with power as low as 22 dB-Hz to be tracked.
|Original language||English (US)|
|Number of pages||12|
|Journal||Navigation, Journal of the Institute of Navigation|
|State||Published - Jan 1 2005|