GPS/WAAS Enhancement With Novel Estimators Involving Parallel Kalman Filters

Rajendra Kumar and Prem Munjal

Abstract:	This paper proposes a novel estimation approach involving a parallel bank of Kalman filters for accurate and real-time compensation of ionospheric propagation delay down to centimeter level in dual frequency GPS receivers. Increased accuracies in estimating ionospheric delay can result in more than an order of magnitude improvement in dual frequency receivers currently in use in various military applications where ionospheric delays are estimated with accuracies of between 0.5 m to 2 m. For civilian applications, the technique is applicable to WAAS stations, and possibly codeless receivers. It can also be applied to future Block IIF receivers in the event that the dual frequency option for civilian use is exercised. The high precision obtained by the proposed algorithm in ionospheric delay estimation makes it possible to satisfy by a significant margin the FAA requirements for vertical navigation error limits in the precision approach and landing phase. Such margin will increase safety and availability of WAAS Category I precision approach and landing phase services to a larger coverage area. Moreover, proper operation of WAAS requires that divergence between code and carrier phase in the signal broadcast from WAAS GE0 satellites be strictly controlled so that the signal closely mimics GPS signals wherein code and carrier are coherently generated onboard the GPS satellite. However, in the WAAS network, signals are generated at the GE0 Earth station and code-carrier divergence can arise on the GE0 uplink or in the GE0 bent pipe transponder. By making very accurate estimates of uplink ionospheric delay, the proposed algorithm can adequately maintain required coherence by tracking C-band and L, frequencies.
Published in:	Proceedings of the 1996 National Technical Meeting of The Institute of Navigation January 22 - 24, 1996 Loews Santa Monica Hotel Santa Monica, CA
Pages:	917 - 931
Cite this article:	Kumar, Rajendra, Munjal, Prem, "GPS/WAAS Enhancement With Novel Estimators Involving Parallel Kalman Filters," Proceedings of the 1996 National Technical Meeting of The Institute of Navigation, Santa Monica, CA, January 1996, pp. 917-931.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In