Enabling CAT I capabilities on dual-frequency WAAS

This paper investigates the potential vertical guidance performance of WAAS when the modernized GPS and Galileo are available. According to the protection level calculation defined in the WAAS MOPS (DO-229C), there are four major parameters: the fast and long term correction degradation confidence (sigma_flt), user ionosphere range error confidence (sigma_UIRE), airborne receiver code noise and multipath (CNMP) confidence (sigma_air), and troposphere delay confidence (sigma_tropo). Currently, the user ionosphere range error confidence (sigma_UIRE) is the dominant factor in the availability of single frequency GPS/WAAS. Fortunately, after the modernization of GPS and WAAS, there will be two frequencies available so that a user can calculate ionospheric delay directly in the airplane. This direct use of multiple frequencies is more accurate and offer higher availability. The previous research has shown many advantages of GPS modernization. The new civil signals on L2 and L5 significantly enhance the availability of the augmented GPS system for aviation. The nominal performance with all 3 signals increases to 100% availability for the LPV (Vertical Alert Limit (VAL) = 50 m) approaches in CONUS. Furthermore, with one signal interfered with, the availability is 99.9% for 100% of CONUS. This paper assesses the following two questions. First, can WAAS achieve 20 m VAL (APV II) over CONUS with improved signal models? Second, can WAAS be a CAT I (12 m VAL) system or possibly achieve 10 m VAL over CONUS with the additional new civil frequencies and satellites from Galileo? This paper first investigates the airborne code noise multipath (CNMP) factor (sigma_air). CNMP will be the dominant factor in the availability of a dual-frequency GPS/WAAS user. This paper uses the MATLAB Algorithm Availability Simulation Tool (MAAST) to determine the required values for the airborne CNMP so that a dual-frequency GPS/WAAS user can meet 20 m VAL (APV II) and 12 m VAL (CAT I) over CONUS. A modified MAAST that includes the Galileo satellite constellation is created. This modified MAAST is used to simulate several possible user configurations. The simulation results is used to determine under what user configurations WAAS could be an APV II (VAL = 20 m) system or a CAT I (VAL = 12 m) system over CONUS. Furthermore, this paper examines combinations of the possible improvements in signal models and the addition of Galileo to determine if WAAS could achieve 10 m VAL (better than CAT I) within the service volume.