GPS Based Receiver Autonomous Integrity Monitoring (RAIM) for Onboard Aircrafts over the Indian Subcontinent

Abstract

The introduction of Global Positioning System (GPS) has revolutionized the field of navigation particularly in the
field of navigation. The GPS is a reliable, all weather satellite based radio navigation system that provides
accurate three dimensional (3D) positions, velocity and timing information up to 10-6 seconds accuracy anywhere
on or above the earth’s surface.However, a navigation system is required to deliver alarm when the error is the
computed user position solution exceeds an allowable level. This warning must be issued to the user with in a
given period of time and with a given probability. Global Positioning System (GPS) is the next generation
navigational aid and is currently in use for En-Route and landing phases of all the civilian aircrafts. All modern
satellite navigation systems should provide the integrity service in critical applications such as airplane landings
or safe approach to harbor. Unfortunately, there is a finite probability that a particular GPS satellite may fail
causing the transmission of potentially misleading navigation information. In such case, pilot in the aircraft
requires timely warnings whether to use the navigational information or not. All over the world, several
algorithms are developed for providing the integrity information to the users of their own country/territory only,
because, integrity monitoring is a function of the GPS satellite geometry and is location dependent. To suit the
Indian subcontinent (60N–360N latitude region), a new algorithm called Constant False Alarm Rate (CFAR) based
Receiver Autonomous Integrity Monitoring (RAIM) is proposed and presented in this paper. The proposed
algorithm detects and isolates the faulty satellite in position determination. The algorithm is validated with the
satellite constellation visibility data obtained from the 3 Indian stations viz. IISc Bangalore, NGRI Hyderabad and
Airport Visakhapatnam. In this paper, results of the proposed algorithm are presented data due to the IISc,
Bangalore.
Keywords: Pseudorange, Dilution of Precision, Availability