Gaussian and Mixed Gaussian Methods of LAAS Overbounding

Christopher Varner

Abstract:	A LAAS ground facility (LGF) broadcasts GPS pseudorange corrections (PRC) to aircraft approaching a LAAS supported airport. The LGF must also transmit an estimate of the PRC uncertainty ( gnd pr _ ó ). System integrity requires the aircraft to assume that the uncertainty is associated with a Gaussian error process. Since the observed error process can be non-Gaussian, the observed PRC uncertainty must be inflated (overbounded) before it is broadcast to the aircraft. This paper describes two methods of overbounding called Gaussian and Mixed Gaussian Overbounding. gnd pr _ ó is different for different GPS satellites and changes as a discrete function of satellite elevation and azimuth. The Gaussian overbounding method directly computes the overbound for each individual value of gnd pr _ ó but requires an enormous amount of data when gnd pr _ ó changes frequently. When this is the case, the Mixed Gaussian overbounding method provides an estimate of the inflation factor with less data. The Mixed Gaussian method may provide overbounding results in a reasonable period of time, but the inflation factor does not necessarily provide an absolute overbound for errors associated with the individual values of gnd pr _ ó .
Published in:	Proceedings of the 2002 National Technical Meeting of The Institute of Navigation January 28 - 30, 2002 The Catamaran Resort Hotel San Diego, CA
Pages:	531 - 538
Cite this article:	Varner, Christopher, "Gaussian and Mixed Gaussian Methods of LAAS Overbounding," Proceedings of the 2002 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2002, pp. 531-538.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In