What Is The System Definition Document (Part-2)

System Overview

System Overview

• System Description

The Wide Area Augmentation System (WAAS) is a GPS-based navigation and landing system that provides precision guidance to aircrafts at thousands of airports and airstrips, where there is currently no precision landing capability. WRS’s and integrity monitors are widely dispersed data collection sites that contain GPS/WAAS ranging receivers that monitor all signals from the GPS, as well as the WAAS geostationary satellites.  The reference stations collect measurements from the GPS and WAAS satellites so that differential corrections, ionospheric delay information, GPS/WAAS accuracy, WAAS network time, GPS time, and UTC can be determined. The WRS and integrity monitor data are forwarded to the central data processing sites.  These sites process the data in order to determine differential corrections, ionospheric delay information, and GPS/WAAS accuracy, as well as verify residual error bounds for each monitored satellite. The WAAS-NIES provides a simulation of the accuracy of the WAAS system that monitors GPS constellation of satellites.  The WAAS-NIES subsystem hardware is scalable to meet requirements for simulating the WAAS system.  The software of the WAAS-NIES subsystem is portable to other platforms (such as a PC) to allow re-use in smaller-scale simulations for single-task use. 

• System Goals and Objectives

The goals and objectives of the WAAS-NIES are:

•    To provide an accurate simulation of the operation of calculating the delta error in a WAAS system
•    To aid in the precision guidance of shuttle spacecraft to have a precise landing.
•    To provide enough capacity for simulation of twenty five separate WRS stations.
•    To allow users to control the delta error calculations through input from the Environment Simulator
•    To provide the framework for future use to simulate a WAAS system to determine accurate calculations for landing for shuttle spacecrafts
 

• Driving Factors

Driving factors for the selection of the system architecture include the following:

• The visual model complexity combined with the number of WRS stations available at one time drives the need for the simulator to operate at 70% of the processor, memory, and input/output capability.

• The future use of the system for modeling GPS-based navigation and landing system that provides precision guidance for shuttle space crafts is a higher need to the return  to flight missions and for the government agency continue exploration.

• Custom reporting of various input files will provide a more realistic visual model of complex signals in space

o    Allows more detail to more easily confirm landing situations.
o    Drives the architecture requirements to programmable graphics processing units 

• Graphics processor capabilities are improving at a remarkably high rate.  New technology has made it possible to perform high bandwidth graphics processing with personal computer (PC) and network architectures that just a year ago could only be performed on high-end dedicated commercial off the shelf (COTS) graphics systems with proprietary architectures.  Conversely, the high rate of change in the industry will drive the industry to abandon current architectures that could be marginally acceptable for the application, but unsupportable in the near future (within 3-5 years).  Higher-end COTS graphics proprietary solutions are also changing, but would likely be supported in the future at significantly high costs.