Title: WAAS MESSAGING SYSTEM: DATA RATE, CAPACITY, AND FORWARD ERROR CORRECTION
Author(s): Per Enge
Published in: NAVIGATION, Journal of the Institute of Navigation, Volume 44, Number 1
Pages: 63 - 76
Cite this article: Enge, Per, "WAAS MESSAGING SYSTEM: DATA RATE, CAPACITY, AND FORWARD ERROR CORRECTION", NAVIGATION, Journal of The Institute of Navigation, Vol. 44, No. 1, Spring 1997, pp. 63-76.
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Abstract: This paper focuses on the design of the Wide-Area Augmentation System (WAAS) messaging system. Specifically, it explains why the data rate is 250 bit& and the messages are 250 bits long. It also explains why forward error correction is used. The paper estimates the signal-to-noise ratio required for reliable WAAS operation, and discusses message availability when the WAAS satellite is at low elevation angles. This paper does not give a bit-by-bit description of the WAAS data format, nor does it detail the spread- spectrum codes used by WAAS. For these topics, the reader is referred to the current version of the Minimum Operational Performance Standards (MOPS) for WAAS avionics. This paper is based on the work of RTCA Special Committee-159, which is charged with studying the integrity of GPS and writing performance standards for the airborne equipment. In particular, this paper owes much to the efforts of Working Group 2, which is developing the WAAS MOPS.