WAAS Ground Segment

WAAS
Title	WAAS Ground Segment
Author(s)	GMV.
Level	Basic
Year of Publication	2011

The Wide Area Augmentation System (WAAS) is an GPS Augmentation system developed by the Federal Aviation Administration (FAA), with the goal of improving its accuracy, integrity, and availability. Essentially, WAAS is intended to enable aircraft to rely on GPS for all phases of flight, including precision approaches to any airport within its coverage area.

WAAS uses a network of ground-based reference stations, in North America and Hawaii, to measure small variations in the GPS satellites' signals in the western hemisphere. Measurements from the reference stations are routed to master stations, which queue the received Deviation Correction (DC) and send the correction messages to geostationary WAAS satellites in a timely manner (every 5 seconds or better). Those satellites broadcast the correction messages back to Earth, where WAAS-enabled GPS receivers use the corrections while computing their positions to improve accuracy.

WAAS Ground Segment

WAAS System

The WAAS Ground Segment is composed of multiple Wide-area Reference Stations (WRS). These precisely surveyed ground stations monitor and collect information on the GPS signals, then send their data to three Wide-area Master Stations (WMS) using a terrestrial communications network. The reference stations also monitor signals from WAAS geostationary satellites, providing integrity information regarding them as well. As of October 2008 there were 38 WRSes: twenty in the contiguous United States (CONUS), seven in Alaska, one in Hawaii, one in Puerto Rico, five in Mexico, and four in Canada.

Using the data from the WRS sites, the WMSes generate two different sets of corrections: fast and slow. The fast corrections are for errors which are changing rapidly and primarily concern the GPS satellites' instantaneous positions and clock errors. These corrections are considered user position-independent, which means they can be applied instantly by any receiver inside the WAAS broadcast footprint. The slow corrections include long-term ephemeric and clock error estimates, as well as ionospheric delay information. WAAS supplies delay corrections for a number of points (organized in a grid pattern) across the WAAS service area.

Once these correction messages are generated, the WMSes send them to two pairs of Ground Uplink Stations (GUS), which then transmit to satellites in the Space segment for rebroadcast to the User segment.

List of reference stations

Each FAA Air Route Traffic Control Center in the 50 states has a WAAS reference station, except for Indianapolis. There are also stations positioned in Canada, Mexico and Puerto Rico. Listed below are the coordinates of the site centroids in North America:

City	ICAO airport code	Location	Elevation
Bethel, Alaska	PABE	60.787898226ºN 161.841705626ºW	52.202 m
Billings, Montana	KBIL	45.803726761ºN 108.539727967ºW	1112.261 m
Barrow, Alaska	PABR	71.282786134ºN 156.789914977ºW	15.581 m
Cold Bay, Alaska	PACD	55.200376531ºN 162.718528459ºW	53.652 m
Fairbanks, Alaska	PAFA	64.809686817ºN 147.847403468ºW	149.888 m
Honolulu, Hawaii	PHNL	21.312783159ºN 157.920876933ºW	24.922 m
Juneau, Alaska	PAJN	58.362530123ºN 134.585495176ºW	16.024 m
Mérida, Yucatán (Mexico)	MMMD	20.931919004ºN 89.662872977ºW	29.157 m
Mexico City (Mexico)	MMMX	19.431653193ºN 99.068389463ºW	2236.638 m
Puerto Vallarta, Jalisco (Mexico)	MMPR	20.679034758ºN 105.249200735ºW	11.077 m
San José del Cabo, Baja California (Mexico)	MMSD	23.160416093ºN 109.717667886ºW	104.286 m
Tapachula, Chiapas (Mexico)	MMTP	14.791340027ºN 92.367991216ºW	54.922 m
Kotzebue, Alaska	PAOT	66.887352636ºN 162.611355542ºW	10.911 m
Iqaluit, Nunavut (Canada)	CYFB	63.731446844ºN 68.543393603ºW	9.998 m
Gander, Newfoundland and Labrador (Canada)	CYQX	48.966447828ºN 54.597532074ºW	146.891 m
Winnipeg, Manitoba (Canada)	CYWG	49.900606898ºN 97.259280113ºW	222.046 m
Goose Bay, Newfoundland and Labrador(Canada)	CYYR	53.308720955ºN 60.419401330ºW	37.842 m
Albuquerque, New Mexico	KZAB	35.173560874ºN 106.567308273ºW	1620.154 m
Anchorage, Alaska	PAZA	61.229174557ºN 149.780364869ºW	80.654 m
Aurora, Illinois	KZAU	41.782616622ºN 88.331308050ºW	195.922 m
Nashua, New Hampshire	KZBW	42.735705193ºN 71.480378445ºW	39.141 m
Leesburg, Virginia	KZDC	39.101556058ºN 77.542750106ºW	80.085 m
Longmont, Colorado	KZDV	40.187286655ºN 105.127181633ºW	1541.389 m
Fort Worth, Texas	KZFW	32.830614792ºN 97.066488376ºW	155.604 m
Houston, Texas	KZHU	29.961833882ºN 95.331462501ºW	10.947 m
Hilliard, Florida	KZJX	30.698824796ºN 81.908178358ºW	2.141 m
Olathe, Kansas	KZKC	38.880140378ºN 94.790729104ºW	305.814 m
Palmdale, California	KZLA	34.603503189ºN 118.083872233ºW	763.546 m
Salt Lake City, Utah	KZLC	40.786007936ºN 111.952158417ºW	1287.420 m
Miami, Florida	KZMA	25.824644475ºN 80.319246501ºW	-7.882 m
Memphis, Tennessee	KZME	35.067423639ºN 89.955391700ºW	68.788 m
Farmington, Minnesota	KZMP	44.637444415ºN 93.152039309ºW	262.667 m
Ronkonkoma, New York	KZNY	40.784293219ºN 73.097181151ºW	6.108 m
Fremont, California	KZOA	37.543019928ºN 122.015922570ºW	-3.459 m
Oberlin, Ohio	KZOB	41.297135898ºN 82.206391657ºW	224.115 m
Auburn, Washington	KZSE	47.286919203ºN 122.188372739ºW	82.128 m
San Juan, Puerto Rico	TJZS	18.431249167ºN 65.993480433ºW	-28.547 m
Hampton, Georgia	KZTL	33.379671593ºN 84.296678124ºW	261.142 m