Introduction - Understanding GPS: Principles and Applications - page 17

A discussion of RTCM message formats for both code- and carrier-based

applications is presented.
Chapter 8 also contains an in depth treatment of SBAS. The discussion first
starts by reviewing the SBAS requirements as put forth by the International Civil
Aviation Organization (ICAO). Next, SBAS architecture and functionality are
described. This is followed by descriptions of the SBAS signal structure and user
receiver algorithms. Present and proposed SBAS geostationary satellite locations
and coverage areas are covered.
GBAS, in particular, the U.S. FAA's Local Area Augmentation System (LAAS),
requirements and system details are then presented. The chapter closes with treat-
ment and discussion of the data and products obtained from the U.S. National Geo-
detic Survey's Continuously Operating Reference Station (CORS) network and the
International GPS Service.
In some applications, GPS is not robust enough to provide continuous user
PVT. Receiver operation will most likely be degraded in an urban canyon where sat-
ellite signals are blocked by tall buildings or when intentional or nonintentional
interference is encountered. Hence, other sensors are required to augment the user's
receiver. This subject area is discussed in Chapter 9. The integration of GPS and
inertial sensor technology is first treated. This is usually accomplished with a
Kalman filter. A description of Kalman filtering is presented, followed by various
descriptions of GPS/inertial navigation system (INS) integrated architectures includ-
ing ultratight (i.e., deep integration). An elementary example is provided to illus-
trate the processing of GPS and INS measurements in a tightly coupled
configuration. Inertial aiding of carrier and code tracking loops is then described in
detail. Integration of adaptive antennas is covered next. Nulling, beam steering, and
space-time adaptive processing (STAP) techniques are discussed.
Next, Section 9.2 covers ITS automotive applications. This section examines
integrated positioning systems found in vehicle systems, automotive electronics,
and mobile consumer electronics. Various integrated architectures for land vehicles
are presented. A detailed review of low-cost sensors and methods used to augment
GPS solutions are presented and example systems are discussed. Map matching is a
key component of a vehicle navigation system. A thorough explanation is given
regarding the confidence measures, including road shape correlation used in
map-matching techniques that aid in determining a vehicle's true position. A thor-
ough treatment of sensor integration principles is provided. Tradeoffs between posi-
tion domain and measurement domain integration are addressed. The key aspects
of Kalman filter designs for three integrated systems—an INS with GPS, three gyros,
and two accelerometers; a system with GPS, a single gyro, and an odometer; and a
system with GPS and differential odometers using an antilock brake system
(ABS)—are detailed.
Chapter 9 concludes with an extensive elaboration of assisted-GPS network
assistance methods (i.e., enhancing GPS performance using cellular network assis-
tance). In applications in which the GPS receiver is part of an emergency response
system, waiting 30 seconds for data demodulation can seem like an eternity. As
such, methods to eliminate the need to demodulate the satellite navigation data mes-
sage directly and to decrease the acquisition time of the signals in weak signal envi-
ronments has been the basis for all assisted GPS work. The FCC requirements for