Navigation Services
GPS Policy - Modernization
The Future of Navigation For several years now, the Global Positioning System (GPS) has been recognized as the future of navigation for most military and civil applications, including those for various modes of transportation. The civil aviation community has been one of the main benefactors of GPS due to its flexibility and worldwide applicability. In 1999, as a direct result of these benefits to the civil community, Vice President Al Gore announced that the U.S. would embark on a GPS modernization effort to extend the capabilities of GPS even further than those of the existing GPS constellation. GPS Modernization One of the main components of this modernization is the addition of two new navigation
signals for civil use. These signals will be in addition to the existing civilian
service broadcast at 1575.42 MHz (L1). The first of these new signals will be
a new civil code, called L2C, which will be added on the existing L2 carrier,
located at 1227.60 MHz. It will be available for general use in non-safety
critical applications. The Block IIR-M satellite, the first to add his capability
was launched September 25, 2005. Benefits of L5 L5 will provide significant benefits above and beyond the capabilities of the current GPS constellation, even after the planned second civil frequency (L2) becomes available. Benefits include precision approach navigation worldwide, increased availability of precision navigation operations in certain areas of the world, and improved interference mitigation. Precision Navigation Operations Worldwide GPS offers the capability to provide a safe and efficient seamless satellite-based
global navigation system that will be responsive to the future needs of civil
aviation. The addition of L5 will provide aviation and other transportation applications
with continuous, highly accurate, three-dimensional position information.
Figure 1: Regions within the GEO footprints represent
the area of the world that will gain precision approach capability
with the addition of L5. The GEO footprints shown here represent
those of the U.S. Wide Area Augmentation System (WAAS), the European
Geostationary Navigation Overlay Service (EGNOS), and the Japanese
MTSAT Satellite-Based Augmentation System (MSAS).
Increased Availability of Precision Navigation Operations GPS modernization is compatible with and complements the WAAS. The L5 signal will be available on additional WAAS GEOs launched in September and October 2005. When both L1 and L5 are available, avionics will use a combination of signals to provide the most accurate service possible, thereby increasing availability of the service. These avionics will use ionospheric corrections broadcast by WAAS, or self-generated onboard dual frequency corrections, depending on which one is more accurate.
Figure 2: The shaded areas represent conceptual
SBAS service areas where L5 will improve the availability of precision
approach operations.
Interference Mitigation
Due to the low power of GPS signals, interference has been identified
as a challenge related to the use of GPS. Despite this, the technical
feasibility of using augmented GPS as the only means of navigation
in the aircraft as well as the only navigation service provided by
the Federal Aviation Administration (FAA) was confirmed as technically
feasible in an independent study conducted by Johns Hopkins University
Applied Physics Laboratory. However, the study did recommend efforts
to mitigate the effects of intentional interference, unintentional
interference, and atmospheric disturbances on GPS and its augmentation
systems. The mitigation of interference is not only important to
aviation, but to other GPS applications as well. To mitigate the
effects of interference and any impact on civil aviation safety-of-life
operations, the FAA is planning to use the new navigation signal
at L5 (1176.45 MHz) for both WAAS and the Local Area Augmentation
System (LAAS). |


