"Operational enhancements of the next-generation Global Positioning System promise major breakthrough improvements
for public, private and scientific use - - however, extreme care shall be employed
on application and implementation of in-vehicle, vehicle-to-vehicle, infrastructure-to-vehicle, and vehicle-to-infrastructure applications
to ensure adequate back-up system (such as to employ a non-GPS dependent electronic
high precision compass module). Due to multiple vehicles in high speed mobile
network environment (such as, for example, a five lane highway with heavy vehicle traffic moving
fast simultaneously in a given magnetic orientation), and due to intravehicle critical time safety emergency warning requirements,
(intra-beacon precision target footprint microwave radio communications) Intelligent Vehicle Technologies, LLC, does not recommend
nor endorse primary navigational dependency on GPS. An intelligent system shall
employ a high precision compass memory module (or IVT Beacon system coded
orientation) for primary direction cognizance - - by default, a primary GPS direction cognizance system may be
followed (or backed-up) by a compass module, inherently making the system operationally fail-safe
should the loss of GPS service occur."
The following are excerpts from the 2005 Federal Radionavigation Plan (see full report @ USCG link below)
As the full civil potential of GPS and its augmentations is realized, the services provided
by other Federally provided radionavigation systems may be phased down to match the
reduction in demand, provided those services are not a part of a back-up navigation
strategy for critical applications or safety-of-life services.
The Federal Government operates radionavigation systems as one of the necessary elements to enable safe transportation and encourage commerce within the United States.
A goal of the Government is to provide radionavigation services to the public in the most
cost-effective manner possible.
As the full civil potential of GPS services and its augmentations are implemented, the
demand for services provided by other Federally provided radionavigation systems is
expected to decrease. The Government will reduce non-GPS-based radionavigation services with the reduction in the demand for those services. However, it is the policy of
the U.S. Government not to rely on a single system for positioning, navigation, and
timing.
The United States Government will maintain back-up capabilities to meet (1) growing
national, homeland, and economic security requirements, (2) civil requirements, and (3)
commercial and scientific demands. Operational, safety, and security considerations will
dictate the need for complementary navigation systems to support navigation or conduct
certain operations. While some operations may be conducted safely using a single
radionavigation system, it is Federal policy to provide redundant radionavigation service
where required. Backups to GPS for safety-of-life navigation applications, or other
critical applications, can be other radionavigation systems, or operational procedures, or
a combination of these systems and procedures to form a safe and effective backup.
Backups to GPS for timing applications can be a highly accurate crystal oscillator or
atomic clock and a communications link to a timing source that is traceable to UTC.
When the benefits, including the safety benefits, derived by the users of a service or
capability are outweighed by its cost, the Federal Government should no longer continue
to provide that service or capability.
A suitable transition period will be established prior to decommissioning of Federal radionavigation services, based on factors such as user
equipment availability, radio spectrum transition issues, cost, user acceptance, budgetary
considerations, and the public interest. International commitments will affect certain
types and levels of navigation services provided by the Federal Government to ensure
interoperability with international users.
Radionavigation systems established primarily for safety of transportation and national
defense also provide significant benefits to other civil, commercial, and scientific users.
In recognition of this, the Federal Government will consider the needs of these users
before making any changes to the operation of radionavigation systems.
The U.S. national policy is that all radionavigation systems operated by the U.S.
Government will remain available for peaceful use subject to direction by the President in
the event of a war or threat to national security.
Operating agencies may cease operations or change characteristics and signal formats of radionavigation systems during a dire
national emergency. All communications links, including those used to transmit differential GPS corrections and other GPS
augmentations, are also subject to the direction of the President.
GPS is a multi-use, space-based radionavigation system owned by the U.S. Government,
and operated by the DoD, to meet National and homeland security, civil, commercial, and
scientific needs. The U.S. Space-based PNT Policy established a new National Spacebased
PNT Executive Committee (National PNT EXCOM) co-chaired by the Deputy Secretaries of the Department of Defense and Transportation.
The DoD will maintain a nominal 24-satellite constellation. Replacement satellites will
be launched on an anticipated need to maintain the constellation as satellites age and
ultimately fail. The DoD will provide a 48-hour advance notice of changes in the constellation
operational status that affect the service being provided to GPS SPS users in peacetime,
other than planned GPS interference testing. DoD will also provide 48-hour notice of any
planned periods for which GPS will not be capable of providing SPS as specified in the
GPS Standard Positioning Service Performance Standard (Ref. 8).
Coordination of planned interference testing activities nominally begins 60 days before
testing events. Users are notified by the USCG as soon as an activity is approved, and by
the FAA typically not earlier than 72 hours before an activity begins. The DoD notice
will be given to the USCG Navigation Information Service (NIS) and the FAA Notice to
Airmen (NOTAM) system. The NIS and NOTAM systems will announce unplanned system outages resulting from system malfunctions or unscheduled maintenance.
The GPS Modernization effort focuses on improving position and timing accuracy, availability, integrity monitoring support capability and enhancement to the operational
control segment. As these system enhancements are introduced, users will be able to
continue to use existing IS-GPS-200 (Ref. 9) compliant receivers, as signal backward
compatibility is a requirement for both the military and civil user communities. Although
current GPS users will be able to operate at the same, or better, levels of performance that
they enjoy today, users will need to modify existing user equipment or procure new user
equipment in order to take full advantage of any new signal structure enhancements.
GPS modernization is a multi-phase effort to be executed over the next 15 or more years.
Additional signals are planned to enhance the ability of GPS to support civil users and
provide a new military code. The first new signal will be the new civil code on the L2
frequency (L2C - 1227.60 MHz). This signal, designated L2C, will enable dualfrequency
code-based civil receivers to correct for ionospheric error. A third civil signal
will be added on the L5 frequency (1176.45 MHz) for safety-of-life applications and
other applications as appropriate. L5 can serve as a complementary signal to the GPS L1
frequency (1575.42 MHz) with a goal of assurance of continuity of service potentially to
provide precision approach capability for aviation users. In addition, a secure and
spectrally separated Military Code (M-Code) will be broadcast on the L1 and L2 frequencies. The first launch of an L2C capable satellite is scheduled for 2005, and the
first launch of a L5 capable satellite is scheduled for 2007. Twenty-four L2C capable
GPS satellites are projected to be on orbit by approximately 2013, and 24 GPS L5
capable satellites are projected to be on orbit by approximately 2015. Prior to declaration
of Full Operational Capability (FOC), not all performance parameters of the new civil
signals will be met, and therefore the new signals will be available to users at their own
risk.
GPS SPS does not meet all the different user performance requirements for civil navigation, positioning, and timing applications.
Various differential techniques are used to augment the GPS to meet specific user
performance requirements. However, it is important to note that civil differential systems
and users of civil differential systems are dependent upon being able to receive the GPS
civil signal in order to compute a position using differential techniques.
GPS and its augmentations offer navigation services that far exceed what was envisioned
only a few short years ago. With the tremendous success of GPS and its current augmentations, new applications requiring even more precise accuracy, integrity, and
availability are being discovered. FHWA, USCG, NOAA, and other Federal agencies, as
well as State and local governments, agencies, academia, and industry are working
together to develop more precise and robust augmentations for GPS, creating terrestrial
navigation systems that will significantly improve the safety and economic well being of
the nation. The goal is to achieve 10 cm real time navigation, a three to five second
integrity function, and an availability of greater than 99 percent. For non-safety-of-life
applications, the accuracy goals may be as stringent as 1 cm or better in real time.
Public References available @
http://www.navcen.uscg.gov/pubs/frp2005/
* * * * *
