The Federal Radionavigation Plan

I’ve intended to write about the 2008 Federal Radionavigation Plan (FRP) for quite some time. It is an important document because it is the official policy document that drives the United States’ radio navigation (including GPS) program planning. According to the FRP, it includes the introductions, policies, radionavigation system user requirements, system descriptions, and operating plans of various radionavigation systems. The FRP is updated biennially. The 2008 FRP was approved in January 2009.

The FRP preface states that it is prepared jointly by the Department of Defense, Department of Homeland Security, and Department of Transportation with assistance from other government agencies. The document covers radionavigation systems used by both the civilian and military communities. It does not cover radionavigation systems used exclusively by the U.S. military.

The FRP is a fascinating document because it encompasses GPS, GPS augmentation systems, and “back-up” systems. In this column, I’m going to extract several statements from the FRP and comment on them. If you’d like to read the FRP in full (184 pages), you can do so here. Briefly, the FRP includes the following navigation technologies: GPS, WAAS, DGPS, LORAN, and VOR/DME/TACAN/ILS/MLS/NDB (all aviation-oriented).

By way of background and according to the FRP, the first version of the FRP was released in 1980 as part of a Presidential Report to Congress.

For the remainder of this column, I’ll provide quotes from the FRP that I think are relevant and add some commentary.

From the executive summary:

“A major goal of DoD and DOT is to ensure that a mix of common-use (civil and military) systems is available to meet user requirements for accuracy, reliability, availability, continuity, integrity, coverage, operational utility, and cost; to provide adequate capability for future growth; and to eliminate unnecessary duplication of services. Selecting a future radionavigation systems mix is a complex task, since user requirements vary widely and change with time. While all users require services that are safe, readily available and easy to use, unique requirements exist for military as well as civil users. For example, the military has more stringent requirements including performance under intentional interference, operations in high-performance vehicles, worldwide coverage, and operational capability in severe environmental conditions. Similarly, civil users desire higher accuracy and integrity for future highway, rail, and other safety-of-life applications. Cost is always a major consideration that must be balanced with a needed operational capability.”

EG Comment: As I did, you may think the “civil user desires” described in the executive summary are a small subset of actual consumer users, and that’s true. But, it’s important to remember that this document is focused on U.S. government users rather than commercial users.

However, it does raise a point about the consideration given to civilian users when program decisions are being made regarding GPS such as features, satellite launch schedules, ground infrastructure, and constellation management. I’m sure when a congressperson, who is making decisions regarding budgets, is researching the subject he or she will read this executive summary. The statement “civil users desire higher accuracy…” will mislead the reader. While there is a demand for high accuracy in the commercial civil user community, there is a much larger demand for products in the low and medium accuracy commercial markets.

While I’m not criticizing the executive summary for being incorrect, it seems to me that the people who control the purse strings (Congress) may not be given enough information to grasp the “big picture” regarding the GPS user community.

“Interoperability considerations —

“National and international radionavigation systems are sometimes used in combination with each other or with other systems. These combined systems are often implemented to provide improved or complementary performance. In the case of GPS, the USG encourages future interoperability with foreign space-based PNT systems for civil, commercial, and scientific uses worldwide. Examples of existing or future foreign space-based PNT systems are Russia’s Global Navigation Satellite System (GLONASS), the European Union’s Galileo, Japan’s Quasi Zenith Satellite System (QZSS), China’s Compass, and India’s Regional Navigation Satellite System (RNSS). Properly designed receivers that take advantage of these systems may benefit from additional satellite signals, increased redundancy, and improved performance over that obtained from just one system alone. A critical aspect of system interoperability is ensuring compatibility among radionavigation services. For example, the USG has concerns about radionavigation signal structures that could adversely impact the military and civil use of GPS. The USG has also fostered the use of interoperable augmentations through its adherence to international standards for DGPS and space-based augmentation system services.These include Maritime DGPS and the Wide Area Augmentation System.”

EG Comment: I have to say that the U.S. government has done a good job in the area of interoperability. In the 2001 Federal Radionavigation Plan, interoperability wasn’t discussed nearly to the degree it is in the 2008 FRP.

From the 2001 FRP: “Radionavigation systems are sometimes used in combination with each other or with other systems. These combined systems are often implemented so that a major attribute of one system will offset a weakness of another.…a few manufacturers have of navigation and positioning equipment have developed combined GPS/GLONASS receivers to take advantage of these benefits. Some receivers are on the market with others in the planning stage.”

From 2001 to 2008, the U.S. government’s position has morphed from recognizing that some GPS/GLONASS receivers exist to actually encouraging interoperability with all “foreign-based PNT systems for commercial, civil, and scientific uses worldwide.” That’s quite a transformation.

“General policy statement —

“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 USG will reduce non-GPS-based radionavigation services with the reduction in the demand for those services. However, it is a policy objective of the USG not to be critically dependent upon a single system for PNT. The USG 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, economic, safety, and security considerations will dictate the need for complementary PNT systems. 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.”

EG Comment: I wrote to someone the other day about this. Back-ups to GPS is a serious issue. I think very few would argue that it’s not. The reality is that
there is no single back-up for GPS. It depends on the application. In aviation, it’s maintaining a minimal infrastructure of VOR/DME/ILS rather than Loran, according to the FAA. In maritime, it’s the legacy visual aids and charts according to the U.S. Coast Guard. For high precision users, it’s legacy technology like optical instruments and new technology like Locata and pseudolites.

“GPS backup —

“With respect to transportation to include aviation, commercial maritime, rail, and highway, the DOT has determined that sufficient alternative navigation aids currently exist in the event of a loss of GPS-based services, and therefore Loran currently is not needed as a back-up navigation aid for transportation safety-of-life users. However, many transportation safety-of-life applications depend on commercial communication systems and DOT recognizes the importance of the Loran system as a backup to GPS for critical infrastructure applications requiring precise time and frequency.”

EG Comment: The continuing Loran saga.

“Civil Signals —

“In addition to the L1 Coarse/Acquisition (C/A) signal, the USG will add three additional coded signals to support future civil applications:

• L1C, frequency 1575.42 MHz, providing better performance than the current C/A signal being used by civilian receivers;

• L2C, frequency 1227.6 MHz; and

• L5, frequency 1176.45 MHz, to meet the needs of critical safety-of-life applications, such as civil aviation.

“The L1C signal is designed to be interoperable with the European Galileo system and is being promoted as a future world standard for incorporation into Global Navigation Satellite Systems (GNSS). The next generation of GPS satellites, GPS III, will begin broadcasting L1C around 2014.

“The performance specifications in the current SPS PS apply to users of the L1 C/A (1575.42 MHz) signal. As new modernized GPS civil signals (L1C, L2C, and L5) achieve initial operating capability (IOC), performance standards for services utilizing these signals will be developed.”

EG Comment: Nothing new here, but the schedule of actually implementing the new civil signals is a moving target. There are only seven satellites broadcasting L2C at this time. The first Block IIF satellite with L5 should launch in the first or second quarter of this year. Satellites broadcasting L1C (Block III) won’t launch until at least 2014 and a full constellation won’t be operational for many years after that.

“Discontinuation of codeless and semi-codeless GPS access —

“As published in the Federal Register on September 23, 2008 (Volume 73, Number 185), the USG commits to maintaining the existing GPS L1 C/A, L1 P(Y), L2C and L2 P(Y) signal characteristics that enable codeless and semi-codeless GPS access until at least 31 December 2020. To enable an orderly and systematic transition, users of semi-codeless and codeless receiving equipment are expected to transition to using civil-coded signals by this date.”

EG Comment: I’ve written a lot about this. You can read some here.

“Military signals —

“Currently, GPS military users are provided P(Y) code signals on L1 and L2. These will be supplanted in the future by the M-Code, the next generation military GPS signal. The first GPS Block IIR-M satellite began broadcasting M-Code in September 2006. M-Code will significantly improve exclusivity of access because, in addition to being encrypted, it will be spectrally separate from civilian signals and other radionavigation satellite service signals, thereby enabling U.S. navigation warfare operations through spectral separation. Navigation warfare involves protecting U.S. and allied use of GPS while simultaneously preventing hostile forces access to GPS services and preserving peaceful civil GPS use outside of an area of military operations. The M-Code will permit higher power operation than the present signal design and will facilitate localized tactical denial of GPS civil signals to prevent their use by hostile forces. Military GPS receivers, when tracking the encrypted military signals, are much more resistant to interference than commercial GPS equipment. The newest generation of military GPS receivers that can access military GPS signals directly are even more resistant to interference; however, future improvements in signal availability and receiver performance will continue to be necessary.”

EG Comment: The key phrase is “localized tactical denial of GPS civil signals…”. Wow, what can I say about that? Come on GLONASS/CDMA, and Galileo, hurry up!

“Military use of GPS civil signals —

“DoD does not have an operational requirement to use the GPS civil signals, designated L1C, L2C, and L5, or the Wide Area Augmentation System (WAAS), with the exception of the Army validated WAAS requirement documented in the Global Air Traffic Management (GATM) Operational Requirements Document (ORD). Since DoD policy prohibits the use of civil signals or augmentation systems in wartime environments and dual equipage is not fiscally practical, type approval of military aviation receivers is required to eliminate the need for civil GPS equipage on military aircraft. This will provide an enhanced capability to span the operational environment for military aviation—from flight in civil airspace in peacetime to combat operations worldwide. Commercial operators of Civil Reserve Air Fleet (CRAF) airframes may elect to equip with L5 and/or WAAS if there is a demonstrated.”

EG Comment: Interesting.

“Mitigating Disruptions in Aviation Operations —

“A loss of GPS service, due to either intentional or unintentional interference, in the absence of any other means of navigation, would have varying negative effects on air traffic operations. These effects could range from nuisance events requiring standard restoration of capabilities, to an inability to provide normal air traffic control service within one or more sectors of airspace (the NAS is divided into hundreds of air traffic control sectors. A single air traffic controller has the responsibility to keep aircraft safely separated from one another within each sector and from other sectors. Sector dimensions vary, and are established based on predominant traffic flows, altitude, and controller workload) for a significant period of time.

“In addition to FAA plans of retaining a minimum network of VOR, DME, and ILS facilities to serve as a backup to GPS for the
near future, several other solutions have been identified to help mitigate the effects of a satellite navigation (SATNAV) service disruption:

“The L5 civil frequency planned for GPS will help mitigate the impacts of both solar activity and unintentional interference, but it may be 2018 before a full constellation of dual-frequency satellites (L1 and L5) is available. The dual frequency capability with L5 will address ionospheric scintillation by enabling receivers to calculate
actual ionospheric corrections, thereby preserving LPV capability during severe ionospheric storms.

• Modern transport-category turbojet aircraft with inertial systems may be able to continue navigating safely for a period of time after losing radionavigation position updating depending on the route or procedure being flown. In some cases, this capability may prove adequate to depart an area with localized jamming or proceed under visual flight rules during good visibility and high ceilings, however, inertial performance without radionavigation updates degrades with time and will eventually fail to meet airspace requirements.

• Integrated GPS/inertial avionics having anti-jam capability could reduce the area affected by GPS jamming or unintentional interference. Industry research is proceeding to develop this technology, with an expectation that it might be marketed to the general aviation community at some point in the future.

• Users may have an option to equip with instrument flight rules (IFR)-certified Loran avionics, pending the improvements needed to achieve a nonprecision instrument approach capability with eLoran. A combined eLoran/SATNAV receiver could provide navigation and nonprecision instrument approach service throughout any disruption to SATNAV service.

EG Comment: This is a good description of the GPS strategy for aviation operations. But, honestly, if there’s a disruption once the National Airspace System (NAS) is fully reliant on GPS, it’s hard to see there not being major, major hiccups in the air traffic system.

“Mitigating disruptions in land operations —

“Surface transportation users currently use radionavigation services from GPS and its augmentations to supplement other available nonradionavigation systems. Under this operational paradigm, users seamlessly use other existing techniques to mitigate both the short-term loss of GPS due to obstructions and the longer-term loss due to failed on-board user equipment and adverse operating environments. In future applications, accuracy requirements are expected to become much more stringent, and GPS and its augmentations are likely to play a more critical role. The loss of GPS and its augmentations will be carefully evaluated within the overall operational environment to ensure continued safe and efficient operation of the land transportation system.

“Surface transportation agencies are working with industry to ensure that safety critical systems that use GPS and its augmentations consider the loss of these radionavigation services and are able to mitigate its effects in order to continue safe and efficient operation of the nation’s surface transportation infrastructure. This is accomplished today by outreach to user groups and local transportation agencies and defining minimum operational or functional standards. In the future, training for application developers, state and local highway and transit agencies, and motor carriers on the operational capabilities of GPS as well as what to do when failures occur may be necessary. Finally, since it is expected that signal availability from GPS may not be adequate for surface users experiencing canopy/urban obstructions, alternate systems that perform a verification test on the GPS navigation solution and that support continued operation in the event of a loss of GPS will be employed in a system-of-systems configuration.”

EG Comment: A great argument for multi-constellation receivers.

“Mitigating disruptions in non-navigation applications —

“Common positioning applications include: surveying and mapping; precision agriculture; emergency response and law enforcement; fire services; environmental resource management; utility location and management; asset inventory and management; and logistics. These applications have a highly variable duration and involve sporadic areas of operation. Because of the flexible character of positioning applications, operations will typically be halted until the GPS or GPS Augmentation signal is restored in an area. Optical and inertial surveying equipment are back-up options that could meet the accuracy requirements of these applications, depending on the capabilities and preparation of these operators.”

EG Comment: Multi-constellation receivers have already proven their value in non-navigation applications.

“Operating Plans – GPS —

“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. The USG provides notification of changes in constellation operational status that affect the service being provided to GPS users or if a problem in meeting performance standards is anticipated. In the case of a scheduled event affecting service provided to GPS users, the USG will issue an appropriate Notice Advisory to Navstar Users (NANU) at least 48 hours prior to the event, in accordance with the GPS Standard Positioning Service Performance Standard (Ref. 9).

“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 FAA typically not earlier than 72 hours before an activity begins. 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.

“GPS will be the primary Federally provided radionavigation system for the foreseeable future. GPS will be augmented and improved to satisfy future military and civil requirements for accuracy, coverage, availability, continuity, and integrity. Current policy states that DoD will maintain a nominal 24-satellite constellation, and that replacement satellites will be launched on an anticipated need to maintain the constellation as satellites age and ultimately fail.”

EG Comment: Good policy statement on notification to civil users. You can sign up to receive NANU’s here.

Note the statement regarding maintaining a 24-satellite constellation. There are currently upwards of 30 operational GPS satellites. That’s a healthy number, but the problem is that they are still positioned as 24 satellites. In other words, several are “paired up” so the effective constellation is still only 24. There is discussion within the USG about repositioning some of the satellites to optimize the constellation and improve coverage. More on that soon I hope.

“Maritime and nationwide differential GPS —

“USCG began development of the MDGPS system in the late 1980s to meet the needs of the Coastal and Harbor Entrance and Approach (HEA) phases of
navigation and to enable automated buoy positioning. MDGPS service was certified fully operational in March 1999 after the network met the performance standards required for HEA navigation. PL 105-66, Title III, § 346 (111 Stat. 1449) authorizes the Secretary of Transportation to improve and expand the USCG’s MDGPS into a Nationwide DGPS, or NDGPS, by adding an inland segment. RITA coordinates this inland program and is acting chair of the NDGPS Policy and Implementation Team. Today, multiple Federal agencies, several states, and scientific
organizations are cooperating to provide the combined national DGPS utility, with plans to complete NDGPS system coverage throughout the lower 48 states.

“Each NDGPS facility meets all operating parameters established to qualify a MDGPS facility for operational availability, as established by USCG. NDGPS was not designed to meet aviation integrity requirements.

“In addition to providing a real-time broadcast of differential corrections, the U.S. DGPS services provide a robust operational backbone to the DOC’s CORS application for post-processing survey applications and Webenabled location solutions, the National Weather Service’s Forecast Systems Laboratory for short-term precipitation forecasts, and the University NAVSTAR Consortium (UNAVCO) for plate tectonic monitoring. Where operational considerations allow, additional operational capability may be added, such as the broadcast of navigational or meteorological warnings and marine safety information (i.e., NAVTEX data) to support safe navigation at sea.

“Currently 39 USCG and nine USACE broadcast sites provide service for maritime coverage CONUS, the Great Lakes, Puerto Rico, portions of Alaska and Hawaii, and portions of the Mississippi River Basin. The inland NDGPS segment complements the MDGPS segment and is planned to provide dual coverage of the CONUS and selected portions of Hawaii and Alaska as a combined national DGPS utility. There are currently 38 DOT sponsored sites in the NDGPS network providing 92 percent of the contiguous 48 states with single coverage and 65 percent with dual coverage. The combined DGPS service will provide uniform coverage of the CONUS and portions of Hawaii and Alaska, regardless of terrain, or man-made and other surface obstructions. This coverage is achieved by using a medium frequency broadcast optimized for surface applications. The broadcast has been demonstrated to be sufficiently robust to work throughout mountain ranges, difficult terrain and other obstructions. The combined DGPS service will provide a highly reliable GPS integrity function to users to meet the growing requirements of surface users (transportation, precision agriculture, natural resources and environmental management, emergency management and response, and surveying and construction communities).

“As each new Nationwide site is added to the DGPS network, it is evaluated and tested to ensure that it meets the full operational capability specifications commensurate with a safety of life service. Once a site is declared fully operational, the site is monitored and maintained by the USCG to ensure support for safety applications. System coverage for a specific location can be obtained from the USCG Navigation Center (NAVCEN) website, http://www.navcen.uscg.gov.

“The two major deployment milestones have been established as nationwide single station coverage and nationwide dual station coverage (CONUS only). Under single station coverage, predicted to occur no earlier than 2010 (pending funding availability), users anywhere within CONUS will be able to receive at least one DGPS differential correction broadcast. The second major milestone is full coverage by at least two DGPS broadcasts, is expected to occur no earlier than 2012.”

EG Comment: This is a great example of where policy and the presidential budget don’t necessarily agree. NDGPS has been on the budget chopping block for several years. At this point, DOT has only budgeted to maintain the existing system…about $4.6M annually for the 38 DOT-sponsored sites. The 39 USCG and nine USACE sites provide safety-of-life service so their budgets are secure.

“High Accuracy NDGPS —

“The HA-NDGPS research program is sponsored by FHWA and FRA to enhance the performance of NDGPS. The first HA-NDGPS station began broadcasting in a test mode in 2001 with funding from the Interagency GPS Executive Board (IGEB). IGEB recognized the potential benefit to many Federal agencies, states, and the general public of having a nationwide high accuracy system. Two HA-NDGPS reference stations are currently operational and providing 10 to 15 cm accuracy throughout the coverage area. Further improvements to accuracy and the development of 1 to 2 second time-to-alarm integrity are anticipated. Once these improvements are complete, a HA-NDGPS standard will be developed.

“To support this, several approaches are being investigated. They can be grouped into three general categories: improved ionosphere and troposphere prediction; increased data throughput to support broadcast of GPS observables; and the addition of pertinent data to the current broadcast.”

EG Comment: The HA-NDGPS program is one that’s been around a long time. It’s a technology in search of an application. The growth of RTK networks threatens to render HA-NDGPS obsolete. An interesting rumor I heard is that DOT is considering streaming NTRIP data from NDGPS and possibly HA-NDGPS. Essentially, that means one could receive RTCM corrections over the internet via Wi-Fi, mobile phone networks, etc.) and eliminate the bulky and expensive beacon receivers required to use NDGPS today.

“Wide Area Augmentation System (WAAS) —

“WAAS, an SBAS operated by FAA, provides increased navigation accuracy, availability, and integrity for aircraft navigation during departure, en route, arrival, and approach operations. Although designed primarily for aviation applications, WAAS is widely available in receivers manufactured for navigation use by other communities.

“FAA commissioned WAAS in 2003. WAAS service supports departure, en route, arrival, and approach operations, including nonprecision approaches and approach procedures with vertical guidance. The WAAS service may support additional capabilities such as advanced arrival and departure procedures (curved and segmented), more efficient en route navigation and parallel runway operations, runway incursion warnings, high-speed turnoff guidance, and airport surface operations.

“WAAS will be modified to utilize the L5 signal provided by modernized GPS satellites, in lieu of the current semi-codeless L2 signal being utilized to determine ionospheric corrections. New dual-frequency WAAS avionics using L1 and L5 will improve the availability of LPV service.

EG Comment: Note that WAAS is bypassing L2C. It says something about the future of L2C and if it’s really needed. That’s another discussion altogether. Like GPS, WAAS, and SBAS in general is being used in many applications beyond its original intent. There are hundreds of thousands (several million if you include the consumer WAAS users) that outnumber by orders of magnitude the number of WAAS users in aviation.

“The U.S. Continuously Operating Reference Station (CORS) System —

“NOAA’s NGS, an element of DOC, has established a CORS system to support non-navigation post-processing applications of GPS, especially precise 3-dimensional positioning at the few centimeter level. More recently, the CORS network has also served the atmospheric science community as a tr
oposphere and ionosphere monitoring network, and it has served the geophysics community as a crustal motion monitoring network. Additionally, the CORS system is being modernized to serve as the foundation for future applications that support real and near real-time positioning (that differ from navigation applications by the lack of redundancy and integrity monitoring required for safety-of-life applications). The CORS system provides code range and carrier phase data from a nationwide network of GPS stations for access by the Internet.

“As of June 2008, data were being provided from more than 1,200 stations. The NGS manages and coordinates data contributions from GPS tracking stations established by more than 200 other groups rather than by building an independent network of reference stations. In particular, use is being made of data from stations operated by components of DOT and DHS that support real-time navigation requirements (mostly WAAS and NDGPS augmentations). These real-time stations make up approximately 17 percent of all CORS stations. Other stations currently contributing data to CORS include stations operated by NOAA, NSF, and NASA in support of crustal motion activities; stations operated by state and local governments in support of surveying and mapping applications; and stations operated by NOAA’s Earth Systems Research Laboratory, in support of meteorological applications. The breakdown of CORS partners is illustrated in Figure 5-1.

“The national CORS system is a GPS augmentation system managed by NOAA that archives and distributes GPS data for precision positioning and atmospheric modeling applications. It serves as the basis for the National Spatial Reference System, defining high accuracy coordinates for all Federal radionavigation systems. Historically, CORS served postprocessing users of GPS, but is being modernized to support real-time users at a similar level of accuracy.”

EG Comment: What can you say about the CORS system other than that it’s a model for other CORS systems around the world. It says something about the success of the program in that it’s allocated an entire page in the FRP.

Phew, there’s more in the FRP I could quote and discuss but I’ve touched on the major items. Hopefully, this gives you an idea of what the USG thinks about when it makes strategic and tactical decisions about the GPS program. However, keep in mind that in many cases policy and budget don’t match, and if there’s a conflict between the two, budgets usually win.

As a side note, I’ve started a Twitter. You can find me at http://twitter.com/GPSGIS_Eric.