Garmin International Inc., a unit of Garmin Ltd., has launched the GPS 3000, a high-integrity GPS position sensor that interfaces to existing avionics to help meet Automatic Dependent Surveillance-Broadcast (ADS-B) Out requirements.
Also, targeting the air transport and defense markets, the GPS 3000 is designed as a WAAS/SBAS position source for select Flight Management Systems (FMS).
Aircraft that are eligible to utilize the GPS 3000 as an ADS-B position source include the Embraer E135/E145 and the Legacy 600/650. Supplemental Type Certification (STC) for the GPS 3000 in these aircraft is currently available from FTI Engineering, in cooperation with Atlas Air Service in Germany, and can be installed throughout the entire Garmin dealer network.
“Garmin continues to lead the industry with the most fielded ADS-B solutions that span all segments of aviation, including a wide-range of commercial, defense, regional and business aircraft,” said Carl Wolf, vice president of aviation sales and marketing. “We are thrilled to provide these aircraft with a solution that is cost-effective and is an easy to install alternative to the existing avionics manufacturer’s service bulletin.”
A rugged, stand-alone and certified Wide Area Augmentation System (WAAS)/Satellite-Based Augmentation System (SBAS) GPS, the GPS 3000 meets DO-160 and DO-178B standards and is designed specifically for the harsh environmental conditions encountered by commercial aircraft.
This compact and remote-mount solution utilizes enhanced WAAS/SBAS GPS satellite signals to provide precise position data through a standard interface. It also meets applicable high-integrity ADS-B position source standards, including TSO-C145d Class 3, the company said.
The GPS 3000 is also designed to interface with select FMS to support GPS guidance throughout terminal, enroute and approach navigation. When configured appropriately, the GPS 3000 is capable of providing position information to an existing FMS to meet requirements for Required Navigation Performance (RNP) and can support GPS-based vertical approach navigation, such as Localizer Performance with Vertical (LPV) approach guidance.
European Aviation Safety Agency (EASA) STC of the GPS 3000 in the Embraer E135/E145 and Legacy 600/650 is available from FTI Engineering, in cooperation with Atlas Air Service, as well as Garmin dealers. FAA validation of the STC is pending.
By Juan Vázquez, Elisabet Lacarra, Jorge Morán and Miguel A. Sánchez, ESSP SAS, and Julian Rioja and Jimmy Bruzual, Topcon Agriculture
The European Geostationary Navigation Overlay Service (EGNOS), a satellite-based augmentation system (SBAS), provides corrections and integrity information to GPS signals over Europe and is fully interoperable with other SBAS such as North America’s WAAS. Among its services is the internet-based EGNOS Data Access Service (EDAS).
EDAS gathers raw data from GPS, GLONASS and EGNOS GEO satellites collected by receivers at approximately 40 EGNOS ground stations distributed over Europe and North Africa. EDAS reformats and disseminates GNSS data in real time and through an FTP archive to EDAS users and service providers.
Additionally, EDAS provides differential GNSS corrections to the GPS and GLONASS satellites in view by the EGNOS system network through its Ntrip service.
The tests summarized in this article focused on the EDAS Ntrip Service, which can be used for differential positioning. An earlier test near Seville, Spain, concluded that these corrections could support pass-to-pass accuracies in the order of 20 centimeters in a consistent manner and with a high degree of repeatability.
To assess EDAS performance validity for agriculture applications, two additional tests were done in Lisbon, Portugal, and York, UK. These locations provide diversity with respect to the Seville test, especially in terms of distance from the farm to the selected EGNOS reference station (≈320 km in York and 40 km in Lisbon, versus the 110 km baseline of the test in Seville) and also geographically. In all tests, a real-time kinematic solution operated in parallel to the EDAS DGPS solution to provide the required reference for the post-processing of the recorded data. Nine different runs with a total of 78 passes were performed in these two campaigns.
Considering the results from the three tests, the pass-to-pass accuracy supported by EDAS DGPS corrections was below 10 cm for more than 60% of passes and below 20 cm for more than 85 percent of the passes. These figures exceed the earlier results and confirm that EDAS DGPS corrections can deliver pass-to-pass accuracies in the order of 10 to 20 cm in a consistent manner.
Cumulative distribution of P2P accuracy, in centimeters. (Chart: Topcon)
The stability of the results and the very good pass-to-pass accuracy levels observed in the York scenario, where baselines larger than 300 km were tested, deserve highlighting. For grain and dry soil cultivation, at least 1 meter (95th percentile) of absolute horizontal accuracy is required. It can be assumed that, within the area where EDAS DGPS supports sub-meter horizontal accuracies (up to 260 km from the selected EGNOS station, according to previous studies), EDAS DGPS corrections can also support pass-to-pass accuracies in the order of 10-20 cm.
Such performance levels are considered to be appropriate for most grain farm operations. In particular, the observed performance is sufficient to support the following precision agriculture applications:
Space Based Augmentation Systems (SBAS) – known in North America as the Federal Aviation Administration’s (FAA’s) Wide Area Augmentation System (WAAS) – have been fully operational in one form or another for several years. The FAA’s incremental improvements to integrity, accuracy and reliability in WAAS have brought the system to a point where we have precision en-route navigation for aircraft, and we can also land aircraft using WAAS signals at thousands of airports in the US and in Canada.
Why not Mexico, which also benefits from the same WAAS coverage? More on that later, as we piece together the many parts of the complex SBAS mosaic.
SBAS precision approach coverage, May 2016. Graphic: FAA Tech Center, Lockheed Martin, GMV
Europe benefits from high-accuracy en-route navigation, and there are also hundreds of operational approaches using the European Geostationary Navigation Overlay Service (EGNOS) SBAS.
In India, the GPS Aided Geo-Augmented Navigation (GAGAN) system provides accurate en-route navigation and approach capability. However, ionospheric disturbance may limit some aspects of performance.
Japan established the Multi-functional Satellite Augmentation System (MSAS) SBAS, and has benefited from improved en-route navigation, but it’s possible that the more limited geographic distribution of GPS ground reference stations has restricted improvements to approach capabilities.
But what happened to the International Civil Aviation Organization (ICAO) concept from 2007, supported by all the ‘aviation-going’ countries of the world, that SBAS would evolve and eventually multiple national systems would provide coverage around the rest of the world, maybe even by 2016?
Countries in Asia, South America, Africa and the continent of Australia all appear to have looked closely into establishing their own SBAS, but nothing seems to have come out of these investigations. Technical issues, cost, and political obstacles have all hindered global SBAS progress.
The ionospheric challenge. Graphic: GMV and Lockheed-Martin
Technical Issues. Ionospheric scintillation problems around the Equator seem to be at the root of most technical problems for SBAS. Getting to the required level of probable, bounded system error is hugely difficult. The iono disturbance ‘blob’ follows the sun around the Equator and wipes out any chance of satisfactory system performance when it passes over Equatorial countries.
As total electron count (TEC) increases, the ionospheric grid, which most SBAS use to predict ionospheric variation across their geographic area between fixed reference stations, well, it just doesn’t work anymore.
Cost. The capital cost of building a satellite-based augmentation system and the on-going cost of maintaining a bunch of geographically distributed reference sites, building and launching GEO satellites or renting transponders on someone else’s orbiting asset, establishing, operating and maintaining redundant uplink stations, redundant terrestrial data links, and setting up control systems that collect and create the SBAS uplink message — it all adds up. Millions and maybe even billions of dollars or equivalent, in total, have been spent by those select countries who could afford their own SBAS. Others named above have lesser financial resources upon which to draw.
Political Obstacles. One of the trickiest issues is sovereignty: the need for a country to control its own navigation and landing system. This has likely been the source of most resistance to more SBAS systems being set up and shared by bordering countries around the world.
For a large number of smaller countries, SBAS would only make sense if it was shared across a number of neighboring countries, but that means relinquishing sovereignty to some degree. In several regions of the world a number of geographically adjacent countries don’t particularly like each other, never mind thinking of such sharing/collaboration.
National sovereignty, by the way, isone of the main reasons that existing satellite navigation systems underpinning SBAS, such as Galileo, GLONASS, IRNSS (now NAVIC), QZSS and of course BeiDou have all been put in place.
Another problem with potential SBAS sharing across adjacent countries stems from responsibility for liability. Should something not work and an accident ensues from such a malfunction, who’s liable? Mexico seems to have adopted the view that since the US provides WAAS on what could be called an ‘as-is’ basis, then the potential liability issue seems to trump using the system.
Solutions? Technical issues with the ionosphere may soon be resolved by using dual-frequency L1/L5 airborne receivers that directly calculate their own ionospheric corrections, rather than using the computed SBAS iono grid. If we add in dual-frequency E1/E5a signals from Galileo, things start to get even better. New requirements and prototype equipment are already being developed for dual frequency multi-constellation airborne receivers. Airbus anticipates equipping aircraft with such receivers around 2025. Could this solve the SBAS technical issue for Equatorial countries?
ARINC (now a UTC/Rockwell Collins company) and SITA (in Europe) have been providing commercial aircraft with operational communications services on a pay-for-use basis for a number of years, and this is notarized as an accepted means of compliance within ICAO policy/requirements:
From ICAO Doc. 9161, Sec. 3.99: “A group of states or a regional organization might also undertake to operate the augmentation satellite service required, either by themselves or by contracting a commercial or government organization to do so on their behalf.”
ARINC en-route coverage. Graphic: ARINC
Aireon has partnered with NAV CANADA, the Irish Aviation Authority (IAA), Enav, NATS and Naviair, as well as Iridium Communications and Harris Corporation to provide real time ADS-B data (GPS position output from aircraft) to air-traffic control providers. Aireon’s payloads on the new Iridium NEXT Low-Earth Orbit (LEO) satellite constellation will receive aircraft ADS-B messages and relay them to Air Traffic Controllers in real-time.
There are 66 Iridium NEXT satellites in operation, with significant overlap and redundancy built into the system to enable this safety-of-life service to be provided on a pay-for-use basis to the aviation industry. We could at last know the location of every suitably equipped aircraft in the air, in almost real-time. The ICAO requirement is for an update rate of 15 minutes.
Inmarsat ADS-C is a similar service available to aircraft on a contracted, pay-for-use basis via Inmarsat GEO satellites.
Market Solutions. If a substantial company showed up with a worldwide distributed SBAS solution and offered it on a fee for service basis, why wouldn’t countries that are already accustomed to ARINC and SITA pay-for-use communications? The Aireon international aircraft tracking system, to be provided on the same basis, adds to the credibility of such a pay-for-use service.
So why wouldn’t these accepted services demonstrate to those countries concerned about control and national sovereignty that an SBAS service could be provided on this basis?
The liability for provision of service sits with the providers, so user countries/airlines would have someone to turn to about liability issues, and there presumably could be contract terms to provide system performance guarantees.
No huge capital costs, no system to construct, nor staff to operate or maintain, and yet a level of control similar to that which has been around for commercial aircraft communications for decades.
Would this be of interest to countries that have not yet jumped on the SBAS bandwagon? A definite ‘maybe,’ we could imagine? What’s not to like?
The punch line to all this is that Lockheed Martin and GMV (Spain) have teamed to challenge these non-SBAS countries with a solution which may appeal.
Uralla reference test site. Photo: Lockheed-Martin
To present convincing evidence that it would work, a dual frequency GPS (L1/L2) + Galileo (E1/E5a) reference site has been set up in collaboration with Geoscience Australia and Land Information New Zealand. The reference site is located at Uralla, New South Wales on Australia’s East Coast, where it gathers data demonstrating bounded errors within the operational range which could enable GNSS approach capability.
L1 (2006) vs. DFMC (2018) SBAS at Bangkok. Graphic: Lockheed-Martin, GMV
Another test site in Bangkok, Thailand has demonstrated that existing L1-only SBAS in this area cannot manage this performance (all current SBAS are L1 only), but that with dual-frequency multi-constellation (DFMC) GPS L1/L2+Galileo E1/E5a, the required performance limits could be met.
Lockheed Martin has also been using the Uralla uplink site to test the uplink and downlink of dual-frequency SBAS-like test messages.
The Moral of the Story. There are no miracles as yet, but interest in the pay-as-you-go SBAS concept appears to be growing, and the LM/GMV team continues to work to bring their approach to market.
A large number of countries could well benefit from the high accuracy, integrity and continuity of SBAS service if this all comes together.
The Federal Aviation Administration’s Geosynchronous Earth Orbiting 5 Wide Area Augmentation System (WAAS) navigation payload, developed by Raytheon’s Intelligence, Information and Services business, is now operational and fully integrated into the WAAS network.
The GEO 5 payload joins two others already on orbit in correcting GPS satellite signal ionospheric disturbances, timing issues and minor orbit adjustments, giving users increased coverage, improved accuracy and better reliability, Raytheon said.
“GPS alone can’t meet the FAA’s stringent requirements for accuracy, integrity and availability,” said Matt Gilligan, vice president of Raytheon’s Navigation, Weather and Services mission area. “The WAAS network corrects even the slightest errors, and that provides peace of mind when it comes to safety of flight.”
In operation since 2003, WAAS increases GPS satellite signal accuracy from 10 meters to 1 meter, ensuring GPS signals meet rigorous air navigation performance and safety requirements for all classes of aircraft in all phases of flight, Raytheon added.
WAAS provides precision navigation service to users across the United States from Maine to Alaska, as well as portions of Canada and Mexico.
For aviation users, WAAS offers pilots more direct flight paths, precision airport approaches and access to remote landing sites without depending on local ground-based landing systems.
Raytheon is the system integrator on the GEO 5 system, which includes a WAAS navigation payload on Eutelsat’s GEO satellite, two ComSAT ground sites and SED Systems specialized equipment.
With great sadness we must report that Per Enge passed away on April 22, at home and surrounded by family. Per was a genial friend and colleague to many, and a pillar of the PNT community. He is greatly missed by all.
At the culmination of his long, fruitful career he served as the Vance and Arlene Coffman Professor of Engineering at Stanford University, where he also directed the Stanford Center for Position Navigation and Time.
For many years he conducted research funded by the Federal Aviation Administration, directed at safe and secure air navigation and leading to development of the Wide Area Augentation System (WAAS) and Local Area Augmentation Systems (LAAS). WAAS became fully operational for aviation in the United States in 2003 and is currently carried by more than 110,000 aircraft; similar systems have been deployed in Europe, Japan and India.
Per Enge at National Cheng Kung University (courtesy Shau Shiu Jan).
He received the Kepler Award from the Institute of Navigation in 2000 and was inducted into the GPS Hall of Fame by the U.S. Air Force in 2012. He served as a member of the Space-Based Position Navigation and Time Federal Advisory Committee since 2007. In 2013 he received the GNSS Leadership Award for Signals from this magazine, for signal design including national differential GPS, satellite-based augmentation systems, and alternative positioning, navigation and timing sources. He co-wrote Global Positioning System: Signals, Measurements, and Performance.
Always an educator, Per served as instructor, mentor and gentle encourager of many, many Ph.D. and other graduate-level students at Stanford who have gone on to distinguished careers of their own. In a lifetime marked by great achievements, this is perhaps his greatest and ultimately will be the most far-reaching.
Born in Norway and brought to the U.S. at age 2, he received a B.S.E.E. from the University of Massachusetts and M.S.E.E. and Ph.D. degrees from the University of Illinois.
Speaking at GPS World dinner, accepting Signals Leadership 2013 award. (Photo: GPS World file)
In remarks on accepting the GNSS Leadership Award for Signals, Per cited Faflick’s theorem, “that you will never ever work on any projects that are both interesting and important.” After calling out both GNSS and WAAS as exceptions to the theorem, he identified a third outlier: spoofing.
“Today’s e-security is based on three security factors: what we know (passwords), what we carry (key fob), and what we are (fingerprints, iris scan). And it is not enough. To meet this challenge, we need to rejuvenate the original security factor: location. In the past, transactions were secured by our presence. In the world of e-commerce, this factor has disappeared, and we must use GNSS to approximate this ancient and effective security factor.
“All of this will require the best effort of this precious community of ours.”
Further biographical details are available in an article published by the Stanford News. Among the tributes included there is this one by Brad Parkinson, who recruited Enge to Stanford in the early 1990s. “Anyone who works in GPS is aware of Per and his influence. He was just an intellectually talented person who could understand many scientific nuances and integrate them in ways others could not.”
Teaching the massive online open course.
The article also reminds us that he co-originated and co-taught, with Frank van Diggelen, a massive open online course to share GPS knowledge with a worldwide audience, far beyond Stanford’s walls. Titled “GPS: An Introduction to Satellite Navigation, with an interactive Worldwide Laboratory using Smartphones,” it enrolled 31,000 people from 192 countries. It is available here.
Per’s Stanford colleagues Sherman Lo, Todd Walter and Sam Pullen assisted GPS World with this article and provided these photos from personal archives. The Stanford group is working on setting up a scholarship in Per’s name. More information on it and how to support it will be on the SCPNT website once it becomes available.
Frank van Diggelen has sent further photos, below.
At the Stanford GPS Lab with colleagues from Stanford and DLR (German aerospace agency).
Dinner discussions with US-EU bilateral group.With Alan Chen, Sherman Lo and an early spectrum image of GIOVE-A (or Galileo).Visiting Neuschwanstein Castle in Bavaria after 2005 European Navigation Conference.At the Stanford Center Position, Navigation and Time, which he co-founded in 2005.Team China Consumers at GPS World dinner 2010. The winning team in the Grand Game of GNSS.Fierce “opponents” (examiners) for Ph.D. defense of Ignacio Fernández Hernández of EC/Galileo. Aalborg University, Denmark.Prepared to come aboard in Kobenhavn.The co-authors of Global Positioning System: Signals, Measurements, and Performance (with Pratap Misra).
A road warrior for GNSS.
Faculty of the GNSS Summer School at Svalbard, Norway (Arctic Ocean, 78.7° N).
Becker Avionics Diversity Mode S Transponder with ADS-B certified.
Avionics technology provider Becker Avionics has received certification for the company’s BXT6500 family Mode S transponder, designed for the rigorous flying environment characteristic of helicopter operations.
Paired with a FreeFlight Systems’ 1203C SBAS/GNSS sensor, the remote-mounted solutions provide helicopter operators a complete and cost-effective way to equip with ADS-B Out for the upcoming Jan. 1, 2020, mandate.
The Becker BXT6500 family Mode S transponder is diversity-capable and available for installation on non-TCAS equipped aircraft. A non-diversity option is also available.
The FreeFlight SBAS/GNSS (WAAS/GPS) 1203C sensor.
In addition to providing clients with ADS-B compliance, the system features enhanced privacy settings that can disable both ADS-B and Mode S transmissions — a feature unique to the BXT6500 family.
“We are pleased to announce this new milestone in our transponder product line,” said Forrest Colliver, managing director. “This new system showcases how we tailor our compact, robust and durable avionics to our clients’ requirements in order to provide the best solution for where and how they fly.”
The system is a part of the company’s robust BXT6500 line of ADS-B Mode S transponders. Manufactured with a standard ARINC 429/743 output, this transponder easily integrates with the FreeFlight Systems Model 1203C SBAS/GNSS sensor for complete ADS-B Out compliance, and can be installed either as dual installation for primary transponder interrogations or as single install for a dedicated ADS-B transmission.
For more information, visit with Becker Avionics at booth C4935 and FreeFlight Systems at booth C1137 during HAI’s Heli-Expo happening this week in Las Vegas, Nevada.
We examine the performance of EGNOS in Finland, which lies near the northeast periphery of the coverage area, and how this performance can be improved now and in the future.
By Mohammad Zahidul H. Bhuiyan, Heidi Kuusniemi, Auryn Soderini, Salomon Honkala and Simo Marila
INNOVATION INSIGHTS with Richard Langley
“[O]NE ORBIT, WITH A RADIUS OF 42,000 KM, has a period of exactly 24 hours. A body in such an orbit, if its plane coincided with that of the earth’s equator, would revolve with the earth and would thus be stationary above the same spot on the planet. … [A] transmission received from any point on the hemisphere could be broadcast to the whole of the visible face of the globe, and thus the requirements of all possible services would be met.” So wrote writer and futurist Arthur C. Clarke in his October 1945 Wireless World article “Extra-terrestrial Relays: Can Rocket Stations Give World-wide Radio Coverage?,” envisaging the geostationary orbit (GEO) communication satellite.
The first GEO satellite was Syncom III, orbited by the United States in August 1964. Since then, more than 1,000 satellites have been launched into what is known as the Clarke Belt and around 450 are presently active. Most of them are used for civil or military communication. Some are used for direct-to-user TV and radio. Some are used for weather monitoring and other kinds of surveillance. And some are used for augmenting GPS.
While GPS is a remarkable positioning system, its real-time accuracy using L1-frequency pseudorange measurements and its instantaneous integrity are not sufficient for some applications such as aircraft navigation. That is why the U.S. Federal Aviation Administration developed the Wide Area Augmentation System (WAAS), the first satellite-based augmentation system (SBAS). WAAS provides differential correction data and integrity information to GPS users in real time throughout most of North America using a “bent pipe” from a ground station through the GEO satellite to a user’s equipment. It uses a state-space-domain correction approach, which provides corrections for the satellite orbit and clock data transmitted by GPS satellites along with ionospheric propagation delays, all computed from measurements collected by a continent-wide tracking network.
The WAAS concept has been duplicated for other regions. Three other SBASs are in full operation: the European Geostationary Navigation Overlay Service (EGNOS), Japan’s Multifunctional Transport Satellite Satellite-based Augmentation System, and India’s GPS-aided GEO Augmented Navigation System. Russia’s System for Differential Correction and Monitoring is currently in development.
One hitch with GEO satellites whatever their function is their inability to service high latitudes well. At a latitude of 65°, a GEO satellite has an elevation angle of only around 17° at most and at 75°, it’s about 6° or less. Even if a GEO satellite is above the local horizon, communication might be difficult due to the longer signal path length between the satellite and the user.
And so it is with GEO satellites used for SBAS at high latitudes. And there is an additional problem that even if the signals from an SBAS satellite can be received, corrections for some GPS satellites will not be received if they are outside the coverage area of the SBAS tracking network. In this month’s column, we examine the performance of EGNOS in Finland, which lies near the northeast periphery of the EGNOS coverage area, and how this performance can be improved now and in the future.
FIGURE 1. Finnish national GNSS network, FinnRef. The three stations highlighted in red had the worst positioning accuracy in our analyses.
The European Geostationary Navigation Overlay Service (EGNOS) is the first European-operated satellite navigation system and is a precursor to Galileo, Europe’s independent global navigation satellite system (GNSS), now being deployed. EGNOS, as a satellite-based augmentation system (SBAS) similar to the U.S. Wide Area Augmentation System (WAAS), was developed with the vision to improve the performance of GNSSs, such as GPS and Galileo. At the moment, EGNOS only augments GPS, making it suitable for safety-critical applications such as flying aircraft or navigating ships through narrow channels.
Additionally, EGNOS also supports new applications in many different sectors, such as agriculture (for high-precision spraying of fertilizers), transport (enabling automatic road-tolling or pay-per-use insurance schemes) or even precise personal navigation services for general and specific use.
At present, there are two operational geostationary Earth orbiting (GEO) satellites and until March 2017, these satellites had pseudorandom noise code (PRN) numbers 120 and 136 that simultaneously broadcast EGNOS correction messages to European GPS users. The PRN satellites 120 and 136 are located at 15.5°W and 5.0°E. (Since March, PRN 123 has replaced PRN 136 as one of the operational EGNOS satellites.) The use of EGNOS in the northern Europe is much more challenging than elsewhere in Europe due to the relatively low-elevation angle of some EGNOS satellites as seen from there of about 14° or less.
To improve our understanding of the true performance of EGNOS in Finnish territory, we recently carried out a project entitled “Finland’s EGNOS Monitoring and Performance Evaluation (FEGNOS).” At the northeastern edge of the EGNOS coverage area, the availability of the EGNOS geostationary satellites is compromised due to their low-elevation angles. The Finnish Geospatial Research Institute (FGI) at the National Land Survey of Finland (NLS) maintains a network of 20 permanent GNSS reference stations (FinnRef) all over Finland. The core objective of the FEGNOS project is to evaluate the performance of EGNOS at all of those reference stations to determine if the EGNOS system performance reaches its target in Finland.
Building on our initial research, in this article we report on the analysis of EGNOS performance at all 20 FinnRef stations for a year-long time-frame from November 2015 until October 2016. As it is of importance to compare the performance of EGNOS in a geographic region where EGNOS satellite visibility can be poor due to low-elevation angle, we assessed the performance of EGNOS by comparing the receivers’ own decoded SBAS messages against the SBAS messages provided by the EGNOS Data Access Service (EDAS). The daily EDAS SBAS messages can be freely downloaded from the EDAS server with prior authentication from EDAS. The performance analysis has been carried out for the following three cases:
Applying EGNOS corrections obtained from the EDAS server
Applying EGNOS corrections obtained from the receiver-decoded (Rx-decoded) EGNOS messages
GPS stand-alone solution without any EGNOS corrections.
We carried out the data analysis using the EGNOS analyzing tool called PEGASUS (which originally stood for Prototype EGNOS Analysis Using SAPPHIRE, where SAPPHIRE stands for Satellite and Aircraft Database Programme for System Integrity Research) from Eurocontrol. The results show that the Rx-decoded EGNOS performance is not as good as the performance obtained from the EDAS-offered message corrections. The ongoing experience and knowledge learned from the project has helped to identify weaknesses of the EGNOS system at high northern latitudes.
FINNISH NATIONAL GNSS NETWORK, FINNREF
The Finnish National GNSS network, FinnRef, was established on the initiative of the Nordic Geodetic Commission and the director generals of the Nordic Mapping Authorities in the 1990s. FinnRef is part of the Nordic GNSS network, and some stations of the FinnRef network also contribute to the global International GNSS Service (IGS) network and to the European Permanent Network (EPN). The primary function of FinnRef is to offer geodetic-grade GNSS measurements, which have been continuously used for forming and maintaining the national coordinate system (EUREF-FIN). In addition, the FinnRef network is used for many GNSS-related research activities. For example, it is now possible to analyze the positioning performance of different augmentation services via the FinnRef network. Currently, FinnRef also offers an open positioning service based on the differential GNSS (DGNSS) corrections for GPS and GLONASS.
The FinnRef network was renewed during the 2012–2013 timeframe. The renewed FinnRef network now consists of 20 GNSS reference stations, as shown in FIGURE 1. The raw GNSS data from all 20 reference stations is used in the FEGNOS project for EGNOS performance monitoring and analysis.
DATA COLLECTION
EGNOS signal monitoring at all FinnRef stations was carried out for one year from Nov. 4, 2015, until Oct. 31, 2016. There are in total about 360 days of data from the 20 stations out of a possible 366 days (2016 was a leap year). The day-of-year (DOY) information for the collected data set is detailed in TABLE 1. No data was available during DOY 233 and 234 of 2016 due to a technical fault at the FinnRef stations. There are 57 days of data from the year 2015 and 303 days of data from 2016.
Table 1. DOY information for the year-long data set.
Each FinnRef station is equipped with a dual-frequency geodetic-grade receiver. Each receiver generates 1-hour binary proprietary data files with a 1-Hz data rate. Data is pushed to the network server and saved at the conclusion of each hour. This means that there are in total 24 data sets for each single day for one single station. All the stations’ binary data files are then organized under one directory, which is named after DOY for that particular year. The FEGNOS data Collection Tool (FEGCoT) was developed in Matlab to collect data every day automatically from all 20 FinnRef stations.
These three steps are followed for automatic data collection:
Collect: 1-Hz hourly data is collected from the FinnRef server, and then saved to the local hard disk for further processing.
Convert: The saved raw binary-formatted hourly data files from the receivers are converted to RINEX observation, navigation and SBAS data files via the receiver manufacturer’s converter.
Combine: In this step, all 24 one-hour data sets from each station are combined into one single 24-hour data set for every RINEX file type (that is, observation, navigation and SBAS files).
The combined 24-hour RINEX data file for each station is then processed using the PEGASUS software. The key configuration parameters used in the data analysis are listed in TABLE 2. (Note that airborne accuracy designator refers to specifications in the WAAS Minimum Operational Performance Standards, MOPS.)
TABLE 2. PEGASUS configuration parameters.
Two PEGASUS modules are used for data analysis:
Convertor module: The Convertor module translates the RINEX observation, navigation and SBAS data into a generic format, which can then be used by the GNSS_Solution module for detailed analysis. Convertor can also use input from different GNSS/SBAS receivers and then transform the recorded binary data into readable ASCII data.
GNSS_Solution module: The GNSS_Solution module is used to compute a position solution in conformance with the MOPS for GNSS receivers used in avionics (GPS, SBAS or ground-based augmentation systems). In other words, the GNSS_Solution module can be considered as a post-processing MOPS-compliant GNSS receiver. It interfaces with other PEGASUS components, notably the Convertor module.
The elevation cut-off angle and the minimum accepted signal-to-noise ratio are kept low so as to have more satellites available for user-position computation. (The European Global Navigation Satellite Systems Agency (GSA) advises that range measurements from EGNOS satellites not be used for position computation.)
A Matlab-script was written to download EDAS-provided daily SBAS messages automatically from the EDAS server. All the PEGASUS-related processing was also executed by a Matlab-based script.
ANALYSIS OF RESULTS
We analyzed the EGNOS/GPS performance for the above-mentioned cases with the collected year-long data set from the 20 FinnRef stations. The operational time or uptime of each FinnRef station was monitored throughout the FinnRef network nodes on a daily basis. The average uptime of each station for the one-year data set is shown in FIGURE 2. The “b” in station names indicates one of the two data streams available from each station. The figure shows that most of the stations were up for more than 98% of the time, while only few have uptimes close to 95%.
FIGURE 2. Station uptime for all FinnRef stations for the year-long data set.
According to EGNOS Open Service (OS) horizontal and vertical accuracy requirements, the 95% Horizontal Navigation System Error (HNSE) should be less than 3 meters, and the 95% Vertical Navigation System Error (VNSE) should be less than 4 meters in the EGNOS service provision area. The horizontal and vertical position errors at a defined time epoch are computed as the difference between the estimated navigation position and the actual position in horizontal and vertical planes, respectively. The HNSE (95%) and VNSE (95%) were computed for all FinnRef stations with the year-long data set.
The yearly EGNOS performance in terms of HNSE (95%) and VNSE (95%) are shown in FIGURES 3 and 4, respectively. It can be observed that GPS+EGNOS offers significant accuracy improvement compared to GPS stand-alone solutions for all of the stations. Vertical accuracy improvement for EGNOS is greater than the horizontal improvement, mostly due to the better mitigation of ionospheric error compared to stand-alone GPS. We also observed that the Rx-decoded EGNOS performance is not as good as the performance when corrections are obtained from the EDAS server. This might be due to the poor visibility of the EGNOS satellites at northeastern latitudes, which resulted in data aging or partial data loss of EGNOS messages.
FIGURE 3. HNSE (95%) for all FinnRef stations.FIGURE 4. VNSE (95%) for all FinnRef stations.
In FIGURES 5 and 6, the daily EGNOS performance in terms of VNSE (95%) are shown for the two cases: 1) applying EGNOS corrections from EDAS-provided EGNOS messages, and 2) applying EGNOS corrections from Rx-decoded EGNOS messages, respectively.
FIGURE 5. VNSE (95%) performance over time with GPS+EGNOS (EDAS) corrections.FIGURE 6. VNSE (95%) performance over time with GPS+EGNOS (Rx-decoded) corrections.
For a better understanding, the percentage of EGNOS OS requirement failure when analyzed on a daily basis with EDAS offered corrections is presented in FIGURE 7.
FIGURE 7. Percent of EGNOS OS requirement failure with EDAS-provided EGNOS correction messages.
The percentage of EGNOS OS requirement failure was computed from the number of days where the HNSE (95%) ≥3 meters in the case of horizontal navigation solution error and VNSE (95%) ≥ 4 meters in the case of vertical navigation solution error. As observed from Figures 5 and 7, the EDAS offered EGNOS corrections fail to meet the OS requirement only in a few instances. Similarly, the percentage of EGNOS OS requirement failure when analyzed on a daily basis with Rx-decoded corrections is presented in FIGURE 8. It can be easily seen from Figures 6 and 8 that the Rx-decoded EGNOS performance fails to meet the OS requirement in many instances. However, the daily fluctuations are averaged out when the year-long data is taken into account, providing satisfactory performance on the whole.
FIGURE 8. Percent of EGNOS OS requirement failure with Rx-Decoded EGNOS correction messages.
The yearly EGNOS performance in terms of VNSE (99%) is shown in FIGURE 9.
FIGURE 9. Sorted VNSE (99%) performance with GPS+EGNOS (EDAS) corrections for all FinnRef stations.
The three stations with the worst accuracy are highlighted in red in Figure 1. These stations are located on the northeastern border of the EGNOS coverage area. The EGNOS User Differential Range Error Indicator (UDREI) figure for three stations (FINb, VIRb, and SAVb) is shown in FIGURE 10(a), 10(b) and 10(c), respectively.
FIGURE 10. EGNOS UDREI as seen at (a) FINb, (b) VIRb and (c) SAVb.
The stations were chosen so that they represent a wide geographical spread over Finland. According to Figure 10, the satellite UDREI values are in the range of 14 and 15 (marked as blue) at the northeastern edge of the sky plot. A UDREI of 14 indicates “not monitored” and 15 indicates “do not use” for a particular satellite. Even though the satellites had a moderate elevation angle with respect to the user, the EGNOS system was unable to offer corrections to those satellites in the northeastern sky. Relatively lower availability of GPS satellites coupled with the lower number of EGNOS Ranging and Integrity Monitoring Stations (RIMS) at northeastern latitudes contributed to the poorer than expected positioning performance in the northeastern coverage area of EGNOS.
CONCLUSIONS
In this article, we presented a summary of an analysis of EGNOS in Finland for a year-long period, and we explained our automated data collection and data analysis procedure. The following key observations can be made based on the analysis of the year-long data set:
The use of EGNOS significantly improves the positioning performance compared to GPS stand-alone operation.
The vertical accuracy improvement for EGNOS is higher than the horizontal improvement compared to GPS stand-alone performance.
The performance of EGNOS with the receivers’ own decoded message corrections is not as good as the performance obtained through EDAS-provided EGNOS corrections.
EGNOS does not offer corrections for those GPS satellites that are setting in the northeastern sky of the EGNOS coverage area.
The percentage of EGNOS OS requirement failure when analyzed on a daily basis with Rx-decoded corrections is significant. This is mostly due to the poor visibility of GEO satellites from northeastern latitudes.
These findings emphasize the fact that there is a great need at northeastern latitudes for an alternative solution to the GEO satellites broadcasting EGNOS corrections. The existing alternative solution is to download the corrections from the Internet through EDAS at the cost of an additional communication link. The other possible alternative could be to broadcast corrections via inclined geosynchronous orbit satellites, or by some other means.
ACKNOWLEDGMENTS
This article is based on the paper “Performance of EGNOS in North-East European Latitudes” presented at the 2017 International Technical Meeting of The Institute of Navigation held Jan. 30–Feb. 1, 2017, in Monterey, California. The research was conducted within the FEGNOS project, funded by the Finnish Transport Agency and the Finnish Geospatial Research Institute at the National Land Survey of Finland. More information about the FEGNOS project can be found at www.fegnos.net.
MANUFACTURER
The receivers in the FinnRef network are JAVAD GNSS Inc. Delta-G3Ts and the antennas are JAVAD RingAnt_DMs with SCIS radomes.
MOHAMMAD ZAHIDUL H. BHUIYAN received his Ph.D. degree in 2011 from the Department of Electronics and Communications Engineering, Tampere University of Technology, Finland. He is a research manager in the Department of Navigation and Positioning at the Finnish Geospatial Research Institute (FGI) of the National Land Survey of Finland in Kirkkonummi. He is also the acting deputy head of the institute’s Satellite and Radio Navigation Research Group.
HEIDI KUUSNIEMI is the director of FGI’s Department of Navigation and Positioning. She is also an adjunct professor in the Department of Built Environment at Aalto University in Espoo and in the Department of Electronics and Communications Engineering at Tampere University of Technology. She is also the current president of the Nordic Institute of Navigation. She received her M.Sc. and D.Sc.(Tech.) degrees from Tampere University of Technology in 2002 and 2005, respectively.
AURYN SODERINI is an M.Sc. student in the Department of Electronics and Communication Engineering at Tampere University of Technology. He received his B.Sc. in 2012 from the Department of Electronics Engineering at The Third University of Rome.
SALOMON HONKALA is a researcher at FGI. He holds an M.Sc. (Tech.) degree in electrical engineering from Aalto University.
SIMO MARILA is a research scientist in FGI’s Department of Geodesy and Geodynamics. He received an M.Sc. degree in 2011 from Aalto University.
FURTHER READING
• Authors’ Conference Paper
“Performance of EGNOS in North-East European Latitudes” by M.Z.H. Bhuiyan, H. Kuusniemi, A. Soderini, S. Honkala and S. Marila in Proceedings of the 2017 International Technical Meeting of The Institute of Navigation, Monterey, California, Jan. 30–Feb. 1, 2017, pp. 627–636.
• Authors’ Related Work
“Performance Comparison of Differential GNSS, EGNOS and SDCM in Different User Scenarios in Finland” by S. Marila, M.Z.H. Bhuiyan, J. Kuokkanen, H. Koivula and H. Kuusniemi in Proceedings of ENC 2016, European Navigation Conference 2016, Helsinki, Finland, May 30–June 2, 2016, doi: 10.1109/EURONAV.2016.7530550.
“Low-Cost Precise Positioning Using a National GNSS Network” by M. Kirkko-Jaakkola, S. Söderholm, S. Honkala, H. Koivula, S. Nyberg and H. Kuusniemi in Proceedings of ION GNSS+ 2015, the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation, Tampa, Florida, Sept. 14–18, 2015, pp. 2570-2577.
“Finnish Permanent GNSS Network: From Dual-frequency GPS to Multi-satellite GNSS” by H. Koivula, J. Kuokkanen, S. Marila, T. Tenhunen, P. Häkli, U. Kallio, S. Nyberg and M. Poutanen, in Proceedings of UPINLBS 2012, the 2nd International Conference and Exhibition on Ubiquitous Positioning, Indoor Navigation and Location-Based Service, Helsinki, Finland, Oct. 3–4, 2012, doi: 10.1109/UPINLBS.2012.6409771.
• European Geostationary Navigation Overlay Service
EGNOS – the European Geostationary Navigation Overlay System – A Cornerstone of Galileo, edited by J. Ventura-Traveset and D. Flament, ESA SP-1303, European Space Agency, Noordwijk, The Netherlands, 2006.
• EGNOS Data Access Service
“EDAS (EGNOS Data Access Service): Differential GNSS Corrections for Land Applications” by J. Vázquez, E. Lacarra, M.A. Sánchez and Pedro Gómez in Proceedings of ION GNSS+ 2016, the 29th International Technical Meeting of the Satellite Division of The Institute of Navigation, Portland, Oregon, Sept. 12–16, 2016, pp. 3550–3561.
“Satellite Based Augmentation Systems” by T. Walter, Chapter 12 in Springer Handbook of Global Navigation Satellite Systems, edited by P.J.G. Teunissen and O. Montenbruck, published by Springer International Publishing AG, Cham, Switzerland, 2017.
Minimum Operational Performance Standards for Global Positioning/Satellite-Based Augmentation System Airborne Equipment, RTCA/DO-229E, prepared by SC-159, RTCA Inc., Washington, D.C., Dec. 15, 2016.
Per Enge, Professor and Director, Stanford university Center for Position Navigation and Time
Satelles, a secure time and location solutions company, has appointed Per Enge to its board of directors. Satelles provides a time and location solutions delivered over the Iridium constellation of 66 low-earth-orbiting satellites.
Enge is the Vance and Arlene Coffman Professor of Aeronautics and Astronautics for Stanford University, where he is also the director of the Stanford Center for Position Navigation and Time.
“I am eager to join the Satelles Board of Directors and look forward to supporting the management team,” Enge said. “I am encouraged by the progress Satelles has made and continue to have confidence in the leadership team and future growth of the business.”
Enge’s laboratory has worked with the U.S. Coast Guard to design a medium frequency radio system to broadcast differential GPS corrections to maritime users, and this system has been implemented as a worldwide standard.
His laboratory also worked with the U.S. Federal Aviation Administration to develop WAAS, the Wide-Area Augmentation System that provides GPS integrity data to airborne users. Today, WAAS is carried by more than 100,000 aircraft, and similar systems have been implemented in Europe, India and Japan.
Enge also serves on the board of directors of Amida Technologies, and he serves as a technical advisor to Polaris Wireless.
He has received the Kepler, Thurlow and Burka Awards from the Institute of Navigation for his work. He is a Fellow of the Institute of Electrical and Electronics Engineers. He is a member of the National Academy of Engineering and a fellow of the Institute of Navigation.
Enge received his Ph.D. in electrical engineering from the University of Illinois in 1983. In 2012, the U.S. Air Force inducted Enge into the GPS Hall of Fame.
“It is with great pleasure that we welcome Per to Satelles Board of Directors,” said Michael O’Connor, Satelles CEO. “Per has distinguished himself as a technology innovator and brings to our board of directors deep expertise in global navigation satellite systems. His wealth of experience and expertise in GPS and other technologies adds new depth to our board as we continue to deliver Satellite Time and Location to users around the world. We look forward to working with Per on our mission is to deliver trusted time and location solutions that augment and enhance existing solutions — including GPS.”
The eclipse across America on Aug. 21 was not only a magnificent visual event, it was also observed indirectly by the impact that it had on the propagation of radio signals — including those of global navigation satellite systems.
There was a decrease in the number of free electrons in the part of the Earth’s ionosphere along the eclipse path where sunlight was temporarily blocked by the moon. While not as significant as the daily variation as day turns to night, the effect was clearly seen in the signals received on the ground from GPS satellites.
GPS signals are routinely used to monitor the behavior of the ionosphere. The density of electrons in the ionosphere affects the speed of propagation of radio signals and this effect is slightly different at different frequencies.
By combining measurements made on the L1 and L2 legacy signals transmitted by all GPS satellites using high-grade receivers, scientists and engineers can measure the total electron content (TEC), which is the number of electrons in a column with a cross-sectional area of one meter squared along the path of the signal from satellite to receiver.
This value can then be projected to the vertical direction using a simple equation. Given the large number of electrons in the column, we measure the TEC in TEC units (TECU), where 1 TECU = 1016 electrons per square meter.
TEC time series from two continuously operating GPS monitoring stations near the path of totality, BREW at Brewster, Washington, and NISA at Boulder, Colorado, show a small dip of about 2 TECU or so around 18:00 UTC on Aug. 21, coincident with the timing of the eclipse. These time series are illustrated in FIGURES 1 and 2. Also shown in the figures are the time series for the day before, Aug. 20, which just show the normal diurnal ionospheric variation.
Figure 1. Time series of vertical total electron content observed using all GPS satellites observed at Brewster, Washington, on Aug. 21, 2017, the day of the eclipse (in blue) and the time series from the previous day, Aug. 20., 2017, for comparison (in red).Figure 2. Time series of vertical total electron content observed using all GPS satellites observed at Boulder, Colorado, on Aug. 21, 2017, the day of the eclipse (in blue) and the time series from the previous day, Aug. 20., 2017, for comparison (in red).
The effect of the eclipse was also be seen in the real-time correction data transmitted by the U.S. Wide-Area Augmentation System (WAAS) using geostationary satellites.
WAAS provides enhanced accuracy, integrity and availability for GPS single-frequency users using a network of dual-frequency GPS receivers all across North America. Corrections include a grid of ionospheric propagation delay values, updated every 5 minutes, which are used to account for the delay in receiver measurements.
FIGURE 3 shows part of the grid transmitted by WAAS and the path of totality across the U.S. Three of the grid points are close to the path and the time series of delay values of these points are shown in FIGURE 4.
Figure 3. Map showing the locations of a subset of the grid points used for the WAAS ionospheric delay corrections highlighting the three grid points close to the eclipse path of totality used to examine the effect of the eclipse along with one grid point far removed from the path for comparison.Figure 4. Time series of ionospheric vertical delay values of three WAAS ionospheric grid points along the eclipse path of totality on Aug. 21, 2017, along with the values from a grid point far removed from the path.
We see clear dips in values of up to about 50 centimeters. This is equivalent to what we see in the TEC time series from the BREW and NISA monitor stations since 1 TECU equates to 16 centimeters of propagation delay at the GPS L1 frequency.
Furthermore, the times of the dips correspond to the times of totality as the eclipse quickly moved across the country from west to east. Also shown for comparison in Figure 4 are the delay values for a grid point far removed from the path of totality, which show only the normal diurnal variation.
Not only does a total eclipse mesmerize the general public, it excites many scientists and engineers, too. A number of university research groups organized special eclipse observing campaigns to collect data from GPS receivers as well as other ionospheric monitoring tools to better understand exactly how the ionosphere reacts to a total eclipse of the sun.
And although we expect future analysis of the data will show features of great interest to science, the immediate results from the total eclipse of Aug. 21 show no significant impacts on the position, navigation and timing service GPS provides.
GPS “weathered” the eclipse with flying colors.
(Attila Komjathy, Siddharth Krishnamoorthy, Anthony J. Mannucci, Lawrence C. Sparks, Lawrence E. Young and Giorgio Savastano from the NASA Jet Propulsion Laboratory operated by the California Institute of Technology; Gerald W. Bawden from NASA HQ Earth Science Division; and Hyun-Ho Rho and Richard B. Langley from the University of New Brunswick, Fredericton, Canada, contributed to this article.)
Raytheon Company has launched its GEO 6 satellite payload into orbit for its 12-year mission. It is the latest payload to support the Federal Aviation Administration’s (FAA) Wide Area Augmentation System (WAAS), which enhances the reliability and accuracy of GPS signals for directing air travel.
The Raytheon-developed payload is a key element of WAAS, which offers commercial, business and general aviation pilots more direct flight paths, greater runway capability and precision approaches to airports and remote landing sites without dependence on local ground-based landing systems.
“This latest payload launch is the next step in our journey with the FAA to bolster navigation safety and efficiency for commercial and general aviation,” said Bob Delorge, vice president of transportation and support services for Raytheon Intelligence, Information and Services.
In June 2016, Raytheon launched WAAS GEO 5, which was recently accepted by the FAA for integration into the operational WAAS system. Both WAAS GEO 5 and GEO 6 were launched to replace aging satellites and enhance GPS precision for the FAA. WAAS increases GPS accuracy from 10 meters to approximately two meters and supports nearly all of the national airspace.
The WAAS GEO 6 payload is hosted on a geostationary satellite, SES-15, owned and operated by SES. The satellite was successfully launched May 17 from Arianespace’s Guiana Space Center in French Guiana aboard a Soyuz launch vehicle.
The United States Federal Aviation Administration (FAA) has released its Performance-Based Navigation (PBN) National Airspace System (NAS) Navigation Strategy 2016, the result of a concerted year-long effort by FAA and aviation industry stakeholders. It describes how the FAA intends to transition U.S. NAS operations over the near- (2016–2020), mid- (2021–2025) and far-term (2025–2030) from predominantly point-to-point navigation, reliant on hundreds of ground-based navigation aids, to PBN-centric operations relying on systems and services supporting Area Navigation (RNAV) and Required Navigation Performance (RNP).
Performance-based navigation specifies the aircraft area navigation performance in terms of accuracy, integrity, availability, continuity and functionality needed to conduct specific operations in a particular airspace.
While promoting the PBN benefits of GNSS such as the GPS and the Wide Area Augmentation System (WAAS), the PBN Strategy also recognizes the need to maintain resilient PBN capabilities that remain unaffected in the event of GNSS interference, and that can continue to support PBN operations or provide safe navigation alternatives. It is a well-constructed, valuable document that provides detail on the means by which many of the Operational Improvements (OIs) described in the FAA’s Next Generation Air Transportation System (NextGen) implementation Plan (NGIP) will be achieved.
The FAA began the introduction of PBN operations following the release of its Roadmap for Performance-Based Navigation in 2003, which promoted more efficient and higher capacity operations based on the capabilities of modern aircraft and emerging GNSS-supported PBN procedures. By 2010, many PBN procedures were in use across the NAS, and especially at the busiest airports and most complicated and congested airspace. Building on this experience, the 2016 PBN Strategy recognizes that the U.S. NAS is not a homogeneous entity; its needs vary based on both location and time. To best serve NAS users and to continue to provide the safest, highest capacity, most efficient airspace in the world, some of the key concepts of the strategy are to provide:
the right procedure to meet the need;
structure where beneficial and flexibility where possible;
shifting to time- and speed-based air traffic management;
and delivering and using resilient navigation services.
To provide correct procedure and structure where needed, the PBN Strategy defines six Navigation Service Groups (NSG) and services potentially available at the airports within each group. NSG 1, now comprising about 15 airports, is reserved for the busiest large hubs that would benefit from common aircraft performance capabilities to maximize capacity. NSG 2 contains the remaining large-hub and all medium-hub airports. Small and non-hub airports comprise NSG 3. NSG 4 includes more than 500 airports, including national and regional general aviation (GA, or private plane) airports, and NSG 5 2,400 local and basic GA airports. NSG 6 consists of thousands of small airports not part of the National Plan of Integrated Airport System (NPIAS).
Time- and speed-based navigation is essential to optimal utilization of airport capability and capacity for both arrival and approach and departure operations. The ability of aircraft to more precisely follow PBN procedures because of onboard navigation capability and space- and ground-based navigation services maintains safety, increases airspace and runway utilization, and — because of more efficient, precise routing — minimizes fuel burn and carbon footprint.
The PBN Strategy also recognizes the need to maintain resilient PBN services and, while GNSS-provided PNT services are able to support both RNAV and RNP procedures, GNSS is vulnerable to both intentional and unintentional interference. To preclude loss of efficiency and capacity benefits in the event of GNSS interference, the FAA will maintain and improve the ground-based Distance Measuring Equipment (DME)/Tactical Navigation (TACAN) network to support DME-DME RNAV 2 in the enroute domain and RNAV 1 in the necessary terminal domains. Because of plans to fill gaps in coverage at high altitudes (FL 180 and above) and remove single DME facility criticality, aircraft without inertial reference units (IRUs) will be able to fly these procedures using DME-DME RNAV, although at the much lower altitudes associated with terminal operations, an IRU may still be required. For aircraft without DME-DME RNAV capability, for example General Aviation, the FAA will maintain a Minimum Operational Network (MON) of Very High Frequency Omnidirectional Ranges (VORs) to either support navigation out of a GNSS interference area or navigation to an airport where approach and landing is supported by either an Instrument Landing System (ILS) or VOR.
Commentary
PBN services depicted across Navigation Service Group airports represent the standard in the far term, 2026–2030.
The FAA’s plan to maintain resilience, while admirable, does have some issues. All of the VORs, DMEs and TACANs that provide resilient navigation services are extremely old, the vast majority designed in the 1970s and installed in the 1980s. There is no current plan to modernize or recapitalize them.
As for researching and developing an Alternate Position, Navigation and Timing capability that would support resilient PBN capability for all of aviation, maintain the ability for aircraft to report their positions via Automatic Dependent Surveillance – Broadcast (ADS-B), and support the rapid and vast emergence of unmanned aerial vehicles (UAS) and benefits, the PBN Strategy states that “During the far term and moving out into the 2030 timeframe and beyond, the FAA will continue to research the best methods for Alternate Position, Navigation and Timing (APNT).”
This delay is unfortunate, as further delay in implementing PNT resilience for all aspects of aviation, as well as for all critical infrastructure areas is, at best, imprudent, as recent agency attempts to develop and implement other resilient PNT capabilities — Enhanced DME (eDME) and Enhance Loran (eLoran) — have been suspended.
The release of the 2016 PBN Strategy is a significant event. It will help guide the agency and the aviation community forward. It will help clarify policy, facilitate decisions, drive equipage, and provide for a safe, higher capacity and more efficient NAS. It is a good start, which could be improved by recognizing the significant investments needed in resilient PNT equipment, architecture and systems.
The U.S. Federal Aviation Administration (FAA) and NovAtel have exercised a bilateral option to produce a Wide Area Augmentation System (WAAS) G-III—Galileo prototype receiver. Maintaining core NovAtel WAAS G-III functionality for GPS and SBAS signal processing, the new receiver will operate in the WAAS reference station test environment to facilitate research on multiple GNSS constellation utilization.
The prototype receiver will also add functionality to support tracking and demodulating associated navigation data for Galileo satellites including:
Galileo E1 and E5a tracking
Ephemeris and almanac reporting/processing from E1 or E5a
Automatic channel assignments
Time solution computed from Galileo
Correlator information for signal deformation on Galileo signals
The WAAS G-III—Galileo prototype receiver will be developed on NovAtel’s existing WAAS G-III receiver hardware and application software, and delivered as a field-loadable firmware package. The WAAS G-III—Galileo receiver will not be qualified to DO-178B Level D as part of this contract.
NovAtel’s WAAS G-III reference receiver platform was designed with expandability and multi-GNSS SBAS evolution in mind, and can be customized to meet the needs of individual satellite networks. NovAtel has already delivered G-III based reference receivers to several programs worldwide, including the WAAS G-III receiver (US WAAS, FAA), IRIMS G-III receiver (India IRNSS, ISRO), and QZSS G-III receiver (Japan QZSS, NEC) variants.
The company’s reference receivers and uplink station equipment have been a central element of the U.S. WAAS since its inception. The WAAS third-generation reference receiver (G-III) uses fully updated hardware, and tracks all GPS signals including the legacy GPS L1 C/A, L2P(Y) (semi-codeless), and the modernized L2C, L5, L1C signals as well as the WAAS L1 C/A and L5 signals.
The WAAS G-III reference receiver provides a rich set of range measurement data, signal integrity metrics, and logs for processing by the system’s data communication processor, NovAtel said. The WAAS G-III – Galileo prototype receiver is the first G-III platform evolution for the FAA, an important step towards possible GPS + Galileo dual-GNSS SBAS operations in the future.
