China successfully launched a pair of BeiDou-3 navigation satellites into medium Earth orbits on Oct. 15, according to GB Times.
Four hours after the launch, the two satellites were inserted into their intended orbits, according to the China Aerospace Science and Technology Corporation (CASC). The satellites, numbered M15 and M16, are the 39th and 40th launched as part of China’s Beidou system, following the launch of the first in 2000.
Another pair of BeiDou satellites is expected to be launched in November, according to Richard Langley’s Upcoming Satellite Launches.
Liftoff of the Long March 3B rocket sending the Beidou-3 M15 and M16 satellites into orbit. (Photo: CALT)
For the Oct. 15 launch, a Long March 3B rocket with a Yuanzheng-1 upper stage lifted off from the Xichang Satellite Launch Centre in southwest China at 04:23 universal time (12:23 local, 00:23 Eastern).
The China Academy of Launch Vehicle Technology (CALT), which developed the Long March 3B rocket, reported that data logging and active tracking equipment was placed aboard for tests to determine to altitude and timing for future parachute landings for boosters.
Expended rocket boosters frequently land in or near populated areas downrange of Xichang. The trial phase of parachute booster landings is expected in 2019.
NCTech, a developer of reality imaging systems, will showcase its iSTAR Pulsar mobile 360-degree data capture system at Intergeo in Frankfurt, Germany.
Companies at Intergeo, including GeoSLAM and Orbit Geospatial Technologies, will also unveil innovative developments that incorporate iSTAR Pulsar.
iSTAR Pulsar is NCTech’s professional edge-to-cloud big data system, optimized for capture on the move. iSTAR Pulsar is designed to capture 360-degree data while mounted on a vehicle, drone or on foot.
At Intergeo, NCTech will be showing a demonstration of a future feature in its cloud-based processing software VR.WORLD that uses artificial intelligence and image recognition to analyse the images captured by iSTAR Pulsar. This means that objects like cars, trucks, traffic lights, road signs, pedestrians and cyclists can be automatically identified in images, the company said.
Photo: NCTech
Handheld 3D mobile mapping company GeoSLAM also will introduce new developments at Intergeo, including an innovation that integrates with iSTAR Pulsar.
“We immediately saw the potential for collaboration when NCTech introduced the iSTAR Pulsar,” said Mark Reid, head of strategic business development, GeoSLAM. “And now we’re excited to show the attendees at Intergeo what we’ve been working on.”
Orbit GT has updated its mobile mapping software to enable iSTAR Pulsar data to be integrated into its smart 3D mapping solutions.
“We’re very pleased to announce that Orbit GT solutions now support data from NCTech’s iSTAR Pulsar,” said Peter Bonne, CEO, Orbit GT. “We’ll be showcasing the great 360-degree imagery captured by iSTAR Pulsar at our booth.”
“We launched iSTAR Pulsar earlier this year, so it’s great to see that key industry players like GeoSLAM and Orbit GT are already leveraging its capabilities in their own developments,” said Andrew Baddeley, technical sales director, NCTech. “Combined with the exciting new AI developments from our labs, we look forward to showing everyone at Intergeo how we are helping to virtualize the world.”
Drone Rescue will present its parachute systems DRS-5 and DRS-10 to the professional public for the first time at Intergeo, at stand 12.0B.112 in Hall 12, Oct. 16-18.
Parachute rescue system DRS-5 is designed for multicopters with a total weight of up to 8 kg. The system consists of a carbon cage in which the parachute is stored, as well as the associated electronics.
The electronics, including the sensors, monitor the flight status of a drone independent of the flight controller. A sophisticated algorithm merges this sensor data, through which an automatic crash detection can be realized, the company said. In an emergency, the pilot no longer needs to react and press an eject button. (Often, this is technically no longer possible anyway, such as with a failure of the radio link.)
Furthermore, the algorithm reacts faster than the pilot: the system ejects the parachute itself. All flight data and movements are recorded in a black box. In an emergency, these can be read out at the request of the customer and made available to insurance companies or authorities.
“Our goal is to ensure that even in an emergency beyond visual line of sight the drone can be safely intercepted. With our parachute system, that is always possible, due to the electronics that are completely separate and independent of the flight controller,” said Andreas Ploier, CEO and co-founder of Drone Rescue. “In addition, our system has the advantage that it manages completely without explosive, pyrotechnical solutions. Consequently we have a system that is considerably lighter, and functions even in a worst-case scenario.”
DRS10 system. (Photo: Drone Rescue)
The reliability of the system has been verified in extensive tests by Joanneum Aeronautics in Graz, Austria. In the framework of the tests, 100 flights were conducted during which the parachute system was ejected.
Half of the flights were conducted with a DJI F550 weighing 1.6 kg. The rest of the tests were performed with the 3.8 kg Vulture, which was developed by the FH Joanneum.
In both cases, the DRS-5 was attached to the side of the main body of the drone. In each of the tests the parachute was ejected at a height of 30 meters. Every test was documented.
Furthermore, the data were saved both in the flight controller as well as in the DRS-5 sensor system. After every 10th test, the parachute system was subjected to a visual examination and checked for possible damage or wear.
“After conclusion of the tests, it can be recorded that all 100 flights were successfully completed,” Ploier said. “In every test the multicopter landed safely. Thereby, the kinetic energy was significantly below the limit of 79 J. All requirements specified by the European Aviation Safety Agency (EASA) were observed.”
Besides the DRS-5, the structurally identical parachute system DRS-10, which is designed for multicopters with a total weight between 5 and 20 kg, will also be presented at Intergeo 2018. “The DRS-10 system functions exactly the same as the DRS-5 and falls back on the same components. These are constructed identically, just oriented for a higher payload. The functioning method of both parachute systems is identical,” Ploier said.
With flight tests for the DRS-5 completed in late summer, the first systems will be delivered to end customers in winter 2018.
The Air Force Space Command will conduct the 12th Schriever Wargame Oct. 11 at the Maxwell Air Force Base in Alabama.
The Schriever Wargame scenario, set in the year 2028, will explore critical space issues and investigate the integration activities of multiple agencies associated with space systems and services. Schriever Wargame 2018 (SW 18) will include international partners from Australia, Canada, France, Germany, Japan, New Zealand and the United Kingdom.
The objectives of the wargame are centered on:
examining how international partner capabilities can deter an adversary from extending or escalating a conflict into space;
gaining insight into resiliency, deterrence, and warfighting through international partner synchronization of space and cyberspace operations;
exploring various combined command and control (C2) frameworks to employ and defend air, space and cyberspace capabilities in support of global and geographic/regional operations;
identifying the strategic and operational contributions of space and cyberspace in a multi-domain conflict; and
exploring partnerships framed by a whole of governments approach (international, civil, commercial) to combined space and cyberspace operations.
The SW 18 scenario depicts a notional peer space and cyberspace competitor seeking to achieve strategic goals by exploiting those domains. It will include a global scenario with the focus of effort towards the U.S. Indo-Pacific Command (USINDOPACOM) Area of Responsibility.
A 2016 wargame involving the Air Force and Navy at the Naval Postgraduate School. (Photo: U.S. Navy)
The scenario will also include a full spectrum of threats across diverse operating environments to challenge civilian and military leaders, planners and space system operators, as well as the capabilities they employ.
The Schriever Wargame Team will conduct the wargame on behalf of Air Force Space Command, headquartered in Colorado Springs, Colorado. Approximately 350 military and civilian experts from more than 27 commands and agencies around the country, as well as seven international partners, will participate in the wargame.
U.S. commands and agencies participating in Schriever Wargame 2018 include:
The U.S. Army is drafting new rules for the use of GPS receivers in weapon systems to combat spoofing and jamming attacks, as well as signal loss in GPS-denied environments, according to news reports.
The six- to seven-page capabilities requirements document is awaiting a signature from Army leadership, according to Willie Nelson, director of the assured PNT (positioning, navigation and timing) cross-functional team. Nelson spoke to reporters Oct. 9 at the Association of the U.S. Army annual meeting in Washington, D.C.
The Army has been trying for years to complete a GPS requirements document, a “system of systems architecture for assured PNT.” But with virtually every device equipped with GPS, the document would have been too big and too broad, Nelson said.
(Photo: U.S. Army)
The approach now is for separate sets of requirements: one for mounted equipment (now complete and awaiting the signature), a dismounted requirement, and situational awareness.
The difficulty facing the Army is the plethora of PNT systems in use. For instance, an armored personnel carrier may have five to seven unconnected GPS receivers, some with encryption, some without. The weakest receiver could negatively affect the vehicle, Nelson said.
With the new requirements, Army vehicles will have a consolidated, networked, software-based PNT solution. Dismounted receivers used by soldiers will have similar requirements.
Industry will be asked for specific solutions within each of the PNT sectors rather than an “all of the above” solution.
The Army is also expected to create a training program for soldiers that operate PNT systems.
Mobile app creates new connections for the vehicle finance industry and extends the value of GPS to consumers.
Image: Spireon
Spireon Inc., the vehicle intelligence company, has introduced GoldStar Connect, a full-featured connected car mobile application that gives Buy Here Pay Here (BHPH) dealers and lenders the opportunity to increase customer loyalty and profitability.
As the newest addition to the GoldStar GPS solution suite, GoldStar Connect helps dealers and lenders recoup the cost of GPS, while also increasing value, convenience and safety for consumers, the company said.
The BHPH sector has long used GoldStar GPS to mitigate risk. Dealers and lenders rely on GoldStar to stay connected to their customers in order to facilitate payment collection, monitor default predictors, and streamline recoveries when necessary.
With the new GoldStar Connect mobile app, consumers now have access to all the benefits of connectivity — real-time location access, trip history, vehicle health alerts and recovery solutions for stolen cars — as an add-on at the time of purchase, the company added.
“In marrying the GoldStar solution with a consumer-facing mobile app, our dealer and lender customers not only improve asset management and protection, but also can offer their consumers a significant value add — modern connected car benefits regardless of the vehicle make, model and year,” said Reggie Ponsford, senior vice president of sales at Spireon. “We have had a number of larger BHPH dealers piloting the GoldStar Connect solution in the past few months and seeing up to 90 percent consumer sell-through.”
With GoldStar Connect, consumers gain a host of added benefits with their car purchase, including:
Safety and Security. GPS tracking and geofencing capabilities enable consumers to know the location of the vehicle at all times, helping to ensure the safety of the vehicle and the driver
Trip History. provides visibility to the activity of the vehicle by date, time and duration
Smart Alerts. consumers receive notifications of speeding, geofenced locations and battery condition directly to their mobile devices
Stolen Vehicle Recovery. an in-app recovery guide provides vehicle location data and instructions to assist in reporting and recovery of a stolen car
Insurance Discounts. Many carriers provide discounts of up to 15%
“Consumers want connected vehicle features and benefits, and the app helps dealers and lenders build customer loyalty while also driving additional revenue and margin,” continued Ponsford. “By bundling the purchase into the vehicle loan, it’s seamless and easy for dealers and buyers.”
“We’re excited to help our customers in the vehicle finance industry evolve their thinking about GPS from solely managing risk to now providing an opportunity to increase consumer loyalty and profitability,” said Brian Deeley, director of product management at Spireon. “The GoldStar solution is trusted by more BHPH dealers than all of our competitors combined. The addition of GoldStar Connect creates even more distance between Spireon and the rest, maintaining GoldStar as the GPS gold standard for BHPH.”
GoldStar Connect is now available and will be demonstrated in booth #208 at the National Alliance of Buy Here, Pay Here Dealers (NABD) Buy Here Pay Here Subprime Conference, Oct. 8-10, at the MGM Grand in Las Vegas. To book a demonstration at the conference, see Spireon at NABD.
Researchers from NASA’s Frontier Development Lab (FDL) and Intel are proposing a way to navigate on a new planet using artificial intelligence (AI).
The researchers presented their planetary navigation research during an Intel event on Aug. 16.
The immense challenge of building GPS-similar constellations around every planet or moon could be avoided by using imagery, according to researchers Andrew Chung, Philippe Ludivig, Ross Potter and Benjamin Wu.
The team developed a system for simulating the Moon’s surface so that AI could be used for navigation on the surface.
How It Works. The researchers created a highly detailed digital model of a virtual moon using 2.4 million images of its surface. The images represent ones that might be taken by a rover.
The AI learned what this moon looks like by being fed the millions of images, and then used its neural network to create a model of the virtual moon.
According to the team’s presentation, this was enough to effectively enable navigation on the virtual moon’s surface.
With the model in place, a person merely needs to take a photo of their surroundings on the surface. Based on the photo, the AI determines the person’s location and shows how to navigate to a destination. The AI would even understand the distortions of known features from the point of view of the camera.
The team wants to try to do the same thing with a real celestial body: Mars. They think they have enough satellite images to make it work.
If they’re right, the first Martian visitors could navigate the Red Planet by photo.
Multi-GNSS will open up PPP to a much wider range of applications.
By Francesco Basile, Terry Moore, Chris Hill, Gary McGraw and Andrew Johnson
INNOVATION INSIGHTS by Richard Langley
ARE WE THERE? In a multi-GNSS world, that is. We’ve asked that question from time to time in this column over the years. So, are we there yet? That depends. One definition of “multi” is more than one. In this sense, we were in a multi-GNSS world as long ago as 1996. In that year, we had two fully populated constellations of satellites: GPS and GLONASS. Unfortunately, the full GLONASS constellation was short-lived. Russia’s economic difficulties following the dissolution of the Soviet Union hurt GLONASS, and by 2002 the constellation had dropped to as few as seven satellites. But GLONASS was reborn, and by Dec. 8, 2011, a full 24-satellite constellation was again operational.
But another meaning of “multi” is many, implying more than two. In the late 1990s, the first satellites to host transponders for satellite-based augmentation systems were launched. So, by the mid-2000s, even though GLONASS was still undergoing its rejuvenation, we were already in a three-constellation world. And receivers then on the market provided the necessary raw measurement data to yield positioning solutions from this system of systems with potentially more continuity and greater accuracy than those obtained using GPS alone.
And so in July 2008, we featured the article “The Future is Now: GPS + GLONASS + SBAS = GNSS.” And then in June 2010, we had “GPS, GLONASS, and More: Multiple Constellation Processing in the International GNSS Service.” In the introduction to that article, we asked that same question: Are we there yet? We concluded that, for early adopters of GPS plus GLONASS data and products, we were. With Galileo test satellites in orbit and an early version of the BeiDou system operational, it was already clear that by the end of the current decade, it wouldn’t just be the early adopters who would be benefiting from multi-GNSS but virtually all users of satellite-based positioning and navigation.
Although we aren’t quite there with fully operational Galileo and BeiDou constellations, we are getting pretty close. And so researchers are looking hard at how to make the best use of multiple-constellation observations in a variety of positioning and navigation scenarios. In this month’s column, a team of such researchers examines the potential benefit of combining GPS and Galileo observations for improving precise point positioning in urban environments, following the advice we read in the Book of Ecclesiastes: “Two are better than one.”
Over the years, precise point positioning (PPP) has been applied to many real-time applications that require sub-decimeter-level accuracy over a wide area or on a global scale. It is currently a standard in scenarios characterized by open-sky conditions, where a receiver is likely to have continuous track of GNSS satellites. On the other hand, PPP’s typically long convergence time means the technique has not been widely used in constrained and transient signal environments associated with urban areas. Analysis with both simulated and real data has shown that, once Galileo reaches final operational status, the PPP convergence time will be cut by more than half when using both GPS and Galileo observations. Accordingly, multi-GNSS will open up PPP to a much wider range of applications.
To begin, we assessed the positioning performance of GPS and Galileo signals, alone or used together, in open-sky conditions. A Simulink-based software simulator was used to simulate 24-hour-long observation sessions from 10 static (fixed location) receivers spread worldwide, which were then processed with the POINT software (developed by the University of Nottingham and three other British universities) in static (receiver assumed fixed) PPP mode with an elevation cutoff angle of 10° and with carrier-phase ambiguities estimated as real or floating-point values. For each station, the simulator was run 55 times to provide a sufficient number of data points to characterize the general behavior of the processing algorithms; therefore, a total of 550 points were considered.
For better GPS-Galileo interoperability, PPP results based on the ionosphere-free (IF) combination between GPS L1 and L5 and Galileo E1 and E5a observables were considered.
The metrics used to define the positioning performance are the errors in the north, east and down components of the position once all of a daily file has been processed and the time these errors take to converge below 10 centimeters.
The open-sky condition always guarantees excellent geometry and signal continuity even considering only one constellation.
PPP Results. TABLE 1 shows the root mean square (RMS) of the errors and convergence times of the three components of position for the different configurations for the 550 points considered. Both single- and dual-constellation systems are able to provide a sub-decimeter-level accuracy after a few tens of minutes. On average, positioning with Galileo E1-E5a IF performs better that GPS L1-L5 IF: the Galileo solution is more accurate and converges faster than the GPS solution.
TABLE 1. Comparison between GPS-only, Galileo-only and GPS plus Galileo PPP results. RMS of the positioning errors and convergence times for the stations considered.
The reason for this behavior is the assumed lower noise on Galileo pseudoranges. It is well known that the quality of the pseudoranges affects the convergence time of the PPP solution.
For this reason, one would expect some improvements by employing the Galileo Alternative BOC (AltBOC) modulated E5 signal. Thanks to its very large signal bandwidth of at least 51 MHz, Galileo E5 is characterized by excellent rejection properties of both long-range and short-range multipath. However, as shown in Table 1, when comparing the PPP solutions obtained using the Galileo E1-E5 IF and E1-E5a IF combinations, they have nearly the same performance. The reason for this apparent contradiction can be found in the use of the IF combination with E1. Given that E1 represents the dominant source of error in the IF combinations, its noise is amplified by a factor of 2.34 in the IF combination with E5 and by a factor of 2.26 when combined with E5a. Also, the smaller errors (with respect to E1) in E5a are amplified by 1.26, while the one in E5 is amplified by 1.34. Therefore, depending on the noise level in the Galileo pseudoranges, there might be instances where the noise in the E1-E5 IF combination is close to the one in the E1-E5a IF combination.
The number and the geometry of the observed satellites also affect the convergence time. For this reason, when using the two systems together, the time the vertical errors take to go below 10 centimeters was reduced by 50 percent with respect to the GPS-only case and by 18 percent with respect to the Galileo-only case.
URBAN ENVIRONMENTS
The poor signal visibility and continuity associated with urban environments, together with the slow (re)convergence time of PPP, usually make the technique unsuitable for land navigation in cities. However, as demonstrated in the previous section, using a dual-constellation not only improves the visibility conditions, but also reduces the PPP convergence time. Therefore, it might be possible to extend the applicability of PPP to land navigation in certain urban areas.
To assess the positioning performance of two-constellation GNSS in these constrained environments, we analyzed the signal availability and geometry of five different simulated sites in the neighborhood of the University College London (UCL) campus. We adopted building boundaries, which determine the minimum elevation angles above which GNSS signals can be received due to building obstruction. FIGURES 1 and 2 illustrate the location and the building boundaries for each site. FIGURE 3 shows the junction (site B) between Gower Street (site A) and University Street (site C).
FIGURE 1. Locations of the urban sites that are considered in the analysis.FIGURE 2. Building obstruction masks controlling satellite visibility for each site.FIGURE 3. Google Map image showing the junction (site B) between Gower Street (site A) and University Street (site C) in the midst of the University College London main campus.
When processing data from multi-constellation GNSS, the differences between the system time of the different constellations need to be considered. For this reason, when GPS and Galileo are used simultaneously for precise positioning, the Kalman filter state vector (in general) includes the three position components, the receiver clock offset, and the GPS-Galileo Time Offset (GGTO) — whether or not a predicted value might be available in a navigation message from one of the constellations. On the other hand, in PPP processing, the multi-constellation precise products used are based on the same system time, and therefore, in theory, it is not necessary to estimate the GGTO. However, existing intersystem biases may affect the PPP performance, and so it is advisable to estimate them in the Kalman filter.
Traditionally in PPP, the state vector also includes the residual zenith wet tropospheric delay and the carrier-phase ambiguities. Therefore, the minimum number of satellites required for GPS plus Galileo PPP is six. The geometry conditions are also an important factor for assessing the GNSS positioning performance. For land navigation, the horizontal dilution of precision (HDOP), which provides information about the achievable horizontal precision (and, assuming a bias-free solution, accuracy), is particularly relevant. For many land applications, such as precision agriculture and urban positioning, horizontal accuracy is more critical than vertical accuracy. Assuming that the ranging error in the carrier phase is 20 centimeters, to have decimeter-level horizontal accuracy HDOP needs to be no larger than 5. In most cases, HDOP values as small as 2 are desired.
TABLE 2 gives an overview of the visibility and geometry conditions at the selected sites. A dual-constellation (GPS and Galileo) receiver placed at one of the two road junctions will always, or almost always, see at least six satellites with an HDOP better than 5. At sites A and C, these minimum requirements for signal availability and geometry are met for more than 75 percent of the day. Obstructions due to high buildings, such as at site E, allows us to have at least six satellites for only 13 percent of the time.
TABLE 2. Percentage of epochs in 24 hours for which dual-constellation GNSS meets the minimum visibility (number of satellites, N) and geometry requirements (horizontal dilution of precision, HDOP).
From our preliminary study, it seems clear that high-accuracy positioning in urban environments is possible, but only in some areas where buildings are relatively short, providing good signal availability and geometry. Things can slightly improve by considering additional systems, such as GLONASS and BeiDou, and by exploiting the non-line-of-sight (reflected) signals. However, it is well known that an additional obstacle for PPP in urban environments is signal discontinuity. Indeed, when a GNSS receiver loses lock on the carrier, the positioning filter needs to be reinitialized, meaning that further tens of minutes are required before reconvergence.
To test the reconvergence time of PPP in transient signal environments, a pedestrian carrying a multi-GNSS receiver was simulated to be walking along the path in FIGURE 4. The receiver was simulated to be located for the first half hour of the simulation in the front yard of UCL’s Wilkins Building (where the simulation begins and ends), before starting to move. This is to allow the initial convergence of the PPP filter.
FIGURE 4. The measured trajectory of the simulated pedestrian kinematic test.
FIGURE 5 shows the visibility for a given GNSS satellite. Only the epochs when the receiver is moving are considered. Therefore, the first 30 minutes, when the receiver is static, are not included in the plot. Data gaps due to building obstructions are visible, with the largest being about 12 minutes and the average less than 2 minutes. As a consequence, the carrier-phase ambiguities need to be estimated all over again; and, as previously mentioned, this process usually requires tens of minutes before reconvergence.
FIGURE 5. Satellite availability during the kinematic test.
FIGURE 6 shows the HDOP and the number of visible satellites for the kinematic test, while FIGURE 7 shows the RMS, over 50 simulations, of the horizontal components of the positioning error when GPS L1 and L2 and Galileo E1 and E5, linearly combined into the IF combination, are processed in kinematic PPP mode with the POINT software. At the beginning of the kinematic test, when the HDOP is well below 5, the horizontal error is at the centimeter level, while, after 33 minutes from the beginning of the simulation, building obstructions don’t permit a converged solution below the 20-centimeter accuracy level.
FIGURE 6. Horizontal dilution of precision and number of visible satellites for the kinematic test.FIGURE 7. RMS of the position errors for the kinematic test.
This short example clearly demonstrates that two-constellation PPP has, in theory, the potential to precisely navigate ground vehicles in some urban environments; however, it is too sensitive to signal discontinuity. Slow solution reconvergence to the few decimeter/centimeter level still represents the main limitation to the use of PPP for high-accuracy applications in cities. Nonetheless, GPS plus Galileo PPP easily enables sub-meter-level horizontal accuracy for most of the simulations we have carried out. After signal loss, it only took a few tens of seconds to have a horizontal accuracy of better than a meter.
SMOOTHED CORRECTIONS
As an alternative to ambiguity-fixing methods aimed to improve the (re)convergence time, we propose a method that mitigates the effect of the ionosphere and which thereby reduces the reconvergence time of the PPP solution after initial convergence has been achieved. In this new approach, while the two-frequency carrier phases are linearly combined in the traditional IF combination, the uncombined pseudoranges are corrected by a pre-smoothed ionospheric delay (via a Hatch filter), computed using the geometry-free combination of two-frequency pseudoranges.
Once the Hatch filter has converged, ideally we have IF pseudoranges with lower noise than the traditional ones. Therefore, in case the PPP filter needs to restart, we can obtain a quicker reconvergence thanks to the lower noise on the ionosphere-corrected pseudoranges. Indeed, provided that the signal gap is not very large, the ionosphere smoothing filter doesn’t need to be restarted from the raw values.
It is possible to predict the ionospheric delay computed from two-frequency carrier-phase measurements using a linear fitting model from previous measurements within a sliding time window. As an example, high-rate data recorded on July 25, 2017, from station DAEJ in Daejeon, Republic of Korea, were used to analyze the ionosphere prediction error.
In FIGURES 8 and 9, the RMS of the prediction errors for different time windows have been plotted against the data gap length. The prediction error depends on both the time latency of the observation and the elevation angle of the satellite. It increases with the data gap length, but larger time windows can damp the divergence of the error. A time window of 120 seconds was used both for satellites above and below 30° elevation angle. In this case, the error for a 5-minute prediction is about 4 centimeters for a satellite above 30° and 7 centimeters for satellites with a low elevation angle. These values are much smaller than the noise in the pseudorange measurements and can, therefore, be neglected.
FIGURE 8. RMS of the prediction errors vs. data gap length for satellite elevation angles greater than 30°.FIGURE 9. RMS of the prediction errors vs. data gap length for satellite elevation angles less than than 30°.
Multi-Frequency Combinations. The method introduced in the previous section allows users to be free from the constraint of IF observables and, therefore, to look for multi-frequency combinations aimed to minimize the noise on the pseudoranges. The next-generation GNSS satellites will broadcast open signals over three frequencies. The triple-frequency, geometry-preserving combination aimed to reduce the noise, instead of mitigating the ionosphere, can be used for positioning purposes.
TABLE 3 summarizes the assumed values for the ratios ni between the noise on different GPS and Galileo pseudoranges and the ones on L1/ E1. FIGURE 10 shows a color map of the noise amplification factor associated with different linear combinations between GPS L1, L2 and L5. The x-axis is α3, the coefficient multiplying the pseudorange on L5 in the combination, while the y-axis is the ionosphere amplification factor of the triple-frequency combination with respect to L1, q. The noise for this combination can be as little as 0.57 times the noise on L1, while the corresponding ionosphere amplification factor is 1.49. Once the smoothed ionosphere correction has converged, we can potentially have an IF pseudorange 81 percent less noisy than the L1-L2 IF, and, therefore, a much faster reconvergence.
TABLE 3. Assumed noise, ni, on GPS and Galileo pseudoranges, i, and their ionospheric delay, q, with respect to L1/ E1.FIGURE 10. Geometry-preserving surface in the space q-α3-n (ionosphere amplification factor – L5 pseudorange multiplier – noise amplification factor) for GPS L1-L2-L5 combinations.
Similar conclusions can be drawn by considering Galileo signals. Using triple-frequency combinations with E1, E5a and E5b, we can obtain 81 percent less noise than E1-E5a IF, while a reduction of the noise in the IF pseudorange up to 90 percent was observed using E5 alone. Triple-frequency combinations involving E5 don’t bring such large improvements with respect to using E5 alone. Indeed, a maximum of 16 percent less noise can be registered when combining E1, E5a and E5 with respect to the E5 uncombined case. TABLE 4 illustrates the minimum noise amplification factor for each triple-frequency combination and its ionosphere amplification factor.
TABLE 4. Minimum noise achievable through GPS and Galileo triple-frequency pseudorange combinations and their ionospheric delay with respect to L1/ E1.
The noise associated with the ionosphere-corrected multi-frequency pseudorange combination is as large as meter level before converging to centimeter level. For this reason, a proper weighting method, which considers the varying noise on the ionosphere correction, needs to be employed.
To test the benefit of the new approach for the reconvergence time, three hours of simulated GPS and Galileo data from a static site in La Misere, Seychelles, were processed with the POINT software in kinematic mode. After 90 minutes, the PPP filter was forced to restart to simulate reconvergence. The multipath time constant was set to 5 seconds, which is a typical value for kinematic multipath. The performance of the traditional L1- L2 IF combination was compared with the triple-frequency pseudorange combination, corrected by the smoothed ionosphere delay coming from the Hatch filter.
FIGURE 11 shows the precision (RMS error over 50 simulations) of the horizontal components after filter restart. The new approach has much faster reconvergence than the traditional PPP method based on the IF combination. Indeed, while the traditional method takes about 11 minutes to have a horizontal error below 10 centimeters, using the low-noise combination, this accuracy is achieved after 171 seconds. Even better performance can be achieved considering the Galileo E5 signal (see FIGURE 12).
FIGURE 11. RMS error of the horizontal position components of static site using GPS data after filter restart.FIGURE 12. RMS error of the horizontal position components of static site using Galileo data after filter restart.
The E1-E5 IF combination requires 10 minutes for the horizontal convergence, while using E5 with the Hatch filter we have the horizontal solution converged in about 30 seconds. It is worth noticing that in the presence of static multipath, the proposed weighting method may lead to an overly optimistic weighting of the pseudorange measurements in the PPP filter and to a slower reconvergence of the positioning solution. Indeed, the long correlation time in the static multipath, of the order of a few minutes, makes it hard to filter out by the Hatch filter, hence the corrected measurements have larger errors than expected.
The effect of static multipath in the new configuration is visible in FIGURE 13, where the reconvergence of the horizontal component for the L1-L2 IF combination is compared with the new approach. In this case, the time constant of the simulated multipath was set to 1 minute. In this scenario, the triple-frequency low-noise combination corrected by the smoothed ionosphere combination quickly converges below 20 centimeters; however, it takes significantly longer than the L1-L2 IF combination to reach the 10-centimeter accuracy level.
FIGURE 13. RMS error of horizontal position component of static site using GPS data after filter restart with 1-minute multipath time constant.
Also, the new method was tested with the kinematic simulation as in the previous section. Here, the GPS triple-frequency combined pseudorange and Galileo E5 pseudorange (both corrected with the smoothed ionosphere) are processed in kinematic PPP mode with the POINT software. FIGURE 14 compares the RMS of the horizontal errors with the IF configuration. Less than a minute after the receiver lost lock on the satellites, the solution reconverged below the 20-centimeter level, while it took less than 30 seconds to go below 50 centimeters.
FIGURE 14. RMS error of the horizontal position components of kinematic trajectory using GPS and Galileo data and the smoothed ionosphere approach after filter restart.
CONCLUSIONS
In this article, we described a comparison that we carried out between GPS-only, Galileo-only and GPS plus Galileo PPP. Results based on simulated open-sky conditions demonstrated that Galileo performs better than GPS thanks to an assumed lower E1-E5a IF noise with respect to L1-L5. Two-constellation PPP enables faster (re)convergence compared to the single constellation case.
An analysis of GNSS signal availability, continuity and satellite geometry was also performed to study the feasibility of PPP in urban environments. Preliminary results, based on simulations, showed that dual-constellation (GPS plus Galileo) PPP is possible in urban areas with relatively short buildings in which a satellite minimum availability requirement is met most of the time. However, signal discontinuity still represents the major problem for traditional PPP in urban environments, due to long reconvergence times.
Finally, we proposed a new PPP configuration based on triple-frequency combinations, intended to minimize the noise on the pseudorange and corrected by a smoothed ionospheric delay. This configuration seems to provide faster reconvergence than the traditional PPP with the IF combination if applied to kinematic scenarios. In static applications, the very slow varying multipath error makes the proposed weighting method, based on the error in the smoothed ionosphere correction, overly optimistic. In such cases, the IF combination reconverges more quickly to high-accuracy levels better than 20 centimeters.
ACKNOWLEDGMENTS
The research described in this article was sponsored through a studentship agreement between the University of Nottingham and Rockwell Collins UK Limited. The article is based on the paper “Multi-Frequency Precise Point Positioning Using GPS and Galileo Data with Smoothed Ionospheric Corrections” presented at the 2018 IEEE/ION Position, Location and Navigation Symposium, held in Monterey, California, April 23–26, 2018. All figures attributed to the authors unless otherwise specified.
FRANCESCO BASILE is a postgraduate research student at the Nottingham Geospatial Institute of the University of Nottingham in the United Kingdom. He received his M.Sc. in space and astronautic engineering from the University of Rome – La Sapienza and his B.Sc. in aerospace engineering from the University of Naples – Federico II, both in Italy.
TERRY MOORE is the director of the Nottingham Geospatial Institute where he is the Professor of Satellite Navigation. He is a fellow and the president of the Royal Institute of Navigation (RIN) and also a fellow and a member of council of the Institute of Navigation (ION).
CHRIS HILL is an associate professor in the Faculty of Engineering at the University of Nottingham and a member of the Nottingham Geospatial Institute research group. He holds a Ph.D. in satellite laser ranging and he is a fellow of the RIN.
GARY MCGRAW is a technical fellow with the Rockwell Collins Advanced Technology Center in Cedar Rapids, Iowa. McGraw is a fellow of the ION and is a senior member of the IEEE.
ANDREW JOHNSON is a chief engineer at Rockwell Collions UK in Winnersh, Berkshire, United Kingdom. Johnson has a B.Sc. in electronic and electrical engineering from the University of Surrey in Guildford, United Kingdom.
FURTHER READING
Authors’ Conference Paper
“Multi-Frequency Precise Point Positioning Using GPS and Galileo Data with Smoothed Ionospheric Corrections” by F. Basile, T. Moore, C. Hill, G. McGraw and A. Johnson in Proceedings of PLANS 2018, the Institute of Electrical and Electronics Engineers / Institute of Navigation Position, Location and Navigation Symposium, Monterey, California, April 23–26, 2018, pp. 1388–1398, doi: 10.1109/PLANS.2018.8373531.
“Multi-Constellation GNSS Performance Evaluation for Urban Canyons Using Large Virtual Reality City Models” by L. Wang, P.D. Groves and M.K. Ziebart in Journal of Navigation, Vol. 65, No. 3, July 2012, pp. 459–476, doi: 10.1017/S0373463312000082.
“Potential Benefits of GPS/GLONASS/GALILEO Integration in an Urban Canyon – Hong Kong” by S. Ji, W. Chen, X. Ding, Y. Chen, C. Zhao and C. Hu in Journal of Navigation, Vol. 63, No. 4, October 2010, pp. 681–693, doi: 10.1017/S0373463310000081.
Multi-Constellation Use in Aviation Applications
“Assessment of Alternative Positioning Solution Architectures for Dual Frequency Multi-Constellation GNSS/SBAS” by G. McGraw, B.A. Schnaufer, P.Y. Hwang and M.J. Armatys in Proceedings of ION GNSS+ 2013, the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation, Nashville, Tennessee, Sept. 16–20, 2013, pp. 223–232.
“Undifferenced GPS Ambiguity Resolution Using the Decoupled Clock Model and Ambiguity Datum Fixing” by P. Collins, S. Bisnath, F. Lahaye, and P. Héroux in Navigation, Vol. 57, No. 2, Summer 2010, pp. 123–135, doi: 10.1002/j.2161-4296.2010.tb01772.x.
“Integer Ambiguity Resolution on Undifferenced GPS Phase Measurements and Its Application to PPP and Satellite Precise Orbit Determination” by D. Laurichesse, F. Mercier, J.-P. Berthias, P. Broca and L. Cerri in Navigation, Vol. 56, No. 2, Summer 2009, pp. 135–149, doi: 10.1002/j.2161-4296.2009.tb01750.x.
Hatch Filter
“Combinations of Observations” by A. Hauschild, Chapter 20 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.
“The Synergism of GPS Code and Carrier Measurements” by R. Hatch in Proceedings of the Third International Geodetic Symposium on Satellite Doppler Positioning, Las Cruces, New Mexico, Feb. 8–12, 1982, Vol. II, pp. 1213–1232.
Dilution of Precision
“Dilution of Precision” by R.B. Langley in GPS World, Vol. 10, No. 5, May 1999, pp. 52–59.
Kalman Filtering
“Least-Squares Estimation and Kalman Filtering” by S. Verhagen and P.J.G. Teunissen, Chapter 22 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.
The European Commission (EC) has awarded Thales Alenia Space a contract to develop and build an operational ground station on La Reunion Island to track GNSS satellites in medium Earth orbit. The ground station will be an operational part of the Galileo search-and-rescue (SAR) system.
The contract includes one Medium Orbit Local User Terminal (MEOLUT), engineering support and maintenance services for one year, and the hosting site on La Reunion Island.
Using Thales Alenia Space’s powerful and compact MEOLUT Next phased-array solution, the EC and European GNSS Agency (GSA) will improve their contribution to the Cospas-Sarsat system.
Thales Alenia Space is a joint venture between Thales (67 percent) and Leonardo (33 percent).
The ground station will receive and process 406-MHz distress beacon signals from the MEO satellites being tracked, and relay them to the SAR/Galileo network via the French Mission Control Center (FMCC) at the CNES facility in Toulouse. The contract also included the procurement of the best possible hosting site for this ground station.
Image: International Cospas-Sarsat Programme
This MEOLUT Next will enhance the EC’s contribution to the Cospas-Sarsat SAR system by extending its coverage in the South Indian ocean, contributing to worldwide coverage. It complements the three MEOLUTs that are already deployed around Europe — in Larnaca (Cyprus), Maspalomas (Grand Canaria) and Spitzbergen (Norway) — and under responsibility of the GSA.
The MEO system, which replaces the legacy LEO (low Earth orbit) system, is designed to offer a faster response and better location data in near real time for search-and-rescue authorities, using spacecraft and ground facilities to detect and locate signals from the 406-MHz distress beacons.
The MEOLUT Next will also support the second generation of Cospas-Sarsat beacons. The SAR/Galileo site on La Reunion will be fitted with reference and calibration beacons to monitor the performance of the extended SAR ground segment and precisely calibrate MEOLUT measurements.
“Using Thales Alenia Space’s powerful and compact MEOLUT Next phased array solution, the European Commission will benefit from the world’s first spaceborne search & rescue system of this type,” said Philippe Blatt, vice president, Navigation France at Thales Alenia Space. “We are very proud that our advanced technology is now recognized by many customers worldwide. The performance logged by our MEOLUT Next units in service far exceeds requirements, which not only benefits our customer countries, but also makes travel even safer. It’s worth remembering that the Cospas-Sarsat system, operational since 1988, saves some 1,500 lives a year.”
Thales Alenia Space designs, operates and delivers satellite-based systems for governments and institutions, helping them position and connect anyone or anything, everywhere. Since commissioning in 2016, MEOLUT Next has delivered unrivaled performance, detecting distress signals from more than 5,000 kilometers away. Several countries have already chosen or are interested in the technology, including Canada and Togo.
Keolis Canada and Montreal suburb City of Candiac have launched a long-term demonstration project of an autonomous electric shuttle on public roads in Canada. The shuttle will complement the public transit services currently available in Candiac.
The pilot project will take place over a period of 12 months, with about eight months dedicated to serving citizens.
This initiative was made possible through the financial support and expertise of the Quebec government and the collaboration of Propulsion Québec, the Cluster for Electric and Smart Vehicles and the Technopôle IVÉO.
Screenshot from Keolis Canada video.
The NAVYA autonomous shuttle will operate along a two-kilometer route between the park-and-ride lot and exo’s bus terminal and the intersection of Marie-Victorin and Montcalm North boulevards with several stops along the way, including City Hall, a retirement complex and local businesses.
The autonomous shuttle, which will coexist with regular traffic, will allow employees in the area to reach their workplaces from the bus terminal.
Along the route, the shuttle will go through a railway crossing and an intersection where it will communicate with four traffic lights. During the winter period, a research and development project, without passengers on board, will test how the autonomous electric shuttle adapts to Quebec winter conditions.
“This initiative is exciting because it’s the first pilot project in Canada, and the way it’s carried out will set the course for the next one,” said Marie Hélène Cloutier, vice president, Passenger Experience, Marketing & Sales for Keolis Canada. “For Keolis Canada, multimodal service is the key to the future of transportation. Autonomous electric shuttles are a great example of this because they complement existing services. The enthusiasm for this project has surpassed our expectations, which is very promising for the future.”
“We are extremely proud to be enabling Candiac residents to participate in this historic achievement,” said Normand Dyotte, mayor of Candiac. “It’s an outstanding opportunity for our citizens to be able to travel aboard the first-ever electric autonomous shuttle on a public road in Canada. We invite all public transit users and anyone who is curious or interested to come and try it now.”
Atlantic Microwave, a U.K.-based satellite communications company, has announced the maiden flight of its DSS Satellite Simulator product on board an eight-rotor drone.
Off-air testing of ground- and vehicle-based satellite communications systems has developed into a major industry need with the current explosion of satcom applications in multiple industries, Atlantic Microwave said.
Atlantic’s satellite simulator and loop-test translators were aboard the drone in a first flight in Denmark, using frequencies in the Ku band for proof of concept. Atlantic is also offering similar payloads in Ka band (which delivers greater bandwidth), X band for the military, as well as future Q and V band operations.
“We are in an exciting age where new technologies are shaping our current and future lifestyles,” said Atlantic’s CEO, Geoff Burling.”At Atlantic Microwave, we embrace these advances and seek, innovatively, to create solutions in all kinds of communications industries.”
Atlantic Microwave, based in Braintree, U.K., provides satellite simulation with antenna and cabled-in based products, which have been supplied to major satcom operators, integrators and manufacturers on all continents.
European students and researchers are invited to compete in a new Galileo smartphone app competition sponsored by the European Space Agency (ESA).
The goal is to develop an app capable of performing fixes using raw Galileo satnav measurements. An earlier Galileo smartphone app competition has already resulted in the winning app becoming publicly available.
This year’s event challenges teams to make use of the dual-frequency capability of the latest Android 8.0 smartphones, to compute dual-frequency positioning solutions from raw satnav signals to compare them with their single frequency equivalents.
The competition is run by ESA in collaboration with the European Global Navigation Satellite Systems Agency (GSA) plus the European Commission with the support of Google.
The Galileo app competition is open to all students from European universities and trainees in posts at European research and development organizations.
“The inaugural Galileo smartphone app competition was open solely to ESA graduate trainees, but the response was so great that this time we have opened up to students and young researchers across Europe, forming teams of three to five people,” explained ESA Galileo Services Engineering Manager Rafael Lucas Rodriguez.
The set objective is to reach sub-meter accuracy worldwide in unobscured sky conditions. The app should allow the user to select Galileo-only positioning, GPS-only positioning and the combination of both on a simultaneous basis, with the potential to include other satnav constellations in turn.
The receiver chipsets inside smartphones routinely make use of Galileo in combination with several other satnav constellations — the U.S .GPS, Russian GLONASS and Chinese BeiDou. These chipsets function in “black box” style, making the resulting positioning fixes accessible to users, but without giving any option to the user to select which constellation to employ — or information on Galileo’s particular contribution to the phone’s overall positioning performance.
However, in newer Android smartphones it has become possible to access the raw signal measurements used to compute position, opening the door to the development of applications where the user can indeed select which constellations to employ.
The very latest models also allow the use of dual satnav frequencies, giving a major boost to positioning precision. The higher chip rate of the additional frequency allows the chipset to compensate for signal propagation errors from the signals’ journey through the ionosphere — the electrically active outer layer of atmosphere — and reduces false ‘multipath’ detections caused by signals reflecting off buildings.
“As a first step, teams submit a proposal of not longer than 20 pages, summarizing the application to be developed,” explained ESA navigation engineer Nityaporn Sirikan. “These proposals will be evaluated by a jury composed of representatives of ESA, GSA, the EC and Google, with the top five proposals selected to develop their app further, receiving on loan a state-of-the-art dual frequency satnav smartphone and receiving general guidance and technical support.”
The competition launched on Sept. 24; teams are invited to submit their proposals to [email protected] by Nov. 12, and will be informed of the jury’s response to their proposal by Nov. 26. The competition final is scheduled for April 18, 2019, at ESA’s ESTEC technical centre in Noordwijk, the Netherlands. Terms and conditions of the competition are posted here.
The first- and second prize-winning teams will win attendance to the ESA and EC International Summer School on Global Navigation Satellite Systems in Portugal. Additional prizes will be available to the most innovative app and the winner of a public online vote, to be undertaken during the final.
