Positioning company u‑blox has acquired full ownership of Sapcorda Services GmbH, a joint venture formed by u‑blox, Bosch, Geo++ and Mitsubishi Electric in 2017.
Sapcorda — SAfe and Precise CORrection DAta — provides advanced GNSS augmentation services for the high-precision GNSS mass market. The joint venture was formed by the four companies to bring scalable, affordable and high-quality GNSS positioning solutions to industrial, automotive and consumer applications.
Relevant industrial applications include autonomous vehicles, such as unmanned aerial vehicles (UAV) and unmanned ground vehicles (UGV), machine automation, surveying, monitoring and other advanced navigation applications.
Within the automotive sector, applications include automated driving and advanced driver-assistance systems (ADAS), lane-accurate navigation, telematics and vehicle-to-everything (V2X) communication.
Sapcorda Services GmbH is a GNSS service provider focusing on the emerging high-precision GNSS mass markets. The company has designed its technology and service offerings to serve high-volume automotive, industrial and consumer markets.
Sapcorda developed its advanced SAPA service based on open formats, and has specifically tailored it for industrial and automotive markets. It uses real-time kinematic (RTK) and precise point positioning (PPP).
Launched in January 2020 in the U.S. and Europe, SAPA Services have been expanded to full coverage of the contiguous U.S. and 32 countries in Europe. Distribution of the service via an additional geostationary satellite L-band signal also has been announced.
“We appreciate the support and cooperation of all the joint venture shareholders. As a part of u‑blox, I see enormous potential for our technology,” said Botho Graf zu Eulenburg, CEO of Sapcorda.
The acquisition of Sapcorda expands u‑blox’s suite of location services complementing its existing data services, including its assistance data and communication service offerings. Sapcorda has focused on establishing a platform from which to bring GNSS augmentation services to the mass market by delivering on robustness, reliability and end-to-end security as it relates to performance.
Full ownership of Sapcorda will also enable u‑blox to serve customers more efficiently, the company said, by streamlining certain processes, including reducing implementation time to market and simplifying the integration process for customers.
“The acquisition of Sapcorda reinforces our position as a leader driving innovation in the most advanced areas of GNSS positioning technology,” said Thomas Seiler, CEO of u‑blox. “It represents another step forward in the execution of our strategy, which is to deliver value to our customers by means of a comprehensive ‘silicon-to-cloud’ set of solutions and offerings.”
Sapcorda operates in Europe and in the U.S. with offices in Berlin and Hanover in Germany and in Scottsdale, Arizona, in the U.S.
New tech can track vehicles, drones and cargo remotely within centimeters — key to safe adoption of autonomous vehicles, flying objects and machinery
Vodafone has successfully used new precision positioning technology to remotely track a vehicle to within 10 centimeters of its location, an improvement of more than three meters compared to its current system.
Vodafone is working in partnership with Sapcorda, using Vodafone’s global internet of things (IoT) platform, which has 118 million connections worldwide.
Vodafone expects the technology to enable applications that warn autonomous trucks of obstacles, tell first responders the position of critical medical drones, and give operators the precisely location of important cargo.
Pinpoint accuracy is critical to the acceptance and mass adoption of autonomous vehicles on the road and in factories, airports, dockyards and any site where machines are in motion. A matter of centimeters can be crucial to ensuring the safety of passengers on a driverless bus, or knowing the precise location of a medical drone. a
The tracking technology will also allow an autonomous truck to mind other road users, including cyclists, whose e-bikes can automatically transmit their position and intended direction of travel.
“We might not be able to locate a needle in a haystack yet, but we are getting close,” said Vodafone Business Platforms and Solutions Director Justin Shields. “What we can do now is take new digital services like this one, integrate it with our global IoT platform and fast networks, and offer it securely at scale to many millions of customers.
“Our in-building 5G and IoT services already allow manufacturing plants, research laboratories and factories to carry out critical, and often hazardous, precision work with robots. Now we are applying the same levels of accuracy to the outdoor world.”
Vodafone is redefining its network and technology on a Telco as a Service (TaaS) model. It makes key network capabilities available through common APIs in a cloud platform to deliver new software, video and data applications at scale, in addition to gigabit-capable connectivity.
Vodafone said the TaaS model will benefit large enterprises, improving their ability to locate critical assets, precisely align machines such as driverless trains at platforms, and let farmers, airports, and fleet operators know the exact whereabouts of their autonomous vehicles.
Vodafone IoT-enabled vehicles, machinery and devices — when linked with Sapcorda’s comprehensive network of GNSS receivers and augmentation technology — improves location accuracy by correcting for things like the curvature of the earth, atmospheric delays and clock differences of global positioning satellites. This offers corporations hyper-precise positioning that they can use to ensure a safe environment for their employees, their customers, the public and their machines.
Combined with video and onboard diagnostics, the technology will also allow vehicle operators to carry out accurate location-sensitive remote inspections and even pause machines such as grass cutters on public footpaths when they encounter people.
PPP-RTK method. Vodafone is adopting the precise point positioning – real-time kinematics (PPP-RTK) method with ground-level GNSS stations to achieve the best error correction. GNSS signals are processed and GNSS corrections are sent out to enhance the position accuracy of the vehicles receiving them.
Vodafone is able to equip any number of vehicles with an in-built IoT SIM, and deliver the positioning data at speed using its gigabit-capable networks.
Vodafone recently put this to the test by tracking in real-time the exact lane that vehicles were traveling in during a combined journey of more than 100 kilometers in varying weather conditions.
Sapcorda provided the data feed, which enabled the GNSS signal to be corrected, to deliver the critical-level of positional accuracy. A precise positioning service complements the existing asset tracking and fleet telematics solutions already provided by Vodafone Business for enterprise customers across 54 countries.
GNSS augmentation solution targets North America and Europe with safe and precise centimeter-level accuracy performance from two geostationary satellites.
Sapcorda Services GmbH is now testing its GNSS augmentation services for the L-band signal in North America and Europe. The testing lays the foundation for a Dec. 1 launch of what Sapcorda said will be the strongest, most reliable GNSS augmentation signal for safety-critical navigation in autonomous vehicles and machinery.
Available in areas without GSM coverage or mobile internet signal, the new Sapcorda L-band beam solutions from two geostationary satellites provide PPP-RTK data-feed redundancy in real-time by swapping to a second data feed when internet connectivity is not available. This automated swapping significantly improves reliability for life-critical applications such as autonomous cars.
“To use GNSS in mass-market safety-critical applications, manufacturers need GNSS augmentation services that provide correction data with safety-critical positioning,” said Botho zu Eulenburg, CEO, Sapcorda. “By expanding our SAPA services with L-band transmission, we enable a high-power correction data stream for homogeneous performance and end-to-end data security with continental coverage in the United States and Europe — thus improving accuracy, reducing convergence time, and enabling the use of lower-cost receivers and antennae.”
The Sapcorda L-band signal will be transmitted in the open SPARTN format, a format specifically developed for IP-based and geostationary satellite distributions. It will be invaluable for safety-critical applications in automotive (such as V2X and autonomous driving, AD/ADAS) and maritime, as well as a wide variety of uses across sectors such as industrial, robotics and drones.
The L-band satellite beam coverage will be available on December 1, 2020. Sapcorda’s safe and precise augmentation (SAPA) service will broadcast SAPA Basic and SAPA Premium correction data streams.
These data streams feature:
99.9% service availability with fast convergence and an accuracy of less than 10 cm, delivering the precision required for safety- and life-critical applications
Redundancy through dual data streams when internet connectivity isn’t available, ensuring uninterrupted broadcast streaming
Demodulation by any L-band demodulator on the market, simplifying hardware design and reducing bill of materials
Availability of service coverage areas in North America and Europe, allowing manufacturers to use a single GNSS augmentation services’ solution for major global regions
Distributed in the same open format as IP-delivery channels (SPARTN)
Sapcorda’s SAPA services are supported by experienced engineering teams dedicated to systems integrators and enterprise business customers. The Basic and Premium SAPA services for L-band signal operation begins in both regions on Dec. 1.
The basic ArduSimple RTK kit includes Sapcorda SAPA. (Image: ArduSimple)
ArduSimple has integrated Sapcorda’s SAPA Premium Service into its new simpleRTK2B+SSR GNSS receiver. The user-friendly integration based on SSR technology allows plug-and-play real-time kinematic (RTK) without the need for a base station. Users can connect the receiver to their PC or tablet to achieve centimeter-level accuracy.
Based in Berlin, ArduSimple develops user-friendly, affordable RTK receivers and tools for evaluation of multi-band GNSS technology.
The simpleSSR basic starter kit includes a multi-band RTK receiver, SSR receiver, one year unlimited data package and one year SAPA Premium license. Accurate position is available via USB, UART and I2C, as well as via Bluetooth, Wi-Fi or RS232 with the corresponding accessory.
“ArduSimple’s vision is to make RTK technology affordable and accessible to everyone. Removing the hassle of the base station is a key step towards it,” said Josep Olivart, Senior Consultant at ArduSimple. “The decision to select Sapcorda was clear: best in class service performance at affordable mass market price, supported by a highly skilled and committed team.”
Sapcorda provides GNSS augmentation services for the internet of things (IoT), automotive, and industrial applications across the United States and Europe including up to 20 kilometers off coastlines, delivered with low-bandwidth data over internet and satellite, and providing uniform, high-integrity instantaneous sub-decimeter positioning on a continental scale with enterprise-level service availability.
“Sapcorda aims to establish GNSS precise positioning in mass-market applications and ArduSimple is an ideal partner for the integration of our services into a high precision GNSS hardware,” said Botho Graf zu Eulenburg, managing director at Sapcorda. “The combination of our advanced services with ArduSimple’s new platform provides an easy to use and affordable high precision solution to everyone.”
Septentrio has entered into a commercial agreement with Sapcorda, a global provider of sub-decimeter GNSS corrections.
Through the collaboration with Sapcorda, Septentrio will pioneer an no-hassle corrections integration into a new line of products for the high-accuracy industrial market.
These new products will consist of Sapcorda’s SAPA Premium corrections integrated directly into Septentrio’s latest GNSS receiver technology. The result is sub-decimeter accuracy, which is available to users right out of the box. This significantly simplifies the user’s GNSS receiver set-up process and eliminates the hassle of corrections service subscription and maintenance.
Such GNSS receivers acquire corrections via internet as well as via satellite broadcast and deliver reliable, broadly available sub-decimeter positioning to high-volume industrial applications.
Sapcorda integration program
Sapcorda release its SAPA augmentation service integration program on May 14, following the launch of its SAPA Premium service. The integration program targets companies integrating GNSS chips or receivers and looking to enable their systems to perform in high-accuracy mode.
The program offers step by step service integration and proof of concept guidance for upgrading the integrators’ GNSS systems to deliver down to centimeter-level positioning accuracy.
The program also includes the offering of free service data, used to validate positioning performance on the target application. The program participants also receive commercial support for introducing the correction data on their marketed products.
The SAPA service is delivered using optimized data format and can be integrated by modern or traditional high-accuracy receivers compatible with open standards such as SPARTN and RTCM.
Sapcorda’s SAPA services are designed to bring high-precision GNSS positioning to mass market, as well as general industrial and automotive applications. The correction data stream is optimized for homogeneous performance and end-to-end data security with continental coverage in the United States and Europe.
The service data transmission also provides unmatched low bandwidth consumption, with broadcast transmission via direct IP connection or geostationary satellite signal (L-band).
Sapcorda was established in 2017 to provide an open approach to a safe, broadly available and scalable corrections service. By adding Sapcorda’s SAPA service to its corrections portfolio, Septentrio begins offering sub-decimeter accuracy with quick convergence time anywhere in the U.S. and Europe.
Autonomous vehicles, robots
“This collaboration allows both companies to bring innovative solutions, inspired by the growing market of autonomous vehicles and robots, to the high-accuracy industrial markets,” said Jan van Hees, business development director at Septentrio. “By integrating Sapcorda’s SAPA service into our products, we are completely removing the hassle of managing corrections for the customers. This means faster set-up times and worry-free, always-on high-accuracy positioning throughout the whole receiver lifetime.”
“At Sapcorda our focus is on providing a high-accuracy service suitable for demanding applications where both performance and safety is critical. This includes land robots, UAVs, logistic applications and autonomous vehicles,” said Botho Graf zu Eulenburg, CEO at Sapcorda. “Septentrio’s field-proven high-precision GNSS receivers and their focus on reliability and robustness aligns perfectly with our mission and the capabilities of our SAPA services.”
This broadens the range of Septentrio’s existing GNSS solutions, allowing the company to serve a wide range of customers with various requirements in terms of accuracy, operation location and scalability. Read Septentrio demystifies GNSS corrections for more about GNSS corrections and correction methods such as Sapcorda SAPA (PPP-RTK) service.
A key feature of a new high-accuracy GNSS correction service
Innovation Insights with Richard Langley
INTEGER VITAE SCELERISQUE PURUS. So wrote the Roman poet Horace at the beginning of one of his odes — one which, incidentally, was sung by college choirs at one time. It is usually translated as “upright of life and free from wickedness” and is just about the only common Latin quotation in which we find the word “integer.”
Besides upright, the word can be translated as unimpaired, perfect or whole. It is this latter meaning that the English mathematician Thomas Digges appropriated to describe whole numbers. The modern mathematics definition of the set of integers includes the additive inverses of the whole numbers plus zero. We have to worry about the integer nature of carrier-phase ambiguities when trying to achieve high-precision GNSS positioning but that is a story for another day.
The Latin word integer is the root of the English word integrity. In everyday speech, integrity means the quality of being honest or trustworthy (and having strong moral principles). But it is also used to describe something that is unimpaired or uncorrupted, especially in regard to electronic data such as that provided by a navigation system.
As I wrote in an Innovation column back in 1999, “The performance of any navigation system is characterized by its accuracy, availability, continuity, and integrity. From a safety point of view, integrity is arguably the most important factor. Without some assurance of a system’s integrity, we have no way of knowing whether the information we receive is correct: How are we to know whether a navigation system is actually achieving its advertised accuracy and not misleading us with faulty information?” Navigation systems that provide safety-of-life services must ensure a very high level of integrity. For example, the Wide Area Augmentation System (WAAS) continuously assesses the integrity of GPS satellite signals as well as its own corrections, warning WAAS users when a failure is encountered within about 6 seconds of failure. This helps to ensure that aircraft do not use misleading data that could potentially create hazards.
And now, high-precision GNSS positioning technology using real-time augmentation is being adopted for autonomous applications in the automotive, rail, aviation and marine industries. These applications need high integrity in their position determinations in addition to high accuracy. As with the pioneering non-autonomous aviation use, augmentation services for the new market will need to monitor many aspects of their service to ensure a high level of integrity including the high-end data processing algorithms, real-time data transmission, end-to-end encryption, and functional safety assurance. This will be a challenging task that will require a multi-disciplinary approach, deep understanding of GNSS error modeling and risk assessment.
In this month’s column, we look at the design, construction, operation and performance of the first safety-critical, high-accuracy augmentation service created specifically for autonomous applications.
In addition to the need for high accuracy, the adoption of high-precision GNSS positioning technology for autonomous applications in the automotive, rail, aviation and marine industries has brought with it the need for high integrity and reliability. GNSS integrity concepts had their beginning in safety-critical applications in the aviation and marine industries, which have used GNSS to provide absolute position for precision runway approach, enroute navigation, port approaches, open sea and coastal waterway navigation.
For precision GNSS users (those using precision or high-end equipment) in the surveying, construction and agriculture industries, the focus has primarily been on accuracy. Over the past decade, real-time networks have been developed to offer sub-2-centimeter performance to end users. Although some integrity information has been provided, it has often been in the form of disturbance indices that network operators can use to inform users of suspected down time or periods of poor performance. But the information lacks a functional safety component. Additionally, this information has not typically been integrated in real time into position engines to aid in the generation of reliable integrity parameters for the end users.
Although GNSS does have limitations, particularly in urban environments, GNSS equipment is one of the few sensor types available to system integrators that can provide absolute position in autonomous applications.
This realization — combined with the further miniaturization, lower power consumption and expansion of inexpensive multi-frequency, multi-constellation GNSS chips capable of real-time-kinematic- (RTK-) style processing — has made the adoption of GNSS for mass-market applications very appealing.
Most mass-market applications don’t have the same accuracy requirements that drive the professional high-precision market. TABLE 1 summarizes applications that can benefit from a high-precision GNSS correction service. In most cases, decimeter-to-meter-level accuracy is typically acceptable. Reliability becomes more critical for these applications.
Table 1. Applications that can benefit from a high-precision GNSS service with integrity. (Data: Sapcorda)
The integrity demand, which we define as the degree of difficulty an application poses to the integrity monitoring system, is based on the required accuracy, availability, failure rate and continuity requirements of the application. Applications with a high integrity demand pose the most difficult challenges.
With the spread of autonomous applications in various areas, the likelihood of liability and legal cases being decided based on PVT data provided by the systems is high. This eventuality brings with it a need for a non-proprietary open standard for ensuring consistent implementation of the integrity information and functional safety along with the separation of end-user and provider responsibility. In this article, we describe the requirements and concepts for a high-precision GNSS correction system with high integrity.
SYSTEM OVERVIEW
Our Sapcorda correction service provides high-precision GNSS correction data on a continental scale. Its core component is an underlying tracking network of reference stations used to generate the precise corrections. The reference stations operate in real time and continuously transmit their data to the data control center. The data control center processes the data, computing orbit, clock, instrumental bias and atmosphere corrections and integrity information, and then encrypting the data before broadcasting it to the end user (see FIGURE 1).
The corrections are broadcast in the Safe Position Augmentation for Real Time Navigation (SPARTN) format developed by a consortium of GNSS manufacturers and service providers, via two communication channels, L-band and the internet. The data is then received by the end users who must decrypt it before it is used in processing. The SPARTN correction format consists of a set of messages that broadcast the GNSS corrections in a state-space representation. With our network, Sapcorda can offer a high-accuracy positioning service with fast convergence. An example of positioning performance for a monitoring station in Sapcorda’s European network coverage area is shown in FIGURE 2. The typical accuracy level is close to that of traditional network RTK services.
FIGURE 2. Horizontal position performance for a monitoring site in Europe using Sapcorda’s high-precision service. (Image: Sapcorda)
The system provides coverage for both North America and Europe as shown in FIGURE 3. Unlike traditional local or regional network RTK systems, Sapcorda’s network provides seamless coverage on the continental scale and operates in broadcast-only mode.
The integrity of a system can be described as the trustworthiness of the positions generated by the position engine. Trustworthiness is defined by the protection level associated with a given solution. Many of the concepts related to GNSS integrity originated from the development of the Wide Area Augmentation System (WAAS). The integrity concept was formalized by the Stanford Integrity Diagram, which outlines the key concepts related to integrity. TABLE 2 defines the terminology surrounding the integrity concept.
Table 2. Integrity terms. (Data Sapcorda)
The integrity risk is the probability that a user will experience a position error larger than the alert limit without an alarm being triggered. When this occurs, the user is in a potentially dangerous situation as the system is providing dangerously misleading information to the user, who is unaware.
The protection levels are computed based on the expected behavior of the error sources encountered in a GNSS positioning system. If the protection level is less than the system’s alert limit, then the system is operating within its normal bounds. If the error sources are not properly monitored or quantified, protection levels become optimistic. This occurs when the true position error, which is typically unknown, exceeds the protection level supplied by the system. When this situation occurs, it is labeled hazardously misleading information (HMI) because the system may believe that its position is more accurate than it truthfully is. If the true position error remains less than the alert limit, then this is classified as misleading information. As the true position is not beyond the alert limit, the operator/system can continue to rely on this information without being in a potentially dangerous scenario.
To define the true integrity risk of the system, it is necessary to understand its error sources, threat models, frequency of occurrences and potential failure modes. Many threats could render a correction service unavailable, including hardware failures, data outages or software bugs, atmospheric anomalies and satellite failures. The following section describes these threats along with the capabilities used for monitoring them.
Error Sources. The primary error sources in high-precision GNSS positioning are described in TABLE 3.
Table 3. GNSS network error sources, their magnitude and mitigation approach. (Data Sapcorda)
Although not mentioned in this table, additional error sources include site displacement effects such as solid earth tides, ocean tide loading and polar tides; carrier-phase wind-up at both the receiver and satellite; and satellite and receiver antenna phase-center variations and relativistic delays. These effects must be consistently modeled at both the server and the end-user for centimeter-level positioning.
Based on the error sources described in Table 3, it is necessary to convert this information into a format that can be used by the position engine to derive protection levels for each solution. How the final protection level is derived by a position engine is not within the scope of this article. For this, several approaches can be used including carrier-phase-based receiver autonomous integrity monitoring (CRAIM), solution separation and others.
The following equation can be used to describe the overall error contribution for each measurement:
where
is the total uncertainty for satellite i
is the uncertainty of the ionosphere model
is the uncertainty of the troposphere model
is the uncertainty of the combined orbit, clock and bias (ephemeris) corrections
is the uncertainty of the measurements in the given environment
The terms , and are derived from the real-time reference network operator while the term must be computed by the end-user receiver. This final term is perhaps the most difficult to determine, particularly for kinematic environments, as the value is highly dependent on antenna quality, multipath and measurement quality.
PERFORMANCE AND RESULTS
We processed 24 hours of data at three stations covered by Sapcorda’s European network and within the red circle shown in FIGURE 5.
FIGURE 5. Location of stationary testing carried out within Sapcorda’s European network. (Image: Sapcorda)
The test stations were situated in an open-sky environment with high-quality geodetic antennas and receivers. The position results and protection levels were derived from Sapcorda’s own position engine.
FIGURE 6. Integrity plots for the horizontal error and protection levels for three stations within Sapcorda’s European network coverage area.(Image: Sapcorda)
FIGURE 6 shows the horizontal component integrity plots for the three stations. The protection levels are computed for the five-sigma level. In all three examples, the protection level can properly bound the horizontal position error. In terms of the measured accuracy, the typical performance observed at the three stations is between 3 and 7 centimeters for the 95th percentile.
In addition to the stationary testing, two kinematic trials were carried out in cooperation with a system integrator. The integrator setup consisted of a commercial RTK receiver and position engine being fed with SPARTN corrections. The equipment was mounted onto the vehicle used for the tests. Both tests were carried out in an urban environment, which introduced measurement outages due to trees, overpasses and urban canyons. FIGURE 7 shows the area in which the kinematic trails were carried out, as well as some of the urban conditions with which the system had to contend.
FIGURE 7. Location of kinematic trials using Sapcorda’s North American correction service and examples of the environment encountered during the testing. (Image: Sapcorda)
FIGURES 8 and 9 show the position performance and integrity plots for the two kinematic trial scenarios. The reference trajectory was computed using a short baseline post-processed kinematic solution computed with a third- party application. The typical accuracy of the Sapcorda-enabled solution was on the order of 2 to 4 centimeters, while the maximum error was 10 centimeters. In both cases, the protection levels were able to properly bound the horizontal position error. Figure 8 shows an area of increased position error, which occurs around the 22.6- to 22.7-hour mark of the day. This period coincides with the image in the bottom right of Figure 7, where the vehicle passes into a difficult environment with overhead trees and walkways, as well as significant shading from a tall building. Even in this type of environment, the protection levels were able to properly bound the horizontal position error.
FIGURE 8a. Horizontal position performance for kinematic trial #1. The red line indicates the 1-sigma error of the position engine. (Image: Sapcorda)FIGURE 8b. Horizontal position performance for kinematic trial #1: The 5-sigma integrity diagram. (Image: Sapcorda)FIGURE 8b. Horizontal position performance for kinematic trial #1: The 5-sigma integrity diagram. (Image: Sapcorda)FIGURE 9b. Horizontal position performance for kinematic trial #2: The 5-sigma integrity diagram. (Image: Sapcorda)
In addition to the position performance, re-initialization time plays a critical role for precise positioning systems operating in difficult environments. Due to the regular outage and signal blockages, which occur in urban environments, the re-initialization time is critical to providing high availability. Traditional precise point positioning (PPP) systems, even those that perform ambiguity resolution, can take anywhere from 5 to 20 minutes to re-initialize and achieve an acceptable accuracy level (typically 10 centimeters) after a complete outage. Researchers in both academia and industry have developed several methods to reduce this time by “bridging the gap” after outages.
However, these approaches rely on assumptions about either the vehicle trajectory or the stability of the ionosphere before and after outages. The impact of these assumptions on overall integrity have not been adequately studied. Systems that rely on inertial measurement units (IMUs) to constrain the position after an outage introduce a dependency between what should be two independent sensors in the overall system.
FIGURE 10 shows the re-initialization time of the integrator’s position engine when using Sapcorda’s correction service. In this case, the re-initialization time is computed as the time it takes to return to RTK-ambiguity-fixed mode as indicated in the position engine output after an outage. Results based on comparisons against short-baseline RTK positioning showed typical accuracies below 10 centimeters upon re-initialization. In this definition, the time of the outage is included in the overall re-initialization time. In nearly all of the 42 occurrences, the time to re-initialize is less than 10 seconds. This is sufficient to allow an IMU to provide position updates during the GNSS outage.
FIGURE 10. Re-initialization time of the integrator’s position engine enabled by Sapcorda’s correction service. (Image: Sapcorda)
SYSTEM DESIGN CONSIDERATIONS
In addition to understanding GNSS error sources and performance, it is also important to consider the integrity of the entire system. This includes software development processes, hardware selection, data communication standards and security.
Software Design
Aspects needing to be addressed include:
Software Coding Standards. As software is used more and more in safety-critical scenarios, standards have been developed to minimize common errors and failures. Some standards relevant for safety-critical applications development include International Organization for Standardization (ISO) standard 26262 and Motor Industry Software Reliability Association (MISRA) C/C++ coding standards. Many of these standards can be automated via the static analysis tools described below.
Functional Safety. The objective of this analysis is to understand the possible failure modes of a system, how likely they are to occur, and how to mitigate their risk. Several methods can be applied for functional safety analysis. One such approach is failure mode effect analysis (FMEA). In general, functional safety analysis is a complex task requiring a wide range of experience and expertise. Understanding how design or feature choices impact overall failure modes is also critical for simplifying the number of cases and overall system complexity.
Test Coverage. Unit tests provide the fundamental verification that a function can perform its expected task. Coverage analysis tools provide insight into which sections, paths and combinations are being tested. Various metrics are possible, including:
statement coverage: measures the number of executable lines of code that are evaluated
branch coverage: measures which code paths are being evaluated (for example, if statements, both true and false must be covered)
modified condition/decision coverage (MC/DC): in addition to checking all branches, all combinations of branches must be considered.
The degree of effort to meet target coverage metrics greatly varies based on the type of metric chosen.
Code Quality Metrics. Code quality metrics attempt to reduce the complexity of functions and methods in the software. Code quality metrics may include:
cyclomatic complexity scores
establishing the maximum number of control statements within a function
establishing the maximum number of lines or methods called within a single function.
Static Analysis. Static code analysis provides an examination of source code prior to execution. It can detect common implementation issues such as divide-by-zero errors, bounds overrun, poorly defined loops or control statements, among others. Most commercial products provide support for MISRA C/C++ guidelines and other best practices for safety-critical applications.
Automated Testing. Test automation is critical for monitoring performance changes and ensuring high-quality code changes. Critical scenarios such as leap-second changes, week rollovers and ephemeris failures can be logged and then used as part of the automated test plan. And, as bugs emerge, adding additional test scenarios for these is also beneficial.
Data Communication Protocol
One must also consider several aspects related to the transmission of the correction service to users.
Open Source. A standardization of an open-source data communication protocol for mass-market applications allows for a receiving system to employ multiple corrections from more than a single specific provider without requiring independent functional safety requirements. This can provide a much higher level of redundancy than is possible when depending on only a single service provider.
Integrity and Functional Safety. To properly quantify the protection level, it is necessary to provide quality information about the corrections being provided by the service. Employing “do not use” flags ensures users drop satellites that may be unhealthy or performing poorly. General system status messages identifying the cause of a failure are also critical for proper separation of issues between server and recipient.
Encryption and Anti-Spoofing. As the use of GNSS expands, the threat of spoofing has become more significant. Data message encryption must be robust and resilient to protect the user of the data against external threats.
Self-Contained and Repeatable. Replication of events is important for safety-critical applications. A message format used for such applications should be self-contained and not rely on any external sources for factors such as initialization or the expansion of data. This may include the expansion of time-tagged data, or limiting the expansion of ephemeris to a specific Issue of Data Ephemeris (IODE).
SUMMARY
High-precision GNSS correction services for applications requiring both accuracy and integrity will continue to grow. To meet these demands, GNSS correction services that previously focused on accuracy as their primary goal must begin to work toward providing adequate integrity information to provide reliable positions and protection levels. This requires a multidisciplinary approach to achieve an in-depth understanding of GNSS error sources, integrity concepts and functional safety.
End users will benefit from the clear separation of the server and recipient responsibilities and through an open communication standard that facilitates the use of multiple correction service providers and is developed with safety and integrity at its core.
The adoption of formal safety practices, including software development strategies to reduce risk and mitigate errors, is also critical in achieving a reliable and safe high-precision correction service.
ACKNOWLEDGMENT
This article is based on the paper “Integrity for High Accuracy GNSS Correction Services” presented at ION ITM 2019, the 2019 International Technical Meeting of The Institute of Navigation, Reston, Virginia, Jan. 28–31, 2019.
LANDON URQUHART is the R&D engineering manager for Sapcorda Services Inc., with offices in Berlin and Hanover, Germany, and Scottsdale, Arizona, USA. He obtained his M.Sc.E. from the Department of Geodesy and Geomatics Engineering at the University of New Brunswick (UNB), Fredericton, Canada. His research interests are GNSS correction services for mass-market applications.
RODRIGO LEANDRO is the chief technology officer at Sapcorda Services in Scottsdale. He holds a Ph.D. in spatial geodesy from UNB. Dr. Leandro has been active in GNSS R&D for more than 15 years and has served in engineering leadership roles in various companies in the GNSS industry.
PAOLA GONZALEZ is a product engineer at Sapcorda Services and is based in Hanover. She completed her B.Sc. in geodesy at Zulia University in Maracaibo, Venezuela, and her master’s degree in geomatics at Karlsruhe University of Applied Sciences in Karlsruhe, Germany. In the past few years, she has been working in the GNSS industry, focusing mostly on performance analysis, evaluation and verification of different equipment, software and services.
FURTHER READING
• Authors’ Conference Paper
“Integrity for High Accuracy GNSS Correction Services” by L. Urquhart, R. Leandro and P. Gonzalez in Proceedings of ITM 2019, the 2019 International Technical Meeting of The Institute of Navigation, Reston, Virginia, Jan. 28–31, 2019, pp. 543–553, https://doi.org/10.33012/2019.16709.
• GNSS Integrity
“GNSS Position Integrity in Urban Environments: A Review of Literature” by N. Zhu, J. Marais, D. Betaille and M. Berbineau in IEEE Transactions on Intelligent Transportation Systems, Vol. 19, No. 9, September 2018, pp. 2762–2778, doi: 10.1109/TITS.2017.2766768.
“Carrier Phase-based Integrity Monitoring for High-accuracy Positioning” by S. Feng, W. Ochieng, T. Moore, C. Hill and C. Hide in GPS Solutions, Vol. 13, No. 1, January 2009, pp. 13–22, doi: 10.1007/s10291-008-0093-0.
“New Tools for Network RTK Integrity Monitoring” by X. Chen, H. Landau and U. Vollath in Proceedings of ION GPS/GNSS 2003, the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation, Portland, Oregon, Sept. 9–12, 2003, pp. 1355–1360.
“The Integrity of GPS” by R.B. Langley in GPS World, Vol. 10, No. 3, March 1999, pp. 60–63.
• Satellite-Based Augmentation Systems
“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.
“The Stanford – ESA Integrity Diagram: A New Tool for The User Domain SBAS Integrity Assessment” by M. Tossaint, J. Samson, F. Toran, J. Ventura-Traveset, M. Hernandez-Pajares, J.M. Juan, J. Sanz and P. Ramos-Bosch in Navigation, Journal of The Institute of Navigation, Vol. 54, No. 2, Summer 2007, pp. 153–162.
“Validation of the WAAS MOPS Integrity Equation” by T. Walter, A. Hansen and P. Enge in Proceedings of the 55th Annual Meeting, The Institute of Navigation, Cambridge, Massachusetts, June 28–30, 1999, pp. 217–226.
“WAAS MOPS: Practical Examples” by T. Walter in Proceedings of NTM 1999, the 1999 National Technical Meeting of The Institute of Navigation, San Diego, California, Jan. 25–27, 1999, pp. 283–293.
• Jamming and Spoofing
“Interference” by T. Humphreys, Chapter 16 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.
• Ionospheric Threats
“Ionospheric Impact on GNSS Signals” by N. Jakowski, C. Mayer, V. Wilken and M.M. Hoque in Física de la Tierra, Vol. 20, 2008, pp. 11–25.
“Ionospheric Disturbance Indices for RTK and Network RTK Positioning” by L. Wanniger in Proceedings of ION GNSS 2004, the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation, Long Beach, California, Sept. 21–24, 2004, pp. 2489–2854.
Sapcorda Services GmbH has released its SAPA (Safe And Precise Augmentation) Premium GNSS positioning service.
The SAPA service enables mass-market GNSS devices to operate with increased accuracy and reliability across Europe and the continental United States. The service’s technology unlocks advanced performance with instantaneous sub-decimeter position accuracy for devices used in all market applications.
SAPA is delivered using the open industry-recognized SPARTN format, which allows efficiently delivery of the correction data via internet and satellite broadcast. “When using our service, users across Europe and the United States can experience homogeneous, gap-free, advanced positioning performance with any GNSS hardware designed for high precision positioning,” CTO Rodrigo Leandro said.
The SAPA service is tailored for mass-market applications including innovative mobility solutions, IoT applications, and traditional markets such as maritime.
SAPA was designed from ground up to support safety-critical applications such as autonomous driving.
SPARTN (Safe Position Augmentation for Real-Time Navigation) is a high-accuracy, open- and free-to-use GNSS format tailored for broadcast distribution in mass-market applications.
Sapcorda Services GmbH is a GNSS service provider focusing on the emerging high-precision GNSS mass markets. The company has designed its technology and service offering to serve high volume automotive, industrial and consumer markets.
Guest column by Peter Fairhurst, Director, Product Line Management, Product Center Positioning, u-blox
Peter Fairhurst, Director, Product Line Management, Product Center Positioning, u-blox. (Photo: u-blox)
A new generation of GNSS hardware and pioneering new correction data services are enabling cheaper, more compact and truly scalable high-precision GNSS solutions, ready for the mass market.
High-precision GNSS as employed by specialized markets for more than a decade isn’t aren’t suitable for mass-market autonomous vehicles or other mainstream use cases. As well as being big, heavy and expensive, traditional high-precision GNSS systems don’t scale, which is a critical shortcoming when you consider this capability may very soon need to be built into every car that gets built.
To overcome these challenges, we’re seeing two complementary things coming to market: a new generation of GNSS hardware, and pioneering new correction data services. These two key facets combine to enable cheaper, more compact and truly scalable high-precision GNSS solutions, ready for the mass market.
A new generation of GNSS correction service forgoes the two-way link between customer device and the correction data service that is a hallmark of traditional high-precision GNSS corrections. Instead of sending each device its own, location-specific GNSS correction data, the new-generation services create a real-time model of relevant errors across their entire territory. They broadcast this over satellite and/or the Internet for customer devices to pick up.
Transmitting modeled GNSS error data to receivers across an entire region – as opposed to maintaining a two-way link with each and every device – opens the door to large-scale, mass market applications of high-precision GNSS
The shortcomings of traditional high-precision positioning
Correction data has long been key to high-precision GNSS services. In traditional applications, the customer’s positioning device detects its approximate location and sends this information to its correction service provider. This provider uses a network of base stations to monitor GNSS errors, comparing the readings calculated from the satellite signals to the stations’ known, fixed positions. It uses these insights to send the customer’s device tailored correction data, based on its location.
The technology has successfully been used to provide centimeter-level accuracy in surveying, agriculture and machine control, but annual subscriptions of sometimes more than $1000 per device mean it’s remained confined to specialized markets.
Moreover, traditional correction data services typically only operate in one country, or even one state. While this may not be an issue in some applications (such as localized agriculture), there are other use cases where limited range is a major problem. Imagine, for example, that you regularly need to travel across a state or national boundary in your (semi-) autonomous vehicle, or carry out remote UAV-based surveying in another country: maintaining your high-precision positioning capability is likely to mean roaming contracts and other extra costs.
The other issue with these traditional services is scalability. They use two-way cellular communication to pass data back and forth between the customer device and the correction data provider. And while this works when device density is relatively low, if this number grew to thousands or even millions of end-user pieces of kit trying to access the correction data service, current cellular infrastructure would struggle to deliver the required reliability. Particularly in safety-critical applications, where losing access to the correction data service could put lives at risk, this is unacceptable.
Image: u-blox
Recent developments in high-precision positioning
The new generation of GNSS correction services, creating and broadcasting a real-time model of relevant errors across their entire territory, over satellite and/or the internet for customer devices to pick up, opens the door to large-scale, mass-market applications of high-precision GNSS. Technology using State Space Representation (SSR) is one flavor of these new-generation GNSS correction data services.
Japan has led the way in GNSS error-broadcasting, using the L6 signal of its QZSS satellite network as a proving ground for mainstream use of the approach. Although it’s currently only available within Japan, the Centimeter Level Augmentation Service (CLAS) is generating a lot of interest across the automotive, agricultural and machine-control industries. Mitsubishi Electric, for example, used the CLAS service to field-test its autonomous driving system.
In China, Qianxun Spatial Intelligence Inc. is pioneering a different technique. Instead of broadcasting the data, Qianxun SI is leveraging its special access to the Chinese GNSS reference base stations to push the boundaries of what’s possible using the traditional technique. It provides tailored correction data services to customers including individuals, system integrators and original equipment manufacturers (OEMs). While it’s been a success in China, the approach is less appealing to OEMs who ship worldwide, because it requires their clients to arrange their own, local GNSS correction data.
Another important advance has been the rise of multi-band GNSS receivers, which enhance standalone positioning accuracy, thereby delivering a better customer experience in a variety of use cases. However, even multi-band receivers can’t achieve the centimeter-level accuracy that mobile robotics and autonomous vehicles need: these devices will always need to be complemented by some form of correction service.
Continent-wide GNSS correction data
Particularly in Europe, where there’s a lot of cross-border travel and economic activity, the simplicity of continent-wide GNSS correction services would offer enormous value. Sapcorda, for example, a recently launched joint venture between Bosch, Geo++, Mitsubishi Electric and u-blox, is creating a next-generation GNSS correction data service with coverage on a global scale (Europe, North America, etc), building on the lessons learned in Japan.
Sapcorda will broadcast right across the continent, using cellular networks as well as over satellite links. Customers won’t be tied to a specific GNSS manufacturer. Data will be distributed in an open format, so that device-makers can create exactly the solutions their customers want.
Having access to GNSS correction services continent-wide has the potential to transform high-precision positioning into a mainstream offering, supporting various IoT applications, as well as drones and (semi-) autonomous vehicles.
Addressing the remaining challenges
High-precision GNSS correction services that target the mass market are still relatively new, with different suppliers pursuing different business models. Trimble’s service, for example, doesn’t use an open correction-data format, and is only compatible with devices using its own GNSS receivers. The benefit of this is that it can deliver a seamless, fully integrated solution, with complete interoperability across the Trimble product range (provided the region in question has good coverage). OEMs with customers is geographically broader markets will need to weigh this up against the benefits of global coverage provided by a range of correction-data suppliers offering open-format data.
As we touched on earlier, in safety-critical applications where location-accuracy is essential, any correction data service must be up to the task. This includes ensuring data broadcasts aren’t crowded out when cellular networks become saturated. To this end, u-blox has been working with the 3GPP body to create appropriate standards that can ensure the service meets the required service level agreements.
Lastly, although there’s now country-wide coverage in both China and Japan, Sapcorda is now attempting to provide continent-wide high-precision services. If it’s a success, it could overcome the challenges of national boundaries and country-based cellular providers. It’s as yet unclear how existing correction-data-service suppliers will respond.
Customer satisfaction is paramount
For high-precision GNSS services to achieve mainstream success, they not only need to offer wide coverage and be truly open, but must facilitate innovation and ensure they can broaden the appeal of this capability beyond being a niche specialism. Like in any industry, customer satisfaction is essential if the technology is to achieve this.
Complexity that arises as a result of state boundaries, national borders, conflicting regulations or subscriptions, must be shielded from the end user and dealt with upstream. This is already happening in some areas, where device-makers are partnering with correction data service providers, enabling them to bundle the service cost into the device cost that the end user pays.
A revolution in positioning
As well as helping to realize some of the automated navigation solutions currently under development, new-generation high-precision GNSS services are driving a seismic shift across the whole industry.
The rise of innovative, high-precision GNSS technology, combined with business models that promise to make high-precision a mass market reality, mean the coming years will be tremendously exciting. By disrupting the existing market, the new technology will mean lots of new opportunities for those ready to grasp them.
Peter Fairhurst joined the Product Strategy team in the Product Center Positioning at u-blox AG in 2015. He is responsible for the development of industrial markets, with a specific focus on unmanned systems and mapping solutions. Prior to u-blox, he was part of the Product Management group at Leica Geosystems AG, where his focus was on high-precision GNSS surveying technology.
Fairhurst holds a bachelor degree in Mathematics & Computer Sciences and doctorate degree in satellite geodesy from Newcastle University and an MBA diploma from the University of Strathclyde.
Septentrio, a high-precision GNSS company, and Sapcorda, a specialist in GNSS correction services, will conduct a live demonstration of a safe, high-accuracy positioning and correction solution for automated driving.
“We are running the demonstration during the course of this week just south of Las Vegas city center,” Neil Vacans told GPS World. Vacans is Septentrio’s vice president of global Sales. The demonstration is taking place in Las Vegas during the Consumer Electronics Show, being held Jan. 8-11.
Sapcorda and Septentrio have put together a solution that is ready for demonstration in Europe and North America.
The companies have combined their respective technologies to deliver the benefits of SSR (space state representation) technology seamlessly to OEM automakers and Tier 1 integrators. These benefits include decimeter-accuracy within seconds, anywhere over an entire continent, to support autonomy levels from lane keeping to full autonomy in a totally homogeneous coverage, the companies said.
The GNSS augmentation service is scalable through simple broadcast corrections, and safety-awareness is provided via Sapcorda’s integrity concept and Septentrio’s integrity monitoring engine.
In December 2018, Septentrio announced its mosaic compact multi-constellation GNSS receiver SiP (system-in-package) module, available in 2019. The Septentrio mosaic, a multi-band, multi-constellation receiver in a low-power surface-mount module with a wide array of interfaces, is designed for mass-market applications like robotics and autonomous systems. The mosaic module integrates the latest GNSS and RF ASIC technology, as well as the robust positioning engine from Septentrio.
All Septentrio GNSS receivers and modules feature AIM+ technology, an advanced on-board interference mitigation commercially available. Septentrio GNSS receivers can suppress the widest variety of interferers, from simple continuous narrowband signals to the most complex wideband and pulsed jammers.
“We are excited to be able to provide live demonstrations of Sapcorda’s safe and precise correction service especially designed for autonomous driving,” said Jan Van Hees, business development director at Septentrio. “Sapcorda provides a unique high-precision GNSS correction service designed for fast, homogeneous accuracy at continental coverage, thus ideal for autonomous and mass market applications.”
“Septentrio specializes in high-precision and high reliability GNSS positioning for a variety of industrial and commercial markets,” said Goran Jedrejčić, business development manager at Sapcorda. “They have developed a range of technologies, including unique jamming robustness and integrity positioning to support safety-sensitive applications in various challenging environments. Combining this with our safety-centered correction service, it is a unique solution for developers of autonomous driving systems.”
“With fast and efficient implementation of Sapcorda SSR-based correction service into Septentrio’s GNSS-platform, we were able to demonstrate the efficiency of the technology for automotive use in a robust & highly efficient way,” confirmed Jedrejčić. “Septentrio offers a unique blend of GNSS-based technologies and is an ideal partner for both traditional and new markets, with growing demand for high-precision positioning.”
