Choosing between more or less accuracy has never been much of a consideration (or an option), historically.  The specified requirement has predominantly been “The most! Our device requires the most precise accuracy available.” But today, considering the options, it’s fair to ask: how much accuracy does your device or application need, really?

With RTK came the phrase “addiction to accuracy”. Establishing the subsequent adoption of GNSS receivers to commercial applications – 1cm accuracy was achieved. The forecast benefits for agriculture were immediately realized. Successive swaths over crops no longer had overlap or underlap, improving precision while saving time and diesel fuel. Tractor tires and steering could be guided between crop rows, allowing for seeds to be planted closer together, increasing the crop yield. Pest management programs improved with the adoption of spot treatments (over a blanket approach), ultimately saving costs, with the more precise management of expensive pesticides.

GNSS as a utility was then further developed. Depending on the positioning technique that a positioning engine or GNSS receiver used, accuracies were described by horizontal spread in centimeters, and 2cm accuracy became the golden standard, written into the requirements of many applications. But for a pedestrian use case, what is the technical return on investment for accuracy and what is considered overkill? With the technology and infrastructure,  it is arguable to say accuracy worse than 5 meters in most cases is dismissed as being as good as 100 meters.” Instead of asking  how much accuracy is really needed, perhaps a better question would be “How would you use more accuracy?”

Take the classic  GPS experience: “You have arrived at your Destination”, for example. These GPS devices served us well (for the most part), navigating us through unknown neighborhoods and alleviating our minds of recalling the exact order of left and right turns ahead. GPS allowed drivers to concentrate on driving, and getting lost was no longer an excuse for being late. Even if we missed the turn, the friendly voice let us know it was “recalculating” the route, making the navigational transgression solvable on the fly. Spontaneous trips into an unfamiliar city or neighborhood were now made confidently, and comfortably. But on its inception, this GPS technology delivered accuracies of just tens of meters. Arrival was declared a little late or early and, at worst, there may have been some critical moments when notified to make a turn…immediately.  

Tens of meters of accuracy? How were we still successful with this? Well, our built-in human resources were relied on to take care of the finer details of the trip. Once we could see the destination we could simply park or walk over to it. The two positions relative to each other were the vehicles and the locations. Did it matter if the position said we were at the entrance gate even though we still had about 25 steps to get there? Not really. We still got there. 

Then, on the other hand, there’s surveying. Identifying the exact point on the surface of the planet where the corner of a large building should be located brought legal implications with right of way, and boundary disputes between adjacent neighbors. Land ownership was quantified by boundaries established. The Certified Land Surveyor made this boundary physical with an iron property stake driven into the ground within 2.5 centimeters.  With an Iron stake actually being ~ 2.5cm in Diameter, there is little point (pun intended) in 1mm accuracy.

How about lane level accuracy…a term used to describe the accuracy needed for autonomous vehicles and other vehicle tracking applications? The two objects that need to be positioned relative to one another are the car and the lane it’s intended to be traveling in. The average width of a car is 6.5 ft or 2m. The average width of a highway car lane is 12ft, or approximately 4m. To keep this error budget example simple, assume these figures apply to all cars and all roads. Given these parameters we can estimate the car’s position may have a cross-track error of 1m, assuming the GNSS antenna on the car is right in the middle of it. Knowing that we are safely in the lane (need) is different from knowing where we are in the lane or where we are in the car in the lane (could be more of a want than a need).  

In each of the examples discussed here GNSS data corrections may have been needed for the device to compute the required position accuracy. There is a critical level of accuracy that contributes to the intended outcome.  This level is indeed different based on what the positioning is used for.  After this point, the extra accuracy may not be making any other technical contributions to the overall solution. Given that the complexity of the corrections service has a direct impact on accuracy and cost, hopefully this post helps in identifying the right corrections service to be streamed into your receiver.

Dual Frequency GNSS is considered a giant leap forward in the evolution of GNSS technology. It overcomes ranging errors generated in the Ionosphere, where a storm of electrons bend a single frequency line of sight to the satellite, adding length to the range (for the spatial thinker) or delay (for the frequency time thinker). When you observe two frequencies from the same satellite, the difference between their measured behavior and their known theoretical behavior in the vacuum of space  indicates the ranging error being caused by the Ionosphere.

A logical step forward on the path to ruling out Ionospheric ranging errors further is the introduction of a third frequency into the mix. At the time of writing, GNSS hardware manufacturers are betting on triple frequency GNSS technology lending even more clarity to the Ionospheric effect. If economics were not a constraint in building an ideal infrastructure focused solely on supporting absolute positioning performance, a gold standard like octuple GNSS frequencies would make ranging to a satellite through the Ionosphere equally as accurate as ranging to that satellite through a vacuum….Though the challenges of getting all parties to agree on how to accomplish this could dwarf the economic constraints.

But that is not the focus of this blog post…exactly. What about all of the fielded L1-only receivers deployed since GPS hit the commercial mainstream? Does Single Frequency still make sense today?  

Dual and triple frequency GNSS shipments are projected to have double-digit compound annual growth into 2025.  But the vast majority of GNSS Chipsets out there are Single Frequency L1, and dual frequency L1L2 or L1L5. Triple frequency GNSS shipments are a comparative 1.8 % sliver of the more than 2.2 billion Receivers forecasted to ship in 2025.   

Granted, these forecasts were made before the Covid pandemic and the ensuing supply chain instability that continues to plague the manufacturers of all things electronic. Certainly, there is good reason to make the most of what we have in hand now. Namely, the single frequency receiver. So, let’s examine the case for this humble yet widely fielded positioning device.

A single frequency receiver calculating an autonomous single point position can achieve an accuracy of 5m CEP, and DGNSS accuracy 1m CEP.  With PPP corrections supplied to innovative positioning algorithms, 50 cm accuracy can be established easily in under 30 seconds. With RTK Corrections—within 3km of your local base station—2 cm is possible. Comparing these figures to a multi–Frequency receiver, the expected Single point, DGNSS, PPP and RTK accuracies that are achievable are respectively 1.2m, 50 cm, 20 cm and 1 cm (with the part per million RTK baseline not degrading accuracy until you were 40 km away).  There is no question that including more frequencies helps with positioning performance. And with more satellite observations, positioning becomes more robust.

As a caveat to any GNSS performance specification, there is no way to account for every adversity in the environment. Therefore, every manufacturer of GNSS receivers can only post test results obtained in perfect conditions, with no obstructions or reflective surfaces from horizon to horizon, in all directions, using a geodetic grade antenna, and a perfectly tuned RF cable network connected to the receiver.  Testing is repeated and monitored over months to satisfy the savviest in statistical position punditry. 

The critical point here is that across all positioning techniques single frequency receivers also produce better positioning accuracy when fed corrections their positioning algorithms can consume. Obstructions to direct line of sight affect all receivers, regardless of frequency capabilities, and are mitigated with the ability to track more constellations, increasing the probability of a satellite tracking in a direct line of sight. While justifiable for some applications and even negligible to implement multi frequency, a good bet for products with integrated single frequency receivers could be an update to their firmware for better positioning by connecting to the best corrections possible.  

If the humble single frequency GNSS receivers out there can consume corrections and can be connected to the internet, there is still positioning performance to be realized.  Should your product or service fall within this category, please contact us for an expert consultation on how Rx Networks’ assistance data services can boost the performance of your current positioning engine.

During the CES 2021 keynote, Verizon CEO Hans Vestberg discussed the eight currencies of Verizon’s 5G network vision.  He touched on throughput and service deployment, mobility and connected devices, latency and data volume, and energy efficiency and reliability. This list struck a chord with Rx Networks. In the world of GNSS corrections there are many parallels and, considering that devices now require location awareness, they need corrections to achieve that awareness. Therefore, it begs the question: What are the currencies of GNSS corrections?

Accuracy potential

On the data sheet of most if not all GNSS receivers, accuracy specifications are listed for the different types of corrections streams that can be served to the receiver.  The single point, or autonomous no correction solution, is roughly 1m and improves with a corresponding correction type, implying that every GNSS receiver needs to have corrections to achieve its true accuracy potential.  Accuracy is really up to how the correction is applied in the positioning engine, whether it be in the cloud, edge or onboard, calculating a latitude Longitude and height. The receiver needs to be connected to a correction source.

Convergence time

This currency is two dimensional, as it refers to an acceptable accuracy within a certain amount of time.  The extremities of these two dimensions go from having a very inaccurate position instantly to converging to 1cm solution in hours.  As a note RTK does solve the negatives of both of these extremes, but scalability then becomes an issue. (More on that later.) For now time and accuracy are a trade off, sacrificing one for the other.

Bandwidth constraints

Two main points here. First, corrections need to be delivered through telecommunications equipment and, secondly, very few devices have unlimited connectivity and computing horsepower to process corrections. For some applications, the complete corrections package is broken up into the essentials for the application to ensure delivery. A complete corrections package will cover every conceivable source of error when determining the distance between a GNSS antenna and satellite. Innovations in satellite tracking, GNSS signal integrity and the growing number of constellations put further pressure on telecommunications throughput to deliver this growing package of corrections and assistance data.

Coverage, Reference Network Density and Scalability

This currency is all about the number of receivers in any given area being served the corrections they require. In the smallest network case, a surveyor GNSS RTK base station has a dedicated radio modem connection to a rover, where the distance between the two is never greater than 3km in order to achieve a 1cm accurate position. Here’s where scalability enters the equation. While this network case achieves accuracy instantly, it becomes the antithesis of scalability just as quickly. With the rapidly growing number of users needing accurate positioning, there is a requirement for these GNSS reference networks to become denser over an area. The more dense the network, the better accuracy you will achieve when locating within the proximity of that reference station network.

Compatibility

The diversity of applications along the location dimension are growing exponentially. With diversity comes integration and transformation work to deliver the applied location solution to market. Proprietary formats may add extra value above the traditional universal corrections formats and further benefits can be experienced when served into a receiver and/or positioning engine.

Reliability

Reliability is most simply defined as being there the moment you need it. This is particularly important in a deployed scenario where redundancy, response time, and resilience are key pillars of reliability.  As the saying goes, two is one and one is none, alluding to the criticality of relying on a single system. Resilience refers to the network’s ability to continually deliver through adverse events. Response and repair time for when the system goes through an unforeseen adversity. And 99.999% is the typical requirement for carrier grade service level agreements, where penalties are often stipulated for failure to deliver.

Every positioning application will determine some corrections currencies to be more valuable than others. It is a matter of finding balance for those applications. When evaluating a corrections provider, identifying a demonstrable track record and their protocols for delivering on the corrections currencies discussed here would make for a great start to a thorough review.

Today the GSA and Rx Networks Inc., a leading mobile location technology and services company, announced the results of tests conducted by the company measuring the performance of Galileo when used in various combinations with GPS and GLONASS.

Tests were conducted in real-world environments, including urban canyons and indoors. These environments pose significant challenges to location accuracy due to multipath and obstructed views of satellites. Each test consisted of a three-hour data capture of GNSS signals, which was later replayed to produce hundreds of fixes using a multi-constellation GNSS receiver from STMicroelectronics.

The results showed that using Galileo with one or more other GNSS constellations provides significantly more accurate location fixes compared to GPS alone, when indoors or in urban canyons. As expected, the GPS+Galileo combination did not exceed the performance of GPS+GLONASS, due primarily to there only being four Galileo satellites available at the time of the testing. It is expected that, as more Galileo satellites are launched, the combination of Galileo with GPS will show further improvements in performance.

Timely Results

With the European Commission evaluating the mandate of GNSS location on mobile phones for emergency calling purposes, the test results demonstrate the benefit of including Galileo. According to Gian Gherado Calini, Head of Market Development at the GSA, “Dual-constellation GNSS designs are the standard for many smartphones and other devices. The combination of GPS and Galileo provides a robust solution and is expected to offer performance that will meet or exceed end-user expectations.”

Adrian Stimpson, Senior Vice-President of Sales and Marketing, Rx Networks said, “The results should be encouraging to any GNSS chipset manufacturer who is considering adding Galileo as a competitive differentiator.”

TEST RESULTS 
Recent test results confirm that Galileo significantly improves accuracy in challenging environments:

The tables above show the summary results for various scenarios and constellation combinations. The GPS row shows the absolute 2D errors in meters. All other rows show the improvement (+) or degradation (-) in meters and percentages relative to GPS-only fixes. All measurements are within the 95th percentile.[/caption]

About the European GNSS Agency www.gsa.europa.eu 
As an official European Union Regulatory Agency, the European GNSS Agency (GSA) manages public interests related to European GNSS programmes. The Agency’s strategic objectives include the achievement of a fully operational GALILEO system. This includes the laying of foundations for a fully sustainable and economically viable system and its security.

About Rx Networks Inc. www.rxnetworks.com 
A mobile positioning technology company, Rx Networks develops hybrid positioning solutions that unify GNSS, Wi-Fi, cellular and sensor signals for an unmatched mobile location user experience outdoors, indoors, and in 3D.

Rx Networks Inc., a leading mobile location technology and services company, today announced it is upgrading its GPStream GRN (Global Reference Network) to include support for the BeiDou and Galileo constellations alongside its well proven GPS and GLONASS assistance services. The upgrade will be completed by the end of this year with commercial service starting in 2014.

With the official release of the Chinese BeiDou specifications in late 2012 and the rollout plans for Galileo, several semiconductor vendors will soon be introducing chipsets capable of supporting these new GNSS (Global Navigation Satellite System) constellations. Multi-constellation devices receiving GNSS assistance data from GPStream GRN will have much greater success in areas where satellite visibility is severely limited, such as urban canyons or indoors.

GPStream GRN is the foundation on which Rx Networks’ and third party real-time and predictive Assisted-GNSS products operate, as used by over 700 million smartphones worldwide. Backed by a 99.999% Service Level Agreement, GPStream GRN is already the proven source of real-time assistance data for most North American mobile operators for their E-911 location platforms.

“Our reference network will be the first to commercially support all four constellations,” said Ryan Reilly, Product Manager, “reaffirming our leadership position on Assisted-GNSS solutions for the mobile market.”

For more information, please see the Rx Networks booth at ION GNSS+ 2013 or contact Rx Networks at sales@rxnetworks.com.

About Rx Networks Inc.

Hybrid Positioning. Indoors. Outdoors. Every “Where”.

Rx Networks is a mobile positioning technology company that develops hybrid positioning and assisted-GPS solutions that unify any available GPS, GLONASS, cell tower or Wi-Fi^® information. These solutions, already licensed by leading GNSS semiconductor vendors, device OEMS, network equipment vendors, and mobile operators, bring instant location awareness and help deliver an unmatched mobile location user experience on any device and for any application. GPStream GRN provides global real-time and long-term prediction GPS/GLONASS reference data for use by any mobile network location server. GPStream PGPS adds GPS and GLONASS extended ephemeris support to increase the sensitivity and acquisition speed of any GNSS chipset, while XYBRID RT and XYBRID SUPL LE combine Wi-Fi/Cell positioning with real-time A-GPS/A-GLONASS support to extend the location performance of GNSS chips in difficult areas, such as indoors or urban cores.

###

Media Contacts

Rx Networks Inc.
Adrian Stimpson
+1.604.699.6161
marketing@rxnetworks.com