ION GNSS+ a playground for high precision

September 22, 2016  - By

Every year, some of the brightest minds and most influential people in the GNSS industry that guide the direction of global GNSS system deployments (GPS, GLONASS, Galileo and BeiDou) and design the most advanced GNSS receivers in the world, gather at the ION GNSS+ conference.

I almost always attend this conference, as it provides a look into what GNSS receiver researchers, designers and program managers are working on that will affect high-precision GNSS performance in the next few years and beyond. ION GNSS+ is a playground for someone like me, who’s knee-deep in high-precision GNSS.

The satellite constellations

GPS is what it is. It’s the most mature and reliable constellation of navigation satellites, period. All of the model IIFs have been launched. The U.S. Air Force launched the balance of them in 24-month flurry that ended in May 2016. The next-generation GPS III satellites aren’t going anywhere soon. It will be at least two years before the first GPS III is launched. Would sooner be better? Of course, but either way won’t have a major impact on high-precision GNSS performance since the constellation is capped at 31 satellites for the foreseeable future.

[View the presentation on GPS provided by the U.S. Air Force.]

GLONASS is in the same boat as GPS. It’s not as reliable as GPS (remember this?), but it has been a valuable service for high-precision GNSS users for many years. GLONASS sats don’t necessarily improve GNSS receiver precision, but they certainly improve productivity by allowing high-precision GNSS users to work in impaired environments where GPS-only receivers aren’t nearly as effective. The GLONASS constellation is mature at 24 satellites (You can monitor it here.) and that’s not changing anytime soon. Much like the U.S. with regards to GPS, Russia is in replenishment mode with GLONASS. It is not a growing constellation.

The following is where the magic starts to happen with high-precision GNSS receivers:

Galileo (Europe) is ramping up: currently nine healthy satellites. From my office in Portland, Oregon, Galileo adds up to four additional satellites using a 10-degree elevation cutoff. Four more Galileo satellites are scheduled to launch in a couple of months (Nov. 17). All four are being sent into orbit on a single Ariane-5 rocket from a spaceport in French Guyana. The European GNSS Agency (GSA) reported it is planning similar launches of four in 2017 and 2018.

BDS or BeiDou (China) is also ramping up. Currently there are 17 healthy satellites, with most flying regional orbits in Asia, as opposed to global orbits. While China generally keeps its BDS plans out of public eye, but I’ve heard BDS officials state, on separate occasions, that a full constellation of 30 satellites providing global coverage will be deployed by 2020.

Following is a satellite visibility chart showing the number of GPS (green), GLONASS (red), Galileo (Blue) and BDS (yellow) that are visible from my office in Portland with a 10-degree elevation cutoff.

gnss-planning-gss-eric

As you can see above, a four constellation configuration is starting to become interesting with Galileo and BDS contributing up to 7 additional satellites. In a clear sky environment, this may not be substantial; however, in an impaired environment (e.g. around trees, buildings, terrain), a few additional satellites can make the difference between staying productive or work stoppage. Even further, imagine four years from now when Galileo and BDS constellations are fully operational. In that scenario, there will be upwards of 35 satellites in view. Even before then, like two months from now when four more Galileo satellites are launched, each new satellite in orbit will add a marginal increase in GNSS receiver performance if your receiver is designed to track and use Galileo satellites.

Is more better? Almost certainly. If nothing else, it gives the GNSS receiver more signals to choose from and a lot of redundancy. This is especially true with RTK (real-time centimeter positioning), which is a satellite-hungry technology. RTK is easy in the wide open sky. It’s not so easy in residential areas with lots of trees, areas of rugged terrain and urban areas. More satellites doesn’t mean you’ll enjoy ubiquitous RTK precision in all environments, but it will translate into greater productivity, at the centimeter level, than what is possible today. Will productivity increase 10 percent or 50 percent — or more? That’s the only question.

Another high-precision GNSS technology that was discussed at length, and during several sessions, was Precise Point Positioning (PPP). There were quite a few technical papers and discussion panels on this technology. Real-time PPP services are commercial satellite subscription services like StarFire (Deere), RTX (Trimble), Atlas (Hemisphere) and Terrastar (Veripos). These services rely on a very sparse network of GNSS base stations to compute precise clock/orbit values then deliver them to the user via satellite or internet. The upside is that a dense network of GNSS base stations is not needed like with RTK; however, the downside is that high-precision PPP requires quite a bit of time to convergence to the desired precision (e.g. 10 centimeters). This can be as little as five minutes or as long as 30 minutes or more. This is acceptable in industries like agriculture where there is a clear view of the sky and the farmer only needs to wait for convergence one time in the morning. But, in environments where there are trees, buildings and rugged terrain, PPP convergence gets interrupted many times per day and to a point where it kills productivity. More time is spent waiting for convergence than working.

RTK fares much better in this environment. Yes, it will lose initialization in those environments, but it only takes a few seconds to re-initialize. From a productivity standpoint, I don’t get it. Real-time PPP is a step backwards from RTK. But, who says it has to be one or the other?

RTK’s greatest weakness is the requirement for consistent data connection to an RTK base or network of RTK base stations. By consistent, I mean that every second counts, without a hiccup. Wireless connectivity (like a cell phone network) is the most common RTK communication technology.  Everyone with a cell phone knows that cell coverage can be spotty in certain geographic areas — even densely-populated ones. This is the Achilles heel of RTK, and where real-time PPP, delivered by satellite, can help. Some of the commercial services like RTX, Starfire and Atlas offer a type of hybrid RTK/PPP solution to optimize productivity. When RTK quits working, real-time PPP takes over until RTK returns. Organizations love tools that increase productivity, and this is a powerful combination.

Lastly, I can’t leave you without mentioning a presentation from Broadcom that I attended. Broadcom makes the GNSS chipsets used by Apple and Samsung in their smartphones. It’s crazy to think that Apple and Samsung pay under US$1 for each powerful GNSS chip used in smartphones. The challenge for Broadcom is that GNSS chips have become a commodity, so it’s a race to the bottom when competition starts to separate based largely on price.

To that end, Broadcom is testing a dual frequency L1-E1/L5-E5 GNSS chipset. They aren’t talking RTK … yet. But, they did present some preliminary results showing an increase in accuracy (by four times) over the single frequency GNSS chips being used in smartphones today. Take a look at the following slide.

rtk-broadcom-gss

u-blox, a company based in Switzerland, has developed a similar product, and presented it in a technical session at ION: a consumer-grade chip that does L1 RTK. They are initially looking at UAV use, but this could have many other applications as well. For details and performance data, see the cover story of the October issue of GPS World magazine, out soon.

It’s pretty clear that it’s only a matter of time before high-precision GNSS technology makes it way into mainstream smartphones. It may be another ten years or less, but it will happen. Why?

The answer is the same reason that people dream of ascending Mt. Everest.

Because it’s there.

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This article is tagged with and posted in GNSS/GPS, GSS Monthly, Opinions
Eric Gakstatter

About the Author:

Eric Gakstatter has been involved in the GPS/GNSS industry for more than 20 years. For 10 years, he held several product management positions in the GPS/GNSS industry, managing the development of several medium- and high-precision GNSS products along with associated data-collection and post-processing software. Since 2000, he's been a power user of GPS/GNSS technology as well as a consultant with capital management companies; federal, state and local government agencies; and private companies on the application and/or development of GPS technology. Since 2006, he's been a contributing editor to GPS World magazine and the Geospatial Solutions website. He is the editor of Geospatial Solutions Monthly, a weekly newsletter focused on geospatial technologies. Follow Eric on Twitter at @GPSGIS_Eric.

2 Comments on "ION GNSS+ a playground for high precision"

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  1. Thanks for all,
    please more articles on the subject.