The tremendous benefits of having four complete GNSS constellations
In 2020, with the completion of China’s BeiDou-3 (aka BDS) and Europe’s Galileo, the number of available global navigation satellite system (GNSS) constellations doubled.
Analogously to the addition of GLONASS to GPS a quarter century earlier, but much more so, this sharp increase in the number of available satellites and frequencies greatly improved the precision of satellite-based positioning, the speed of first fix, and the confidence in the results — especially in GNSS-challenged places, such as under thick canopy and in deep urban canyons.
Additionally, this new ability to track three or four GNSS constellations makes the overall positioning solution more resilient to malicious RF interference (jamming and spoofing), to accidental GNSS service disruptions such as Galileo’s one-week service outage in July 2019, and to deliberate withholding of service such as might occur in times of war.
While all this may make little practical difference to a driver needing to know which highway exit to take or to a pedestrian looking for the nearest pharmacy, it is very valuable in high-end applications, such as surveying and construction. In fact, surveyors who have transitioned to using all the available constellations are ecstatic.
This month’s cover story, on the benefits of having four complete GNSS constellations, is in two parts. First, Oliver Montenbruck and Peter Steigenberger discuss “the practical relevance and implications of having four GNSS in parallel for both mass-market and high-end users.” Next, I present the comments of three surveyors and a receiver manufacturer:
- Gavin Schrock, PLS, is a practicing land surveyor, the operator of a cooperative real-time GNSS network in Washington state, and a technology writer
- James Richards is the senior land and utility surveyor at Benchmark Surveys in Venny Bridge, UK
- Choice Sterling is the survey manager at Kiewit Corporation in Federal Way, Washington
- Xiaohua Wen is the CEO and founder of Tersus GNSS, a manufacturer of GNSS surveying receivers based in Australia.
(Satellites from left) GPS: In July 1995, GPS achieved full operational capability (FOC). GLONASS: In December 1995, the (then) Soviet system achieved FOC. BeiDou: On June 23, 2020, China launched the final satellite of the BeiDou-3 constellation. Galileo: The constellation has 21 usable satellites.(Credit: Satellites from public sources; background image: NASA/Chaykovsky Igor/Shutterstock.com)
See also
GNSS today: A four-leaf clover, b
How land surveyors grapple with rapid evolution, discussion with surveyor Gavin Schrock
Thoughts from surveying experts
James Richards
Senior Land and Utility surveyor
Benchmark Surveys, Venny Bridge, UK
James Richards, Benchmark Surveys
What kinds of surveying projects do you run?
We run many different types of surveying projects. From small single-story bungalow extensions and redevelopment to development of new home sites of several hundred acres. We cover land, underground utility, and measured-building surveys of any size project, using the latest equipment in total stations, laser scanners, drones, GPS receivers, ground-penetrating radar (GPR) and electromagnetic location (EML).
How have you transitioned to using multiple constellations?
Ordnance Survey benchmarks in the UK are no longer maintained. Therefore, it has been a must to move forward with the surveying world and use multi-constellation GNSS equipment. We have stayed at the forefront of GNSS receivers, starting with a Topcon GRS1 then moving onto a Trimble R10 and a Topcon HiPer SR. Now, I feel we’ve taken another leap with the Trimble R12i, working in areas where we previously did not even consider using a GNSS receiver.
How does the availability of four complete GNSS constellations, plus two regional ones, benefit your work?
The availability of four complete GNSS constellations and two regional ones gives us more reliability as well as improved position and time accuracy in the data that we receive. It also gives us better coverage over the entire UK, including near buildings and under foliage. The Trimble R12i has 672 available channels, which makes it future-proof to new frequencies and additional space vehicles.
Choice Sterling
Survey manager, Kiewit Corporation
Federal Way, Washington
What kinds of surveying projects do you run?
I am the survey manager on $1–3 billion mega projects, ranging from bridges and highways to tunnels and rail, including a couple of projects for the U.S. Department of Defense.
How have you transitioned to using multiple constellations?
The use of multiple constellations became available as we adopted technologies that could capitalize on their availability. Through the latest hardware and software, we have begun leveraging GNSS to a greater magnitude than we would have just a few years back.
How does the availability of four complete GNSS constellations, plus two regional ones, benefit your work?
Not long ago, the use of GPS for construction staking was an extremely risky proposition given its unreliability, primarily in the vertical component, and lack of confidence in its horizontal accuracy. With residuals exceeding most construction tolerances, GPS was primarily utilized for earthwork or to establish geodetic pairs that could then be traversed to establish control for more precise work. With the utilization of multiple GNSS constellations, we have gained confidence in the accuracy of our results and have started leveraging GPS for construction staking where we were once not willing to take the risk.
Having the ability to leverage GPS under a canopy of trees or against structures or walls has proved invaluable when running traverses or levels, typically enabling us to use a single person rather than a two-person crew. Increased confidence in repeatability and accuracy while using GPS has been a game changer when working on projects where efficiency and cost management are of the greatest importance.
Xiaohua Wen
CEO and Founder, Tersus GNSS
Xiaohua Wen, Tersus GNSS
How have you transitioned to manufacturing multiple-constellation GNSS receivers?
Early in 2016, we produced a GNSS receiver evolution road map to take advantage of GPS/GLONASS modernization, the continuing development of Galileo and QZSS, and the completion of BeiDou-3. In 2019, we released our current GNSS receiver, which has 576 tracking channels and supports all five major GNSS constellations (GPS, GLONASS, Galileo, BeiDou-3 and QZSS) and triple-band broadcasts (GPS L1+L2C+L2P+L5, GLO G1+G2+G3, GAL E1+E5a+E5b, BDS B1+B2a+B2b and QZSS L1+L2C+L5). We expect to release our next generation receiver, with 832 channels, in February 2022. It will support all available constellations (GPS, GLO, GAL, BDS, QZSS, IRNSS/NavIC, SBAS) and all civil signals, including the AltBoc and AceBoc.
How does the availability of four complete GNSS constellations, plus two regional ones, benefit your end users?
The most significant advantage of modern GNSS receivers is their robust high-accuracy performance with the aiding of the new constellations and signals, especially in harsh GNSS environments, such as deep canyons and heavy foliage. It greatly extended the RTK fix capability, and now reliable GNSS RTK fix solutions can be easily achieved in areas where it was impossible to do in the past.
In the past, multipath always has been a problem for RTK GNSS receivers, as it might cause blunder errors. The improved RTK fix reliability based on robust RTK integrity monitoring takes advantage of the redundancy of observations to identify and isolate deteriorated observations and confirm the fixed result. Additionally, RTK achieves RTK fix solutions faster and maintains the RTK fix solutions easier with better accuracy than before.
Compared to the dual-band (L1+L2) of GPS plus GLONASS, the triple-band (and multi-band) can allow long-range RTK capability, which can provide reliable RTK solutions with a remote GNSS base station far from the 20–30 km base and rover separation of the past. It also will provide more confidence in RTK positioning during the coming ionospheric disturbance peak in 2023.