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Ultra-Precise GPS could Unleash a Robot Revolution

Ultra-Precise GPS could Unleash a Robot Revolution
Upgrades are boosting the accuracy of the most powerful global satellite positioning systems from several meters to a few centimeters.
Technology Briefing


More than ever, we rely on technologies that can pinpoint an object's position. Precision agriculture, drone delivery, logistics, ride-hailing, and air travel all depend on highly accurate position detection from space. Now a series of deployments and upgrades are boosting the accuracy of the world's most powerful global satellite positioning systems from several meters to a few centimeters. That could mean your phone knows not only which street you're walking or driving down, but which side of the street you're on.

Soon, that kind of resolution could make it possible for self-driving cars, delivery robots, and other "personal services robots" to safely navigate streets and sidewalks. And as technology improves, so does the accuracy of GPS, as represented by a statistical average of the signal-in-space error measured on a single frequency across the GPS constellation.

The Global Positioning System (GPS), one of the world's first such satellite systems, has dramatically changed the way billions of people move around. Since 1993, at least 24 GPS satellites have been orbiting the Earth and constantly broadcasting their positions. Any GPS receiver can find its current whereabouts within seconds by triangulating signals from at least three satellites in the constellation. Once the signals are processed by a receiver, GPS is generally accurate to within five to 10 meters.

Now the system is in the middle of a years-long upgrade to GPS III, which should improve its guaranteed accuracy to between one and three meters. By November 2020, four of the 10 GPS III satellites had launched, with the rest expected to be put into orbit by 2023. Though consumers won't notice it right away, the accuracy of their navigation systems and smartphone tracking apps should improve as a result.

In June 2020, China finished deploying its BeiDou satellite constellation as a GPS alternative. Expanded over two decades' time from a regional to a global network, BeiDou now has 44 satellites operating in three distinct orbits. It provides positioning services to anyone in the world with an average accuracy of 1.5 to two meters. And because of the system's historical focus on China and Asia, BeiDou's regional users can often get close to one meter in precision. Even with these advances, positioning signals encounter interference and other conditions that can make them go awry.

Correcting these errors requires another layer of technology. Therefore, both BeiDou and the U.S. GPS rely heavily on ground- based augmentation to boost positioning accuracy to the centimeter level. One popular approach is real-time kinematic (or RTK) positioning, which uses a base receiver and a rover receiver, placed kilometers apart, to receive satellite signals and calculate the errors caused by Earth's iono-sphere. This technique can achieve accuracies of better than three centimeters.

A similar but newer technology is precise point positioning (or PPP). It requires only one receiver and works from anywhere on the Earth's surface, giving users decimeter- to centimeter-level accuracy. RTK augmentation is relatively mature and new technology called PPP-RTK is under development. This solution which combines the strengths of PPP and RTK will hopefully be put to use a few years from now. And as the accuracy of satellite positioning improves, we'll no doubt find even more ways to use it.

Our ancestors looked to stars and compasses to figure out where they were; today, we use atomic clocks on satellites in orbit to do the same. These positioning technologies have already changed the way we farm, transport goods, and navigate our world; the latest improvements will bring that world into even sharper focus.

As positioning technology advances to the millimeter level and beyond, the limits of its use will be defined more by our creativity and the legal or ethical bounds we set than by the performance of the technology itself. Given this trend, we offer the following forecasts for your consideration.

First, by 2030, traditional satellite-based positioning systems will reach a nearly insurmountable accuracy limit, probably at around the millimeter level. Fortunately, that kind of precision would make it possible for self-driving cars, delivery robots, and other "personal services robots" to safely navigate streets and sidewalks. And when combined with other sorts of optical and sonic sensors, will unleash a torrent of solutions serving human needs.

Second, by the end of the decade, new positioning technologies will be ready to take us beyond the limit, while reducing our reliance on satellites. Obviously, only a few applications require millimeter-level positioning precision, but every solution that relies upon satellites is vulnerable to EMP attacks, kinet attacks on the satellites themselves, and unpredictable solar storms.

One approach uses the quantum properties of matter to locate and navigate without outside references. When atoms are cooled down to just above absolute zero, they reach a quantum state that is particularly sensitive to outside forces. Thus, if we know an object's initial position and can measure the changes in the atoms (with the help of a laser beam), we can calculate the object's movements and find its real-time location. Such a Quantum Positioning System would be particularly useful as a backup navigation technology for self-driving cars.

A very early version of a quantum positioning system, developed by a firm called ColdQuanta, is already operating on the International Space Station. Third, by mid-decade, indoor service robots will be using ambient signals to pinpoint their locations, without regular access to GPS.

Devices such as smartphones, use so-called inertial measurement units (or IMUs) to calculate how far the device has moved. However, IMUs suffer from large "drift errors," meaning that even minor inaccuracies quickly become exaggerated. In outdoor environments, devices typically use GPS to correct their IMUs. But this doesn't work in indoor areas, where GPS signals are unreliable or nonexistent.

Fortunately, NC State researchers recently demonstrated that it is possible for WIFI signals to work in conjunction with a device's IMU to correct any errors and improve the accuracy of speed and distance calculations. That means a robot could reliably track its location indoors whenever a WIFI signal is available.

And, Fourth, well before end of the decade, small, inexpensive, and highly accurate gyroscopes, will enable drones, autonomous cars and service robots to stay on track without a GPS signal. An inertial measurement unit is made up of three accelerometers and three gyroscopes, one for each axis in space. The gyroscopes found in most smartphones detect the orientation of the screen and help figure out which way we're facing, but their accuracy is poor.

Getting a reliable reading on which way we're going with existing IMU technology is so expensive that it has been too costly, even for high-end consumer applications like autonomous automobiles. Fortunately, a new gyroscope developed at the University of Michigan is 10,000 times more accurate, but only 10 times more expensive than gyroscopes used today in a typical cell phone. And it's 1,000 times less expensive than larger gyroscopes with similar performance.

As devices begin using this technology, GPS reliability and precision will become far less important even though autonomous robotics will become ubiquitous and indispensable.


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