UWB Enables Secure Ranging and Precision – An Introduction to the Technology and How it Works
By Adam SmithOctober 6, 2020
LitePoint’s Adam Smith has developed this three-part blog series on Ultra-Wideband (UWB) technology and testing challenges. Throughout the series of blog posts, you’ll learn the basics of UWB and how it works, which applications UWB is best suited for and what testing solutions LitePoint has available for UWB and how the company is working with the FiRa Consortium.
UWB enables secure ranging and precision and is buzzing in the industry as one of the latest technologies to be incorporated in the next generation of smartphones and other devices, but in reality, the technology is not new.
UWB is actually one of the oldest wireless technologies. In fact, Marconi used UWB to transmit Morse code across the Atlantic Ocean in 1901 with a UWB signal using a spark gap radio transmitter. This would be classified as a very low speed data transmission, but technically speaking, it was using a UWB signal. Then in the 1960s, UWB was used in military radar and is a large part of how radar works today in terms of detecting distance and direction.
In 2002, the FCC approved UWB for consumer / commercial applications. The IEEE standardized 802.15.3 moving to 802.15.4, which is typically what we are referring to when we talk about UWB today. There was a consortium called the Wi-Media Alliance in the early 2000s that branded UWB as a high-speed data transmission technology, actually as a wireless replacement for wired USB. The alliance thought its standard could provide the same high-speed, short distance technology that would get rid of the USB wire. That being said, the alliance was also doing this at a time where Wi-Fi was competing for the same exact application.
Wi-Fi won that battle and UWB went by the wayside – until now.
UWB returned in 2019, updated with the 802.15.4z IEEE standard, rebranded as a technology used for accurate ranging and positioning. When we think of UWB today, we’re no longer talking about high speed data communication, but rather position tracking, distance and direction finding.
How it Works
UWB provides better security against bad actors looking to do bad things. This is because UWB is used to authenticate a user based on location in a very secure way. If you look at some of the other technologies available today, Bluetooth®, for example, uses signal strength (RSSI) to determine range. That signal strength is easy to intercept and hack. UWB however, uses what is called time-of-flight (ToF) to determine position, adding a new layer of security. It is very difficult to “fake” time and UWB’s wide frequency bandwidth is extremely immune to interference.
So how is UWB actually used for ranging? The first requirement is to measure distance using ToF. This requires a “tag” device and an “anchor” device. The tag sends out a polling signal, which is colloquially referred to as a “ping.” And then the anchor receives that signal. There’s a known delay in that anchor and after that known delay, it sends that signal back out as a response to the tag. This is referred to as a “pong.”
The anchor then receives that signal, and based on the delay that’s encoded in that waveform and the time that it measures between when it sent the signal and when it received it, the anchor can calculate distance using time multiplied by the speed of light. This is referred to as single-sided, two-way ranging using the ping-pong methodology.
Additionally (and optionally), the tag can send a secondary polling signal back to the anchor again, another ping. What this allows is both sides of the ranging to coordinate and check each other’s value. This is referred to as double-sided, two-way ranging, or ping-pong-ping. With the double-sided, two-way ranging, UWB can actually have the two devices check each other to make sure that they’re measuring the same distance. It is a little bit more accurate and a bit more secure.
Now that the system has measured distance it now needs to determine location. One way to do this is to actually have multiple receivers in the environment. Pulling from a GPS analogy, if there is one receiver, you know that the location is somewhere on a sphere – it’s somewhere on the radius from where that receiver is receiving that signal.
If there are two receivers in the environment, the signal can be narrowed to a circle where the two spheres intersect. If there are three receivers in the environment, the actual point in space can be determined. And then with a fourth receiver, the system can get to an exact location. So, in an environment where a single intended device is existing, if there are at least four receivers in the environment, we can tell the exact 3D location in space of where the transmitter is located.
Rather than using triangulation, an alternative methodology called angle of arrival (AoA) is more like how a RADAR dish works. Here the receiver actually needs to have multiple antennas. In the triangulation method, receivers can have single antennas, but here, what we’re actually looking to do is look at very small phase differences of when the signal is received so that it can, through signal processing, determine which angle the signal is coming from.
Having calculated the time of flight, UWB knows the distance. Having calculated the angle of arrival, UWB knows the direction. By combining those two, UWB can determine the exact position with time of flight and angle of arrival. By performing this operation multiple times, UWB can then determine the speed and direction of travel.
In the next post, we’ll explore some of the applications that UWB is best suited for, as well as how UWB compares to other technologies. In the meantime, please visit the replay of my webinar on this topic.
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