Precision Finding on the iPhone

Keeping track of the ultra-wideband revolution

Image credit: Apple

After decades in the lab, big tech has finally found a use for a unique wireless technology.

‘Spring Loaded’ was the phrase Apple used to describe its keynote event back in April. The hour-long video presentation captured the attention of everyone in the tech world, primarily thanks to the unveiling of a much anticipated update to the iMac. But it was another product that Apple revealed that the world has been waiting longer for.

An ‘AirTag’ is the size of a large coin and is designed to expand Apple’s tentacles from their grip on adherents’ phones, watches and computers and into the physical world. Simply put, they are small, coin-sized trackers that let you track the location of physical objects, such as your keys, your luggage, or your cat. They’re not dissimilar to devices made by companies like Tile, which have been on the market for several years, but what makes them interesting is that unlike Tile and other Bluetooth trackers, AirTags are the first real mass-market consumer devices to make use of a different technology: ultra-wideband (UWB).

UWB has now spent a couple of decades on the drawing board, and it is only in the last few years that Apple and other phone makers like Samsung have included UWB chips in their phones, in anticipation of compatible products. Now that the first real mainstream UWB devices are on the market, it’s a good opportunity to ask: what took so long?

What is UWB? Most of the wireless technologies we use today are defined by a very select set of frequencies with a narrow bandwidth in which they operate. All GPS signals, for instance, fit on either 1.57542GHz or 1.2276GHz. The first Wi-Fi devices used the increasingly crowded 2.4GHz spectrum and shared the limited bandwidth with Bluetooth and countless other unregulated wireless devices. Later iterations of Wi-Fi expanded to also use 5GHz and most recently 6GHz, offering more bandwidth.

What makes ultra-wideband so, well, ultra-wide, is the range of frequencies or very wide bandwidth, typically at least 0.5GHz wide but some systems span as wide as 3GHz up to 10GHz giving 7GHz bandwidth. What makes it manageable is that it operates at very low power, and therefore over a very short range.

What makes UWB unique is that unlike the rest of the radio spectrum, UWB does not separate out data using different frequencies (in the way that different radio stations are found on different frequencies). It separates out data using time, splitting signals into pulses that are mere nanoseconds long.

“The nice thing about having so much bandwidth is it can manage interference,” explains Dr Tim Brown, senior lecturer in RF Antennas and Propagation at the University of Surrey, who describes how two devices transmitting might conceivably interfere with each other, but through correction techniques with repeating such fast pulses, error cases can be filtered out. This means that over short distances using low power, data can be transmitted at a much greater rate than the likes of Bluetooth.

The striking thing about UWB is just how long it has been in the lab before it was commercialised. The technology has existed for decades, even as far back as World War Two, when experiments were carried out using UWB frequencies. It was in 2002, when America’s Federal Communications Commission deregulated the UWB spectrum, that the industry first started to take consumer applications seriously.

“They could see that this is something that could be worth deploying because it’s so cheap to make,” says Brown. “It would be brilliant, because you could implement [a UWB] radio into so many different devices.”

This opened the floodgates to scientists and researchers trying to figure out what to do with the available bandwidth. And over the last few decades, scientists have experimented with using it for many different purposes.

For example, one proposal was to use UWB like a radar system that could see through walls, as the signals can more easily penetrate walls than other wireless technologies. Others proposed using UWB like a high-bandwidth version of Bluetooth, which could have been used to connect DVD players with televisions, with the increase in bandwidth obviating the need for any wires.

Brown describes how at one point earlier in his career, he worked on a proof-of-concept egg-box containing a passively activated RFID tag with UWB, which would transmit back the number of eggs still inside.

“There were some really amazing dreams in the industry,” says Brown, “but it obviously didn’t come without controversy.” The concern was that UWB, because it covers such a wide swathe of frequencies, could interfere with existing forms of radio communication. “You’ve got the bottom end of the major radar band around 3GHz, and nobody’s really allowed to go near that frequency because you don’t want to be duffing up aircraft radar,” says Brown.

Similarly, there were concerns that UWB could interfere with the frequencies used for satellite uplinks. So ultimately, UWB was only ever going to be viable in low-power applications where the risk of interference is low.

The other stumbling block was more bureaucratic. In Brown’s view, it was the inability of the industry and regulators to agree common standards for the technology that ultimately doomed early attempts at commercialisation.

“It was certainly the spectrum availability, that really is where the doomsday started to hit,” says Brown. He describes how while the FCC created a set of rules for the entire band of UWB frequencies, European and British regulators were concerned about interference, and insisted on a smaller ‘spectral mask’ limiting the power of transmissions in sensitive frequencies.

Although UWB devices could conceivably use filters to get around the restrictions, the lack of common agreement was bad for business. “If you couldn’t build ultra-wideband to the same standard in the UK and Europe as in America and the rest of the world, you couldn’t go making a world business with this and export products,” he explains.

In more recent times, interest in UWB has been on the rise again. And one intriguing implementation of the technology could be in medicine.

“Based on what is happening in the human body, the reflections that delay attenuation [can be] measured,” says Dr Mohammad Ghavami, who is head of bioengineering at London South Bank University.

He is currently studying how nanosecond UWB pulses and their reflections can be analysed using machine-learning technology for medical imaging. “We want to replace MRI with a device that is using electric fields instead of magnetic fields,” says Ghavami. “The technology is supposed to be much cheaper, much smaller and much faster.”

At the moment the technology is at a relatively early stage, but the principles behind it are also what has piqued Big Tech’s recent interest.

The new enthusiasm for UWB from the likes of Apple and Samsung appears to stem from an important realisation that harks back to the work from decades earlier. What’s important isn’t whether UWB can be used to transmit communications data, but that the characteristics of the pulses enable devices to measure something other technology can’t: time of flight.

“It’s like a sonar system in a submarine,” says Leo Scott Smith, CEO of wearables start-up Tended. “It effectively fires out a signal and then it times how long it takes for that signal to come back, and then off the back of that it can work out the reasonably accurate distance of how far away that device is.”

Because UWB pulses are so frequent – down to the nanosecond – and can travel through different materials with relative ease, it means that UWB devices can locate each other with a high degree of accuracy, down to the nearest few centimetres. “It’s effectively like an indoor version of a high-precision GPS,” says Smith.

This is the idea at the heart of Apple’s AirTags. The intention is that you hook a tag on to your keys, and then an app on your phone can guide you to exactly where they have fallen down the back of the sofa, with an on-screen arrow pointing in the exact direction.
Though other Bluetooth trackers have offered similar features in the past, ultimately the laws of physics limit their accuracy, and apps can only estimate distance based on the number of decibels of signal strength. A lot of environmental factors can affect this.
“If you have a person in front of the Bluetooth signal, because humans are basically big bags of water, it means that it will put your accuracy out by five or 10 metres,” says Smith.

Using UWB for location isn’t just something that Big Tech is doing. Smith’s company, Tended, is using UWB chips in wearable wristbands it has developed for industrial spaces, to solve the problem of keeping workplaces safe while social distancing.
“We are monitoring the distance between two employees and alerting them if they come within a pre-set distance that can be set by the employer,” explains Smith. “And then we are also monitoring the time that they spend exposed within that pre-set distance.”

It means that on a factory floor, if two people come in close proximity, the wearables will play an alert and log a close-contact event, which can later be used for contact tracing. The crucial advantage is that unlike other technologies, deploying Tended’s UWB sensors does not require additional positioning equipment to be deployed on a given site.

“Because of the inaccuracy that comes with Bluetooth, and the high power, and large infrastructure that comes with things like RFID, ultra-wideband was one of the only things that was suitable,” says Smith.

Tended was not the only company to see the value in UWB for monitoring social distancing. In fact, Smith says that because of the huge increase in demand, it actually became quite difficult for his company to get hold of UWB components.

Smith also argues that even when the world goes back to normal, there will still be a huge demand for UWB for applications like navigating autonomous robots around factories and other indoor locations.

“Certainly, for low-power devices and Internet of Things (IoT) connectivity, ultra-wideband still could be very useful,” says Brown. “It may not need to go over a very particular long range, and therefore the spectral mask and restrictions will not be as big of a problem for them.”

So with tracking tags, as well as emerging industrial and medical uses of AirTags, it appears that we could be at the dawn of a new era for ultra-wideband. The biggest indication is, of course, Apple and Samsung backing the technology. The iPhone 11, released in 2019, and every iPhone since contains a UWB chip, and last year Samsung’s Note 20 became the first Android device to include the technology, too.

“I think if I’m honest, for smartphones, that the reason ultra-wideband is being added in is because they’ve reached a level of technical limitations with everything else that they have in smartphones,” laughs Smith.

Even if we were to imagine that Apple and Samsung are that cynical, we could still be at a UWB tipping point, and Big Tech’s demand for chips will drive manufacturing.

“When UWB is normalised by Apple and Samsung and things which will happen over the coming years, I think that the cost will come down,” says Smith, pointing to a current constraint being the cost of UWB chips, which are around four or five dollars each at the moment, compared to fifty cents for a Bluetooth chip. But as manufacturing scales and the costs fall, the UWB eco-system will grow. “You’ll get to the position where every high-value asset might have one of the tags on them,” says Smith.

Are we – finally – on the verge of a UWB revolution? Now that Big Tech is on board, UWB might just be ‘spring loaded’ and ready to go.

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