Take the example of a spatially aware door lock. The lock – installed on a car door, a warehouse entryway, or your front door – can sense the approach of the smartphone you’re carrying and automatically unlock when you’re near enough to enter. Similarly, when you leave, the lock can sense your departure and automatically relock when you’re far enough away to indicate that you’ve made your exit.
Another way that spatial awareness can be helpful to us humans is finding things that we’ve misplaced. You tag your wallet, your glasses, or your remote control with a small tracking device, and the next time you can’t find it, your smartphone can use its spatial awareness to locate the item and guide you to it. Your smartphone can even present an on-screen image, with an augmented-reality view, that guides you to your lost object.
Interacting with spatially aware devices is intended to be easy and intuitive, but designing the human-machine experience to support spatial awareness can be fairly challenging, since there are a number of steps involved. Also, developers have found that using two distinct wireless technologies – Bluetooth Low Energy and Ultra Wideband – creates an enhanced solution for spatial awareness.
The Bluetooth Low Energy (BLE) part of the design provides a low-power way to identify the presence of other devices, using passive proximity detection. The Ultra Wideband (UWB) part of the design provides precise localization, based on wideband ranging, to detect small changes in distance and direction of movement. Having detected a nearby object, the BLE side of the design triggers the UWB side, and uses the data generated by UWB to communicate location and direction of movement to the human-machine interface.
Getting these interactions between BLE, UWB, and the human-machine interface can be tricky. It involves complex embedded algorithms and an intricate RF design. Also, the end product needs to be thoroughly tested, to ensure that the two wireless technologies work seamlessly together.
Here’s a closer look at what developers have to consider when working with spatial awareness.
BLE for Proximity Sensing and Communication
Bluetooth is a logical choice for IoT devices, since it’s so widely used. According to the 2021 Market Update of the Bluetooth Special Interest Group (SIG), the standards organization that oversees Bluetooth specifications and licensing, an estimated 13 billion Bluetooth-enabled IoT devices are already in use. The Bluetooth SIG has played an important role in BLE’s success, since they not only define the communication protocol but also enforce compliance with the protocol through their certification program. The results is that BLE is both everywhere and universally interoperable. Developers can be certain that their BLE-enabled devices will be able to communicate with the other BLE-enabled devices they encounter, without forcing their end users to fuss over things like device settings and configuration.
Interoperability makes BLE an excellent choice for short-range data transfer between two points. In an application that uses spatial awareness, that means BLE can be used for configuration, link negotiation, and communication human-machine interfaces.
BLE can also be used for localization, but isn’t as precise as UWB in terms of where, exactly, an item is. BLE calculates distance using a technique called Received Signal Strength Indicator, or RSSI. This is the same technique used by other protocols commonly used for localization, including Wi-Fi. RSSI measures uses signal strength to indicate distance, based on the idea that a stronger signal is a closer signal, but the approach is more susceptible to issues like RF interference and human-body obstructions. If the application needs a level of spatial awareness that’s beyond BLE, that’s where UWB comes into play.
UWB for Pinpoint Accuracy
Recently defined by the IEEE in 802.15.4a/z, UWB is a wireless standard that delivers more precise readings than any other location technology current in use, including BLE (and Wi-Fi). Using Time-of-Flight (ToF) and Angle-of-Arrival (AoA) calculations, UWB can accurately determine location to within +/-10cm.
The latest version of UWB builds on military applications for radar. It’s different from other wireless protocols in that it uses pulse signals that are as short as 2ns. Also, instead of using a narrow band in the more electrically crowded 2.4 GHz spectrum where BLE, Wi-Fi, and a few proprietary solutions operate, UWB uses a wide band of 500 MHz in the 6-8 GHz spectrum.
The unique structure of UWB means it performs secure ranging with pinpoint accuracy, while using very little power to send signals and providing very stable connectivity, with little to no interference, even in challenging RF environments.
A Winning Combination
A wide range of use cases, spanning smart home, automotive, consumer, and industrial, benefit from the combination of BLE and UWB for localization.
Returning to the example of the door lock, and a car door that unlocks as you approach it, BLE and UWB deliver an optimal experience. BLE can perform initial discovery at the outer bounds of proximity, and can then coordinate with multiple anchor points placed around the car’s body to activate UWB ranging. The newly activated UWB anchors can detect the corresponding UWB radio in your smartphone. Using coordinated ToF and AoA measurements, these UWB radios can ensure highly accurate distance measurement.
A similar handoff between BLE and UWB happens in item trackers. Small, battery-powered tags are attached to bags, car keys, the collar around your pet’s neck, or whatever else you might tend to lose. BLE associates the tracker to your phone. Pairing the two BLE endpoints enables encrypted BLE communication, to ensure privacy. Later, when you can’t find what you’re looking for, you use the app on your phone to initiate a search. BLE looks for the associated tag and, once it’s within proximity, BLE activates UWB ranging, and your app guides you to the precise location of your missing item.
Meeting the Design Challenge
Combining BLE and UWB means each protocol can provide key functionality to create a better user experience. But developing a design from concept to product with a combination of wireless technologies presents unique challenges to a developer.
Coding the firmware and designing hardware that realizes the full, combined potential of BLE and UWB requires expertise in each individual technology. Also, developing an understanding of how the two technologies can be integrated cooperatively in a system means being mindful of a number of other factors, including the limitations of nonvolatile memory and RAM, the budgets for system-level current draw, and design constraints of the board.
Benefits of Using One Supplier
Designers need to rely on BLE and UWB solutions that are reliable and easy to integrate on their own and, ideally, are also designed to work in combination with each other in a single system. One way to ensure that the BLE and UWB ICs can be successfully integrated into a product is to work with a single supplier who can provide both ICs.
NXP, for example, offers BLE and UWB ICs in System-on-Chip (SoC) options for space-constrained designs and, through module partners, offer pre-certified PCB module variants of both BLE and UWB solutions. Also, designing hardware using NXP’s reference designs and design guidelines gives system developers a head-start and ensures customer boards will be designed for optimal RF and other performance metrics.
Combining BLE and UWB software in a single project presents its own set of challenges, too. This is another case where choosing a single vendor can help, because you’re more likely to find software components that are designed to work together. NXP’s MCUXpresso SDK, for instance, delivers pre-integrated UWB drivers, Bluetooth LE stacks, other key system components such as a bootloader, and application layer functionality demonstrating UWB-driven use cases in a set of reference examples.
As an added design tool, NXP’s Finder V3 reference board provides optimal hardware design guidelines and tightly integrated embedded software. The reference design demonstrates the finder use case, with a small, battery-powered board that supports BLE proximity and discovery, UWB ranging, and even a demo mobile app with source code.
The Finder V3’s reference design is based on the QN9090 wireless MCU and the Trimension SR040, NXP’s UWB solution tailored for UWB tracking applications. The Trimension SR040 supports Time Difference of Arrival (TDoA) in tags for Real-Time Location Services (RTLS), and is designed with compliance to upcoming FiRa Consortium requirements for UWB in mind.
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Taking advantage of the complementary features of BLE and UWB lets developers unlock innovative user experiences and helps make our connected world and even more seamless and reliable place to be.
