From Nordic: "Bluetooth 5.1 Puts Bluetooth In Its Place"

This week’s release of the Bluetooth 5.1 specification adds accurate positioning capability, a fundamental use case of many desired IoT applications.

After the quantum leap delivered by Bluetooth 5 and all of the associated features, one might think it would be hard to have a show-stopping story this time around. But despite the numbering, Bluetooth 5.1 is a big deal too.

Finding your way with Bluetooth

Direction finding is a major feature of Bluetooth 5.1, which brings the possibility of absolute positioning of products and things in three-dimensional space to the world of low-power wireless connectivity.

It is a very important addition to Bluetooth Low Energy’s capability arsenal. We believe it can have a similar impact for indoor situations as GPS did for outdoor positioning. Where GPS has fundamentally changed the world of traveling and tracking on the macro scale for cars, people and objects, Bluetooth direction finding can make a similar impact on the micro scale inside buildings and properties.

The Bluetooth Special Interest Group (SIG) predict 400 million Bluetooth location services products per annum by 2022.

Building on the success of Bluetooth beacons

Real-Time Location Services (RTLS) using Bluetooth have been available for a few years now. This became possible with the introduction of Bluetooth beacons, which could give an approximation of distance, or proximity, between objects. This might be a customer’s proximity to an airline check-in desk, for example.

The beaconing approach is based on Received Signal Strength Indication (RSSI), which is monitoring the strength of the radio signal from a source. The RSSI approach is useful, but it is painting with a broad brush. What Angle-of-Arrival (AoA) and Angle-of-Departure (AoD) bring is precision of direction in addition to the distance-only information that RSSI traditionally brought.

How it works - Playing the angles

Angle of Arrival (AoA), Angle of Departure (AoD), these two concepts are at the core of direction finding capabilities of Bluetooth 5.1.

In AoA a device, or tag, will transmit a specific direction-finding packet, using just one antenna. The receiving device, or locator, will have multiple antennas. The incoming signal from the tag will arrive at these antennas with very slight time-shifts relative to each other. The shifts in signal phase seen on these antennas are sampled as IQ components of the signal. Then with the use of associated algorithms at the locator, these samples will yield accurate coordinate information as received.

This method is ideally suited to specific item finding and for Point-of-Interest (PoI) applications.

The AoD approach flips this scenario, and the device that is key to determining direction, such as a locator beacon in an Indoor Positioning System (IPS) has an antenna array. This locator beacon transmits a packet via the antenna array. The receiving device in this scenario is most likely a mobile phone, the phone will then make IQ sampling at its antenna, and from there make the coordinate calculation.

Design complexity

There are two sides to a Bluetooth direction finding product design. The locator tag designs do not differ significantly from a regular Bluetooth hardware layout using Nordic devices that support Bluetooth 5.1 direction finding, so this is straightforward and indeed will be the majority case for products employed in Bluetooth direction finding.

Click here for access to the nRF52840 Development Kit

At the locator hub, an antenna array needs to be designed and multiplexed to the Bluetooth SoC because Bluetooth SoCs do not have multiple antenna ports as this would make them prohibitively expensive. There are devices on the market that can compliment Nordic SoCs to achieve this function. Aside from this the antenna array will likely need 360-degree coverage to capture signals or maybe 180 degrees if it is to be a wall-mounted unit.

Realistic expectations

Accurate indoor positioning is a fantastic feature, most people would agree on that. But there should be a little cautionary guidance also. All of this relates to radio waves being transmitted and we cannot have direct control over the paths they take between transmitter and receiver. The less crowded with obstacles, and the more open Line-of-Sight (LoS) the scenario for this technology; the better the accuracy will be. As signals bounce off walls, cupboards, windows and people, so phase and signal strength can be affected and will introduce small or larger errors. However, this is a sophisticated solution to direction finding, that tests have indicated to be very - robust even in quite challenging situations.

In short, this technology needs to be road-tested for its use case. That should give a good idea as to its suitability in your product.

Typical use-cases

As said the more open and uncrowded the scenario likely the better accuracy. First of all, we could look at a position finding system in a stadium. With a locating hub possibly situated above the pitch or stage area, this could receive transmissions from devices being worn. The scenario is very open, and seating is tiered vertically giving good LoS properties, and should work quite effectively.

Another good use-case is finding things in the home or workplace, let’s take keys as the most common ‘where did I put it’ example This could work very nicely indeed with a locator hub in the room. However, a locator hub situated on another floor is unlikely to be able to give you an accurate location, which is reasonable given the physical challenges.

Finally, human location finding for emergencies, a very valuable use case. Take a large shopping mall, or office complex, with adequate locator hubs available to cover all areas. This could give emergency services very accurate information on anyone who may be still in the building in the event of a fire, for example. This would allow emergency crews to get straight to stranded individuals without searching methodically through the complex whilst essentially ‘blind’ as to whether anyone is still trapped inside, saving valuable minutes to make contact and rescue or administer life-saving care in-situ. 

Nordic support for Bluetooth 5.1 and direction finding

Nordic, as the market leader in Bluetooth Low Energy, are committed to offering the latest features to developers as they become available with the specification. Bluetooth 5.1 and direction finding is no exception. The soon to be available nRF52811 [now available - click here for nRF52811 product page] is a multiprotocol Bluetooth SoC that has Bluetooth 5.1 support for direction finding with AoA and AoD. The nRF52811 is an addition to the incredibly popular nRF52 Series SoCs and offers a perfect mix of features to make it a compelling choice for development of direction finding beacon applications, or as a comprehensive multiprotocol connectivity device in locator hubs as a companion device to main application MCUs.

Nordic Semiconductor will be at Embedded World 2019 and Mobile World Congress 2019 with staff available to offer more information and advice on how to use this exciting technology.

Source: https://blog.nordicsemi.com/getconnected/bluetooth-5.1-puts-bluetooth-in-its-place 

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