The future of Bluetooth is faster, more flexible and sounds great

17th May 2021
Joe Bush

With many engineering teams now working regularly with Bluetooth 5.0, it may be overwhelming to think about having to also get up to speed on Bluetooth 5.1 and 5.2. After all, point releases don’t usually warrant this much fanfare, but 5.1 and 5.2 have exciting new features you should certainly familiarise yourself with. Jennifer Gibbs, Field Applications Engineer at Laird Connectivity.

The wireless engineering community has been pleased with the technical advancements included in the Bluetooth 5.0 specification. It delivered major steps forward in Bluetooth Low Energy’s (BLE) speed and range as well as key capabilities like advertising extensions, which supports a wider range of use cases and provides a more powerful radio to work with in their design projects. So, what else could it possibly come up with to outdo itself? The answer is, several things. There are several innovations in Bluetooth 5.1 and 5.2, but for the sake of brevity we’ll only be including some of the highlights here, starting with 5.1.

Takeaways of Bluetooth 5.1

The initial announcement of Bluetooth 5.1 was dominated by the inclusion of Angle of Arrival (AoA) and Angle of Departure (AoD) functionality, but as you’ll see there is much more to it than those features.

New direction-finding capabilities: AoA and AoD methods enable the ability to locate a signal’s relevant position, especially when coupled with other methods like RSSI strength. AoA and AoD leverage multiple antenna arrays from a network of 5.1 devices to triangulate position with precision not previously possible.

In order to get the high accuracy advertised for Bluetooth 5.1 AoA and AoD features, it is necessary to utilise arrays with multiple antennas. Form factor issues can quickly become an issue with a large number of co-located antennas, but embedded antenna technology allows engineers to take advantage of AoA and AoD without running into issues with the collective size of the antenna array.

To many, these new capabilities represent a major step toward what many wireless engineers consider a Holy Grail for wireless devices - Real-Time Location Services (RTLS), which unlocks exciting use cases that have been predicted for the future of wireless. It’s not yet a reality today, but their inception means that this future may be here soon. For now, at least, we know we’re a step closer to being able to use Bluetooth for use cases such as asset tracking in warehouses, wayfinding for visitors in large facilities such as hospitals and museums, limited contact tracing, and more, with indoor accuracy down to centimetres.

GATT caching enhancements: This feature in Bluetooth 5.1 is another that may not be relevant for every design project an engineering team is tackling, but it is significant for those where speed of connection is critical. GATT (Generic Attribute) caching makes it possible for Bluetooth devices to store the GATT table of generic attribute handles when connected to a GATT server, which expedites future connections with GATT servers of the same type and saves energy in the process.

The prior versions of Bluetooth LE performed what was called ‘Service Discovery’ each time a device sought to connect with another one. This required processing power and time to perform, which added up significantly as the number of connections increased. That process is now expedited with known devices, which functions just like skipping introductions when seeing an old friend.

Randomised advertising channel indexing: The last feature of Bluetooth 5.1 worth mentioning is Random Advertising Channel Indexing, which allows the devices to randomly choose advert channels to use, as opposed to going in strict order. This allows for fewer collisions and leads to more efficient connection establishment. Fewer collisions and quicker connection establishments also lead to more efficient battery usage and better reliability.

The Bluetooth SIG designed this enhancement to respond to feedback that the prior methodology of channel selection and data transfer was overly rigid in a way that was inefficient for many applications. In response, they built more flexibility into BLE so that engineering teams could give devices the ability to select between the advertising channels randomly, rather than rigidly following a pre-established order, which is predictable and prone to collisions with other similarly timed advertisers in the area causing slow connections and high-power consumption. This feature helps to randomise transmissions from a device, which makes those collisions with nearby advertisers less likely. As a result, advertising signals are more likely to be heard and connections likely to happen quicker.

Each of these features, individually and collectively, help make BLE faster, more efficient, and more battery-smart by giving engineers the flexibility to fine-tune their designs and their network implementations to align with the use case they are supporting.

The Bluetooth website offers a complete list of enhancements for those who want a closer look, but the three discussed here are key to have in mind as you chart the future of your Bluetooth strategy.

Takeaways of Bluetooth 5.2

Bluetooth 5.2 also has some important enhancements to the specification that might have flown under the radar because they are also in a point release.

LE Audio: LE Audio, in particular the LC3 (Low Complexity Communication Codec) codec, is a feature of 5.2 that has generated a lot of early excitement since the original announcement. It enables engineers to utilise BLE for stereo and other audio applications without a drop in the quality of the audio data.

Up until Bluetooth 5.2, applications requiring quality audio were limited to using Classic Bluetooth, which puts a bigger drain on batteries and has a higher-than-desired latency, which made Bluetooth undesirable for certain real-time audio applications. Another drawback was the power required to stream Classic Bluetooth audio, which limited how long consumer devices like ear buds, wireless headphones, headsets, hearing aids, and wireless speakers could operate between charges. LE Audio gives engineering teams the option to utilise BLE for high quality audio applications, which will be impactful for devices where achieving lower latency and a longer battery life or a smaller form factor is a top priority.

LE Audio also includes multi-streaming connectivity, which will enable new features for consumer devices. Audio-related devices using Bluetooth 5.2 will be able to maintain synchronised audio streams, both incoming and outgoing. For incoming audio, devices with the LE Audio feature can maintain simultaneous connections with audio streams from multiple devices, allowing a single audio-receiving device (such as ear buds) to do far more than previously possible. Wireless headphones are a great example, given how a user might want to use the same headphones to be able to switch seamlessly across audio signals from multiple devices such as a tablet and a smartphone. It also enables the reverse - allowing a single device to broadcast audio to many others via synchronised audio streams.

Other features

The LE Audio capabilities discussed here is thanks in large part to three underlying aspects of the specification that will also have an impact beyond audio features in consumer devices: Enhanced Attribute Protocol (EATT), LE Power Control, and LE Isochronous Channels. Typically associated with audio functionality, these features can also be used for other design benefits and novel use cases where lower latency and multi-casting/multi-stream functionality is beneficial. For example, EATT, which enables the multi-stream functionality for incoming audio in LE Audio can also be utilised for other types of data. Other examples of these three include:

  • Using EATT to allow multiple applications to use the BLE stack simultaneously while minimising the interference that each data flow causes the others. This will be valuable for use cases beyond audio as each data stream can now operate at a lower latency.
  • LE Power extends the battery life of audio applications, but it can also have the same impact on other applications by dynamically optimising the transmit power used based on signal quality when two devices are communicating. The intelligence built into this feature enables the device to identify ways to reduce power consumption in real-time while also ensuring the quality of the signal strength and factoring in the coexistence of other nearby wireless devices.
  • LE Isochronous Channels enable the broadcasting functionality discussed in the LE Audio section, but also have the potential to be used for other applications where the time-synchronised broadcasting of data from one device to many may be impactful.

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