The Key Things You Need to Know About Bluetooth 5.1 and 5.2: Faster, More Flexible, and Enhanced for Audio

Jennifer Gibbs, Field Applications Engineer - Laird Connectivity

Apr 9, 2021

Even though the specification for Bluetooth 5.0 hit the market not that long ago, there are two recent updates to the specification that have notable features that will impact the future of wireless design: Bluetooth 5.1 and 5.2. This article will guide you through key aspects of these updates, so your engineering team can anticipate what functionality will be available for upcoming design projects involving Bluetooth.

Let us start by looking at the key features of Bluetooth 5.1. The announcement of the Bluetooth 5.1 specification was dominated by headlines about the inclusion of Angle of Arrival (AoA) and Angle of Departure (AoD) functionality, but there is more to this release beyond AoA and AoD. 

New Direction-Finding Capabilities

The features that have generated the most excitement in the industry are the enhanced direction-finding features, AoA and AoD, included in Bluetooth 5.1. AoA and AoD methods leverage multiple antennas arranged in arrays to enable the ability to locate a signal source’s relevant direction. When AoA or AoD are coupled with other methods like Received Signal Strength Indicator (RSSI) triangulation or Ultra-Wideband (UWB) they can be used to accurately predict the position of a signal in 3D space with a precision that was previously not possible.

In order to get the high accuracy advertised for Bluetooth 5.1 AoA and AoD features, it is necessary to utilize arrays with multiple antennas. Form factor 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 engineers, the new direction-finding capabilities represent a major step toward what many wireless engineers consider a Holy Grail for wireless devices: Real-Time Location Services (RTLS). There has been a lot of industry discussion on this topic, and the hype is justified because RTLS unlocks use-cases that have been predicted for the future of wireless.

It is true that Bluetooth 5.1 does not make RTLS a reality today, but it enables engineers to make major strides in that direction, especially when AoA and AoD are combined with more powerful chipsets and other technologies that collectively provide more precise, more timely data about relative location, movement, and more.

It is expected that the Bluetooth SIG will continue to make strides in this direction, but in the interim we have a set of features that move us closer to that goal by giving us tools we can use 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.

GATT Caching Enhancements

This feature in Bluetooth 5.1 is another that may not be relevant for every design project, 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 Low Energy performed what is called Service Discovery each time a device sought to connect with another device. Service Discovery requires processing power and time to perform, which adds up significantly as the number of connections increases. By caching the GATT table, that process is expedited with known devices. Think of it as skipping an introduction when you see an old friend: you know each other, so you can skip the pleasantries. GATT caching accomplishes the same thing—saving time and energy for devices where speed and battery power are key priorities.

Randomized 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 as it was previously required. This allows for fewer collisions and can lead to more efficient connection establishment. Going with the theme so far, fewer collisions and quicker connection establishment lead to more efficient battery usage and better reliability.

The engineering community considered the prior methodology of channel selection and data transfer to be overly rigid in a way that was inefficient for many applications. In response to that feedback, the Bluetooth SIG built more flexibility into LE 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 randomize transmissions from a device, which makes those collisions with nearby advertisers less likely. As a result, advertising signals are more likely to be heard successfully and connections are likely to happen more quickly.

Each of these features, individually and collectively, help make LE 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.

Let us shift our focus to the key features in Bluetooth 5.2. Because it was a point release, there may be the misconception that Bluetooth 5.2 did not have major additions, but that is not the case. Bluetooth 5.2 has some important enhancements that may play a significant role in future design projects you work on.

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 from the Bluetooth SIG. It enables engineers to utilize Bluetooth LE 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 previously were limited to using Classic Bluetooth, which puts a bigger drain on batteries and has higher latency, which made Bluetooth undesirable for some real-time audio applications. Another drawback was the power required to stream Classic Bluetooth audio, which limited how long consumer devices like wireless headphones, headsets, hearing aids, and wireless speakers could operate between charges. LE Audio gives engineering teams the option to now utilize LE for high quality audio applications, which will be impactful for devices whose use cases make lower latency, longer battery life, or a smaller form factor a top priority.

LE Audio includes LE Isochronous Channels, or multi-streaming connectivity, which will enable new features for consumer devices. Devices using Bluetooth 5.2 will be able to maintain synchronized audio or data streams, both incoming and outgoing. For incoming audio, devices 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 fitting 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, a smartphone, a stereo, a friend’s phone, etc. It also enables the reverse: allowing a single device to broadcast audio to many others via synchronized audio streams. If you envision a group of teens listening to the same song from a single person’s phone playing Spotify, you can start to see the possibilities of this functionality. This opens the possibility for exciting new features that consumers will see as reasons to upgrade.

Other Features

The features that enable LE Audio in the Bluetooth 5.2 specification will also have an impact beyond audio in consumer devices, these include: Enhanced Attribute Protocol, LE Power Control, and LE Isochronous Channels. You will likely hear those three technologies associated primarily with the audio capabilities covered in the prior section, but engineers can also leverage them for other design benefits and novel use cases where lower latency and multi-casting/multi-stream functionality is beneficial. 

Engineers can use LE Isochronous Channels in applications where the time-synchronized broadcasting of data from one device to many may be impactful. Enhanced Attribute Protocol (EATT) can be used to allow multiple applications to use the LE stack simultaneously while minimizing the interference that each data flow causes the others. One of the key benefits of this is lower latency for each of the data streams, which will be valuable for several use cases beyond audio. LE Power Control plays a key role in extending the battery life of audio applications, but it can also have the same impact on other applications by dynamically optimizing 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.  Together these features provide tremendous potential in new Bluetooth 5.2 devices, both in the audio space and beyond.

About the Author:

Jennifer Gibbs is a Field Applications Engineer for Laird Connectivity, with a focus on Bluetooth, Cellular, and ISM embedded wireless modules and solutions. Jennifer is an electrical engineer specializing in Communications Systems and Digital Signal Processing and has 16 years of experience supporting and designing wireless embedded systems. Jennifer’s previous experience includes positions at Sprint and Garmin before joining Laird Connectivity 10 years ago.