A Primer on Bluetooth 5: Everything You Need to Know Before Integrating Your IoT Product
Picture yourself going to the store to buy a new phone, speaker, headphones, or a mood ring and you notice it supports Bluetooth 4.2. “Hey!” you think to yourself, “this device only supports old, crummy Bluetooth! Where is that new hot Bluetooth I’ve heard so much about? Isn’t it way better or something?”
After wondering what the difference really is, you end up buying AirPods instead because they say they support Bluetooth 5. This isn’t necessarily the wrong choice – AirPods are pretty fantastic! – but Bluetooth 5 is neither as magical nor as mysterious as you might think. In fact, it’s quite familiar.
First, a quick primer on Bluetooth until now. Major Bluetooth versions can be stratified into 3 categories:
- 1.X and 2.X are Bluetooth Classic
- Bluetooth 3 seems to be its own thing
- Bluetooth 4.X and 5.X are the “Low Energy” family – now known as just Bluetooth or Bluetooth 5.
Bluetooth Classic has profiles and is referred to as “stream-oriented.” Once you establish a connection, you more or less get a magical tunnel that data – like audio – can flow down like, well, a stream.
Remember that terrible wireless mouse you got in 2005? It probably required you to download mysterious drivers for your beige Windows XP machine that never quite worked, right? It was probably hard to pair, frequently failed, and only worked with whatever dongle came in the box. That is an early Bluetooth Classic device. As the specification was revised and drivers became part of common operating systems these problems eventually went away.
Bluetooth 3 seems to be its own thing. It added a special “High-Speed” mode which used WiFi as the actual data connection and only did discovery over Bluetooth.
Bluetooth 4.X has, at different times, been called “Bluetooth Smart” or “Bluetooth Low Energy” (BLE or BTLE), but the Bluetooth Special Interest Group (SIG) now recommends you refer to everything as just “Bluetooth” unless you must specify a version, at which point you should use a number. This has a surprising implication, which we’ll talk about later.
BTLE could be referred to as a “message-oriented” protocol. It is designed to efficiently send data like single temperature readings, or single accelerometer readings. BTLE is often used to connect things like activity trackers to your phone, as the BTLE protocol can be very low power when used as intended. BTLE also includes methods for advertising the presence of a device, which is used to create so-called beacons. Specific variants of this process are branded iBeacon by Apple and Eddystone by Google. It’s worth noting that Bluetooth Classic and Low Energy are NOT intercompatible unless the product or radio specifically supports it. Often these are referred to as “dual mode” parts.
Now with all that context, what’s new in Bluetooth 5?
Bluetooth 5 (BT5) is the newest published version of the Bluetooth standard from the Bluetooth SIG. It is built on top of the specification for Bluetooth Low Energy 4.2 – with Length Extension (LE) – which is respectively built on BLE 4.1 and 4.0. Thus, BT5 can be seen as a (fully backwards compatible) revision of Bluetooth Low Energy. It is unrelated to Bluetooth Classic (BT 1.X and 2.X).
It’s worth noting that if you’ve heard of this cool thing called Bluetooth Mesh, that is a specification which does exist, but it’s unrelated to Bluetooth 5. It sits on top of radios which can speak to any of the Bluetooth Low Energy family of protocols (4.X and 5.X).
Bluetooth 5 (fittingly) offers 5 features of particular note to end users, as well as other enhancements:
- Up to 2 x faster throughput with new faster PHY speed (2Mbit)
- Up to 4 x the range of BLE 4.2 with new encoding schemes (these manifest as 1.25Kbit and 500Kbit “Coded PHYs”)
- Up to 8 x larger advertising payloads (especially useful for beacons)
- Better wireless coexistence with LTE and 2.4GHz WiFi
- Higher maximum output power (up to +20dBm)
These are relevant for specific use cases:
- The faster throughput is exactly what it sounds like. All other parameters being equal, a connection using the Bluetooth 5 specific 2M PHY will have double the throughput. The bits move twice as fast.
- In order to support longer range, Bluetooth 5 radios may support other physical layer operating modes which encode data in ways which improve reliability. The effect is that the transmitted data can be “understood” from farther away. There are two of these “Coded PHY” modes, one with a data rate of 500KBits/second and one with a rate of 125KBits/second, offering 1/2 and 1/8 the maximum throughput of the standard 1M PHY respectively. For more information, the Bluetooth SIG has a great blog post.
- There is now a standard for chaining together longer advertising payloads. This allows for beacons which transmit more information, devices to advertise more services, and more.
- When mixing wireless radios on a device, Bluetooth 5 and WiFi radios (both in the 2.4GHz spectrum) will interfere with each other less.
- There are now four classes of Bluetooth devices, grouped by transmit power. Bluetooth 5 adds Class 1, which provides a significantly higher maximum transmit power.
There are a few subtleties to the interactions of the above points which may not be obvious at first glance:
- Bluetooth 5 does not specify an increase in MTU size or minimum connection parameters when compared to Bluetooth 4.2 + LE. If you’re using the 1M PHY (the only one available to previous versions of BTLE) a Bluetooth 5 device and a Bluetooth 4.2 device will perform identically.
- As far as we can tell, there are phones which support the 2M PHY (Galaxy S8/S8+/S9/S9+, iPhone 8/8 Plus/X) but none which support the lower speed/longer range PHYs. This means, as of now, there are no phones which can make use of the new long-range features in Bluetooth 5. This could potentially change with firmware updates to these phones.
- The long-range extensions and higher speed 2M PHY are mutually exclusive. They are also completely independent of any transmit power settings a given board may provide.
The final and perhaps most important note about Bluetooth 5 is that a device supporting “Bluetooth 5” may include any combination of the features above, including none!
That’s right, if you read the Bluetooth SIG’s surprisingly good FAQ and focus on the sections about branding and naming, their recommendations specify that you refer to products as supporting just “Bluetooth”, or “Bluetooth 5” if you must specify a version. This isn’t deceptive, as Bluetooth 5 is entirely backwards compatible with Bluetooth 4.2 + LE. But it does mean that you need to examine any Bluetooth 5 product very carefully to ensure it supports the features you need.