Bluetooth 5.1: What’s New and Why It Matters

January 31, 2019
Location symbol above girl walking in crowded airport
Bluetooth SIG

Bluetooth 5.1 brings new “direction-finding” features that will let Bluetooth devices pinpoint physical location to the centimeter, aiding in indoor positioning. This latest version includes features that will make for more reliable Bluetooth connections, too.

Bluetooth Devices Can Now Pinpoint Your Location

Current Bluetooth proximity systems can guess how far away a device—like your smarthome or smartwatch—is by using signal strength. They might know you’re a few meters away, but they don’t know the direction.

That’s enhanced with a new direction-finding feature in Bluetooth 5.1, which was just announced by the Bluetooth Special Interest Group (SIG,) the industry group that oversees Bluetooth. A positioning system can now determine the direction a Bluetooth signal is coming from. Combining distance and direction, Bluetooth devices can now figure out the precise location of a device down to the centimeter.

diagrams showing AoA vs. AoD methods
Bluetooth SIG

Bluetooth 5.1 offers two different methods for determining direction, named “Angle of Arrival” (AoA) and “Angle of Departure” (AoD). One of the two devices must have an array of multiple antennas, and the data received from those antennas can be used to identify the direction the Bluetooth signal is coming from.

If you’re carrying a smartphone around and that phone has Bluetooth 5.1, a positioning system can have a good idea about your exact location. This could be used to improve navigation indoors, find your lost keys, or enable smarthome hardware to better pinpoint your location.

Faster Connection Initiation With Less Power Spent

As you might expect from the version number, Bluetooth 5.1 isn’t a huge leap with a lot of changes, as Bluetooth 5.0 was. Its other changes are fairly minor, but are still helpful.

Bluetooth Low Energy devices use something called the “Generic Attribute Profile,” or GATT. Whenever a client device connects, it performs “service discovery” to see what the server device supports. This takes time and energy. Bluetooth 5.1 performs more aggressive caching, and clients can skip the service discovery stage when nothing has changed. These “GATT caching enhancements” mean the connection happens faster and less energy is spent.

RELATED: Bluetooth 5.0: What’s Different, and Why it Matters

Connection Advertising Improvements

Bluetooth 5.1 includes several improvements to advertising. The word “advertising” here refers to how a Bluetooth device broadcasts it’s available to connect, advertising its availability to other nearby Bluetooth devices. This should make connections work better.

One new feature is “randomized advertising channel indexing.” Bluetooth 5.0 required devices to cycle through channel 37, 38, and 39 in strict order. Now, devices can select channels at random. This reduces the odds that two Bluetooth devices will interfere with each other and “talk over” each other on the same channels when advertising their readiness to connect, and it’ll be helpful in places with a lot of Bluetooth devices.

diagram showing periodic advertising sync transfer
Bluetooth SIG

Bluetooth 5.0 added the ability for devices to synchronize their scanning for connection with the “advertising” schedule of another device. For example, if you’re connecting your smartphone to a TV over Bluetooth, the TV can tell your phone exactly when it will advertise with a data field named SyncInfo. Your phone doesn’t have to constantly scan for the TV, but knows exactly when the TV will advertise itself. This saves power and could potentially help if the devices need to exchange data at a precise time.

However, this “periodic advertising sync” exchange uses some power, and low power devices may not want to waste their energy on it. With “periodic advertising sync transfer,” connected devices can transfer that data to each other—for example, your smartphone can transfer information about the TV’s advertising schedule directly to your smartwatch rather than forcing your smartwatch to communicate this information with the TV. That could save energy on low power devices, making batteries last long.

More technical details about how exactly these features work are available in the official Bluetooth core specification feature overview document. The document also lists some smaller changes we didn’t mention here.

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