Bluetooth 5’s advertising extensions


In addition to increased range and throughput, the updated Bluetooth 5 specification includes advertising extensions to improve applications like beacons.

When Bluetooth 5 was adopted in December last year, the hype was about the specification’s increased range and throughput enhancements. Perhaps that excitement was understandable as these capabilities added much to Bluetooth Low Energy’s suitability for the Internet of Things (IoT), but Bluetooth 5 did bring other improvements, notably “advertising extensions”.

Bluetooth low energy uses 40 x 2-MHz channels across the 83-MHz wide 2.4-GHz ISM spectrum. Of these, three are dedicated primary advertisement channels (37 (2402 MHz), 38 (2426 MHz), and 39 (2480 MHz)), while the remaining 37 channels (0 to 36) are typically used for data channel transmission once a connection has been made.The advertisement channels are used by devices to “advertise” their presence by broadcasting information to any “observer” devices within range. Observer devices “discover” the broadcasting device and can receive
the information it transmits without a formal connection being made.

Bluetooth 5 technology’s longer data packets and lower on-air transmission speeds while employing extended range operation (for example 125 kbit/s) have the potential to cause the three advertising channels to become congested. This could be a major challenge for applications such as beacons because the devices typically use these advertising channels to send information to nearby smartphones.

Advertising extensions were included in the Bluetooth 5 specification to overcome this problem. Now, advertising information commences as advertising packets sent over some or all of the three primary channels, but extra packets are then accommodated by “offloading” them to a normal data channel (which then acts as a “secondary” advertisement channel). Better yet, advertising extensions enables “chaining” of advertising packets to create greater advertising data payloads
of up to 255 bytes.

Connectionless broadcast
In addition, advertising extensions also bring a capability called periodic advertisements. This functionality comprises packets sent at a fixed interval to synchronized devices via “connectionless” broadcasting. By using periodic advertisements, scanning devices can more consistently “follow” the advertiser and monitor its updates more frequently. Connectionless broadcasting is further boosted because Bluetooth 5 features an eight-times higher broadcast capacity compared to previous versions of the technology. Connected devices can also make use of these enhancements to send more data and allow connections using secondary advertising channels (again freeing-up the primary advertising channels).

Advertising extensions, periodic advertisements, and connectionless broadcast will have a major impact on beacons. Before Bluetooth 5’s advertising extensions, advertising packets were limited to 31 bytes which rationed the information that could be transferred in a connectionless broadcast. Now, for example, instead of being able to send just a URL to a smartphone which a consumer must then visit for more information, a retailer can directly send information about a special deal or new product. And indoor navigation will receive a boost because consumers won’t need to install specific apps or create a connection to receive location-based information. This won’t happen overnight because few current smartphones incorporate Bluetooth 5, but expect beacons to proliferate over the next several years as new smartphones are rolled out.

Nordic’s nRF52810 and nRF52832 Systems-on-Chip (SoCs) support Bluetooth 5’s high throughput and advertising extensions, periodic advertisements, and connectionless broadcast, while the nRF52840 SoC additionally supports range extension. The S132 (v5.0) SoftDevice, a 20-link multirole, pre-qualified, Bluetooth low energy protocol stack with full link concurrency in all role combinations is fully compliant with all features of Bluetooth 5.

No need for specific apps

Advertising extensions will boost indoor navigation because consumers won’t need to install specific apps or create a connection to receive location-based information on smartphones