Bluetooh technical description
Generic advertising frame
BLE5 extended advertising
Advertising extensions in Bluetooth 5 provide the capability to offload advertising data from the three traditional advertising channels to the full set of data channels for more frequency diversity. A more efficient use of the 2.4 GHz band should enable developers to increase the rate of advertised packets, as well as utilize the new PHY modes, paving the way for better streaming and beacon solutions.
All these LE PHY’s supported by Bluetooth 5 can be used for advertisements with the introduction of advertising extensions:
- LE 1M PHY: 1 Mb/s bit rate, 1 Msym/s symbol rate. Each bit maps to a single radio symbol. The same PHY as used in Bluetooth 4.0.
- Coded PHY: 1 Mb/s bit rate, 500 or 125 ksym/s symbol rate. Each bit is coded into 2 or 8 bits using a forward error correction algorithm to provide higher tolerance for bit errors, resulting in improved range.
- LE 2M PHY: 2 Mb/s bit rate, 2 Msym/s symbol rate. Doubles the symbol rate to increase the speed, at a small cost to range.
In Bluetooth 4.0, all advertising was done on just three channels of the 40 - 2.4GHz ISM band channels. Bluetooth 5 improves this mechanism by allowing a small header packet sent on the three primary advertising channels to point to a larger payload sent at a later time on one of the 37 data channels. This removes the need to duplicate the data payload on all three advertising channels, while allowing considerably more advertising data in the area before running into coexistence issues.
- A single advertising packet can hold up to 255 bytes of data, up from 37 in Bluetooth 4.0
- Advertising packets can now be chained together, allowing for even larger beacon payloads than with a single packet (a chain can hold a maximum of 1650 bytes)
- Advertising packets can be sent periodically, allowing observers to lock on to a stream of advertised packets
- Periodic advertisements can be combined with chained packets, allowing an even higher overall data throughput