Bluetooth beacon strength is constrained and can be affected by limits placed on the transmitter power to preserve battery life. Usually, a line of sight is needed for optimal beacon range and signal strength. Shown below is the signal strength to distance curve for typical line-of-sight Bluetooth 4.0 communication.
Bluetooth also has different power levels, ranges, and transmission power based on a classification for each device:
|
Class number |
Max output level (dBm) |
Max output power (mW) |
Max range |
Use case |
|
1 |
20 dBm |
100 mW |
100 m |
USB adapter, access points |
|
1.2 |
10 dBm |
10 mW |
30 m (typical 5 m) |
Beacons, wearables |
|
2 |
4 dBm |
2.5 mW |
10 m |
Mobile devices, Bluetooth adapters, smart card reads |
|
3 |
0 dBm |
1 mW |
10 cm |
Bluetooth adapters |
Bluetooth 5 has improved the range as well as data rate beyond legacy Bluetooth limits. A new radio PHY is available with Bluetooth 5 called LE2M. This doubles the raw data rate of Bluetooth from 1M symbol/second to 2M symbols/second. To transfer an equal amount of data on Bluetooth 5 as opposed to Bluetooth 4, less time will be needed for transmission. This is particularly relevant for IoT devices that operate on coin cells. The new PHY also increases the power from +10 dBm to +20 dBm, allowing for greater range.
With respect to range, Bluetooth 5 has another optional PHY for extended range transmission in BLE. This auxiliary PHY is labeled LE coded. This PHY still uses the 1M symbol/second rate as in Bluetooth 4.0, but reduces lower packet coding of 125 Kb/s or 500 Kb/s and increases the transmission power by +20dBm. This has the effect of increasing the range by 4x over Bluetooth 4.0 and having better penetration within buildings. The LE coded PHY does increase power consumption for the benefit of increased range.