Bluetooth Range

The question about range of Bluetooth Low Energy radios is coming back like a boomerang. While it becomes less of an issue when mesh topology is used to network Bluetooth nodes, a single-hop range is important in many applications.

When using Bluetooth 4, the practical range, demonstrated by us two years ago, was up to 250m in a smartphone - to - a peripheral setup and up to 500m in a peripheral - to - peripheral setup. The difference has been in the sensitivity, power output and antennas used.

For range - optimized peripherals we've been using a front-end PA (Power Amplifier) combined with an LNA (Low Noise Amplifier). The Bluetooth radio we've been using had -95dBm sensitivity and 0dBm output power. The LNA was adding another 3dBm on the sensitivity side and a full +10dBm on the output side. So the peripheral - to - peripheral range has been 108dB (0dBm + 10dBm - (-(95+3)dBm)). Bypassing all theoretical calculations, in many repetitive tests this was giving us reliable 500m outdoor range.

Now a phone - to a peripheral link benefits only from adding a good antenna and a front-end PA+LNA on one side. You cannot easily increase sensitivity or an output power of a smartphone Bluetooth module. But still we were getting respectable 200m-250m range. This by the way has been recently confirmed by our friends at Punch Through - they achieved 250m with their Bean+ module.

Now enter Bluetooth 5, with its long range mode that uses advanced error correction schemes, capable of boosting the range up to 4x. A simple math gives us a node - to - node range of 2 kilometers. It is quite a difference from your father's Bluetooth, isn't it? Of course the long range does not come for free. Error correction lowers the effective bit rate, from the standard 1Mb/s down to 500kb/s or 125kb/s, when using coding scheme of 2 or 8 symbols per bit. You cannot change the physics of wireless propagation, but the beauty is the coding scheme is flexible and is decided by software running on the chip. On the other end of the scale Bluetooth 5 supports 2Mb/s speed when no extreme range is needed.

Soon, with introduction of  the Mesh, this single - hop range that bounds us today, will be looked at from an entirely different perspective. Even assuming conservative 200m, multiplied by 100 hops, gives us 20 kilometers. Quite a game changing number, considering Wikipedia still says "Bluetooth is a wireless technology standard for exchanging data over short distances.". Not anymore.