#135 How does Bluetooth work?

I learned this today. Bluetooth is a short range, low power technology that can transmit data over radio waves.

Bluetooth works on frequencies in the 2.400 to 2.483.5 GHz short-range radio band. Radio frequencies around the world are generally regulated so that different frequencies don’t get mixed up. That is why different radio stations broadcast on different frequencies. 2.4 GHz is reserved for industrial, scientific and medical equipment, along with Bluetooth.

Bluetooth only works if the devices are Bluetooth capable. This is done using a microchip that can send or receive radio wave signals and convert them into data.

The first step in using Bluetooth is to pair the devices. The device you are using to send or receive the Bluetooth signals, often called the Master device, can scan the area for Bluetooth devices that are emitting signals. However, it cannot connect to them without a trust relationship. This is usually done by setting the Bluetooth device, the slave device, to a pairing mode, or inputting an authentication number or code that the master device displays. In the pairing process, the master device and the slave device will share a secret security key. By doing this, the slave device can only connect to the one master device and can’t be intercepted. This security key will be remembered by the master device which means the two devices can connect automatically in the future.

Once the devices are connected, for example the Bluetooth speaker in the picture I have used, they form a personal-area network, often called a piconet. This means that they stay in touch with one another and avoid interfering with other Bluetooth devices. The master device is capable of analyzing which radio frequencies are performing well and it is able to adapt to give the best reception possible.

Once connected, the master device will begin to transmit data using the 2.4 GHz spectrum. However, they don’t stay on the same frequency. Bluetooth uses something called frequency-hopping spread spectrum (FHSS). The signal that the master transmits hops over different frequencies. Different devices do this at different rates, but they can do it at up to 1,600 times a second. There are three reasons why they do this. The first reason is it reduces interference from other devices. Secondly, it allows one device to send information to many devices simultaneously over a single communication channel (called code-division multiple access). And, lastly, it makes it very difficult for someone to intercept the signal and pick up the data. The master device and the slave device share a code that tells them which frequencies to jump to and keeps them in sync.

When the data is received by the slave device, it then has to be decoded. It does this using algorithms that vary from device to device. These algorithms are called codecs and different codecs affect different things: transfer rates, audio quality, power usage, and so on.

Bluetooth devices are regulated by the Bluetooth Special Interest Group (SIG) and new devices are technically supposed to be associate or promoter members of the Bluetooth SIG. It is a way of keeping the technology standardized around the world. There is a qualification process before a new Bluetooth device can be brought to market.

Bluetooth was based on a number of different inventions. Short-link radio technology was invented in 1989 by Nils Rydbeck. He worked for Ericsson Mobile in Sweden and he was trying to make wireless headsets. By 1997, his team had come up with a way of doing it. His team was made up of people from Scandinavia, hence the name they chose. Rydbeck worked with IBM to finalize the system and they brought out the first device in 1999. It was a hands-free mobile and was hugely popular. Both Ericsson and IBM gave the technology away as an open industry standard to allow more people to use it in devices.

The creators of Bluetooth were Scandinavian, so it was natural that they might look for names from their own countries. They choose Bluetooth, which came from the king Harald Bluetooth, and the runes for his names were combined and have become synonymous with Bluetooth. However, it turns out that Bluetooth was not intended to be the name for the technology. They were planning on RadioWire or PAN (Personal Area Networking). The name Bluetooth caught on before they could change it, and the rest is history. And this is what I learned today.

Photo by Burst from Pexels

Sources:

https://electronics.howstuffworks.com/bluetooth.htm

https://www.popsci.com/reviews/how-does-bluetooth-work/