What is Bluetooth?
Tangled of messy wire cables under computer desk.
We’re all use to wireless communication by now, even if we don’t always realize it. Radio receivers and television sets pick up programs beamed in radio waves hundreds (possibly even thousands) of km/miles through the air. Cordless telephones use similar technologies to carry calls from a handset to a base station somewhere in your home. If you use Wi-Fi (wireless Internet), your computer sends and receives a steady stream of Internet data to and from a router that’s probably wired directly to the Net. All these technologies involve sending information back and forth not along copper cables but in radio waves buzzing invisibly through the air.
Photo: Cables can be a real nuisance—that’s the problem wireless technologies such as Bluetooth can help to solve.
Bluetooth is a similar radio-wave technology, but it’s mainly designed for communicating over short distances less than about 10m or 30ft. Typically, you might use it to download photos from a digital camera to a PC, to hook up a wireless mouse to a laptop, to link a hands-free headset to your cellphone so you can talk and drive safely at the same time, and so on. Electronic gadgets that work this way have built-in radio antennas (transmitters and receivers) so they can simultaneously send and receive wireless signals to other Bluetooth gadgets. Older gadgets can be converted to work with Bluetooth using plug-in adapters (in the form of USB sticks, PCMCIA laptop cards, and so on). The power of the transmitter governs the range over which a Bluetooth device can operate and, generally, devices are said to fall into one of three classes: class 1 are the most powerful and can operate up to 100m (330ft), class 2 (the most common kind) operate up to 10m (33ft), and class 3 are the least powerful and don’t go much beyond 1m (3.3ft).
How does Bluetooth work?
Two nearby Bluetooth devices exchange a pairing request.
Bluetooth sends and receives radio waves in a band of 79 different frequencies (channels) centered on 2.45 GHz, set apart from radio, television, and cellphones, and reserved for use by industrial, scientific, and medical gadgets. Don’t worry: you’re not going to interfere with someone’s life-support machine by using Bluetooth in your home, because the low power of your transmitters won’t carry your signals that far! Bluetooth’s short-range transmitters are one of its biggest plus points. They use virtually no power and, because they don’t travel far, are theoretically more secure than wireless networks that operate over longer ranges, such as Wi-Fi. (In practice, there are some security concerns.)
Bluetooth devices automatically detect and connect to one another and up to eight of them can communicate at any one time. They don’t interfere with one another because each pair of devices uses a different one of the 79 available channels. If two devices want to talk, they pick a channel randomly and, if that’s already taken, randomly switch to one of the others (a technique known as spread-spectrum frequency hopping). To minimize the risks of interference from other electrical appliances (and also to improve security), pairs of devices constantly shift the frequency they’re using—thousands of times a second.
When a group of two or more Bluetooth devices are sharing information together, they form a kind of ad-hoc, mini computer network called a piconet. Other devices can join or leave an existing piconet at any time. One device (known as the master) acts as the overall controller of the network, while the others (known as slaves) obey its instructions. Two or more separate piconets can also join up and share information forming what’s called a scatternet.