In the mid-900s, the Danish king Harald Bluetooth united Denmark and part of Norway into one kingdom. In the late 20th century, Swedish engineers at Ericsson developed Bluetooth transmission, a wireless technology that can unite different electronic devices regardless of their type, manufacturer, or operating system. Using low-power radio waves, a Bluetooth transmitter can transmit signals from a computer to a stereo system, from a cell phone to a printer, or from an Apple to a PC.
Remote controls use infrared signals to send information from the remote control to a device like the TV or DVD player. For a remote control to work, however, it must be pointed directly at the TV. With Bluetooth wireless transmitters, devices within 30 feet (10 m) of each other can communicate, even through walls and around corners. This is because a Bluetooth transmitter uses 2.45 GHz radio waves to transmit signals, the same frequency used for baby monitors and newer cordless phones.
When one Bluetooth transmitter senses another one, it automatically establishes a small wireless network, called a piconet, that works as long as the transmitter and receiver are within 30 feet (10 m) of one another. A user might, for example, walk into his house, and his cell phone calls could automatically be forwarded to his cordless land line. As he passes his computer, his emails could be downloaded into his cell phone or PDA, then he can send downloaded music to his stereo and photos from his digital camera to his daughter’s phone. Bluetooth wireless technology eliminates the need for a different cord to allow networking between different devices.
Because the 2.45 GHz frequency is also used for other devices in the home, engineers had to work out a way to prevent interference. They needed to prevent things like a cell phone accidentally causing a garage door to open. To accomplish this, a Bluetooth transmitter uses a very weak signal, just about one milliwatt.
Additionally, a single Bluetooth transmitter can communicate with up to eight other devices at the same time, without interference. This is done with what is called “spread spectrum frequency hopping.” Since the 2.45 GHz frequency actually encompasses the range between 2.402 GHz and 2.480 GHz, Bluetooth can hop between 79 different randomly chosen frequencies at a rate of 1,600 changes per second. This makes it unlikely that any two devices will be using the exact same frequency at the same time, and if they are, the interference will last no longer than a few milliseconds.