Bluetooth is a method for data communication that uses short-range radio links to replace cables between computers and their connected units.
History of Bluetooth
Harald Bluetooth was king of Denmark in the late 900s. He managed to unite Denmark and part of Norway into a single kingdom then introduced Christianity into Denmark. He left a large monument, the Jelling rune stone, in memory of his parents. He was killed in 986 during a battle with his son, Svend Forkbeard. Choosing this name for the standard indicates how important companies from the Nordic region (nations including Denmark, Sweden, Norway and Finland) are to the communications industry.
Logo
Bluetooth is managed by the Bluetooth Special Interest Group, which has more than 15,000 member companies in the areas of telecommunication, computing, networking, and consumer electronics. It has a patent logo.
Working of Bluetooth Network
Bluetooth networking transmits data via low-power radio waves. It communicates on a frequency of 2.45 gigahertz (between 2.402 GHz and 2.480 GHz, to be exact). This frequency band has been set aside by international agreement for the use of industrial, scientific and medical devices (ISM).
One of the ways Bluetooth devices avoid interfering with other systems is by sending out very weak signals of about 1 milliwatt. By comparison, the most powerful cell phones can transmit a signal of 3 watts. The low power limits the range of a Bluetooth device to about 10 meters (32 feet), cutting the chances of interference between your computer system and your portable telephone or television. Even with the low power, Bluetooth doesn't require line of sight between communicating devices. The walls in your house won't stop a Bluetooth signal, making the standard useful for controlling several devices in different rooms.
Bluetooth can connect up to eight devices simultaneously. With all of those devices in the same 10-meter (32-foot) radius, you might think they'd interfere with one another, but it's unlikely. Bluetooth uses a technique called spread-spectrum frequency hopping that makes it rare for more than one device to be transmitting on the same frequency at the same time. In this technique, a device will use 79 individual, randomly chosen frequencies within a designated range, changing from one to another on a regular basis. In the case of Bluetooth, the transmitters change frequencies 1,600 times every second, meaning that more devices can make full use of a limited slice of the radio spectrum. Since every Bluetooth transmitter uses spread-spectrum transmitting automatically, it’s unlikely that two transmitters will be on the same frequency at the same time.
Bluetooth Piconet
Piconet is an ad-hoc computer network using Bluetooth technology. Bluetooth communication always designates one of the Bluetooth devices as a main controlling unit - master unit. Other devices that follow the master unit are slave units. The devices can switch roles, by agreement, and the slave can become the master.
Up to 8 active Bluetooth devices can form or become part of temporary small networks Piconets. Bluetooth allows wireless data connections within the Piconet to be dynamically added and removed between nearby devices. The probability of interfering (overlapping) with another Bluetooth system is less than 1.5%.
Bluetooth Scatternet
Piconets can be setup to interact with other Piconets to form larger networks called Scatternets. Scatternets allow the master in one Piconet to operate as a slave in another Piconet. While this allows Bluetooth devices in one Piconet to communicate with devices in another Piconet (cross-Piconet communication), the use of Scatternets requires synchronization (and sharing of data transmission Bandwidth) making them less efficient. (second Figure is a scatternet set up).
