What is Bluetooth
Bluetooth is a standardized platform developed for the purpose of wireless data communication between various electronic devices such as computers, printers, mobile phones etc. The following are the main technical features of a Bluetooth Network:-
The unlicensed frequency band of 2.4 GHz to 2.483 GHz is used in this technology to provide data rates as high as 723.2 Kbps. Time division multiplexing is used for sharing of the radio channel if more than two devices are a part of the blue tooth network. Frequency Hopping Spread Spectrum technique over a total of 79 channels is used for communication between two devices. In Bluetooth 1.2, adaptive frequency hopping technique is used in order to lessen the interference from devices such as microwaves, wireless cameras etc that operate in the same frequency band as that of Bluetooth. Time Division Duplexing is used to allow for duplex mode of communication between the devices. Each blue tooth device is recognized by a globally unique 48 bit address in the network. The data is transmitted in the form of packets known as Packet Data Units. The range of a Bluetooth device can vary from 1 meter up to a 100 meters depending upon the power rating of the device. Adjustable power schemes are used in devices with higher power ratings.
Let us then briefly see how a Bluetooth connection works:-
One of the Bluetooth devices acting as a Master sends out bursts of inquiry messages on all the channels using its frequency hopping sequence. The second device acting as the slave if placed in discoverable mode will be hopping between these channels at a much slower rate in order to monitor them for any inquiry messages. After a while, the Master and Slave will eventually be present on the same channel and the slave will receive the inquiry message. After waiting a certain period of time to avoid collision with other devices that might also have received the inquiry message, the slave responds to the Master with its Bluetooth address. Thus the Master discovers the slave device. After discovery, pairing of the devices occur. Both devices are asked to enter a pin code to create a secret key between them. Here the pin number entered by both the devices should be same or otherwise the connection will fail.
Once the connection is established, the Master sends the slave its own address and a frequency hopping sequence is determined using the same. Thus the slave is tuned to the hopping sequence of the Master and data communication can proceed.