Bluetooth technology
Bluetooth technology is an research standard with standard no 802.15.1, for wireless networking of small peripheral. The wireless technology is used in many applications, for example wireless headsets for mobile phones. Bluetooth enables a user to replace cables between devices such as printers, desktop computers and many other digital devices. Bluetooth transmitters enable communication between devices up to a maximum distance of 100 meters [1]. Bluetooth devices operates in the unlicensed 2.4 GHz ISM band, for Industrial Scientific Medical. The operating frequency band is 2400 – 2483.5 MHz. 79 RF 1 MHz channels are spaced at the frequencies f = 2402 + k MHz where k=0,…, 78. At the lower and upper band edge a few MHz are used as guard band. The unlicensed ISM band is free to use if the transmitted power is sufficiently low. In connection, output power shall not exceed 4 dBm. Devices are classified into three power classes. If the transmitted power level is over 4 dBm, classified as power class 1, devices must implement power control for limiting the transmitted power. Power control for power class two, devices having a maximum output power of 4 dBm, is optional and could be used for optimizing power consumption . Bluetooth employs frequency hopping for access. Frequency hopping means that the carrier frequency is “hopped” between frequencies according to a chosen code, avoiding interference with other devices. Transmission only remains on a given frequency for a short time, and if any interference is present data will be re-sent when the signal has changed to a different channel which is likely to be clear of other interfering signals.