Bluetooth devices operate at the 2.4 G Hz range in the globally available license free ISM band. This band is reserved for the general use by Industrial, Scientific, and Medical applications, which obey a basic set of power and spectral emission and interference specifications. This means the Bluetooth
has to be robust as there are a great many existing users and interferes of this shared spectrum. The operating band is divided into 1Mhz-spaced channels, each signaling data at 1MHz. The modulation scheme used is GFSK (Gaussian Frequency Shift Keying). After each packet, both devices re tune their radio to a different frequency, effectively hopping from channel to channel using an efficient Frequency Hopping Spread Spectrum technique. Each Bluetooth slot lasts 625 m sec. The radio power is one of three classes (1mW, 2,5mW and 100mW), which provide an operation that ranges of approximately 10 m, 20m, and 100; the lowest power gives 10 m range, and the highest power up to 100m.