ce, as they use distinct hopping achieve a sensitivity of -80 dBm at 2 Mbps and typical schemes. A slave in one piconet could be a master in an- transmit power is 30-100 mW. A link between two other. By having some devices participate in multiple compliant class 3 devices has 30 dB less path loss avail- piconets, they can be linked together to form scatternets. able than a link between two 802.11 devices. The Devices within a piconet can exchange information on receiver noise and transmit power requirements are their capabilities, SO that the user may use printers, correspondingly undemanding: Bluetooth devices must cameras, and other peripherals without the need for be inexpensive to build. manual configuration. Devices use inquiry and paging An example of a link budget calculation is shown in modes to discover their neighbors and form new piconets. Figure 5.1-25. We've assumed a transmit power of 1 dBm The Bluetooth/802.15.1 PHY layer operates in and modest antenna directivity (1 dB relative to an iso- the 2.4-GHz ISM band, which is available at least par- tropic antenna [dBi]) and efficiency (80%) as the antennas tially throughout most of the world. The band in the United States is divided into 79 1-MHz channels (Figure 5.1-23), with modest guard bands at each end to minimize out-of-band emissions. path of phase vs. time During normal operation, all members of the piconet hop from one frequency to another 1600 times per phase= second. The dwell time of 625 usec provides for 625 bit times between hops. When a device is in inquiry or paging mode, it hops twice as fast to reduce the time needed to find other devices. phase at t=T phase at t=0 The signal is modulated using Gaussian minimum- shift keying, GMSK (also known as Gaussian frequency- shift keying). GMSK can be regarded as either a GMSK modulation frequency modulation or phase modulation technique. In each bit time, frequency is either kept constant or changed SO as to shift the phase of the signal by TT by the Figure 5.1-24 Gaussian minimum-shift keying.