e of King Blätand, a piconet end of the period T (Figure 5.1-24). Because the ampli- consists of one device that acts as the master and tude remains constant during this process, the peak-to- a number of other devices that are slaves. Each piconet is average ratio of a GMSK signal is essentially 1, SO such identified by the FH pattern it uses. The hopping clock is signals place modest requirements on transmitter and set by the master device, and slaves must remain syn- receiver linearity. GMSK is similar to BPSK, but BPSK chronized to the master to communicate. Provisions are systems have no such constraint on the trajectory taken made to permit devices both to discover nearby piconets between phase points and thus may have large amplitude and spontaneously form their own. variations during the transition from one symbol to an- Only seven slave devices can be active at any given other. Each GMSK symbol carries only a single bit, and time. Some of the active devices can be placed in thus 1 Msps = 1 Mbps of data transfer capacity. a power-saving sniff state, in which they only listen for Bluetooth radios come in three classes: class 1 can their packets occasionally, or hold states, in which they do transmit up to 20 dBm (100 mW), class 2 is limited to not actively participate in the piconet for some period of 4 dBm (2.5 mW), and class 3 devices, the most common, time before checking back in. Additional members of the operate at 1 mW (0dBm). Bluetooth receivers are re- piconet may be parked: in the parked state, slaves quired to achieve a bit error rate of 0.1% for a received maintain synchronization with the master clock by lis- signal at -70 dBm: that's a raw bit error rate of about tening to beacons periodically but do not otherwise par- 60% for 600-bit packets. These specifications are rather ticipate until instructed to become active. less demanding than the corresponding 802.11 re- Piconets can physically overlap with one another with quirements: recall that an 802.11 receiver is required to minimal interferen