2.15.1 radio, which specifies a frequency hopping spread spectrum system with 1600 hops per second between the 79 channels in the 2.40-2.48 GHz ISM band, and a hopping pattern controlled by the 48-bit MAC address of the master device. In some countries, the hopping pattern is reduced to cover just 23 channels in order to comply with specific local regulations. Gaussian frequency shift keying (GFSK) is used for the standard 1 Mbps PHY layer data rate (Bluetooth 1.2), while enhanced data rate (Bluetooth 2.0) uses t/4-DQPSK at 2 Mbps and 8-DPSK at 3 Mbps. The 2 Mbps rate is mandatory for Bluetooth 2.0 devices, while the 3 Mbps rate, relying on 8-DPSK which has a lower energy per transmitted bit and therefore a lower SNR (recall Eq. 4.1), is optional and only used over sufficiently robust links. To preserve backward compatibility with Bluetooth 1.2, GFSK is still used by Bluetooth 2.0 devices to transmit packet header information. Three classes of RF transmitted power are defined from 0 to 20 dBm (1-100 mW), as shown in Table 10-3. Most Bluetooth devices have class 3 radios, although class 1 adapters are also available, providing a PAN range comparable with an IEEE 802.11b/g wireless Table 10-3: Bluetooth RF Transmitter Power Classes Class Max RF power Range (ft) 100 mW (20 dBm) Up to 300 2.5 mW (4 dBm) Up to 30 1.0 mW (0 dBm) 0.3-3 Transmit power control is mandatory for class 1 radios (optional for class 2 and 3), and requires transmitting devices to dynamically adjust power in order to reduce interference. This also helps to reduce power consumption and extend battery life for portable devices. To implement power control a receiver signal strength indicator (RSSI) is used to determine whether a received signal is within a defined "golden receive power range", typically between 6 and 20 dBm above the receiver sensitivity level. If the received power is outside this power range, the receiver sends a link Wireless PAN Standards manager protocol (LMP) instruction to the transmitter to adjust its transmit power. Baseba