icensed-National Information Infrastructure) band, divided into three sub-bands: - sub-band A covering the frequency band 5.150-5.350 GHz; - sub-band B covering the frequency band 5.470-5.725 GHz; - sub-band C covering the frequency band 5.725-5.825 GHz. 802.11a/g Interfaces The bandwidth of the radio channel is equal to 20 MHz. Table 3.5 provides, for each sub-band, the channel number and the value of the center frequency. Sub-band A Sub-band B Sub-band C Central Central Central Channel Channel Channel frequency frequency frequency number number number (GHz) (GHz) (GHz) 5.180 5.500 5.745 5.200 5.520 5.765 5.220 5.540 5.785 5.240 5.560 5.805 5.260 5.580 5.280 5.600 5.300 5.620 5.320 5.640 5.660 5.680 5.700 Table 3.5. U-NII band at 5 GHz Countries apply their own regulations to authorized channels, authorized users and maximum power levels in these frequency ranges. Table 3.6 summarizes the rules applied in Europe for sub-bands A (5.150-5.350 GHz) and B (5.470-5.725 GHz). Dynamic frequency selection (DFS) allows access points to automatically select frequency channels with low levels of interference. Transmit power control (TPC) automatically reduces output power when other networks are in range. Reduced power means reduced interference problems and increased battery capacity. Wi-Fi Integration to the 4G Mobile Network Radio channels Maximum power TPC function DFS function 36 to 48 200 mW 200 mW 48 to 64 100 mW 100 to 140 500 mW Table 3.6. European regulations 3.2. 802.11g interface The 802.11g interface, called ERP (Extended Rate Physical), must be compatible with the 802.11 interface, called DSSS (Direct Sequence Spread Spectrum), which provides the bit rates at 1 and 2 Mbps. The 802.11g interface must also be compatible with the 802.11b interface, called HR (High Rate)/DSSS, which provides the bit rates at 1, 2, 5.5 and 11 Mbps. The 802.11g interface implements the functions of the 802.11a interface, except that it uses the ISM (Industrial, Scientific and Medical) frequency band at 2.4 GHz. The ERP access point