ary Code Keying) mode; - bits b3, b5 and b6 are set to ZERO for the CCK mode. 60 Wi-Fi Integration to the 4G Mobile Network 3.2.1.2. ERP-OFDM mode The structure of the PLCP frame is described in Figure 3.7. PLCP header Reserved LENGTH Parity SERVICE Signal 4 bits 1 bit 12 bits 1 bit 6 bits 16 bits 6 bits Extension Preamble SIGNAL Signal Extension Figure 3.7. PLCP frame for ERP-OFDM mode The PLCP frame is followed by a period (Signal Extension) without transmission with a duration of 6 us. The SIFS time for the 802.11a interface is equal to 16 us to allow additional time for the convolutional decoding process to complete. To be compatible with the 802.11b interface, the SIFS time for 802.11g interface is equal to 10 us. This extra length extension of 6 us thus makes it possible to ensure that the convolutional decoding process ends. 3.2.1.3. DSSS-OFDM mode The structure of the PLCP frame is described in Figure 3.8. Short / Long header training SIGNAL Signal preamble Extension sequence 802.11a 802.11b OFDM signal Figure 3.8. PLCP frame for DSSS-OFDM mode The SIGNAL field of the PLCP header must be set to a value of 3 Mbps. The PLCP header is similar to that described for the ERP-HR/DSSS mode. 802.11a/g Interfaces The payload of the PLCP frame consists of a long learning sequence, the OFDM SIGNAL field, which provides information on the rate and length of the DATA field, and a signal extension section to provide additional processing time for convolutional decoding. 3.2.2. PMD sub-layer The 802.11g interface operates in the ISM band at 2.4 GHz, covering the 2.4-2.4835 GHz frequency band. The bandwidth of the radio channel is equal to 22 MHz for the 802.11b interface and 20 MHz for the 802.11g interface. Figure 3.9 shows the channel number and the value of the center frequency. To avoid overlapping channels, it is recommended to use channels 1, 6 and 11. Channel 14 has been designated for specific use in Japan. The radio spectrum from 2.400 to 2.450 GHz (channels 1 to 8) is shared with radio amateurs. Channels 1, 5, 