nel 1 Channel 2 Channel 3 Channel 4 Channel 5 10296 528 MHz wide bands, 128 OFDM tones, 100 data, 12 pilots, 10 guards, 6 nulls Figure 4-36: MB-OFDM Frequency Bands and Channels and operating simultaneously on all available bands. Currently, the most important example of this technique is multiband (MB) OFDM, which is being promoted by the MB-OFDM Alliance (MBOA) and has been adopted as the basis for Wireless USB and Wireless FireWire (Wireless 1394). MB-OFDM, as proposed by the MBOA, uses a bandwidth from 3.168 GHz to 10.560 GHz, which is divided into 14 bands of 528 MHz full width - thus meeting the FCC's 500 MHz minimum bandwidth specification. The 14 bands are grouped into 5 band groups or channels, as shown in Figure 4-36. Frequency hopping between bands within a band group can be used to enable overlapping piconets to be formed but unlike Bluetooth, which makes 1600 hops per second across 79 frequencies, the MBOA radio as specified for wireless USB makes 3 million hops per second, one hop after every transmitted symbol, across just 3 frequencies. MBOA specifies two types of time-frequency codes (TFC) as shown in Table 4-21. Time-frequency interleaving (TFI) codes define frequency hopping patterns, while fixed frequency interleaving (FFI) codes define continuous transmission on a single OFDM band. The FFI option can be used to improve the performance of two or more simultaneously operating piconets, by assigning a single OFDM band to each piconet. Within each 528 MHz band, 128 OFDM subcarriers are transmitted, with data modulated onto 100 of these and the remainder used as pilot, guard and null tones. For data rates of up to 200 Mbps, MBOA specifies data modulation using QPSK, while rates of 320 to 480 Mbps use dual carrier modulation (DCM). Chapter Four Table 4-21: MBOA Time-frequency Codes Code number Code type Band number (Band group 1) Spectral shaping is used to avoid interference with other RF services and can be changed under software control to respond to specific local regulations or time-varying co