802.11a, is much faster than 802.11b, with a 54Mbps maximum data rate operates in the 5GHz frequency range and allows eight simultaneous channels.
802.11a uses Orthogonal Frequency Division Multiplexing (OFDM), a new encoding scheme that offers benefits over spread spectrum in channel availability and data rate.
Channel availability is significant because the more independent channels that are available, the more scalable the wireless network becomes. 802.11a uses OFDM to define a total of 8 non-overlapping 20 MHz channels across the 2 lower bands. By comparison, 802.11b uses 3 non-overlapping channels.
All wireless LANs use unlicensed spectrum; therefore they&qt;&qt;re prone to interference and transmission errors. To reduce errors, both types of 802.11 automatically reduce the Physical layer data rate. IEEE 802.11b has three lower data rates (5.5, 2, and 1Mbit/sec), and 802.11a has seven (48, 36, 24, 18, 12, 9, and 6Mbits/sec). Higher (and more) data rates aren&qt;&qt;t 802.11a&qt;&qt;s only advantage. It also uses a higher frequency band, 5GHz, which is both wider and less crowded than the 2.4GHz band that 802.11b shares with cordless phones, microwave ovens, and Bluetooth devices.
The wider band means that more radio channels can coexist without interference. Each radio channel corresponds to a separate network, or a switched segment on the same network. One big disadvantage is that it is not directly compatible with 802.11b, and requires new bridging products that can support both types of networks. Other clear disadvantages are that 802.11a is only available in half the bandwidth in Japan (for a maximum of four channels), and it isn&qt;&qt;t approved for use in Europe, where HiperLAN2 is the standard.