Physical Layer (PHY)
IEEE 802.11g PHY specification

The IEEE 802.11g standard was published (finalized) in July 2003. It provides the same theoretical maximum speed as 802.11a, which is 54 Mbps, but operates in the same 2.4 GHz spectrum as 802.11b. Unlike 802.11a, 802.11g is backward compatible with 802.11b. Interoperability among and between all speeds exists, so the entire WLAN does not need to be upgraded when moving to higher speeds. The operating data rates for the different 802.11 standards, along with the frequency band and modulation used, are summarized in Figures and . 802.11g is expected become the standard of choice over 802.11b.

The 802.11g standard requires the use of OFDM for fast data rates (greater than 20 Mbps), as well as backward compatibility with 802.11b CCK encoding. The standard utilizes a hybrid architecture to provide backward compatibility. Even though legacy 802.11b devices will not be able to decode the packet payload of these frames, they are able to "sense" them on the network. The new frames can coexist with 802.11b, similar to the way 802.11b can coexist with older, 2 Mbps 802.11 systems. The pure OFDM specification, which uses a more efficient OFDM-based preamble/header, does not have the same characteristics. 802.11b devices will not sense 802.11g frames, and vice-versa. By taking advantage of the RTS/CTS elements of IEEE 802.11, in which access points speaking both languages can regulate the transmissions, the two can coexist peacefully.