802.11g

802.11g is backwardly compatible with 802.11b, it uses the same channels and uses OFDM for data rates 6, 9, 12, 18, 24, 36, 48 and 54Mbps; whereas DSSS is used for 1, 2, 5.5 and 11Mbps. Because OFDM is more efficient than DSSS you get better throughput with 'g' for the same distance as 'b'. Multipath Interference occurs because the same signal is reflected off different surfaces and takes multiple paths to the receiver. As a consequence the signals can occur out of phase at the receiver and have an attenuating impact on the final signal. OFDM spreads the data over different frequencies thereby reducing the chance of a signal being attenuated as two frequencies are unlikely to fade at the same point in the signal at the receiver end.

Mixing 802.11b clients with 802.11g clients reduces overall data throughput due to the differing modulation schemes. Generally the data throughput in either of a, b or g modes is about 50% of the data rate, however mixing modes reduces this substantially.

Due to sideband noise with OFDM, to handle peaks of modulation the power must be backed off, this applies to Complementary Code Keying (CCK):

and also for OFDM:

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