Quadrature PSK). In reaching 5.5Mbps and the full rate of 11Mbps, 802.11b uses QPSK, coupled with an error control technique called Complementary Code Keying (CCK). IEEE 802.11a, also published in 1999, makes use of OFDM transmission, increasing the speeds to a theoretical rate of 54Mbps, but with a real throughput experience of 27Mbps or less. This standard operates in the 5GHz range over a smaller coverage range of 150 feet (50 m). (Remember that the higher the fre- quency, the faster the signal loses power, which means the coverage area must be smaller.) IEEE 802. lla is not backward compatible with 802.11b. Published in 2003, IEEE 802.11g uses OFDM and operates in the 2.4GHz band, with a range of up to 300 feet (100 m). Because 802.11g transmits in the same band as 802.11b, the standards are compatible. However, if 802.11b and 802.11g devices are communicating with each other, they perform at the lowest common denomi- nator, SO they operate at the slower 802.11b speed. IEEE 802.11g supports 54Mbps in theory, but it offers an actual throughput of 27Mbps under ideal conditions and Table 15.6 IEEE 802.11b, 802.11a, and 802.11g Standards Capacity Capacity Number Number of Number of Channel Channel Band Used/ Channels Channels Channels Standard (Theoretical) (Actual) Range Technology (U.S.) (Asia) (Europe) 802.11b 11Mbps 5Mbps 2.4GHz/100 n 802.11a 54Mbps 27Mbps 5GHz/501 802.11g 54Mbps 27Mbps 2.4GHz/100 m WLANs less when the distance between the transmitter and receiver is longer. In addition, in networks where the WAPs support a mix of 802.11b and 802.11g, the through- put drops to 18Mbps, and when multiple clients are transmitting, the throughput is further reduced to approximately 6Mbps to 9Mbps. Crowded Bands The 2.4GHz band is getting increasingly crowded, so 802.11b and 802.11g networks share spectrum with the likes of household microwave ovens, cordless telephones, and many industrial, scientific, and medical systems, not to mention a growing number of WMAN and WPAN technologies designed to operate in the un