ess Control) layers of systems in the 10GHz to 66GHz bands, generally known as LMDS. LMDS is characterized by very high data rates and quite short range due to rain and foliage attenuation. The 802.16 standard requires line of sight to the base station. It accounts for high-frequency BFWA, where there is more available spectrum, along with larger frequency allocations. Operating at higher frequencies increases the cost of both base stations and customer premises equipment (CPE). In addition, user antennas require realignment whenever a new cell is added to the network. Several revisions to the 802.16 standard have been released. The 802.16a stan- dard, including 802.16a Revision d (REVd), supports operation in the 2GHz to 11GHz bands, using OFDM to mitigate the impairments fading and multipath. IEEE 802.16 aims to fill the gap between high-data-rate WLANs and high-mobility cellu- lar WANs. The sub-11GHz frequency ranges specified in 802.16a make possible non-line-of-sight systems. Such systems are required for last-mile applications where obstacles such as trees or buildings exist and where base stations may need to be discreetly mounted on homes or buildings rather than on towers. A single 20MHz channel can simultaneously support up to 60 businesses with connectivity at the T-1/E-1 level and hundreds of residences with DSL-rate connectivity. The 802.16a REVd standard uses OFDM and supports fixed and nomadic access in line-of-sight and non-line-of-sight environments. Vendors are developing indoor and outdoor CPE and laptop PC cards. The IEEE 802.16e standard, called Mobile WiMax, calls for operation on fre- quencies below 6GHz and does not require line of sight. It uses Scalable Orthogo- nal Frequency Division Multiple Access (SOFDMA), a multicarrier modulation technique that uses subchannelization, where channel bandwidths are selectable, ranging between 1.25MHz and 20MHz, with up to 16 logical subchannels. The key attribute of IEEE 802.16e is that it introduces mobility, including a handoff capa- bility for use