The Status and Future of 802.11-Based WLANs

T oday's wireless local area networks are designed to support mobile computing in small areas such as a building, park, airport, or office complex. html) defines both an infrastructure mode, with at least one central access point connected to a wired network, and an ad hoc or peer-to-peer mode, in which a set of wireless stations communicate directly with one another without needing a central access point or wired network connection. The main attraction of WLANs is their flexibility. They can extend access to local area networks, such as corporate intranets, as well as support broadband access to the Internet—par-ticularly at " hot spots, " public venues where people tend to gather. WLANs can provide quick, easy wireless con-nectivity to computers, machinery, or systems in a local environment where a fixed communications infrastructure does not exist or where such access is not permitted. These hosts can be stationary , handheld, or even mounted on a moving vehicle. Bandwidth considerations have thus far been secondary in WLAN design and implementation: The original 802.11 standard allowed a maximum channel bit rate of only 2 megabits per second, while the current 802.11b standard—commonly known as Wi-Fi (for " wireless fidelity ")—supports an 11-Mbps maximum rate. However, the widespread deployment of 802.11a and 802.11g standards, which allow a bit rate of up to 54 Mbps, will pave the way for new types of mobile applications , including m-commerce transactions and location-based services. As Table 1 shows, there are a number of IEEE 802.11 standards. One major problem is spectrum availability. The industrial, scientific, and medical (ISM) bands have always been the first choice, with 802.11, 802.11b, and the emerging 802.11g standard all sharing the 2.4-GHz radio band. However, because ISM frequencies are designated for unlicensed commercial use, users can experience significant interference in some locations from ambulances, police cars, taxicabs, and citizen's band radios as well as from other users and many household and office devices operating in ISM bands. The demand for higher bit rates has led to the consideration of wider as well as less crowded bands for WLANs. IEEE 802.11a, for example, uses the 5-GHz band, but because all other working versions of 802.11 use the 2.4-GHz band, backward compatibility is an issue. Dual-band LAN adapters that allow access to both 802.11a and 802.11b are one possible solution but are not widespread. IEEE 802.11g, which is expected to become a standard …