OFDM: Back to the Wireless Future

A key limitation for wireless technologies has been slow transmission rates that didn't come close to providing the capabilities of wireline services. This left the technologies unable to offer fast downloads or handle mul-timedia and other desirable applications. Now, however, wireless approaches that use orthogonal frequency division multiplexing (OFDM)—a modulation technique for transmitting large amounts of digital data over a radio wave—are boasting high speeds. For example, IEEE 802.11a and 802.11g wireless LAN (WLAN) standards offer theoretical maximum speeds of 54 Mbits per second, with real-world data rates of up to 22 Mbps. This is higher than the rates produced by previous WLAN technologies such as IEEE 802.11b. The European Telecommunications Standards Institute's proposed Hiper-LAN2 (high-performance radio LAN 2) and Japan's Mobile Multimedia Access Communications broadband WLAN technologies also use OFDM. In addition to WLANs, vendors like Flarion Technologies and NextNet Wireless are using OFDM to bring higher speeds to fixed-wireless metropolitan area networks (MANs). Service providers are also looking at OFDM for their broadband mobile services , including those used in cellular phones and PDAs. In fact, even as code-division multiple access (CDMA)-based third-generation (3G) mobile wireless data and voice services finally enter the US market, some companies are looking to OFDM to drive faster 4G wireless systems. However, OFDM probably won't experience completely smooth sailing. For example, Allen Nogee, senior analyst for wireless component technology at In-Stat/MDR, a market research firm, said that with cellular 4G, even if OFDM is proven to be superior technology , market-leading CDMA-based vendors and carriers are likely to fight to maintain their large customer base. Also, numerous incompatible OFDM standards may limit the technology's broad usefulness and widespread adoption. While new to wireless technology, OFDM dates back to the late 1960s, as the subject of research into ways to minimize interference among transmission channels close to one another in frequency. OFDM has been used in such disparate ways as asymmetric-DSL broadband Internet access, as well as European digital audio and video broadcast services. The principal driving forces behind OFDM's increased popularity in wireless technology are the general demand for faster approaches and the specific desire to run multimedia applications, which are data intensive and thus require higher speeds. OFDM has become practical for more widespread use because it relies on high-speed digital signal processors, and DSPs have only recently become available at a price that makes OFDM a competitive technology in the …