Orthogonal Frequency Division Multiplexing

 
Orthogonal Frequency Division Multiplexing
802.11a is based on OFDM. OFDM is not a new technique. Most of the fundamental work was done in
the late 1960s, and U.S. patent number 3,488,445 was issued in January 1970. Recent Digital Subscriber
Line (DSL) work (such as High-bit-rate Digital DSL [HDSL], Very high-bit-rate DSL [VDSL], and
Asymmetrical DSL [ADSL]) and wireless data applications have rekindled interest in OFDM, especially
now that better signal-processing techniques make it more practical. OFDM does, however, differ from
other emerging encoding techniques such as Code Division Multiple Access (CDMA) in its approach.
CDMA uses complex mathematical transforms to put multiple transmissions onto a single carrier; OFDM
encodes a single transmission into multiple subcarriers. The mathematics underlying the code | division
in CDMA is far more complicated than in OFDM. OFDM devices use one wide frequency channel by
breaking it up into several component subchannels. Each subchannel is used to transmit data. All the low
subchannels are then multiplexed into one code | division combined channel.