The History and Basics of 802.11

The desire of people to communicate wirelessly spans many generations and technologies. Some might even argue that the ancient activity of lighting fires and using smoke signals was an early attempt to distribute a message without wires. In this book, however, we refer to the term “wireless” in the context of a modern data network. In other words: the ability to transmit and receive binary data from one location to another. A great deal of wireless data technology evolved in the late 20th century. Unfortunately, these wireless devices were typically proprietary and expensive.Their uses included specialized applications, such as remote cash registers and warehouse inventory systems.
After spending the better part of the 1990s engaged in technical discussions, the Institute of Electrical and Electronics Engineers (IEEE) ratified the 802.11 protocol in 1997.The original protocol supported three physical layer definitions: Direct Sequence Spread Spectrum (DSSS), Frequency Hopping Spread Spectrum (FHSS), and InfraRed (IR).The supported data rates for DSSS and FHSS were 1 and 2 Mbps.These protocols operated in the 2.4 GHz unlicensed spectrum. IR remains an interesting footnote in the history of 802.11, as it never achieved any notable commercial success due to its limited range and line of sight requirements.
In 1999, the higher speed 802.11a and 802.11b protocols were ratified. 802.11b added 5.5 and 11 Mbps support using DSSS in 2.4 GHz, making it backwards-compatible with existing 1 and 2 Mbps DSSS gear (but not compatible with FHSS or IR equipment). 802.11a added Orthogonal Frequency Division Multiplexing (OFDM) as a modulation technique in the 5 GHz unlicensed spectrum, with speeds of up to 54 Mbps. In 2003, 802.11g was ratified, which provided higher speeds (up to 54 Mbps). 802.11g works by applying OFDM modulation techniques in the 2.4 GHz unlicensed spectrum. It remains backwards-compatible with 802.11b by integrating DSSS modulation (at 11, 5.5, 2, and 1 Mbps).