Chapter 3. Speeds and Feeds

In this chapter, we discuss the Physical (PHY) layer^[1] protocols that have been developed for IEEE 802.11-based WLANs, with the focus on the speeds and throughput that can be achieved by each. The discussion in this chapter covers the PHY-layer protocols that were defined in the following documents:

^[1] Chapter 2 includes a discussion of the OSI-RM, of which the PHY is the lowest layer.

• IEEE 802.11-1999 (the base specification)

• IEEE 802.11a-1999

• IEEE 802.11b-1999

This chapter also covers the work that has just been completed in the IEEE 802.11 Working Group's Task Group "g" (TGg), which has produced a document that is known as IEEE 802.11g-2003. In terms of the speeds at which the IEEE 802.11g-2003 standard operates, there is a significant overlap with the IEEE 802.11a-1999 standard.

This chapter contains the following information. The first sections involve an overview of the performance of the various PHYs. For many readers, this will be all they want to know about IEEE 802.11 PHY layer protocols, since it summarizes the speeds and modulations that are employed. The overall structure of an IEEE 802.11 implementation is described, including the PHY (which includes the radio frequency (RF) unit and the Baseband Processor (BBP, the modulation/demodulation circuitry), and the MAC, which leads naturally into the next chapter, which begins to cover the MAC sub-layer protocol. This chapter also includes some lower-level details, including the PHY layer encapsulations, and high-level details of the modulation schemes used to achieve the various bit rates over either 2.4 GHz or 5 GHz frequency bands.