Physical-Layer Architecture

The physical layer is divided into two sublayers: the Physical Layer Convergence Procedure (PLCP) sublayer and the Physical Medium Dependent (PMD) sublayer. The PLCP (Figure 10-1) is the glue between the frames of the MAC and the radio transmissions in the air. It adds its own header. Normally, frames include a preamble to help synchronize incoming transmissions. The requirements of the preamble may depend on the modulation method, however, so the PLCP adds its own header to any transmitted frames. The PMD is responsible for transmitting any bits it receives from the PLCP into the air using the antenna. The physical layer also incorporates a clear channel assessment (CCA) function to indicate to the MAC when a signal is detected.

Figure 10-1. Physical layer logical architecture