PLCPs

PLCP stands for Physical Layer Convergence Protocol, a sublayer of the IEEE 802.11 wireless LAN physical layer. It sits between the MAC (media access control) layer and the physical medium-dependent (PMD) layer, providing a standardized interface for transmitting and receiving MAC frames over different physical technologies. The PLCP’s main purpose is to converge the diverse PHY implementations used by 802.11 into a common framing and signaling scheme so that higher layers can operate independently of the underlying radio modulation.

In operation, the PLCP encapsulates the MAC service data unit (MSDU) into a PHY service data unit (PSDU), then adds a PLCP header and a preamble before the PMD modulates and transmits the signal. On reception, the preamble and PLCP header allow the receiver to synchronize, identify the data rate, determine the length of the incoming frame, and correctly demodulate the payload before passing the recovered MSDU to the MAC layer. The PLCP header typically carries control information such as the physical layer rate and frame length, while the preamble aids timing and carrier synchronization.

The exact fields and signaling of the PLCP vary across different 802.11 PHYs (such as DSSS, OFDM-based 802.11a/g/n/ac/ax), but the overarching concept remains constant: it provides a PHY-independent wrapper that enables reliable framing, rate information, and synchronization across diverse physical layers. In practice, the PLCP is a key component for achieving interoperability among devices and ensuring efficient data transfer in wireless networks. See also IEEE 802.11, PHY, PMD, PSDU, and PHR.