WLANs define their frame structure In the physical layer, in which protocol information and data
are mapped. The data of the physical layer are provided with a preamble. In the MAC layer, WLANs according to IEEE 802.11 distinguish between two preamble versions: A longer preamble version, which is used for the transmission of data packets with a data transmission rate of 1 Mbit/s, and a short preamble version for the faster systems with 2 Mbit/s, 5.5 Mbit/s, and 11 Mbit/s. Whereby the length of the preamble is not decisive, but the effective length of the Physical Protocol Data Unit (PPDU). The preamble is followed by the Physical Layer Convergence Procedure (PLCP), in whose data fields the transmission rates and modulation methods are defined.