User`s guide

Appendix
User’s Guide 9-38 BreezeNET PRO.11 Series
9.5.9 Frame Formats
All 802.11 frames are composed of the following components:
Preamble PLCP Header MAC Data CRC
9.5.9.1 Preamble
This is PHY dependent, and includes:
• Synch: An 80-bit sequence of alternating zeros and ones, which is used by the
PHY circuitry to select the appropriate antenna (if diversity is used), and to
reach steady-state frequency offset correction and synchronization with the
received packet timing.
• SFD: A Start Frame delimiter which consists of the 16-bit binary pattern 0000
1100 1011 1101, which is used to define frame timing.
9.5.9.2 PLCP Header
The PLCP Header is always transmitted at 1 Mbit/s and contains Logical
information used by the PHY Layer to decode the frame. It consists of:
• PLCP_PDU Length Word: which represents the number of bytes contained in
the packet. This is useful for the PHY to correctly detect the end of packet.
• PLCP Signaling Field: which currently contains only the rate information,
encoded in 0.5 Mbps increments from 1 Mbit/s to 4.5 Mbit/s.
• Header Error Check Field: Which is a 16 Bit CRC error detection field.