The PLCP supported by 802.11a systems is shown below. The description of the different members of the PLCP is also incorporated.
Fig Courtesy: 802.11 standards
- PLCP starts with training sequence (PLCP preamble), followed by the SIGNAL field and data.
- Both the training sequence and the 24 bit SIGNAL field are transmitted at 6Mbps rate.
- The SIGNAL field tells the receiver at what rate the following data will be transmitted and indirectly defines the subcarriers’ modulation technique employed.
- BPSK, QPSK, 16-QAM and 64-QAM are the available choices. The SIGNAL field also delivers the length (12 bit) of the following data
- The service field consists of seven bits as logic zeros to synchronize the descrambler in the receiver and another nine bits (currently all logic zeros) reserved for future use.
- The total training sequence and SIGNAL field transmission times add up to about 20 µs, which is an overhead equivalent to approximately 140 bytes transmission at the maximum transmission rate of 54Mbps defined by the standard.
- The data is followed by 6 tail bits and padding
The interpretation of the signal field values/scrambler initialization and the timing diagram for the 802.11a PLCP is shown below
The Length field defines the length of the data section in bytes.
The Timing diagram is given below
FIG COURTESY: 802.11 standard
The Rate table description is given below
