Preamble
The preamble is used to communicate to the receiver that data is on its way. Technically speaking, it is the first portion of the Physical Layer Convergence Protocol/Procedure (PLCP) Protocol Data Unit (PDU). The preamble allows the receiver to acquire the wireless signal and synchronize itself with the transmitter. A header is the remaining portion and contains additional information identifying the modulation scheme, transmission rate and length of time to transmit an entire data frame.
Long Preamble:
* Compatible with legacy IEEE* 802.11 systems operating at 1 and 2 Mbps (Megabits per second)
* PLCP with long preamble is transmitted at 1 Mbps regardless of transmit rate of data frames
* Total Long Preamble transfer time is a constant at 192 usec (microseconds)
Short Preamble:
* Not compatible with legacy IEEE 802.11 systems operating at 1 and 2 Mbps
* PLCP with short preamble: Preamble is transmitted at 1 Mbps and header at 2 Mbps
* Total Short Preamble transfer time is a constant at 96 usec (microseconds)
What does this all mean to the end user?
Most access points (AP) and broadband Wi-Fi routers are configured for a Long Preamble or have a setting that automatically detects the preamble and adjusts accordingly. A majority of client Wi-Fi adapters should also be pre-configured in the same manner. This is done as a precautionary measure for networks that may still employ legacy devices. It is not recommended you make changes to default settings. If this becomes necessary, consult with your equipment manufacturer before taking such action.
