non-HT signal field (L-SIG)
The Non-HT SignalField (L- SIG), like the Non-HT Long Training Field ( L-LTF), is a training field in the frame of the Null Data Packet ( NDP) announcement of 802.11a. The L-SIG data field describes the data rate and frame length in bytes that the receiver uses to determine the transmission time for the frame. 802.11ac devices set the data rate to 6 Mbps and derive the frame length from that. The L-SIG data field is only one byte in size and is transmitted in two- phase shift ke ying (BPSK).