Non-HT duplicate transmission is defined by IEEE 802.11ac. It is used to transmit to non-HT OFDM STAs, HT STAs, or VHT STAs that may be present in a part of a 40 MHz, 80 MHz or 160 MHz channel. The L-STF, L-LTF, and L-SIG fields shall be transmitted in the same way as in the VHT transmission, while the VHT-SIG-A, VHT-STF, VHT-LTF, and VHT-SIG-B fields are not transmitted. The data transmission duplicates the transmission of a 20 MHz 802.11a signal over every 20 MHz frequency segment. For example, an 80 MHz non-HT transmission consists of four 20 MHz 802.11a signals placed next to each other, as shown in the following figure. To reduce the PAPR, a different phase rotation is applied to each 20 MHz segment (e.g., ±90 degrees, 180 degrees).
80 MHz non-HT transmission
For reading convenience, the following equation for the Data field is excerpted from the standard (IEEE P802.11ac/D4.0, October, 2012)
Equation excerption from standard