Further, owing to its multi-channel capability, 802.11ac supports enhanced protection in which the RTS/CTS handshake
mechanism is modified to support static or dynamic bandwidth reservation and carry the channel bandwidth information. The idea is that both RTS and CTS frames are transmitted by VHT STA using the non-high-throughput (non-HT) duplicate PHY convergence procedure (PLCP) protocol data unit (PPDU) upon successful clear channel assessment. Accordingly, the
duplication of a 20 MHz non-HT transmission in every adjacent 20 MHz channel of a wider channel bandwidth provides backward compatibility with legacy devices. In this way, legacy STAs could decode the RTS and CTS frames and update their network allocation vector to prevent hidden terminal problem, which will escalate with the multi-channel operations of 802.11ac, on the secondary channels of a VHT
STA. Additionally, the channel bandwidth information in the
RTS and CTS frames together with the 802.11ac channelization
will enable neighboring VHT STAs to gain knowledge of
the VHT STA’s secondary channels.