Chapter 1 What’s New for FortiOS 5.0 : New features in FortiOS 5.0 Patch 6 : 802.11g Protection Mode
  
802.11g Protection Mode
802.11g Protection Mode can now be enabled on managed FortiAP to avoid interference from 802.11b signals. Protection Mode can be set for RTS and CTS protection, or just for CTS.
Syntax
config wireless-controller wtp-profile
edit <name>
config radio-1
set protection-mode {ctsonly | disable | rtscts}
end
end
end