Disclosed herein is a system and method for determining the presence of rotated-BPSK modulation. In addition, disclosed herein is a system and method for determining if a received packet is a Legacy, Mixed-Mode, or Green-Field packet in accordance with the determination of the presence of rotated-BPSK modulation. The presence of a Green-Field packet may be determined by detecting if additional tones are being excited in an LTF symbol of the received packet and/or if a SIG field symbol following the LTF symbol is modulated by rotated-BPSK. The presence of a Mixed-Mode packet may be determined by detecting if the first four bits of the SIG field symbol following the LTF symbol are [1 1 0 1] and/or detecting if a symbol following an L-SIG symbol is modulated by rotated-BPSK. The presence of a Legacy packet may be determined by detecting if the symbol following the L-SIG symbol is modulated by BPSK.