US Patent 10404517 Orthogonal frequency division multiplex data unit generation and decoding

A communication device receives a physical layer (PHY) data unit that includes i) a first orthogonal frequency division multiplexing (OFDM) symbol corresponding to a legacy signal field of a PHY preamble, and ii) a second OFDM symbol that immediately follows the first OFDM symbol. The communication device determines a first bit sequence corresponding to the first OFDM symbol and a second bit sequence corresponding to the second OFDM symbol. The communication device unscrambles the second bit sequence to obtain an unscrambled second bit sequence, and determines whether the unscrambled second bit sequence matches the first bit sequence. If the unscrambled second bit sequence matches the first bit sequence, the communication device decodes the PHY data unit according to a first communication protocol, and if the unscrambled second bit sequence does not match the first bit sequence, decodes the PHY data unit according to a second communication protocol.