A field of a preamble of the data unit is decoded using a tail biting technique, including decoding a received cyclic redundancy check (CRC) included in the field. A first CRC for the field is generated using a first CRC generation scheme, and a second CRC for the field is generated using a second CRC generation scheme. The first generated CRC and the second generated CRC are compared to the received CRC. It is determined that the data unit conforms to a first communication protocol when the first generated CRC matches the received CRC, and it is determined that the data unit conforms to a second communication protocol when the second generated CRC matches the received CRC.