A method for generating a data unit (700, 1200, 1300, 1400) for transmission via a communication channel, the data unit (700, 1200, 1300, 1400) conforming to a first communication protocol, the method comprising: generating a first field (706, 1502) to be included in a preamble of the data unit, wherein the first field includes a first set of one or more information bits that indicate a duration of the data unit, the first field being formatted such that the first field is decodable by a receiver device that conforms to a second communication protocol, but does not conform to the first communication protocol, to determine the duration of the data unit (700. 1200, 1300. 1400) based on the first field (706, 1502): generating a second field (708, 1504) to be included in the preamble, wherein the second field includes a second set of one or more information bits (708-2, 1510) that indicate to a receiver device (14, 25-1) that conforms to the first communication protocol that the data unit conforms to the first communication protocol; modulating the first field using a modulation scheme specified for a field corresponding to the first field by the second communication protocol; modulating the second field using a modulation scheme specified for a field corresponding to the second field by the second communication protocol; generating the preamble to include at least the first field (706, 1502) and the second field (708, 1504): and generating the data unit (700, 1200, 1300, 1400, 1512) to include at least the preamble; wherein generating the second field includes generating the second set of one or more information bits according to an error detection scheme not specified by the second communication protocol (950, 960, 970), including generating a cyclic redundancy check, CRC, for the second field that indicates an error when decoded by the receiver that conforms to the second communication protocol but does not conform to the first communication protocol, characterized in that generating the CRC for the second field comprises: generating a plurality of CRC bits (962, 972) according to a CRC polynomial specified for the corresponding field by the second communication protocol, and encrypting only one or more bits of the plurality of CRC bits (964, 974), the one or more bits being less than all bits of the plurality of CRC bits, to generate the CRC for the second field that indicates the error when decoded by the receiver device that conforms to the second communication protocol but does not conform to the first communication protocol. generating a second field (708, 1504) to be included in the preamble, wherein the second field includes a second set of one or more information bits (708-2, 1510) that indicate to a receiver device (14, 25-1) that conforms to the first communication protocol that the data unit conforms to the first communication protocol; modulating the first field using a modulation scheme specified for a field corresponding to the first field by the second communication protocol; modulating the second field using a modulation scheme specified for a field corresponding to the second field by the second communication protocol; generating the preamble to include at least the first field (706, 1502) and the second field (708, 1504): and generating the data unit (700, 1200, 1300, 1400, 1512) to include at least the preamble; wherein generating the second field includes generating the second set of one or more information bits according to an error detection scheme not specified by the second communication protocol (950, 960, 970), including generating a cyclic redundancy check, CRC, for the second field that indicates an error when decoded by the receiver that conforms to the second communication protocol but does not conform to the first communication protocol, characterized in that generating the CRC for the second field comprises: generating a plurality of CRC bits (962, 972) according to a CRC polynomial specified for the corresponding field by the second communication protocol, and encrypting only one or more bits of the plurality of CRC bits (964, 974), the one or more bits being less than all bits of the plurality of CRC bits, to generate the CRC for the second field that indicates the error when decoded by the receiver device that conforms to the second communication protocol but does not conform to the first communication protocol. generating a plurality of CRC bits (962, 972) according to a CRC polynomial specified for the corresponding field by the second communication protocol, and encrypting only one or more bits of the plurality of CRC bits (964, 974), the one or more bits being less than all bits of the plurality of CRC bits, to generate the CRC for the second field that indicates the error when decoded by the receiver device that conforms to the second communication protocol but does not conform to the first communication protocol.