Physical layer frame format for WLAN
In a method for generating a data unit conforming to a first communication protocol, a first field and a second field to be included in a preamble of the data unit are generated. The first field includes a first set of one or more information bits that indicate a duration of the data unit and is formatted such that the first field allows a receiver device that conforms to a second communication protocol to determine the duration of the data unit. The second field includes a second set of one or more information bits that indicate to a receiver device that conforms to the first communication protocol that the data unit conforms to the first communication protocol. The first field and the second field are modulated using a modulation scheme specified for a field corresponding to the first field and the second field, respectively, by the second communication protocol.
1. A method, comprising:
receiving a data unit, wherein the data unit conforms to a first communication protocol or to a second communication protocol;
decoding a field of a preamble of the data unit, including decoding a received cyclic redundancy check (CRC) included in the field;
generating, based on the field, a first CRC using a first CRC generation scheme, the first CRC generation scheme specified for the first field by the first communication protocol;
generating, based on the field, a second CRC using a second CRC generation scheme, the second CRC generation scheme specified for the field by the second communication protocol;
comparing (i) the first generated CRC and (ii) the second generated CRC to the received CRC;
determining that the data unit conforms to the first communication protocol when the first generated CRC matches the received CRC; and
determining that the data unit conforms to the second communication protocol when the second generated CRC matches the received CRC.
2. A method according to claim 1 , wherein:
generating the first CRC comprises generating the first CRC according to a first CRC polynomial, the first CRC polynomial specified for the field by the first communication protocol, and
generating the second CRC comprises generating the second CRC according to a second CRC polynomial, the second CRC polynomial specified for the field by the second communication protocol, wherein the second CRC polynomial is different than the first CRC polynomial.
3. A method according to claim 1 , wherein:
generating the first CRC comprises generating the first CRC according to a first CRC polynomial, the first CRC polynomial specified for the field by the first communication protocol, and
generating the second CRC comprises:
generating a plurality of CRC bits according to the first CRC polynomial, and
encrypting one or more bits of the plurality of CRC bits to generate the second CRC.
4. A method according to claim 1 , wherein:
generating the first CRC comprises generating the first CRC according to a first CRC polynomial, the first CRC polynomial specified for the field by the first communication protocol, and
generating the second CRC comprises:
generating a plurality of CRC bits according to the first CRC polynomial,
selecting a subset of the plurality of CRC bits, the subset to be utilized for the CRC for the second CRC; and
encrypting one or more bits in the selected subset of the plurality of CRC bits to generate the second CRC.
5. An apparatus, comprising:
a network interface configured to:
receive a data unit, wherein the data unit conforms to a first communication protocol or a second communication protocol;
decode a field of a preamble of the data unit, including decoding a received cyclic redundancy check (CRC) included in the field;
generate, based on the field, a first CRC using a first CRC generation scheme, the first CRC generation scheme specified for the first field by the first communication protocol;
generate, based on the field, a second CRC using a second CRC generation scheme, the second CRC generation scheme specified for the field by the second communication protocol;
compare the first generated CRC and the second generated CRC to the received CRC;
determine that the data unit conforms to the first communication protocol when the first generated CRC matches the received CRC; and
determine that the data unit conforms to the second communication protocol when the second generated CRC matches the received CRC.
6. Apparatus according to claim 5 , wherein the network interface is configured to:
generate the first CRC according to a first CRC polynomial, the first CRC polynomial specified for the field by the first communication protocol, and
generate the second CRC according to a second CRC polynomial, the second CRC polynomial specified for the field by the second communication protocol, wherein the second CRC polynomial is different than the first CRC polynomial.
7. Apparatus according to claim 5 , wherein the network interface is configured to:
generate the first CRC according to a first CRC polynomial, the first CRC polynomial specified for the field by the first communication protocol, and
generate the second CRC at least by:
generating a plurality of CRC bits according to the first CRC polynomial, and
encrypting one or more bits of the plurality of CRC bits to generate the second CRC.
8. Apparatus according to claim 5 , wherein the network interface is configured to:
generate the first CRC according to a first CRC polynomial, the first CRC polynomial specified for the field by the first communication protocol, and
generate the second CRC at least by:
generating a plurality of CRC bits according to the first CRC polynomial,
selecting a subset of the plurality of CRC bits, the subset to be utilized for the CRC for the second CRC; and
encrypting one or more bits in the selected subset of the plurality of CRC bits to generate the second CRC.