Patent ID: 8891435

Claim:
A method comprising: generating, at a network interface device, a first preamble for a first data unit corresponding to a first physical layer (PHY) mode, wherein generating the first preamble includes generating, at the network interface device, a first short training field (STF) having a first duration and including a repeating first sequence, generating, at the network interface device, a first long training field (LTF) following the first STF, and generating, at the network interface device, a first signal (SIG) field following the first LTF, wherein the first SIG field provides information for interpreting the first data unit, and includes a first orthogonal frequency division multiplexing (OFDM) symbol modulated according to a first modulation technique to indicate to a receiver that the first data unit corresponds to the first PHY mode, wherein the first OFDM symbol (i) begins a first time interval after the first LTF begins and (ii) ends a second time interval after the first LTF begins; and generating, at the network interface device, a second preamble for a second data unit corresponding to a second PHY mode different than the first PHY mode, wherein generating the second preamble includes generating, at the network interface device, a second STF having a second duration greater than the first duration and including a repeating second sequence different than the repeating first sequence, wherein a period of the repeating second sequence is equal to a period of the repeating first sequence, and generating, at the network interface device, a second LTF following the second STF, wherein the second LTF includes a second OFDM symbol that is modulated according to a second modulation technique different than the first modulation technique to indicate to a receiver that the second data unit corresponds to the second PHY mode, and at least partially occupies a location in the second preamble that (i) begins a third time interval after the second LTF begins and (ii) ends a fourth time interval after the second LTF begins, wherein the third time interval is equal to the first time interval and the fourth time interval is equal to the second time interval.