A method, in a communication device operating according to a communication protocol, for generating orthogonal frequency division multiplexing, OFDM, signals to be transmitted in a basic service set, BSS, channel, wherein a set of two or more component channels is collectively coextensive with the BSS channel, wherein the communication protocol defines (i) a non-duplicate mode data unit corresponding to a single component channel within the set of two or more component channels and (ii) a non-duplicate mode data unit corresponding to a first set of adjacent component channels within the set of two or more component channels, wherein the non-duplicate mode data unit corresponding to the single component channel has (i) a first number of lower-edge guard tones and (ii) a first number of upper-edge guard tones, wherein the non-duplicate mode data unit corresponding to the first set of adjacent component channels has (i) a second number of lower-edge guard tones and (ii) a second number of upper-edge guard tones, and wherein at least one of (i) the second number of lower-edge guard tones is greater than the first number of lower-edge guard tones or (ii) the second number of upper-edge guard tones is greater than the first number of upper-edge guard tones, the method comprising: determining, at the communication device, that a duplicate mode will be utilized for a first OFDM transmission in the first set of adjacent component channels; and in response to determining that the duplicate mode will be utilized for the first OFDM transmission, generating, at the communication device, a first duplicate mode data unit corresponding to the first set of adjacent component channels, such that the first duplicate mode data unit has one or both of (i) less than the second number of lower-edge guard tones and (ii) less than the second number of upper-edge guard tones, wherein the first duplicate mode data unit includes, for each component channel in the first set of adjacent component channels, one duplicate, in frequency, of the non-duplicate mode data unit corresponding to the single component channel, wherein the non-duplicate mode data unit corresponding to the single component channel has a bandwidth that is greater than or equal to 2 MHz. determining, at the communication device, that a duplicate mode will be utilized for a first OFDM transmission in the first set of adjacent component channels; and in response to determining that the duplicate mode will be utilized for the first OFDM transmission, generating, at the communication device, a first duplicate mode data unit corresponding to the first set of adjacent component channels, such that the first duplicate mode data unit has one or both of (i) less than the second number of lower-edge guard tones and (ii) less than the second number of upper-edge guard tones, wherein the first duplicate mode data unit includes, for each component channel in the first set of adjacent component channels, one duplicate, in frequency, of the non-duplicate mode data unit corresponding to the single component channel, wherein the non-duplicate mode data unit corresponding to the single component channel has a bandwidth that is greater than or equal to 2 MHz. generating, at the communication device, a first duplicate mode data unit corresponding to the first set of adjacent component channels, such that the first duplicate mode data unit has one or both of (i) less than the second number of lower-edge guard tones and (ii) less than the second number of upper-edge guard tones, wherein the first duplicate mode data unit includes, for each component channel in the first set of adjacent component channels, one duplicate, in frequency, of the non-duplicate mode data unit corresponding to the single component channel, wherein the non-duplicate mode data unit corresponding to the single component channel has a bandwidth that is greater than or equal to 2 MHz.