Modulated orthogonal frequency division multiplexing (OFDM) subcarriers generate high sidelobes, resulting in adjacent channel interference (ACI). Current sidelobe suppression techniques, such as inserting guard intervals or cancellation carrier bands, diminish the useful radio spectrum or consume significant wireless device resources. Disclosed is a method of suppressing sidelobes through adding an adaptive extension to OFDM symbols that is calculated to avoid ACI while keeping power consumption to low levels. Bandwidth and user location information are collected by a cognitive radio an utilized to determine the extension used. The method significantly reduces ACI to other bands and reduces the required guard bands, opening the radio spectrum to more efficient use.