Time-reversal filtering may be used to temporally focus a signal to be transmitted. Power can be reduced at the transmitter so that the temporally focused signal is within spectral mask requirements. In one embodiment, the effect of the time-reversal filter on the power spectral density for a particular transmitted signal can be calculated and the predicted power spectral density can be compared to the permitted spectral mask to identify violations, if any, of the spectral mask. The transmitter power can then be reduced by the amount of the violation. In another embodiment, a set of different time-reversal filters that meet the spectral mask requirements can be provided in advance, and the most appropriate filter—e.g., the one with the best signal-to-noise ratio for the particular signal—can be chosen from the set of filters.