A method for operating a communications system includes transmitting a preamble sequence including a plurality of tones. Each tone of the plurality of tones has a first characteristic and a second characteristic. The first characteristic of each of the tones of the plurality of tones has a predetermined relative relationship to the first characteristic of each of the other tones of the plurality of tones and the second characteristic of each of the tones of the plurality of tones has a predetermined relative relationship to the second characteristic of each of the other tones of the plurality of tones. The first and second characteristics may include relative power and relative phase.