A method of adding a secondary channel to a QAM signal mapped in the complex plane is provided. A pair of positions in the mapped complex plane is determined such that one-half the sum of the square of the distances to such positions from the origin is no greater than the square of the distance from the origin to the position of the furthest mapped data point. For secondary channel communication, a data point is shifted from a normal position to one or the other of the new positions with one of said positions assuming a binary "1" for the secondary channel and the other of said positions assuming a binary "0".