Exponential error bounds for incoherent orthogonal signals (Corresp.)

It is well known that arbitrarily small error probabilities can be obtained at any source rate less than capacity for the band-infinite Gaussian channel by block coding binary digits into either coherent or incoherent orthogonal signals. In this correspondence it is shown that the exponential rate at which the error probability approaches zero with increasing block length is the same for the coherent and incoherent orthogonal signals for any source rate less than channel capacity.