A digital communication system uses symmetric binary symbols +a and -a. The channel is AWGN with generic noise variance σ 2 . The symbol spacing is chosen such that a = 3σ, and the two symbols hav

 A digital communication system uses symmetric binary symbols +a and -a. The channel is AWGN with generic noise variance σ 2 . The symbol spacing is chosen such that a = 3σ, and the two symbols have a-priori probabilities P(+a) = 3/5 and P(-a) = 2/5. Calculate the optimal decision threshold and write an expression of the SER/BER in these cases: a) Using the ML (maximum likelihood) principle b) Using the MAP (maximum a-posteriori) principle