In a quaternary communication system, one of the four signals s1(t) = 0s2(t) = Ac cos(2πfct)s3(t) = Ac sin(2πfct)s4(t) = Ac cos(2πfct) + Ac sin(2πfct) is transmitted during the interval 0 ≤ t ≤ T, T = n/fc where n is a positive integer. All signals are equal to 0 outside 0 ≤ t ≤ T. The transmitted signal goes through an additive white Gaussian noise channel with zero mean and power spectral density N0/2. Calculate the nearest neighbor hound for the probability of symbol error incurred by the optimum receiver.