Q2 (Adaptive Modulation and Coding) Suppose that the bit error rate (BER) performance can be approximated by P = 0.2e-1.5yG(r)/(M-1), where y is the SNR, Gc (r) denotes the coding gain of the coding rate r which is given as follows r G(r)(dB) 0.25 9 0.5 8 0.75 6 Given a target bit error rate (BER) of P < 10-6, consider a Gaussian channel with SNR y = 13dB, find the optimal coding rate r = {0.25, 0.5, 0.75} and constellation size M {4, 16, 64}in the following options to achieve the maximum spectrum efficiency for variable- rate M-QAM. Justify your answer by detail derivations. A. r = 0.75, M = 4 B.r = 0.75, M = 16 C. r = 0.5, M = 16 D. r = 0.25, M = 64