A QPSK modulated signal from an additive white Gaussian noise (AWGN) channel is received with an \(E_b/N_o=8.4\) dB at the input of a coherent QPSK demodulator. A maximum likelihood reception method is used in the demodulator.
Assume the complementary error function \[ erfc(u)\cong\left[1/(u\sqrt{\pi})\right]\exp(-u^2). \]
Which is the nearest bit error rate (BER) at the output of the demodulator?