We do coherent demodulation of the BPSK signal at the receiver. Coherent demodulation requires the received signal to be multiplied with the carrier having the same frequency and phase as at the transmitter. The phase synchronization is normally achieved using Phase Locked Loop (PLL) at the receiver. PLL implementation is not done here, rather we assume perfect phase synchronization. Block diagram of BPSK modulator is shown in the figure below. After the multiplication with the carrier (orthonormal basis function), the signal is integrated over the symbol duration ‘T’ and sampled. Then thresholding is applied to determine if a ‘1’ was sent (+ve voltage) or a ‘0’ was sent (-ve voltage).