5. (a) Describe how coherent detection affects the signal to noise ratio in Amplitude Modulation (AM) demodulation. [8 marks] (b) A digital stream 1000110110 is to be modulated using the Quadrature Phase Shift Keying (QPSK) modulation scheme. Sketch the in-phase and quadrature amplitudes for the digital stream against time. [6 marks] (c) Sketch the constellation diagram of the Offset QPSK (OQPSK) scheme and explain how it differs from QPSK modulation. [5 marks] (d) Figure Q5(d) shows a waterfall graph for a variety of digital modulation schemes. A wireless communication system is required that uses a modulation scheme with a minimum Bit Error Rate (BER) of 1e-5. With reference to bandwidth efficiency, power efficiency and resistance to noise, compare the performance of the QPSK and 32-PSK schemes in figure Q5(d) if they were used in the required communication system. [6 marks] Synbol Error Probability, Ps 1 0,1 0,01 0.001 1e-04 1e-85 1e-06 0 Symbol Error rate for various nodulation schenes 5 10 15 20 Es/No, dB Figure Q5(d) 25 BPSK 4PAM QPSK 16QAM 16PSK 64QAM 32PSK 30 35