(a) Given a message signal m(t) = 3cos(2m x 10t) + 5cos(4x10t) + 10cos(12x10t) is to be transmitted over a PCM system. (i) Find the number of bit (M) required if the quantization level (AV) is less than 0.04 V; (3 marks) Find the quantization noise and the Signal to Noise Ratio (SNR) in dB for Nobtained in part (i); (ii) (4 marks) (iii) (iv) If the sampling rate is changed to 9000 samples/sec, can the original signal be completely recovered? Please state the reason. (2 marks) Find the Nyquist frequency and the minimum bit rate required for the PCM signal; and (4 marks) (b) A bit sequence m[n] = 011001 is modulated by Frequency Shift Keying (FSK) xc(t) with a symbol interval of 1 second. (i) (ii) (iii) xc(t) = (5cos4nt for a 1 bit (5cos2nt for a 0 bit Find the frequencies in Hz used for keying "I" bit and "0" bit; (2 marks) (6 marks) Sketch the modulated signal in time domain; and What is the major source of interference for digital modulation? Name one tool to evaluate the interference of digital modulation. (4 marks)