Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Paper format. Engineers Canada national examination 16-Elec-A3 — Signals and Communications, May 2018. Closed book (one approved Casio or Sharp calculator permitted), 3 hours, 4 pages. Five questions, all compulsory, all of equal value (20 marks each). All five are solved in full below, every sub-part answered.
Reference texts. B. P. Lathi & Z. Ding, Modern Digital and Analog Communication Systems, 5th ed. (AM modulation and detection, PCM quantisation, frequency conversion); B. P. Lathi, Linear Systems and Signals, 2nd ed. (Fourier series of pulse trains, signal power); A. V. Oppenheim & A. S. Willsky, Signals and Systems, 2nd ed. (discrete-time LTI systems, convolution, DTFT); J. G. Proakis & D. G. Manolakis, Digital Signal Processing, 4th ed. (difference equations, frequency response); S. Haykin, Communication Systems, 5th ed. (envelope and coherent detection, mixers and image products).
Check: a note on the Question 3 figure. The plotted message and the printed equation agree: the plotted waveform has period 1 in normalised time with peaks of $+1.5$ at $t = 0, \pm 1, \pm 2$ and troughs of $-1.5$ midway between them, which is exactly $m(t) = \cos(2\pi f_m t) + \tfrac{1}{2}\cos(6\pi f_m t)$ evaluated with $f_m t$ as the abscissa. The solution below therefore uses the printed equation, and the peak value $|m|_{\max} = 1.5$ read from it. The paper's "$f_m = 4$ Kz" is read as 4 kHz.
