Communication Systems and Signal Processing
Core concepts
Cover analog modulation (AM, FM) and their bandwidths, then digital modulation (ASK, FSK, PSK, QAM) and error performance. Study sampling theorem, quantisation, PCM, and line coding. Noise figure, SNR, and link budgets are frequent. For signal processing, understand Fourier and Laplace transforms, convolution, z-transform, FIR/IIR filters, and DFT/FFT properties. Aliasing and windowing are common traps.
Traps examiners set
- Sampling must exceed twice the highest frequency, not equal it.
- FM bandwidth by Carson's rule includes both sidebands and the modulating frequency.
- Quantisation noise falls 6 dB per added bit.
- DFT assumes periodicity; spectral leakage arises from non-integer cycles in the window.
- Convolution in time equals multiplication in frequency, and vice versa.
Worked rule of thumb
Carson's rule: BW is about 2*(delta_f + f_m). Example: deviation 5 kHz, modulating tone 3 kHz gives BW = 2*(5+3) = 16 kHz. For PCM, SNR improves about 6 dB per bit; 8 bits gives roughly 50 dB for a full-scale sine.
Practice strategy
Sketch spectra before and after each block; it catches bandwidth and aliasing errors.