DSP Lab Experiments - Digital Signal Processing: An Introduction with MATLAB and Applications - page 345

MATLAB Simulation
In this experiment we will simulate DM and adaptive DM systems and compare
their performance using sinusoidal and LFM input signals.
Task 1
On MATLAB generate the signal x(k) = Asin(x o kT s ), with sampling period
T s = 0.02 s, amplitude A = 0.5 V, frequency f o = 1 Hz, and time vector
0 \ t \ 10 (s). With a step of D ¼ 0 : 07, simulate the delta modulation system
in Fig. D.17 . Plot the input signal, the estimated signal, and the output of the DM
system along with their spectra. Can you find the effect of quantization on the
output signal spectrum? The output signal is a square wave, however, its spectrum
reveals a sinusoidal content.
Task 2
Implement the DM demodulator shown in Fig. D.17 . Use a digital 4th-order
Butterworth low-pass filter. Plot the demodulated signal and its spectrum and
compare with the original signal.
Task 3
Vary the quantization step to 0.03, 0.1, and 0.2. Check the quantization noise
and the slope overload.
Task 4
Repeat Tasks 1, 2, and 3 for a linear FM signal with amplitude 0.2 V, initial
frequency 0.5 Hz, and modulation index of 0.5.
Task 5
Now implement the adaptive delta modulation system as shown in Fig. D.18 ,
with an initial step of 0.03 and a step modification constant K = 1.3. For
sinusoidal and LFM inputs, plot the input signal and its modulated version along
with their spectra. Compare with the non-adaptive DM system.