EE4414 Multimedia Communication Systems II
Experiment One
Color TV Transmission: Multiplexing/Demultiplexing of
YIQ Using Matlab Simulation
Yao Wang and Xiaofeng Xu
1. Introduction
The purpose of this lab is for you to understand the principles of Color TV signal
transmission. In this experiment you will have the opportunity to play with real video
signals, perceive video frames at transmitter and receiver, observe waveforms and
spectrums in all stages of Color TV transmission. Although actual color TV transmission
is done in analog waveforms, we simulate these operations digitally using Matlab.
2. Experiment
1) You will see several Matlab scripts on your local disk (Z:) after you log in a
computer. The main program, “YIQ_QAM.m” (which calls several functions)
performs multiplexing and demultiplexing on a video signal. Read through the given
program and functions to understand how it works. The program requires the
following three input parameters by user: fc, the color sub-carrier frequency, where
the chrominance components are modulated; f_LPF1, the cut-off frequency of the
low pass filter used to separate the luminance and chrominance; f_LPF2, the cut-off
frequency of the low pass filter used to extract chrominance. Explain how you should
choose the values of the above parameters?
2) Run the program and input the following parameters: video file name, fc, f_LPF1,
f_LPF2. The recommended values are fc=30*240/2*225=0.81MHz (8.1E5),
f_LPF1= 30*240/2*150=0.54MHz (5.4E5), f_LPF2=0.2MHz (2E5)). First run the
program with these default frequencies. You can choose either of the two video files
provided: ‘flowergarden1.yuv’,’mobilcal58.yuv’.
a. In the first pause, you will see seven pictures. They are Y, Cb, Cr components,
converted Y, I, Q components and original color video frame.
b. In the second pause, you will see the raster signals of Y, I, Q and their spectrums.
What is the difference between Y and I/Q spectrums? Copy the spectrum figures
of Y, I, Q onto a file for insertion later into your report. You can copy a matlab
figure by choosing “Copy figure” in the “edit” sub-menu in the figure window,
and then paste into a desired document.
c. In the third pause, you will see the signals of QAM multiplexed I and Q, final
composite and their spectrums, and image seen by B/W TV without filtering.
Record and compare the spectrums of the composite signal and the original Y,I,Q
signals. Also record and compare the recovered image and the original Y image.
(using the copy command as described before for copy a figure)
d. In the fourth pause, you will see the extracted QAM I+Q signals and spectrums.
Record and compare the extracted QAM I+Q spectrum with the original QAM
I+Q spectrums.
e. In the fifth pause, you will see the Y signal, its spectrum and image seen by a
B/W TV when a low pass filter is applied to the composite signal to separate the
Y from the QAM I+Q signal. Record and compare the extracted Y spectrum with
the original Y spectrum, and with the spectrum of the composite signal without
filtering. Also record and compare the original Y image, the recovered Y image
without filtering, and the recovered Y image with filtering.
f. In the sixth pause, you will see the original I, demodulated I without filtering, and
demodulated I with filtering, both in spectrum and in images. Record and
compare the spectrum and images.
g. Finally, you will see the original color image at transmitter and the recovered
color image at receiver. Record and compare these images.
3) Repeat 2) by using the same f_c and f_LPF2, but use a lower f_LPF1 (Hint: choose a
value in the range of 0.35 MHz-0.45MHz). The results should be the same as 2) in
steps (a)-(d). You should record the spectrums and images obtained after step (d), and
compared the corresponding spectrum and images obtained in 2) with this lower
f_LPF1.
4) Repeat 2) by using the same f_c and f_LPF2, but use a higher f_LPF1 (Hint: choose a
value in the range of 0.65 MHz-0.75MHz). The results should be the same as 2) in
steps (a)-(d). You should record the spectrums and images obtained after step (d), and
compared the corresponding spectrums and images obtained in 2) and 3) with this
new f_LPF1.
5) Repeat 2) by using the same f_LPF1 and f_LPF2, but use a lower f_c (Hint: choose a
value in the range of 0.65 MHz-0.75MHz. You should choose a number so that the
harmonic peaks of the QAM signal are in between harmonic peaks of the Y signal.).
The results should be the same as 2) in steps (a)-(b). You should record the spectrums
and images obtained after step (b), and compare the corresponding spectrums and
images obtained in 2) with this new f_c.
Options: If you wish, you can vary f_LPF2 while keeping f_c and f_LPF1 fixed and
observe the difference. You can also try other combinations.
3. Report
Your report should start with a general description of what you did in this experiment,
followed by the results and observations you obtained. You should answer all the
questions (written in italics in the proceeding instructions), with the corresponding
figures (spectrums or images) next to your answers.