Digital Data Transmission by Baseband Pulse Amplitude
Modulation(PAM)
Aim of the Experiment:
In this experiment, you will learn the basics concepts of digital
communications like pulse shaping filters, Nyquist criterion, eye diagram,
inter-symbol interference and clock recovery. You will learn digital data
transmission using baseband pulse amplitude modulation.
Before you start with the experiment, it is necessary that you have an
understanding (at some level) of the following concepts:
- Baseband PAM
- Nyquist criterion
- Inter-symbol Interference (ISI)
- Pulse shaping (raised cosine baseband filtering)
- Eye diagrams
- Interpolation filter bank
- Symbol clock recovery
Equipment to be checked out
- Two BNC - BNC Jack cables
- Two BNC - stereo pin (DSP) cables
List of tasks to complete for the lab
Important files
LabVIEW Implementation:
A lab5.vi contains a skeleton for the LabVIEW
implementation.
You will need to set the "Sample Rate" constant and
connect the "Format Eye Diagram" and "Display Eye Diagram" VIs.
The part that converts an array to a waveform has already been provided.
Lab Report:
- Do everything in Section 11.6 using Matlab [including 11.6.4].
Discuss how the roll-off factor "alpha" affects the eye diagrams,
theoretical error plots, etc.
(Hint: there is a function named "eyediagram". Your entire Matlab
program will likely be only a few (~5) lines.)
- Consider using the "PAM" function from the Johnson and Sethares book.
- Don't worry about gray-coding and you may use the built-in
random number generator
- Consider using the "rcosflt" and "eyediagram" functions in Matlab.
- For above, please put all error probabily plots in the same graph.
(This will allow you to accurately compare them).
- How could pulse shaping be implemented using only a single "filter"
(not a bank of filters).
Practically, why would this be undesirable?
- In the clock recovery system, discuss the need for a Prefiltering.
For a symbol rate of 2 kHz, what would be the output if the prefilter
attenuated all frequencies greater than 900 Hz?
Would it be possible to recover the transmitter's symbol frequency
(using the same squaring operation and post-filters as in the lab)?
If not, give a short reason why.
Oscilloscope Notes:
- For best viewing of the eye-diagram,
Press /DISPLAY->VECTORS->OFF
- Trigger settings can be set by pressing "SOURCE"
[Right-hand-side]
Coding Guidelines:
- The rascos.exe and
sqrascos.exe programs provide the filter
coefficients as a 2D array [directly usable for the interpolation
filter bank].
This is intended to help you.
Recommend main program loop over this array to do the convolutions.
The QAM lab will involve a similar filter with 16 sub-filters.
- You wrote functions for the previous labs [FIR/IIR filtering,
scrambler, etc.].
Recitation Slides for Lab 5
by Prof. Steven Tretter
Recitation Slides for Lab 5 by Mr. Akshaya Srivatsa:
Part 1
PAM class notes by Dr. Guanghan Xu
Assignment
Submitting this assignment is optional,
but doing it would be useful with your QUIZ preparations
Assignment
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