Fundamentals of Quadrature Amplitude Modulation
Aim of the Experiment
This experiment primarily concerns the design and implementation of
a Quadrature Amplitude Modulation (QAM) transmitter.
QAM is a widely used method of transmitting digital data over bandpass
channels.
QAM is a popular choice because of its bandwidth efficiency and its
ability to compensate for linear channel distortion.
Before you start with the experiment, it is necessary that you have
an understanding at some level of the following concepts:
- Representation of baseband signal in signal constellations
- Differential encoding
Equipment to be checked out:
- Two BNC - BNC Jack cables
- Two BNC - stereo pin (DSP) cables
Downloads
Lab #6 Handout
explaining milestones for the lab.
Updated Nov. 13, 2011.
Reuse TI C6748DSP files
for lab #5 as a single zip file
(7-zip free zip program).
Overview Slides by
Prof. Steven Tretter, University of Maryland (from Jan. 2008 lab manual)
Pulse shaping impulse response and filter bank coefficients:
OLD: LabVIEW Virtual Instrument
for test and measurement of results on the C6713 DSK
- Thousands of samples are needed to get all 16 points
of the constellation plot to show as white.
- For unknown reasons, this is currently very slow.
Notes:
- Unlike the PAM lab, there are 16 subfilters in the filter bank
instead of 4. In this lab, for-loops are your friend.
- This lab contains elements from all the previous labs.
Modular programming techniques can greatly ease the process and
reduce debugging time.
- In this lab, we cannot use a 9.6 kHz sampling rate.
So design for an 8 kHz sampling rate and a
500 Hz symbol rate, and 1 kHz
carrier frequency.
Also note that this would not be interoperable with a
standard-compliant modem.
Lab Report
In addition to the standard lab report format, please answer the
following questions:
- The QAM signal can be viewed as the sum of two PAM signals that
each have been modulated by a carrier.
How is the bandwidth of the QAM signal related to the bandwidth of
its two (carrier-modulated) PAM components?
- Briefly explain what encoding schemes in the QAM transmitter are
needed to help the QAM receiver combat symbol rotation.
Assignment
Submitting this assignment is optional, but doing it would
be useful with your QUIZ preparations
Assignment
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