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:

• Transmitter design
  • Conversion of a bit stream to a discrete-time baseband signal
  • Conversion of a discrete-time basedband signal to a continuous-time signal for transmission
• Receiver design
  • Conversion of a continuous-time received signal to a discrete-time basedband signal
  • Conversion of a discrete-time baseband signal to a bit stream

Reading Assignment

• Real-Time Digital Signal Processing from MATLAB to C with the TMS320C6x DSPs (Jan. 2012) by Thad B. Welch, Cameron H. G. Wright and Michael G. Morrow
  • Chapter 18
• Software Receiver Design by C. Richard Johnson, Jr., William A. Sethares and Andrew Klein
  • Sections 12.1-12.4
  • Sections 13.1-13.3
  • Chapter 16
• Course reader
  • Lecture 15 slides on QAM Transmission
  • Lecture 16 slides on QAM Reception
  • Appendix H Modulation Example Handout
  • Appendix I Modulation Summary Handout
  • Appendix M Symbol Recovery Handout
  • Appendix P Communication Performance of PAM vs. QAM Handout

Downloads

Recitation slides on the QAM transmitter and QAM/QPSK receiver by Mr. Yeong Choo and Mr. Sam Kanawati, The University of Texas at Austin

Instructions by Mr. Yunseong Cho and Mr. Dan Jacobellis, The University of Texas at Austin

MATLAB code:

• lab6_transmitter.m
• lab6_record.m
• lab6_receiver.m
• tree.png

Overview slides by Prof. Steven Tretter, University of Maryland (from Jan. 2008 lab manual)

Supplemental Information

LabVIEW transmitter demonstration by Dr. Zukang Shen to show how labs 1-6 fit together

Notes and Troubleshooting:

• This lab contains elements from all the previous labs. Modular programming techniques can greatly ease the process and reduce debugging time.

• In the CD ROM for the Welch, Wright and Morrow book, there are two files that define a scaling constant for the baseband signal.
  • For 4-QAM, impulseModulatedQPSK_ISRs_revA.c defines QPSK_SCALE to be 10000, which does not appear to work well. Try a value of 20000 instead; if that doesn't work, then try 30000.
  • For 16-QAM, impulseModulatedQPSK_ISRs.c defines the scaling factor to be 16000, which works well.

Lab Report

In addition to the standard lab report format, please answer the following question:

• 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?

Assignment

Submitting this assignment is optional, but doing it would be useful with your QUIZ preparations

Assignment

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