Efficient MultiRate Implementation of QAM Modulators and Demodulators
Objective:
To implement a QAM modulator and demodulator by
traditional techniques using pulse amplitude and sinusoidal modulation;
to implement QAM demodulator by traditional techniques using
sinusoidal modulation and matched filtering; to implement QAM
modulators and demodulators efficiently using multirate techniques.
Traditional QAM modulation and demodulation
Efficient multirate QAM modulation and demodulation
If you get stuck, click here to see an example block diagram.
Note that some of the details of the implementation given in the Simulink block diagram are hidden inside the blocks. Therefore, simply copying the block diagram will not produce a working system. Working out the details of the polyphase filters with pencil and paper will guide you in implementing these blocks.
Your goal is to get the two modulators and demodulators to produce identical outputs.
Traditional QAM modulation and demodulation
 In Simulink, implement the QAM modulator shown in Figure 4.19 (page 154) in the textbook.
 Implement an additive white Gaussian noise channel by adding a Gaussian signal to the output of your QAM modulator.
 Implement the QAM demodulator shown in Figure 4.21 (page 156) in the textbook.
 Ts (symbol period) = 1 sec
 N = 4 samples per symbol period
 T = Ts/N seconds per sample

Fc = 0.25 cycles per sample (discretetime carrier frequency)
which corresponds to pi/2 rads per sample
 A = 1 volt
 Squareroot raisedcosine pulse with 50% excess bandwidth truncated to plus and minus six (Lp=6) symbol periods
 Eb/N0 = 20dB signal to noise ratio
 M=4 square QAM modulation
Efficient multirate QAM modulation and demodulation
 In Simulink, implement the efficient multirate QAM modulator shown in Figure 4.27 (page 165) in the textbook.
 Implement an additive white Gaussian noise channel by adding a Gaussian signal to the output of your QAM modulator.
 Implement the efficient multirate QAM demodulator shown in Figure 4.31 (page 174) in the textbook.
If you get stuck, click here to see an example block diagram.
Note that some of the details of the implementation given in the Simulink block diagram are hidden inside the blocks. Therefore, simply copying the block diagram will not produce a working system. Working out the details of the polyphase filters with pencil and paper will guide you in implementing these blocks.
Your goal is to get the two modulators and demodulators to produce identical outputs.
Copyright 2008,
by the Contributing Authors.
Cite/attribute Resource
.
admin. (2006, June 28). Efficient MultiRate Implementation of QAM Modulators and Demodulators. Retrieved January 07, 2011, from Free Online Course Materials — USU OpenCourseWare Web site: http://ocw.usu.edu/Electrical_and_Computer_Engineering/Communication_Systems_I/Efficient_MultiRate_Implementation_of_QAM_Modulators_and_Demodulators.html.
This work is licensed under a
Creative Commons License