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# Efficient Multi-Rate Implementation of QAM Modulators and Demodulators

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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.

1. In Simulink, implement the QAM modulator shown in Figure 4.19 (page 154) in the textbook.
2. Implement an additive white Gaussian noise channel by adding a Gaussian signal to the output of your QAM modulator.
3. Implement the QAM demodulator shown in Figure 4.21 (page 156) in the textbook.
In your implementation, use the parameters below:
• Ts (symbol period) = 1 sec
• N = 4 samples per symbol period
• T = Ts/N seconds per sample
• Fc = 0.25 cycles per sample (discrete-time carrier frequency) which corresponds to pi/2 rads per sample
• A = 1 volt
• Square-root raised-cosine 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
If you get stuck, click here to see an example block diagram.

Efficient multi-rate QAM modulation and demodulation
1. In Simulink, implement the efficient multi-rate QAM modulator shown in Figure 4.27 (page 165) in the textbook.
2. Implement an additive white Gaussian noise channel by adding a Gaussian signal to the output of your QAM modulator.
3. Implement the efficient multi-rate QAM demodulator shown in Figure 4.31 (page 174) in the textbook.
Use the parameters given above.

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 Multi-Rate 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_Multi-Rate_Implementation_of_QAM_Modulators_and_Demodulators.html. This work is licensed under a Creative Commons License