Project

RF, Digital Radio and Metamaterial Fundamentals

Project

Digital Radio Undersampling, Upsampling, Downsampling, and Digital Downconversion

Overview

Work in assigned project groups.

The objective of this project is to simulate QAM digital radio and observe the IQ constellation diagram.

NOTE: Use the Project Report Template and keep answers to questions on consecutive sheets of paper with all plots at the end.

IN NO CASE may code or files be exchanged between students, and each student must answer the questions themselves and do their own plots, NO COPYING of any sort! Nevertheless, students are encouraged to collaborate in the lab session.

Part 1: Undersampling, Upsampling, Downsampling, and Digital Downonversion Simulation

In this part, we investigate Digital Radio Undersampling, Upsampling, Downsampling, and Digital Downconversion.
For details on radio design concepts, see:

Load and run the Mattlab digital radio Simuulink file as follows:

Download tfile twDigRadioUpDown2c.slx.zip and unzip it to your preferred Maatlab directory/folder

Run Maatlab program, and click the MenuBar::Simuulink button to run
Open the "twDigRadioUpDown2c.slx" design, and the following schematic should appear.
The upper-left dashed-blue box below encloses a simple upsampler
The upper-right dashed-cyan box below encloses a simple downsampler
The center-right dashed-magenta box below encloses a simple DDC (digital down converter)
The bottom-right solid-red box below encloses a simple undersampling downconverter

Fig 001

Save a snapshot of the schematic for your report.

Downsampling

Double-click the run button (green arrow above) to simulate.
Double-click spectrum analyzer 1 (cyan arrow above) to observe the QAM spectrum similar to below (your spectrum should have a different carrier frequency and bandwidth)

Fig 002

Save a snapshot for your report.
The output of the downsampler is given by spectrum analyzer 2 (cyan circle in the schematic above)
Double-click the run button (green arrow in the schematic above) to simulate.
Double-click spectrum analyzer 2 (cyan circle in the schematic above) to observe the downsampled QAM spectrum similar to below (your spectrum should have a different carrier frequency and bandwidth)

Fig 003

Make sure that the full frequency range is plotted and y-axis goes from +10 to -90 dB
Save a snapshot for your report.
Did the frequency of the carrier change after downsampling?
Did the bandwidth of the signal change after downsampling?
What changed?

Digital downconverter (DDC)

Double-click the run button (green arrow above) to simulate.

Double-click spectrum analyzer 3 (magenta arrow in the schematic above) to observe the digital downconverter QAM spectrum similar to below (your spectrum should have a different carrier frequency and bandwidth)

Fig 004

Make sure that the full frequency range is plotted and y-axis goes from +10 to -90 dB
Save a snapshot for your report.
Did the frequency of the QAM carrier change after digital donconversion?
Did the bandwidth of the signal change after digital donconversion?
What was the frequency of the digital local oscillator?
Note the downsampler in the DDC output to reduce data rate!

Undersampling downconverter

Double-click the run button (green arrow above) to simulate.
The output of the is given by spectrum analyzer 4 ( red arrow in the schematic above)
Double-click spectrum analyzer (red arrow in the schematic above) to observe the undersampling downconverter QAM spectrum similar to below (your spectrum should have a different carrier frequency and bandwidth)

Fig 005

Make sure that the full frequency range is plotted and y-axis goes from +10 to -90 dB
Save a snapshot for your report.
What was the undersampler sampling frequency set by the zero-order hold (red circle in the schematic above)
Did the frequency of the QAM carrier change after undersampling?
Did the bandwidth of the signal change?

Upsampler

Double-click the run button (green arrow above) to simulate.

The upsampler makes use of the baseband signal, and converts it to a higher frequency

The upsampler places "zeroes" between the original samples, and increases the clock rate proportionally

However, the upsampler generates many harmonic aliases of the original spectrum

The baseband signal is given by spectrum analyzer 5 (blue arrow in the schematic above)
Double-click spectrum analyzer 5 (blue arrow in the schematic above) to observe the baseband QAM spectrum similar to below (your spectrum should have a different carrier frequency and bandwidth)

Fig 006

Make sure that the full frequency range is plotted and y-axis goes from +10 to -90 dB
Save a snapshot for your report.
Next, a digital filter is used to remove all but one of the many harmonic aliases
The filtered upsampler output is given by spectrum analyzer 6 (blue circle in the schematic above)
Double-click spectrum analyzer 6 (blue circle in the schematic above) to observe the filtered upsampler output QAM spectrum similar to below (your spectrum should have a different carrier frequency and bandwidth)

Fig 007

Make sure that the full frequency range is plotted and y-axis goes from +10 to -90 dB
Save a snapshot for your report.
Did the upsampler shift the baseband signal to a carrier frequency?
What clock determines the carrier frequency?

Save your work!

See report template below

Report Data

============================ WARNING !! ====================================
**** WARNING **** YOU MUST USE THE PROJECT REPORT TEMPLATE Below:

See the Project Report Template at bottom of this page
A well-written report/paper is EXPECTED
STRONGLY RECOMMEND that you read IEEE authorship series: How to Write for Technical Periodicals & Conferences
Clearly describe everything, including:

variables in block diagrams
variables in formulas
units of variables kHz, pF, nH, m, s,
all traces on plots
all curves on plots
all results in any tables

Minimum required data content for your report and demos

Required theory/formulas numbered as below:

(1) formula for downsampling output y[n], given input x[n]
(2) formula for upsampling output y[n], given input x[n]

Required figures:

Any illegible plots receive zero credit (must be able to read all numbers, axes, labels, curves, grids, titles, legends)
All plots must of professional quality as in IEEE papers

LEGIBLE block diagram of the experiment as in Fig 001 above (will be somewhat illegible because it it so large)
LEGIBLE simulation spectrum of QAM signal as in Fig 002 above, with appropriate caption
LEGIBLE simulation spectrum of downsampled QAM signal as in Fig 003 above
LEGIBLE simulation spectrum of DDC downconverted QAM signal as in Fig 004 above
LEGIBLE simulation spectrum of undersampling downconverted QAM signal as in Fig 005 above
LEGIBLE simulation spectrum of the filtered upsampled QAM signal as in Fig 007 above

Required tabular data content:

Table with 2 columns: parameter, then value of the parameter,

Row 1: QAM signal carrier frequency of spectrum analyzer1 in MHz
Row 2: QAM signal bandwidth of spectrum analyzer1 in MHz (bandwidth at points 20 dB down from peak of passband)
Row 3: QAM signal carrier frequency of spectrum analyzer2 (downsampler output) in MHz
Row 4: QAM signal carrier frequency of spectrum analyzer3 (DDC output) in MHz
Row 5: QAM signal carrier frequency of spectrum analyzer4 (undersampler output) in MHz
Row 6: QAM signal carrier frequency of spectrum analyzer6 (upsampler output) in MHz
Row 8: sample rate of the DDC output at analyzer2
Row 9: sample rate of the undersampler output at analyzer4
Row 10: sample rate of the upsampler at analyzer2

See report template below

NOTE ReportTemplate: Use the Project Report Template

YOU MUST ADD CAPTIONS AND FIGURE NUMBERS TO ALL FIGURES!!

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