HY330-Assignment 1 Solved

General Information
For each assignment some code examples with complete working flowgraphs or blocks are provided, but in some cases there are missing elements.

For every assignment you should provide your report, containing your findings (flowgraphs).

Exercise 1
The goal of this exercise is to help you to become familiar with the GNU Radio platform and the Nyquist frequency. Furthermore, you will be able to visually inspect/observe signal properties on-the-fly using the corresponding GNU Radio graphical tool.

First, open the lab1_1.grc flowgraph, using the GNU Radio Companion.

1.   Execute the flowgraph. Show that you are able to handle the Time Sink functions in order to inspect visually the signals.

2.   Are the signals provided going to be properly transmitted without loss of information? Report!

3.   Perform the proper modifications to produce visually smoother signals, without changing the frequency of the signals. Compare the CPU usage between the previous run and the new one and report your findings.

4.   Which is the minimum possible sampling rate that you can use at the flowgraph? Report!

5.   Why the flowgraph has the Throttle block? Does the parameter Sample Rate of this block affects the signal? If no, what it is actually affects? Report!

Exercise 2
The second exercise explores signal properties on the frequency domain rather than the time domain. It will help you become familiar with the spectrum analysis graphical tool of GNU Radio and learn some basic properties of the Fourier Transform. Copy the flowgraph of the previous exercise as lab1_2.grc.

1.   Drop the Time Sink and insert a Frequency Sink. At the Spectrum Width option select Half.

2.   Instead of fixed parameters for the frequency and amplitude of the signals, use QT widgets to dynamically and graphically change their values. Which are the minimum and maximum values allowed? Report!

3.   Set the frequency of both signal A and B at 4 kHz.

(a)   What do you observe about the spectrum of signal A+B compared to the spectrum of signal A and B respectively? Report!

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(b)   Why the spectrum of signal A and signal B is the same regardless the fact that the first is a cosine and the second a sine? Report!

Exercise 3
This exercise will help you understand the notion of signal phase and what happens when two signals are transmitted concurrently. Open the lab1_3.grc file. The flowgraph included is incomplete and you should perform some modifications.

1.   Without adding any other block, try to produce a zeroed signal for the A+B signal. You are not allowed to alter the signal sources parameters or the sampling rate.

2.   Which is the value that you used for the parameter of the delay block? Why and how did you choose this value? Report!

Exercise 4
The goal of this exercise is to present the insights of sampling, aliasing and filtering.

Open the lab1_4.grc file. The flowgraph provides a signal source block that operates on a sampling rate of 32 kHz. This signal is plotted using the Frequency Sink block of GNU Radio. In order to emulate properly a down sampled signal, the flowgraph utilizes the Keep 1 in M block which drops out 3 of every 4 samples and keeps only the first (down-sampling/decimation by a factor of 4). The resulting signal is also plotted together in the same Frequency Sink block.

1.   Use the slider to change the frequency. What do you observe? Report!

2.   Which is the frequency range of the down-sampled signal? Why? Report!

3.   Before the down-sampling (keep 1 in M block), insert a proper filter block in order to cutoff the undesired aliasing effect. GNU Radio provides a variety of filter blocks under the category Filters. Report the type of the filter you chose, the parameters you applied, and the reasoning.

4.   Think of and report a simple way/function to calculate/predict the frequency falias of the alias, by two parameters: sampling frequency fs & signal frequency fsignal.