INTRODUCTION TO 2-D J-DSP

LAB-01

 

INTRODUCTION

            The objective of this first lab exercise is to help students to understand two- dimensional (2-D) signal processing concepts in a java-based DSP laboratory. Therefore, this lab is a good starting point for the beginners to learn some of the basic concepts about 2-D signals and systems using 2-D J-DSP simulations.

 

Fig. 1 shows the 2D J-DSP editor. In fig. 1, the 2D blocks that are placed in the vertical line on the left hand side are called permanent blocks and are shown in green color. The blocks placed in the horizontal line are shown in yellow color and can be changed by selecting one of the options given in the drop-down menu on the top left corner of the screen. It is always recommended to use any 2-D block separately before it is connected with others and to read the [Help] screen of every new block you use.

 

Fig. 1 2D J-DSP.

 

Let’s start with a simple two-dimensional (2-D) J-DSP simulation.

 

Exercise 1.1

First, place the 2D SigGen block in the workspace of the J-DSP editor as shown in Fig. 1. Double click on the 2D SigGen block to open the main dialog box. In this dialog box, you will find a list of different pre-defined signals with editable horizontal and vertical widths as shown in the Fig. 2. The user can perform some basic operations on the defined/selected signal by going into the Customize dialog box, and one can also edit/view the numerical values of the signal by clicking on the [Edit Signal] in the Customize dialog box.

 

 

Fig.2 Main dialog box for 2D SigGen.

 

Exercise 1.1.1

Once you have opened the main dialog box of the 2D SigGen block, set

 

 

Click on [Update].

Your signal will look as shown in Fig. 3.

 

Fig.3 Main dialog box for 2D SigGen after [Update].

 

Note: Clicking on the [Update] button is very essential, not only for the changes to take effect but later you will see it is also required for the new data to be transferred to the next attached block.

 

Now click on the [Customize] button in the main dialog box. A new dialog box will open as shown in Fig. 4(b).

 

Change the values in the shift fields as follows:

 

Click on [Update].

The position of blue dots in the main dialog and some values in the Customize dialog box will change and are shown in Figs. 4(a) and 4(b) respectively.

                                 

Fig. 4(a) “Rectangular” signal after shift.                       Fig. 4(b) Customize dialog after shift.

 

Look at the values in the “Region of support” (ROS) fields. These values changed because ROS is usually taken to be the smallest rectangular region that contains all non-zero values/samples in the signal/sequence.

Before going to the next step, adjust all the dialog boxes, which you have opened so far, in such a way so that you can see all of them at the same time.

 

Exercise 1.1.2

Now click on the [Edit Signal] button in the Customize dialog. This will open the Edit dialog box that shows the numerical values of the data samples in the region of support shown as blue dots in the main dialog box.

 

Let’s try to insert a point at:

 

But this time click on [Apply], instead of [Update].

The Edit dialog box will look as shown in Fig. 5.

Fig. 5 Edit dialog box after inserting a point at (2, 2).

Note that the signal type in the main dialog has changed from “Rectangular” to “User-defined” and compare the new values in the ROS fields with those shown in Fig. 4(b).

 

Click on [Undo] in the Edit dialog box to go back to the previous settings. You will find your “Rectangular” signal back. Close the Edit dialog.

 

Exercise 1.1.3

In the Customize dialog, set

 

 

Click on [Update].

Look at the numerical values in the Edit dialog that shows the values in one period of the periodic signal. Close this dialog box.

 

Exercise 1.1.4

Set the parameters in the Customize dialog box as,

 

 

Click on [Update].

 

Again, open the Edit dialog box to see the values.

 

a)       What change did you observe in the signal values?

b)       Does this remind you of aliasing/overlapping? Give reason.

c)       What are the precautions one should take to avoid aliasing?

 

Click on [Restore Default] in the Customize dialog, you will find your original “Rectangular” signal back.i.e., all the values are set to their initial default ones for that particular signal. Before going to the next part, close all the dialog boxes.

 

 

 

 

 

Connecting different blocks

 

Exercise 1.2

Until now, we have been working on a single block. Let’s connect some of the blocks together. There is a 2D Plot block in the permanent blocks. Click on it and drag it in the workspace of the J-DSP editor. Your workspace now contains two blocks as shown in Fig. 6(a).

 

Fig. 6(a) J-DSP editor workspace after placing 2D plot block.

 

 

Exercise 1.2.1

As you can see, 2D SigGen block has one outlet/output-node and 2D Plot has one inlet/input-node. If you click on the output node of the 2D SigGen block and drag it to the input node of the 2D Plot, it will establish a connection between the two blocks as shown in Fig. 6(b). Now what has happened internally? The 2-D signal that you have generated in the 2D SigGen block will transfer to the 2D Plot block. Double-click on the 2D Plot block and set:

 

 

 

Fig. 6(b) J-DSP editor workspace after making connection

between the two blocks.

 

If you don’t see any signal, you need to re-open the 2D SigGen block and press [Update] button in the main dialog box.

 

Note: Whenever you make/establish a connection between any two blocks, you need to press [Update] button in order to transfer the signal/data to the next block.

 

            If you click on the [Values] button in the 2D Plot dialog box, another dialog window pops up that shows the values transferred from the 2D SigGen block to the 2D Plot. Fig. 7 shows the dialog window in the 2D Plot block, when “Line” was selected in the 2D SigGen block.

 

Fig. 7 Dialog window in the 2D plot block.

 

Now if you make your signal periodic, the 2D Plot block will show the same periodic signal in the main dialog box of the 2D Plot block, but the Values dialog will show only the values in one period.

 

Exercise 1.3

Let’s try to work on a very basic 2-D arithmetic operation. First, click on the connection between the 2D SigGen and 2D Plot blocks and hit the “Delete” button on your keyboard. Place 2D Arith and another 2D SigGen block as shown in the Fig. 8(a).

Fig. 8(a) J-DSP editor workspace after placing 2D Arith and another 2D SigGen blocks.

 

Exercise 1.3.1

Establish the connections between the blocks in the similar fashion as you did in the exercise 1.2.1. Your current J-DSP workspace should look as shown in the Fig. 8(b).

 

 

Fig. 8(b) J-DSP editor workspace after establishing connections between the blocks in Fig. 8(a).

 

Exercise 1.3.2

Set the following signal settings in one of the 2D SigGen block.

 

 

Click on [Update].

Similarly, in the second 2D SigGen block set the following.

 

 

Click on [Update].

Double click on the 2D Arith block and select,

 

 

Click on [Update].

To see the final values, double click on the 2D Plot and click on the [Values] button in it.

 

a)       Does this arithmetic operation change the ROS of the input signals? If yes, how?

 

Exercise 1.3.3

Now work on the same system as in fig. 8(b) and use the same “Line” signal as in the last step, but make the following changes in the above “Rectangular” signal.

 

 

Click on [Update].

Double click on the 2D Arith block and select,

 

 

Click on [Update].

 

a)       What is the ROS of the output signal? How it is calculated?

 

This concludes the introduction to 2-D J-DSP.