This is a guide for students attempting error control coding (one of the three encoding subtopics) in digital technologies achievement standard 2.44 (AS91371)

This is an achieved level guide.

Remember that you only need to do one of the three encoding topics (compression, encryption, and error control coding) to the excellence level. If you are either not interested in getting more than achieved, or are doing either encryption or compression to the excellence level, then this is the right guide for you. If you were wanting to do error control coding up to the excellence level, then you should select the excellence guide that uses check digits instead. Note that we do not currently have an excellence guide for parity.

In order to fully cover the standard, you will also need to have done projects covering the topics of encryption and compression to at least the achieved level (with one of them to the excellence level if you are attempting to get more than achieved), and projects covering the topics of representing data using bits and human computer interaction, and include these in your report.

Encoding has the following bullet points in achievement standard 2.44 which this guide covers.

Achieved: “describing the concept of encoding information using compression coding, error control coding, and encryption; and typical uses of encoded information”

As with all externally assessed reports, you should base your explanations around personalised examples.

You should read and work through the interactives in the following sections of the CS Field Guide in order to prepare yourself for the assessed project.

Read all of these sections, as they give the necessary introduction of the topics

What’s the Big Picture?

The Parity Magic Trick

Start this section by writing an introduction to the topic of error control coding. Briefly explain what error control coding is, what it is used for, and what kinds of problems would exist if there was no such thing as error control coding. Briefly describe what parity bits are, and how they fit into the larger topic of error control coding. This introduction only needs to be a few sentences - you are just showing the marker that you understand the bigger picture of what error control coding is, and some of the typical uses of it.

You will need to choose somebody else (e.g. a classmate, or even somebody at home) to be your helper. You take the role of the magician, and they take the role of laying out the initial grid (before you add parity bits) and flipping a card while you are not looking.

Carry out the parity trick with your helper, taking the following photos.

  • The original 5x5 grid that your helper lays out (you might want to take this photo at the very end if your helper hasn't seen the trick before - you don't want to draw attention to what you are doing and ruin it for them!)
  • The grid after you have added the parity bits.
  • The grid after your helper has flipped a card (edit the image afterwards, circling the flipped card).

For each of your photos, you will need to write (briefly, remember this is only at the achieved level) what was done. Where you added the parity bits, you should describe how you knew which way up to put the cards. For the final photo where you identify the flipped card, you should describe how you knew which it was.

Finish this section by briefly (one or two sentences) describing what the cards represent, and what flipping a card represents. This should be straightforward - you are simply linking the parity trick back to actual computers.

  • Put error control coding in its own section (your report should have suitable headings and subheadings for each topic to make it clear for the marker) and ensure that you briefly introduce the topic. It is important that your report clearly demonstrates that you know the difference between encryption, error control coding, and compression, and what their different purposes are.
  • You will need to get a good balance between displaying photos which are clear, but not using too much space. Ask your teacher for advice on this if you are unsure.
  • This project will take up slightly more space than the other encoding achieved projects. As long as you are following our other maximum page length recommendations (which are below the 14 pages maximum), this shouldn't be an issue. With your photos and explanations, you could expect it to take between 1 and 2 pages.