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The programme looks at the use of error correcting codes for enhancing the accuracy of digital signals. The Mariner 9 photographs from Mars are used as an example of a practical application.
Metadata describing this Open University video programme
Module code and title: TM361, "Graphs, networks and design"
Item code: TM361; 14
First transmission date: 16-09-1981
Published: 1981
Rights Statement:
Restrictions on use:
Duration: 00:24:16
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Producer: John Stratford
Contributors: Roy Nelson; J.H Van-Lint
Publisher: BBC Open University
Keyword(s): Code; Error-correction; Mariner 9
Footage description: Film shots of Mariner 9 probe being launched and of shots of Mars. Introductory commentary gives a brief history of the Mariner programme. Roy Nelson places the picture signal strength from Mariner 9 into perspective by comparing its power (20 watts) with that of the Crystal Palace Television transmitter (40,000 watts) Nelson goes on to explain how the Mariner 9 pictures were transmitted. He points to an array of black/grey squares which taken together make up a picture and explains that each shade of grey is represented in the signal by a digital code. Prof. Van Lindt lets viewers listen to examples of 'noise' which is always present in space and causes errors to appear in transmitted signals. Using a Fano plane and a noisy telephone call, Roy Nelson demonstrates that, by building redundancy into a system, correct information can be obtained from a noisy signal. This build-in redundancy he explains, is the basis of all error correcting codes. Prof. Van Lint follows by showing how redundancy is built into a digital code. He demonstrates a simple code based on the incidence matrix of the Fano plane. This can detect the presence of three errors and correct one. Using a 'wallpaper' pattern made up of a matrix of squares, Roy Nelson builds up a complex code based on the Kroneker product and Hademard matrices. This code is of similar construction as that used in the Mariner 9 signals but is not quite as complex. Prof. Van Lint demonstrates another way of building up the above pattern. Using this method, he explains, will enable patterns of any size and length to be attained. The error correcting code worked out above is demonstrated in practise by Roy Nelson. He shows the effect of using the code on a transmitted photograph and points out the improvement in quality which results.
Production number: FOUT123J
Videofinder number: 1535
Available to public: no