Data Coding and Transmission : Go to the description of the applet

Applet to demonstrate Digital Coding and Transmission

Dr P.M. Fenwick, Computer Science, The University of Auckland, March 2000

Description of the Applet

This applet demonstrates coding techniques for digital data transmission (or recording) and transmission in the presence of noise. It provides a wide variety of digital encoding methods, a variety of noise levels and adjustable bandwidth or transmission response.

Signal flow and page layout.

Details of each section.

Eye diagram.

The eye diagram is a standard method of evaluating noisy data transmission. An oscilloscope is triggered by the signal and set to display just a few data bits. Many traces, for many data bits, overlay each other on the display. Any noise in the signal tends to move individual traces vertically and horizontally, giving broad bands of possible signals. With luck, or low noise, or good design, there will be eye-shaped areas along the central axis where the signal never occurs. If these coincide with the clock times at which the signal is sampled we will get reliable conversion back to digital. If any signals encroach on these areas we may get transmission errors.
The eye diagram is drawn with horizontal lines corresponding to +/- 10% of the total display height; the signal should remain outside these areas for reliable operation.
Note that the eye diagram has a constant width in bit-periods and is largely independent of the "Bit-clock Interval" control which affects the other displays.