ENVS 1200 Chapter Notes - Chapter 15: Error Detection And Correction
13 May 2018
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ENVS 1200 Chapter 15 Notes – Summary
Introduction
• Error correction can be particularly effective in the presence of bursts of noise.
• The operation of a repeater
• Digital signals can also be multiplexed to allow different signals to share a channel.
• Time division multiplexing (TDM) is normally employed for this purpose.
• A time division multiplexer is being used to share a communication channel among
three digital signals.
• We’e used the idea of a rotar sitch to illustrate the operatio of the ultiplexer,
although the switch is actually electronic.
• Each signal is sampled in turn, at a rate high enough to assure that no data is lost.
• The number of bits in each sample depends on the application.
• The data is combined and transmitted over the channel.
• At the other end of the channel the process is reversed.
• Each sample is sent to its respective destination. TDM has one potential shortcoming.
• If there is a lot of data in one incoming channel and very little in another, TDM is
inefficient.
• There will be empty slots from the lightly used channel while data is backlogged in
another.
• An alternative form of TDM, called statistical TDM, solves this problem by adding a small
header to each slot of data that identifies its channel.
• In this way, every slot can be filled when the data load requires it.
• The bandwidth of a channel is also important for digital transmission.
• Remember that even digital signals can be represented as a sum of sine waves of
different frequency.
• The higher the data rate, the higher the frequencies of the sine waves that make up the
signal.
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