Data Communications

Page 1 of 21

Data Communications

By | April 2008
Page 1 of 21
Encoding methods and Modulation schemes
25.P.1
Computers use digital signalling, digitals signals are represented by the base 2 numbering system “Binary”. Binary bits are shown as 1 or 0, where 1 means ON and 0 means OFF. In a network where digital devices exist, digital signalling will be used. Dependant upon the encoding method used, a high voltage on a communications medium can represent a logical 1 and a low voltage of can represent a logical 0. Different methods of encoding exist these are used for different types of communication between electrical devices. Distortion, noise, and cross talk on a cabling medium are factors that prevent the accuracy of transmitted data to be intact. For these reasons different encoding methods exist. An example is when 2 wires are used to transmit music data to a speaker Digital signals don’t always have to be carried over to the receiving end by electricity, light can also be used for digital communication. Fibre Optics use light to transmit data through optical fibre within the cable. The strength of the light ray can also be a determining factor to what logic the ray represents, either 0 or 1. Digital signals are complex waveforms that can be described as a discontinuous waveform having a finite range of levels. You can recognise a digital signal by the wave created, if the wave keeps going up and down in straight lines and forms squares and rectangles these are digital signals. Digital signals assume two states (logic 0 and logic 1). Where the signal changes from one state to another, the signal can be said to be discontinuous. As the signal state changes from 0 to 1, a finite time is required for the voltage to increase to the maximum value, and a corresponding time is required for the voltage to fall when the signal state changes from 1 to 0. Each voltage pulse in a digital signal is a signal element. Encoding each data bit into signal elements transmits binary data. There are many encoding schemes...