Introduction The multiplexing is used to combined a number of independent signals into a composite signal suitable for transmission over a common channel . It is a method by which multiple analog message signals or digital data streams are combined into one signal over a shared medium. The aim is to share an expensive resource. For example, in telecommunications, several telephone calls may be carried using one wire. A device that performs the multiplexing is called a multiplexer (MUX), and a device that performs the reverse process is called a demultiplexer (DEMUX or DMX). Types of Multiplexing Frequency-Division Multiple Access ...
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DATA COMMUNICATION Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable. Characteristics Must be a Sender and Receiver A protocol is a set of rules which governs the transfer of data between computers. Protocols allow communication between computers and networks. Handshaking is used to establish which protocols to use. Handshaking controls the flow of data between computers Protocols will determine the speed of transmission, error checking method, size of bytes, and whether synchronous or asynchronous Examples of protocols are: token ring, CSMA/CD, X.25, TCP/IP Every communication system has ...
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BLOCK CODING Unlike line codes which operate on a stream of information bits, block codes operate on block of information bits. Redundant bit(s) are added to each block of information bits to ensure synchronization and error detection
Line Coding Unipolar Only two voltage levels are used. (1 means sending something, 0 means not sending) All signal levels are on one side of the time axis – either above or below NRZ – Non Return to Zero scheme is an example of this code. The signal level does not return to zero during a symbol transmission. Unipolar NRZ Scheme Polar The voltages are on the both sides of the time axis. Ex: Polar NRZ Polar alternatives : NRZ, RZ, Manchester, Differential Manchester Polar NRZ scheme can be implemented with two voltages. E.g. +V for 1 and -V for ...
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Introduction The process of converting digital data to digital signals. Digital data – sequences of bits. Characteristics Data rate vs. signal rate Data rate (bit rate) – the number of data elements in a unit time (bps). Signal rate (pulse, modulation rate, baud rate) – the number of signal element in a unit time (baud). No. of Signal Levels Two data levels, Two Signal levels Two data levels Three signal levels DC components It is the mean value of the waveform. If the mean amplitude is zero, there is no DC offset. unable to pass a low-pass filter or Over one ...
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