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MULTIPLEXING

MULTIPLEXING

  • In telecommunications and computer networks, multiplexing (also known as muxing) 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 DE multiplexer (DEMUX).
  • IMUX has the opposite aim as multiplexing, namely to break one data stream into several streams, transfer them simultaneously over several communication channels, and recreate the original data stream.

TYPES OF MULTIPLEXING

Multiplexing technologies may be divided into several types, all of which have significant variations: space-division multiplexing (SDM), frequency-division multiplexing (FDM), time-division multiplexing (TDM), and code division multiplexing (CDM).

SPACE-DIVISION MULTIPLEXING

  • In wired communication, SDM simply implies different point-to-point wires for different channels.
  • Examples include an analogue stereo audio cable, with one pair of wires for the left channel and another for the right channel, and a multipair telephone cable.
  • Another example is a switched star network such as the analog telephone access network (although inside the telephone exchange or between the exchanges, other multiplexing techniques are typically employed) or a switched Ethernet network.
  • In wireless communication, it is achieved by multiple antenna elements forming a phased array antenna.
  • Examples are multiple-input and multiple-output (MIMO), single-input and multiple-output (SIMO) and multiple-input and single-output (MISO) multiplexing.

FREQUENCY-DIVISION MULTIPLEXING

  • FDM is inherently an analog technology. FDM achieves the combining of several digital signals into one medium by sending signals in several distinct frequency ranges over that medium.
  • One of FDM’s most common applications is cable television. Only one cable reaches a customer’s home but the service provider can send multiple television channels or signals simultaneously over that cable to all subscribers.
  • Receivers must tune to the appropriate frequency (channel) to access the desired signal.

TIME-DIVISION MULTIPLEXING

TDM is a digital (or in rare cases, analog) technology.

TDM involves sequencing groups of a few bits or bytes from each individual input stream, one after the other, and in such a way that they can be associated with the appropriate receiver.

CODE-DIVISION MULTIPLEXING

  • CDM or spread spectrum is a class of techniques where several channels simultaneously share the same frequency spectrum, and this spectral bandwidth is much higher than the bit rate or symbol rate.
  • CDM techniques are used as an channel access scheme, namely Code Division Multiple Access (CDMA), e.g. for mobile phone service and in wireless networks, with the advantage of spreading intercell interference among many users.
  • Another important application of CDMA is the Global Positioning System (GPS).

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SCIENCE AND TECHNOLOGY

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