Multiplexing is a term used in computer networking, signal processing and telecommunications to refer to the way in which more than one digital or analog signal is combined into just one signal. A commonly-used and ever-evolving contemporary technology, the technology dates back to the days of the telegraph in the 19th century. This technology was developed to enable signals to share expensive resources, increasing efficiency and signal delivery. Types of this technology differ depending upon the types of channels, timing, and signals (digital or analog).
Space-division is used for both wired and wireless communication of digital and analog signals. Examples of wired space-division are stereo cables, with one pair of wires for each speaker, and switched ethernet networks for hardwired computer networks. Wireless space-division multiplexing is accomplished with multiple antenna elements. Outputs may either be multiple, single, or combined. For example, a wireless router with a certain number of antennas may communicate with an equivalent number of multiplexed channels, increasing its peak bit rate by the number of antennas that are able to be multiplexed.
Frequency-division is an analog technology that is most commonly used today for cable and radio broadcasting. It involves sending signals in several different frequency ranges over a single transmission medium such as a cable. Only one television cable goes into customers’ neighborhoods, but multiple signals are transmitted at the same time to various subscribing homes at the same time with no problems.
In contrast to frequency-division, which works with analog signals, time-division multiplexed transmissions are primarily a digital technology. The signals are separated by brief sequenced units of time using the same transmission medium. Picture four computer terminals at a hotel lobby desk. Each communicates at a relatively low data speed with a central server. Rather than using four individual circuits connecting the terminals to the server, each is shared over one modem and one communications circuit.
Able to achieve much higher rates of transmission and efficiency, code-division multiplexed signals incorporate several channels which share the same frequency spectrum. The total bandwidth of the spectral frequency offers much more flexibility than a single bit rate or symbol rate. Using coding techniques and transmitting a series of short, time-dependent pulses, each signal can be transmitted via a single cable, radio channel, or any other medium. A real-world application of this technology is GPS, the Global Positioning System.
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Other multiplex signal transmission technologies include polarization-division and orbital angular momentum multiplexed transmissions, a technology that is currently in the research phase. A basic concept in telecommunications educations and delivery, multiplexing is an approach to sharing resources with either digital or analog signals. The signals can be transmitted wirelessly or via a hard wire or cable. The ways multiplexed signals are shared over one channel primarily break down into creative uses of physical space, time, distance, or coding. Multiplex devices are abbreviated as “mux,” while de-multiplexers are referred to as “demux.”
The next time you send a picture over your mobile device or watch a video, remember that multiplexed data makes it all possible.