WHAT IS MULTIPLEXING?
A multiplexer (MUX) is a network device that allows one or more analog or digital input signals to travel together over the same communications transmission link. The purpose of multipplexing is to combine and transmit signals over a single shared medium in order to optimize efficiency and decrease the total cost of communication.
Essentially, a MUX functions as a multiple-input, single-output switch that allows multiple analog and digital input signals and to be routed through a single output line. At the receiving end, another device called a demultiplexer recovers the original individual signals.
History of Multiplexing
The concept of Multiplexing was originated in telegraphy in the 1870s. Nowadays, it is widely used in communications.
George Owen Squier is called the father of Multiplexing in telephony. He was credited for the development of telephone carrier multiplexing in 1910.
What Is Multiplexer In Computer Science?
Multi-signal multiplexing (sometimes called muxing) is a method of combining multiple analog and digital signals over a shared medium in telecommunications and computer networks. The use of one wire for several telephone calls, for example, is common in telecommunications.
Multiplexing techniques have become useful network optimization tools during the age of the Internet of Things, edge computing and 5G. It’s important to note, however, that multiplexing itself is quite old in terms of post-industrial technologies. In its earliest forms, multiplexing can be traced back to the 1800s and when it was first used to optimize legacy communication channels like the telegraph and radio.
Today, the following communication applications would be prohibitively expensive without multiplexing: telecom, satellites, telemetry and broadcasting.
How Multiplexing Works
Today, frequency division multiplexing, time division multiplexing and wavelength division multiplexing are the types of multiplexing most closely associated with telecom.
For analog signals in telecommunications and signal processing, a time division multiplexer may select multiple samples of separate analog signals and combine them into one pulse amplitude modulated (PAM)wide-band analog signal. When there are two input signals and one output signal, a MUX is referred to as a 2-to-1 multiplexer; with four input signals it is a 4-to-1 multiplexer — and so on.
For digital signals in telecommunications on a computer network or with digital video, several variable bit-rate data streams of input signals (using packet mode communication) may be combined, or multiplexed, into one constant bandwidth signal. With an alternate method utilizing a TDM, a limited number of constant bit-rate data streams of input signals may be multiplexed into one higher bit-rate data stream.
A multiplexer requires a demultiplexer to complete the process, to separate multiplex signals carried by the single shared medium or device. Often a multiplexer and a demultiplexer are combined into a single device (also often just called a multiplexer) in order to allow the device to process both incoming and outgoing signals.
Alternately, a multiplexer’s single output may be connected to a demultiplexer’s single input over a single channel. Either method is often used as a cost-saving measure. Since most communication systems transmit in both directions, the single combined device, or two separate devices (as in the latter example), will be needed at both ends of the transmission line.
The Future of Multiplexing
One of the most fascinating application of multiplexing is the new communication paradigm like 5G in which different hardware and setup capacities provide for different types of signal transfer. For example, waveform multiplexing for 5G involves partial and full connectivity designs that use sub-arrays connected to radiofrequency chains to optimize this type of multiple signal transmission.
Experts describe the use of small cell technologies offering wideband and multi-gigabyte rates for supporting data intensive activities like HDTV and wireless gaming. Digital beam forming architecture, they note, can be useful in downlink transmitters and other aspects of mobile applications.
In general, the future of multiplexing is tightly coupled with the types of connectivity that allow more diverse traffic on a given hardware system. For instance, virtual local area networks or VLANs are setups where a physical LANs, comprised of different hardware pieces, can carry more than one bandwidth trajectory across the network. So signals meant for different components are moving in the same lines, and effectively handled with virtualization schemes.
Multiplexing is similar in that it promotes the ability to transfer data coming from different pairs of equipment, in a kind of tunnel system where the multiplexer and demultiplexer complement each other.
Essentially, the idea of multiplexing is inherent in trying to find efficiencies for telecom or similar systems using a “pipeline” for communications. This type of traffic control is behind enormous advances in communications technology throughout the last several decades.
Key points of Multiplexing
- Multiplexing is a technique that allows multiple simultaneous analogs or digital signal transmission across a single data link.
- The main motive behind the development of Multiplexing is to provide simple and easy communication, proper resource sharing and its utilization. This is the best way to utilize and share a limited resource equally among multiple devices.
Multiplexing can be classified into the following four types:
- Frequency Division Multiplexing (FDM)
- Time Division Multiplexing (TDM)
- Code Division Multiplexing (CDM)
- Space Division Multiplexing (SDM)
Use Image of Multiplexing
Frequency Division Multiplexing (FDM)
Frequency division multiplexing or FDM is inherently an analog technology. As the name specifies, in Frequency Division Multiplexing, the frequency dimension spectrum is split into smaller frequency bands. It combines several smaller distinct frequency ranges signals into one medium and sends them over a single medium. In FDM, the signals are electrical signals.
FDM’s most common applications are a traditional radio or television broadcasting, mobile or satellite stations, or cable television.
For example: In cable TV, you can see that only one cable is reached to the customer’s locality, but the service provider can send multiple television channels or signals simultaneously over that cable to all customers without any interference. The customers have to tune to the appropriate frequency (channel) to access the required signal.
In FDM, several frequency bands can work simultaneously without any time constraint.
Advantages of FDM
- The concept of frequency division multiplexing (FDM) applies to both analog signals and digital signals.
- It facilitates you to send multiple signals simultaneously within a single connection.
Disadvantages of FDM
- It is less flexible.
- In FDM, the bandwidth wastage may be high.
It is used in Radio and television broadcasting stations, Cable TV etc.
Time Division Multiplexing (TDM)
The Time Division Multiplexing or (TDM) is a digital or analog technology (in rare cases) that uses time, instead of space or frequency, to separate the different data streams. It is used for a specific amount of time in which the whole spectrum is used.
The Time frames of the same intervals are divided so that you can access the entire frequency spectrum at that time frame.
Although the concept of multiplexing is relatively straightforward—enabling data from multiple sources to be delivered through a single medium—there are numerous methods for accomplishing this task. The most common multiplexing techniques include:
- Space Division: Space division multiplexing was often employed in early telecommunications systems and is still found in some modern digital exchange networks. It involves switching the physical connections between different signal paths.
- Frequency Division: This method involves wideband channels divided into multiple sub-channels, with each signal separated according to frequency. Frequency division multiplexing (FDM) designates a fixed carrier frequency for each channel and modulates the carrier according to the input for each channel. Radio and television broadcasts often use FDM.
- Time Division: Time division multiplexing (TDM) is designed to combine numerous low bit rate data channels onto a single high bit rate channel. Each low bit rate channel is assigned to a particular time slot on the high bit rate channel, with small segments of data sent across the common channel in a specific time sequence. TDM performance cycles, allowing the smaller channels to use the full bandwidth for the duration of their time slot, so that in a system with four multiplexed channels, each channel will receive full access one-quarter of the time.
- Wavelength Division: Wavelength division multiplexing (WDM) is similar to frequency division, but it relies on optical fibers and light waves with different wavelengths to transmit multiple data streams on a single fiber. Several light beams are combined into one beam that is sent down the channel and then split again at the receiving end into individual streams.
- Dense Waveform Division: Dense waveform division is similar to wavelength division, but can handle higher bandwidths through the use of several virtual channels, each composed of multiple smaller channels, combined onto one large physical fiber. Continuing advances in dense waveform division multiplexing are increasing the number of individual channels that can run on a single channel.
Multiplexer Performance Criteria
Multiplexer units come in a variety of forms and can operate under several types of input switching principles. The major factors that can influence the effectiveness of a multiplexer in a given application include:
- Accuracy: This can be measured by the level of signal distortion that occurs as input is fed through the device.
- Size: Multiplexer size is typically determined by the number of channels for which a single device is responsible.
- Signal Requirements: An input signal can have a variety of characteristics that affect multiplexer performance, such as source impedance common mode rejection, polarity, and voltage range.
- Crosstalk: Channel crosstalk can be caused by stray inductance or capacitance and can lower the level of separation between channels.
- Power Requirements: The voltage load and power consumption during operation can be an important factor in determining whether a multiplexer can handle a specific project.
- Line Switching: A multiplexer system’s suitability for a given application often depends on whether switching occurs with a single-ended line, two differential lines, or three lines with a shield included at each multiplexer point.
ADVANTAGE OF MULTIPLEXING
The advantage of multiplexing is that we can transmit a large number of signals to a single medium. This channel can be a physical medium like a coaxial, metallic conductor or a wireless link and will have to handle multiple signals at a time. Thus the cost of transmission can be reduced.
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