Why multiplexing is required in data communication

Once the switch releases at the surface of the multiplexer ahead of a connection, then it has a chance of sending a unit into the lane. Similarly, once the switch releases at the surface of the de-multiplexer ahead of a connection a chance to receiving a unit from the lane. This procedure is named interleaving. The statistical TDM is applicable to transmit different types of data simultaneously across a single cable. The transmission of data can be done from the input devices which are connected to networks like computers, fax machines, printers, etc.

The statistical TDM can be used in the settings of telephone switchboards to control the calls. This type of technique is comparable to dynamic bandwidth distribution, and a communication channel is separated into a random data stream number. The term CDM stands for code division multiplexing. It is one kind of technology that works with spread spectrum communication.

In this type of communication, a narrowband signal can be transmitted through division across several channels or over a larger frequency band. It does not compress the bandwidths of frequencies otherwise digital signals.

It is less liable to intrusion, so providing enhanced data communication capacity as well as a more safe private line. Once code division multiplexing is used to permit several signals from different users to transmit a communication channel commonly, then this technology is known as CDMA or Code Division Multiple Access.

OFDM-based early systems found the processing which is necessary for the signal format fairly high, however with progress in technology, this kind of technique presents few issues in terms of the required process.

Space division multiplexing is one kind of technique where radio, metallic otherwise optical transmission media are separated physically through insulation and space or waveguides keeps channel separations. In each physically different channel, numerous channels can be attained through time, frequency, otherwise WDM.

Some POV Passive Optical Network implementations use SDM or space division multiplexing, through the downstream transmissions which occur on one of a duplex FOC fiber optic cable whereas upstream transmission occurs on the remaining fiber. When an ON condition of digital pulse exists, then carrier will be switched to one frequency, and when an OFF condition encounters the carrier, it will be switched to another frequency, i.

Frequency shift keying. Its advantages include lower probability of error and provide high signal-to-noise ratio. It has higher immunity to noise due to constant envelope. Therefore the probability of error-free reception of data is high. It is not preferred for the high-speed modems because with increase in speed, the bit rate increases.

The principle of phase shift keying is that the phase of the carrier wave is modulated in accordance with the digital message signal, i. Here the carrier signal changes its phase depending on the nature of the transmitted bit, i.

In two levels of PSK, the difference of phase shift is used between binary 1 and binary 0 Figure Phase shift keying. The disadvantage of PSK includes lower bandwidth efficiency. The binary data is decoded by estimation of phase states of the signal.

These detection and recovery algorithms are very complex. Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution 3. Help us write another book on this subject and reach those readers. Login to your personal dashboard for more detailed statistics on your publications. Edited by Somayeh Mohammady.

We are IntechOpen, the world's leading publisher of Open Access books. Built by scientists, for scientists. Our readership spans scientists, professors, researchers, librarians, and students, as well as business professionals. Downloaded: Abstract In any communication system that is either digital or analog, we need a communication channel for transmission. Keywords frequency division multiplexing time division multiplexing code division multiplexing wave length division multiplexing orthogonal frequency division multiplexing amplitude shift keying frequency shift keying phase shift keying.

Introduction Multiplexing is the process of transmission of information from more than one source into a single signal over a shared medium. Types of multiplexing Multiplexers are mainly classified as shown in Figure 1. Frequency division multiplexing Frequency division multiplexing [ 1 , 2 , 3 , 4 ] is a networking technique which combines many signals into a single one and then transmitted the combined signal through a common communication channel.

Wavelength division multiplexing Fiber-optic communications require a different kind of multiplexer called a wavelength division multiplexer WAD [ 2 , 4 ].

It is easier to reconfigure. Optical components are more reliable and provide higher bandwidth. Provide high security and faster access to new channel. Low cost and easy system expansion. Simultaneous transmission of various signals. Disadvantages of WDM Scalability is a concern as optical line termination OLT ; optical line termination has to have transmitter array with one transmitter for each optical network unit ONU.

The cost of the system increases with addition of optical components. Frequency division multiplexing FDM [ 1 , 2 , 3 , 4 ] is based on sharing of the available bandwidth of a communication channel among the signals to be transmitted. Advantage of FDM multiplexing A large number of signals channels can be transmitted simultaneously. Demodulation of FDM is easy. Due to slow narrowband fading, only a single channel gets affected.

Disadvantages of FDM The communication channel must have a very large bandwidth. Intermodulation distortion takes place. A large number of modulators and filters are required. FDM suffers from the problem of cross talk. All the FDM channels get affected due to wideband fading. FDM is used in television broadcasting. First-generation cellular telephone also uses FDM.

Time division multiplexing In time division multiplexing TDM [ 1 , 2 , 3 , 4 ], all signals operate with the same frequency at different times, i. Synchronous time division multiplexing In synchronous TDM the slots are arranged in a round robin manner, i. Disadvantages The channel capacity cannot be fully utilized when some source do not want to send the data. It is very complex to implement. Asynchronous time division multiplexing In synchronous TDM if a particular terminal has no data to transmit at a particular time period, the corresponding slot in a frame is wasted or an empty slot will be transmitted.

Disadvantages Frames have different sizes. Code division multiplexing Code division multiplexing CDM [ 3 ] is a form of multiplexing in which the transmitter encodes the signal by using a unique chip code which is generated by a pseudorandom sequence generator. In CDM more number of users can share the same bandwidth. It is scalable. It is well-matched with other cellular technologies. Interference is reduced because different code words are allocated to each user.

Efficient utilization of fixed frequency spectrum. Disadvantages The system is more complicated. As the number of users increases, the overall quality of services decreases. More complex system and primarily it is used in wireless transmission. Orthogonal frequency division multiplexing Orthogonal frequency division multiplexing OFDM [ 4 , 5 ] is a multiplexing technique used in broadband communication system.

OFDM system uses pilot subcarriers to prevent the frequency and phase shift errors. Four-in-one multiplexer The logic symbol and circuit for a four-input multiplexer are shown in Figure Eight-in-one multiplexer The logic symbol and data selector of eight-in-one multiplexer is shown in Figure Working When the three selector switches are actively low, then the three inputs of the first AND gate become actively high because the selector outputs are NOTed and given to the first AND gate.

Amplitude shift keying The principle of amplitude shift keying is that the amplitude of the carrier wave is modulated in accordance with the digital message signal, i. ASK advantages and disadvantages The major advantage of ASK includes high bandwidth efficiency and simplicity in its design. Application Used in our infrared remote controls Used in fiber optical transmitter and receiver. Frequency shift keying The principle of frequency shift keying is that the frequency of the carrier wave is modulated in accordance with the digital message signal, i.

Advantages and disadvantages of FSK Its advantages include lower probability of error and provide high signal-to-noise ratio.

Javatpoint Services JavaTpoint offers too many high quality services. Why Multiplexing? The transmission medium is used to send the signal from sender to receiver. The medium can only have one signal at a time. If there are multiple signals to share one medium, then the medium must be divided in such a way that each signal is given some portion of the available bandwidth. For example: If there are 10 signals and bandwidth of medium is units, then the 10 unit is shared by each signal.

When multiple signals share the common medium, there is a possibility of collision. Multiplexing concept is used to avoid such collision.

Transmission services are very expensive. History of Multiplexing Multiplexing technique is widely used in telecommunications in which several telephone calls are carried through a single wire. Multiplexing originated in telegraphy in the early s and is now widely used in communication. George Owen Squier developed the telephone carrier multiplexing in Concept of Multiplexing The 'n' input lines are transmitted through a multiplexer and multiplexer combines the signals to form a composite signal.

The composite signal is passed through a Demultiplexer and demultiplexer separates a signal to component signals and transfers them to their respective destinations. Advantages of Multiplexing: More than one signal can be sent over a single medium. The bandwidth of a medium can be utilized effectively. Frequency Division Multiplexing is a technique in which the available bandwidth of a single transmission medium is subdivided into several channels.

In the above diagram, a single transmission medium is subdivided into several frequency channels, and each frequency channel is given to different devices. Device 1 has a frequency channel of range from 1 to 5. The input signals are translated into frequency bands by using modulation techniques, and they are combined by a multiplexer to form a composite signal. The main aim of the FDM is to subdivide the available bandwidth into different frequency channels and allocate them to different devices.

Using the modulation technique, the input signals are transmitted into frequency bands and then combined to form a composite signal. The carriers which are used for modulating the signals are known as sub-carriers.

They are represented as f1,f FDM is mainly used in radio broadcasts and TV networks. FDM process is very simple and easy modulation. A Large number of signals can be sent through an FDM simultaneously. It does not require any synchronization between sender and receiver. It suffers the problem of crosstalk. If a source does not have data to send, the corresponding slot in the output frame is empty. Empty slots.

One problem with TDM is how to handle a disparity in the input data rates. If data rates are not the same, three strategies, or a combination of them, can be used. Multilevel multiplexing is a technique used when the data rate of an input line is a multiple of others.

Multilevel multiplexing. Multiple multiplexing is a technique used to allot more than one slot in a frame to a single input line. Multiple-slot multiplexing. Sometimes the bit rates of sources are not multiple integers of each other. Then to make the data rate compatible , dummy bits are added to input lines. This technique is called pulse stuffing, bit padding, or bit stuffing.