Why is multiplexing useful in data communication

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. The process which is used to transmit multiple signals over a single physical medium is known as multiplexing.

The main advantages of multiplexing include the following. The applications of multiplexing include the following. Thus, this is all about an overview of multiplexing in networking and its types like analog multiplexing and digital multiplexing.

Analog type uses analog signals which are multiplexed based on their frequency or wavelength. Digital type uses discrete data bits. This kind of technique is classified into different types like time division, synchronous and asynchronous. From the above information finally, we can conclude that by using these types of multiplexing techniques we can transfer and receive the data efficiently. Digital signals are divided in frames, equivalent to time slot i.

TDM works in synchronized mode. Both ends, i. Multiplexer and De-multiplexer are timely synchronized and both switch to next channel simultaneously. When channel A transmits its frame at one end,the De-multiplexer provides media to channel A on the other end. On the other end, the De-multiplexer works in a synchronized manner and provides media to channel B. Signals from different channels travel the path in interleaved manner.

Light has different wavelength colors. In fiber optic mode, multiple optical carrier signals are multiplexed into an optical fiber by using different wavelengths. Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites.

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It is a multicarrier modulation scheme. Now it is used in 4G broadband communication system and next-generation systems. OFDM is popular in broadband wireless systems due to its resistance to multipath fading. OFDM has high data rate capability with reasonable computational complexity. OFDM divides a broadband channel into multiple parallel narrowband subchannels, and each channel carries a low data rate stream of signals.

Finally these signals are summing and then transmit as a high data rate stream. In an OFDM transmitter, the input signal bits are mapped into a bank of quadrature amplitude modulator which encodes these into complex symbols. This is fed to an inverse fast Fourier transform IFFT to ensure the orthogonality of the subchannels. This output is converted into parallel to serial, modulated into a carrier wave, and then transmitted into the air.

At the receiver the reverse process is performed for recovering the original signal. The advantages of OFDM are that its low computational complexity because OFDM may be viewed as a many slowly modulated narrowband signals rather than a rapidly modulated wideband signal. For OFDM transmitter, a serial stream of binary digits is considered as the input. The input is converted into N parallel streams using inverse multiplexing. The transformation of N parallel streams into the state-space mechanism is performed by means of modulation techniques like quadrature amplitude modulation QAM and phase shift keying PSK.

OFDM transmitter. A digital modulation system for data communication by varying or modulating the phase of the reference signal or the carrier wave signal is known as PSK.

A finite number of phases is involved in PSK with each phase having a distinctive pattern of binary digits. An integration of trouble-free AM and simple phase modulation is called QAM in which the large amount of data is transmitted over the same bandwidth due to the synergistic effect of simple amplitude modulation and phase modulation.

Hence, QAM increases the efficiency of data transmission for radio communication systems Figure OFDM transmitter simple block diagram. To provide a set of complex time-domain samples, IFFT is calculated for each set of symbols. Later, the time-domain samples are quadrature mixed to passband in the normal way.

By the use of digital-to-analog converters DACs , the real and imaginary components are primarily converted to the analog domain. Such analog signal helps to modulate corresponding cosine and sine waves at the carrier frequency.

Finally, those signals are summed up to provide the transmission signal. The transmitter-generated signal is further transmitted over the channel for receiving. The receiver receives the baseband OFDM signals, and then it passes through a low-pass filter to remove the unwanted signals. The baseband signals are then sampled and digitized using ADCs, and a forward FFT is used to convert back to the frequency domain. By means of an appropriate symbol detector, the frequency domain signals are converted to N parallel streams, and each stream is converted to a binary stream.

A sequential stream combining all binary stream acts as an estimate of the original binary stream at the transmitter side. OFDM signal is robust and more tolerant in multipath propagation environment to delay spread. OFDM is more resistant to frequency selective fading than single carrier transmission systems. OFDM system gives good protection against co-channel interference and impulsive parasitic noise. OFDM system has also certain limitations rather than the abovementioned potential capabilities.

OFDM is very sensitive to carrier frequency offset and hence becomes difficult to synchronize during sharing of subcarriers different transmitters.

Digital multiplexer [ 6 , 7 , 8 ] or data selector is a logic circuit that has several input lines and a single output line. It also consists of data selector switch which is used to select the inputs and permit the data into the device to output.

The logic symbol and circuit for a four-input multiplexer are shown in Figure Circuit diagram of four-in-one multiplexer. Here D0, D1, D2, and D3 are data input lines. S0 and S1 are data selector or logic switches. Thus the data from D0 line is outputted through this AND gate. At that time the other gates are in 0 output position. In this manner D2 and D3 are inputted to consecutive switch positions. Here an OR gate is used to combine these four output lines as a single output Figure Circuit symbol and selector switch pattern of four-in-one multiplexer.

The logic symbol and data selector of eight-in-one multiplexer is shown in Figure Logic symbol and switching pattern of eight-in-one multiplexer. If input is 2, then one data selector switch is needed; if input is 4, then two selector switches are needed; if input is 8, then three selector switches are needed; if input is 16, then four selector switches are needed; and so on.

Logic diagram of eight-in-one multiplexer. 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.

At that time all other gates are in 0 output position. Demultiplexer [ 6 ] is a logic circuit that performs the reverse multiplexer function.

Demultiplexer receives signal from a single line serial input and transmits these information into multiple output lines and parallel output lines Figure Circuit diagram of one-to-eight demultiplexer.

In analog communication we use different modulation schemes like amplitude modulation, frequency modulation, phase modulation, etc. In digital communication we use the following schemes: Amplitude shift keying ASK. The principle of amplitude shift keying is that the amplitude of the carrier wave is modulated in accordance with the digital message signal, i.

The time period for which the carrier is present or absent depends on the time interval for which the unipolar pulses are present. Here the amplitude of carrier signal is varied to represent binary 1 and binary 0 data inputs, while the frequency and phase of the carrier signal remain constant. Voltage levels are left to designers of the modulation system Figure Amplitude shift keying. The major advantage of ASK includes high bandwidth efficiency and simplicity in its design.

In ASK the modulation and demodulation processes are comparatively inexpensive. Its disadvantages include lower power efficiency, and it is very susceptible to noise interference.

The principle of frequency shift keying is that the frequency of the carrier wave is modulated in accordance with the digital message signal, i. 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.