Digital Communication – Bandwidth, Information Transfer Rate, Baud Rate

November 22, 2007

Bandwidth

(1) A range within a band of frequencies or wavelengths.

(2) The amount of data that can be transmitted in a fixed amount of time. For digital devices, the bandwidth is usually expressed in bits per second(bps) or bytes per second. For analog devices, the bandwidth is expressed in cycles per second, or Hertz (Hz).

The bandwidth is particularly important for I/O devices. For example, a fast disk drive can be hampered by a bus with a low bandwidth. This is the main reason that new buses, such as AGP, have been developed for the PC.

Information Transfer Rate

In telecommunications, information transfer is the process of moving messages containing user information from a source to a sink.

Baud Rate

The baud rate of a data communications system is the number of symbols per second transferred. A symbol may have more than two states, so it may represent more than one binary bit (a binary bit always represents exactly two states). Therefore the baud rate may not equal the bit rate, especially in the case of recent modems, which can have (for example) up to nine bits per symbol.

For example, a Bell 212A modem uses Phase Shift Keying (PSK) modulation, and each symbol has one of four phase shifts (of 0(deg), 90(deg), 180(deg), or 270(deg)). Since it requires two bits to represent four states (00, 01, 10, and 11), the modem transmits 1,200 bits/s of information, using a symbol rate of 600 baud.

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What are the Advantages and Disadvantages of Digital Communication

November 21, 2007

Definition of Digital – A method of storing, processing and transmitting information through the use of distinct electronic or optical pulses that represent the binary digits 0 and 1.

Advantages of Digital –
Less expensive
More reliable
Easy to manipulate
Flexible
Compatibility with other digital systems
Only digitised information can be transported through a noisy channel without degradation
Integrated networks

Disadvantages of Digital –
Sampling Error
Digital communications require greater bandwidth than analogue to transmit the same information.
The detection of digital signals requires the communications system to be synchronised, whereas generally speaking this is not the case with analogue systems.

Some more explanation of advantages and disadvanatages of analog vs digital communication.

1.The first advantage of digital communication against anlog is it’s noise immunity.In any transmission path some unwanted voltage or noise is always present which cannot be eliminated fully.when signal is transmitted this noise gets added to the original signal causing the distortion of the signal.However in a digital communication at the receiving end this additive noise can be eliminated to great extent easily
resulting in better recovery of actual signal.Incase of analog communication it’s difficult to remove the noise once added to the signal.

2.security is another priority of messaging services in modern days.Digital communication provides better security to messages than the analog communication.It can be achieved through various coding techniques available in digital communication.

3.in a digital communication the signal is digitised to a stream of 0 s
and 1 s.So at the receiver side a simple decision has to me made whether received signal is a 0 or a 1.Accordingly the receiver circuit becomes simpler as compared to the analog receiver circuit.

4.Signal when travelling through it’s transmission path gets faded gradually.So on it’s path it needs to be reconstructed to it’s actual form and re-transmitted many times.For that reason AMPLIFIERS are used for analog communication and REPEATERS are used in digital communication.amplifiers are needed every 2 to 3 Kms apart where as
repeaters are neede every 5 to 6 Kms apart.So definitely digital communication is cheaper.Amplifiers also often add non-linearities that
distort the actual signal.

5.Bandwidth is another scarce resource.Various Digital communication
techniques are available that use the available babdwidth much efficiently than analog communication techniques.

6.when audio and video signals are transmitted digitally an AD(Analog to Digital) converter is needed at tansmitting side and a DA(Digital to Analog) converter is again needed at receiver side.While transmitted in analog communication these devices are not needed.

7.Digital signals are often an approximation of the analog data(like voice
or video) that is obtained through a process called quantisation.The digital representation is never the exact signal but it’s most closely approximated digital form.So it’s accuracy depends on the degree of approximation taken in quantisation process.

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