Digital Communications System
Definition of digital communication system:
Block diagram of digital communication system:
Elements of Digital Communications System:
This is a transducer which takes a physical input and converts it to an electrical signal . This block also consists of an analog to digital converter where a digital signal is needed for further processes.
A digital signal is generally represented by a binary sequence.
2.Source encoder:
The source encoder compresses the data into minimum numb Hoer of bits. This process helps in effective utilization of the bandwidth. It removes the redundant bits
3. Channel encoder:
The channel encoder, does the coding for error correction. During the transmission of the signal, due to the noise in the channel, the signal may get altered and hence to avoid this, the channel encoder adds some redundant bits to the transmitted data. These are the error correcting bits
4. Digital modulator:
The signal to be transmitted is modulated here by a carrier. The signal is also converted to analog from the digital sequence, in order to make it travel through the channel or medium.
5. Channel:
The channel or a medium, allows the analog signal to transmit from the transmitter end to the receiver end.
6. Digital demodulator:
This is the first step at the receiver end. The received signal is demodulated as well as converted again from analog to digital. The signal gets reconstructed here.
7. Channel decoder:
The channel decoder, after detecting the sequence, does some error corrections. The distortions which might occur during the transmission, are corrected by adding some redundant bits. This addition of bits helps in the complete recovery of the original signal.
8. Source decoder:
The resultant signal is once again digitized by sampling and quantizing so that the pure digital output is obtained without the loss of information. The source decoder recreates the source output.
9. Output transducer:
This is the last block which converts the signal into the original physical form, which was at the input of the transmitter. It converts the electrical signal into physical output .
10. Output signal:
This is the output which is produced after the whole process.
Advantages of Digital Communications system:
:
- The digital communication systems are simpler and cheaper compared to analog communication systems because of the advances made in the IC technologies.
- In digital communication, the speech, video and other data may be merged and transmitted over a common channel using multiplexing.
- Using data encryption, only permitted receivers may be allowed to detect the transmitted data. This property is of its most importance in military applications.
- Since the transmission is digital and the channel encoding is used, therefore the noise does not accumulate from repeater to repeater in long distance communications.
- Since the transmitted signal is digital in nature, therefore, a large amount of noise interference may be tolerated.
- Since in digital communication, channel coding is used, therefore, the errors may be detected and corrected in the receivers.
- Digital communication is adaptive to other advanced branches of data processing such as digital signal processing, image processing and data compression, etc.
Disadvantages of digital communications system:
- Due to analog to digital conversion, the data rate becomes high. therefore more transmission bandwidth is required for digital communication.
- Digital communication needs synchronization in case of synchronous modulation.
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