lect-1-introduction in digital communication
- 2. Digital communication – analog to digital The communication that occurs in our day-to-day life is in the form of signals. These signals, such as sound signals, generally, are analog in nature. When the communication needs to be established over a distance, then the analog signals are sent through wire, using different techniques for effective transmission.
- 3. The necessity of Digitization The conventional methods of communication used analog signals for long distance communications, which suffer from many losses such as distortion, interference, and other losses including security breach. In order to overcome these problems, the signals are digitized using different techniques. The digitized signals allow the communication to be more clear and accurate without losses. The following figure indicates the difference between analog and digital signals. The digital signals consist of 1s and 0s which indicate High and Low values respectively.
- 5. Advantages of Digital communication As the signals are digitized, there are many advantages of digital communication over analog communication, such as ❑ The effect of distortion, noise, and interference is much less in digital signals as they are less affected. ❑ Digital circuits are more reliable. ❑ Digital circuits are easy to design and cheaper than analog circuits. ❑ The hardware implementation in digital circuits, is more flexible than analog. ❑ The occurrence of cross-talk is very rare in digital communication. ❑ The signal is un-altered as the pulse needs a high disturbance to alter its properties, which is very difficult.
- 6. Continue… ❑ Signal processing functions such as encryption and compression are employed in digital circuits to maintain the secrecy of the information. ❑ The probability of error occurrence is reduced by employing error detecting and error correcting codes. ❑ Spread spectrum technique is used to avoid signal jamming. ❑ ❑ Combining digital signals using Time Division Multiplexing (TDM) is easier than combining analog signals using Frequency Division Multiplexing (FDM). ❑ The configuring process of digital signals is easier than analog signals. ❑ Digital signals can be saved and retrieved more conveniently than analog signals. ❑ Many of the digital circuits have almost common encoding techniques and hence similar devices can be used for a number of purposes. ❑ The capacity of the channel is effectively utilized by digital signals. ■
- 7. Elements of Digital Communication
- 8. Following are the sections of the digital communication system. Source Encoder ■ The source encoder compresses the data into minimum number of bits. This process helps in effective utilization of the bandwidth. It removes the redundant bits (unnecessary excess bits, i.e., zeroes). 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. 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.
- 9. continue ■ Channel The channel or a medium, allows the analog signal to transmit from the transmitter end to the receiver end. ■ 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. ■ 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.
- 10. Continue ❑ 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. ❑ 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 (Example: loud speaker). ❑ Output Signal This is the output which is produced after the whole process. Example − The sound signal received. This unit has dealt with the introduction, the digitization of signals, the advantages and the elements of digital communications. In the coming chapters, we will learn about the concepts of Digital communications, in detail.