 Hello everyone. Welcome to this video lecture. Myself Dipali Wadkar working as assistant professor at WIT Solapur. Today we will study the introduction to digital communication system. At the end of this session, student will be able to examine block diagram of digital communication system. Student will be able to state advantages and disadvantages of digital communication system. These are the contents, introduction to digital communication system, block diagram of digital communication system, then the advantages and disadvantages of digital communication system. What is digital communication? It is the communication in which any message passed through digital devices. It is the communication system in which any type of information is sent digitally. It is the mode of communication where the information or thought is encoded digitally as discrete signals and electronically transferred to the recipient. So what are the examples of digital communication? E-mailing in computer, texting in cell phone, fax, teleconferencing and video conferencing. This is the block diagram of digital communication system. Here basically two blocks. One is a transmitter, another is a receiver. In transmitter, first block is source, then source encoder, channel encoder, modulator, transmitting antenna. At the receiver side, receiving antenna, detector, channel decoder, source decoder and destination. In between transmitter and receiver communication channel is present. Let us see one by one working of each block of this communication system. First block that is the information source which contains information source as well as input transducer. We know that the communication system serves to communicate information or message signal. The information or message signal is originated from information source. Source of information generate a message signal. For example, human voice, telephone pictures, teletype data, atmospheric temperature or pressure. The information source which produces the information or message signal may or may not be in the form of electrical signal. In case if that message signal is not in the electrical signal, then the input transducer is used to convert that message into time-variant electrical signal. So the input transducer is a device that converts one form of the energy into another form. For example, in case of radio broadcasting, microphone is used as input transducer which converts the information in the form of sound into the electrical signal. So this is the output at the first block that is the information source. The next block that is the source encoder. The signal which is produced by the source is converted into digital signal consists of ones and zeros. We should like to use very few binary digits as possible to represent this signal. The process of converting output of analog or digital source into sequence of binary digits is called as a source encoding. So at the output of source encoder, there is a sequence of digital data. Source encoder basically consists these three blocks that is the sampler, quantizer and encoder. Sampler used to convert continuous time signal into digital signal, quantizer converts the amplitude of analog signal to the digital value and encoder which assigns a binary code to the quantized signal. Next block that is the channel encoder. It controls the noise, it detects and corrects the error that can occur in a transmitted data due to noise. The basic working of channel encoder that is to introduce redundancy or redundant bits into the input digital data which is used to detect and correct the error at the receiver at the channel decoder. So this is the output at the channel encoder that is the data bits plus redundant bits. Next block that is the digital modulator. It converts the sequence into electrical signal for a transmission over a channel. The digital modulator maps the binary sequence into the signal waveforms. These are the some examples of digital modulations. ASK that is the amplitude shift king, FSK, frequency shift king and PSK phase shift king. This is the one of the example that is the amplitude shift king which is the digital modulation. In this the digital data that is the 10110 it is gate multiplied by the analog carrier signal so this carrier digital modulator modulates this carrier signal according to the digital datum. If the digital data is 1 the carrier is present. If the digital data is 0 here the amplitude of this carrier is 0. So in this way this digital data is transmitted over the analog carrier by using this ASK modulation. So this is the output at the digital modulator. Next in between the transmitter and receiver there is a communication channel. This modulated signal is transmitted over a transmitting antenna towards the receiver. The communication channel is the physical medium that is used for transmitting signal from transmitter to receiver. Channels for digital communications are wired telephone channels, coaxial cable, optical fire. There also wireless communication channels that is the microwave radio or satellite channel. Each physical channel has a certain limited range of frequencies that is called the channel bandwidth. Physical channel has an important limitation this is nothing but noise. Now the question what will the working of demodulator? We have seen the working of modulator that modulate a carrier signal according to the input modulated signal. That means it adds a carrier signal. Now what will the working of demodulator? Pause the video for a while and think. So demodulator digital demodulator it removes the carrier signal and reverse the process of modulator. The digital demodulator processes the channel corrupted transmitted waveforms and reduces the waveform to sequence of number that represent estimates of transmitted data signal. This is the output at the digital demodulator which converts this analog signal into the digital signal that is the binary digital numbers which data bits and redundant bits. Now the next block that is the channel decoder. It attempts to reconstruct the original information signal from the knowledge of code used by the channel encoder and redundancy contained in the received data. Channel decoder removes the extra bit which are get added at the channel encoder. Next is a source decoder and output transducer. It decodes the sequence from the knowledge of encoding algorithm and which results in the approximate replica of input at the transmitter end. Finally we get the desired signal in desired format analog or digital. So this is the output at the source decoder. So this is the digital data is get converted into the electrical signal again. Next this is nothing but destination. At the destination there is an output transducer. So this output transducer converts this electrical signal into original information. For example speaker which converts this electrical signal into the sound signal. Next advantages of digital communication system. Digital communication can be done over a large distances through internet and other things. Digital communication gives the facilities like video conferencing which saves lot of time, efforts as well as money. It is easy to mix signals and data using digital technique. It is fast, easier and cheaper. It can be tolerated the noise interference. It can be detect and correct error easily because of channel coding. It has excellent processing techniques such as data compression, image processing, channel coding and equalization. Disadvantages of digital communication system. It requires reliable synchronization. It requires A to D conversion at high rate. It requires larger bandwidth and the probability of error or bit error rate is high. These are the some references. Thank you.