 Hello everyone. Welcome to this session. I am Dipali Vadkar, working as assistant professor at WIT Solapur. In this session, we will study PCM TDM system. At the end of this video lecture, student will be able to describe concept of multiplexing and student will be able to explain working of PCM TDM system. These are the contents. Let us see the multiplexing and demultiplexing. Multiplexing is the technique by which we can transmit number of input signal over single communication channel. Here the multiplexer device is present at the transmitter side. And the demultiplexing is the technique where the multiplex signals are recovered separately. And this demultiplexer device is present at the receiver side. Now we will see the need of multiplexing. The process of transmitting two or more signals by setting up one transmitter receiver pair for each channel. This process is expensive. In a multiplexing technique, single cable or radio link can handle multiple signals simultaneously. Cost saving can be gained by using the single channel to send multiple information signals. The basic types of multiplexing. In that first, that is the frequency division multiplexing, FDM. Next, the wavelength division multiplexing, WDM. Basically it is used for optical fiber, optical communication. Third, time division multiplexing. Time division multiplexing can be used for analog as well as digital multiplexing system. And next, code division multiplexing, CDM. It is used in a cell phone mechanism. The time division multiplexing in this, the complete signal gets transmitted by occupying different time slot. Here the same bandwidth can be used for transmission of number of signals. There is one example. Suppose there are three source A, B and C. If these three source want to transmit signals over a same communication channel. Then here the multiplexing technique is used. And in this multiplexing technique, the time division multiplexing is used. So, in that the source A, its data is get divided first into three units A1, A2 and A3. Similarly, for B data is divided into B1, B2, B3 and C. Its data is divided into C1, C2 and C3. Then one unit from each source collected and these units are combined to form frame. So these number of frames are transmitted over a same communication channel. So this process is continued. Here same communication channel or same bandwidth is used to transmit these all frames. Now the implementation of TDM. TDM signal is implemented by two way. One is a synchronous TDM and another is a asynchronous TDM. In the synchronous TDM, the time slots are assigned at the beginning irrespective of idea about the presence of data at the source. This leads to the wastage of channel capacity. As in the absence of any data unit, that particular time slot gets entirely wasted. Next is a synchronous TDM. It is also termed as statistical or intelligent TDM technique as it eliminates the drawbacks of wastage of time slot present in a synchronous TDM. Particular frame is transmitted by the transmitting end only when it gets completely filled by the data unit. So it exhibits higher efficiency than that of the synchronous TDM system. Let us see the PCM TDM system. Before going to the PCM TDM system, pause the video for a while and recall what is PCM? PCM that is Perl's code modulation. It is the digital representation of analog signal that takes the samples of amplitude of analog signal at regular interval. The sample analog data is converted into the binary data. So you will see the PCM TDM system. First, here part is a low pass filter and commutator. This is connected to the PCM transmitter. Then the repeaters are used and one communication channel, maybe it may be optical fiber or coaxial cable. Then here the PCM receiver. After that, second commutator switch is used and then it is again given to the low pass filter and then original data. Let us see working of this PCM TDM system. In this, at the beginning these low pass filters are used. This low pass filter basically works as an anti-alizing filter. So these are used to eliminate the alizing effect. So here we can give the input number of sources. Consider here four sources are present. Here the commutator switch S1 is used which is at the transmitter. When this commutator switch rotates, then it selects the signal from this respective source and it takes the sample and place that sample on the communication channel. So this commutator switch rotates at the speed of FS means its frequency is FS. So this is nothing but sampling frequency. So when this commutator switch makes the contact with the second channel, then it selects that samples and place that sample on a channel. Then it will make the contact with the third channel. It selects the sample and place that sample on the communication channel. Similarly for fourth. So in this way it selects the sample for a respective channel and whatever the result is there, that result it is nothing but PAM signal. This PAM signal is obtained by time division multiplexing. So we can say that this is the TDM PAM signal. Now this TDM PAM signal is given to the PCM transmitter. Here this PCM transmitter converts this TDM PAM signal into code. So this is nothing but PCM signal. Now this code is transmitted over this communication channel. In between this communication channel there are repeaters are used. These repeaters are nothing but regenerators. This regenerates these signals, amplifies that signals and removes the distortion which is in between this range. Now this signal is given to the PCM receiver. At the PCM receiver it converts this code into again TDM PAM signal. Now here the commutator switch S2 is present at the receiver. This commutator switch is synchronized with the commutator switch S1 which is at the transmitter. The commutator switch is rotated at the same speed for the proper de-multiplexing. Now when this commutator switch is rotated at that time it plays that respective sample to the respective destination or respective channel. Then according to the rotation of this switch S2 these samples are separated. Here third and next is a fourth sample. Then these samples are given input to the low pass filter. Then at the output of low pass filter we get the original signal X1 of t, X2 of t, X3 of t and so on. So in this way we can transmit the number of signal over a single communication channel by using this PCM TDM system. Now one of the application of this PCM TDM system that is the T1 carrier system. This T1 carrier system it is nothing but transmission 1. T1 stands for transmission 1 and specifies a digital carrier system using the PCM encoded analog signal. Here the 24 voice channels are used and this 24 voice channel transmits its samples over a single communication channel. Multiplexing here use that is nothing but TDM. So here this 24 voice channel encoded into 8 bits each channel having 8 bits. Each frame here consists total 24 channels and each channel having 8 bits. So the bits per frame we can calculate 24 channels per frame into 8 bits per channel. So total bits per frame that is nothing but 192 bits per frame. So for each frame 192 bits and one extra bit is used here that is for a synchronization purpose. Next term that is nothing but bit rate. This data is sample at 8000 samples per second at this rate. So the bit rate we can calculate 192 bits per frame into 8000 frames per second. So its bit rate is 1.5 mbps. So these are the references. Thank you.