 Welcome to the session on digital modulations. This is Dayanand Patil, faculty member of computer science and engineering department, Walshchan Institute of Technology, Solapur. At the end of this session, you will be able to understand digital modulation techniques. What is digital modulation? The modulation that is adding information to a carrier signal. The carrier signal that is a original signal that carries the analog information. That modulation is a process by which some characteristics of carrier wave is varied in accordance with a modulating signal. That original wave is that is analog carrier signal. In modulation process, some characteristics of original carrier signal is modulated accordance with the digital data that is being transmitted. The sine wave on which the characteristic of the information signal are modulated is called carrier signal. That is the sine wave that is the original analog signal on which we are applying the different characteristics for modulation. Those three characteristics are frequency, phase and amplitude. In a digital modulation, the modulation signal is a binary data or an MRA data, encoded version and the carrier wave to be modulated is of usually sinusoidal wave with fixed frequency. The sinusoidal wave is the original analog signal that is having a fixed frequency. While transmitting a binary data, we are modulating the original signal with the three characteristics. Digital Modulation Techniques There are three basic digital modulation techniques. Amplitude Shipped King, Frequency Shipped King and Phase Shipped King. The amplitude, frequency, phase are the three characteristics we are using to modulate the signal. So, these are the three techniques. The first technique is Amplitude Shipped King or that we shortly we will call it as ASK. In ASK, the amplitude of carrier wave is changed according to the digital input signal. Therefore, ASK is analogous to analog amplitude modulation. So, in this ASK technique, we are modulating the analog signal by using the character amplitude. So, in this technique, the amplitude is changed and the frequency and phase of the original carrier signal is kept constant. That is the ASK is using On-off King, that is the amplitude is set to high or set to 0. So, this is the mathematical formula for ASK that A naught cos of 2 phi f c t. So, here that A is amplitude f is frequency and t is time. So, in binary or digital transmission, we are transmitting either 0 or 1. With respect to or 0, we are using the amplitude A 0 and for binary 1, we are using the amplitude A 1. So, as we are using On-off King, for transmitting a binary 0, we are using the amplitude low. For 1, we are using the high amplitude that is off for 0, high that is on for transmitting a binary 1. So, here the amplitude is varied and the remaining two characteristics frequency and time remain constant for while transmitting both the binary 0 and binary 1. So, this is example of ASK. So, here in this diagram, we can visualize. So, this is the carrier signal that is the original signal that carries the analog information. This is the analog signal. Here we can see that it is there is a frequency is same and amplitude is same. So, assume that we are transmitting the binary data 1 0 1 1 0, assume that we are transmitting this data. So, while transmitting 1, we are using the amplitude high from the previous example. So, here we can see for binary 1, we are using the amplitude high that is on A 1. For binary 0, we are using the low that is on off King. See here. So, while transmitting a 1, we are using the amplitude high, while transmitting 0, it is set to 0. Similar, next the 1 and 1 are transmitted, the amplitude is high, here the 0 is being transmitted again the amplitude is low. So, this is the modulated signal. This is the original signal. This is the binary data we are transmitting. This is 1 for high and 0 is at low is for 0. Next technique frequency shift King in short form we will call it as FSK. In FSK, the frequency of carrier wave is changed according to the digital input signal. Therefore, FSK is analogous to analog frequency modulation. So, in this technique, so the frequency is modulated as we have discussed in the ASK. Now, this is the second technique is FSK. Now, you think and write the question is which parameter is varied and which parameters are constant in FSK. Also write mathematical module for FSK. For this question, you think and write the answer. Now pause the video and write the answer. The frequency of carrier signal is varied to represent binary 1 or 0 peak amplitude and phase remains constant. The characteristic frequency is varied with respect to binary 1 and 0, the peak amplitude and phase remains constant in this technique. The previous one that ASK that amplitude was changed. So now in this technique, the frequency is changed and the remaining two characteristics are constant and the mathematical formula is this is the mathematical formula. You can see here the amplitude is same. The amplitude is same for both binary 0 and 1. Here the frequency is varied that F1 and F2 that is that we are setting one frequency for binary 0 other frequency for binary 1 and the phase remains constant that is T that is common for both 1. We can see in this example, assume that we are transmitting the binary 0 1 0 1 0 1 0 1. So this is the data we are transferring transmitting. So now we can see that we are using the two frequencies that frequency 1 for the binary 1 and frequency 2 for binary 0. So here we can see the frequency is varied and the amplitude line that phase remains constant. So here you can see the frequency is high for 1 and low for 0. Here while transmitting 1, the frequency is high. While transmitting 0, frequency is low. Again it is high frequency for 1 and low frequency for 0 similarly high, low and high. So this is here the frequency is changed that the frequency is varied for the different binary data high for 1 and low for 0. So this is the example for FSK. Next is phase shift keying. So in this PSK, the phase of carrier wave is changed according to the digital input. Therefore the PSK is analogous to the analog phase modulation. So the peak amplitude and frequency remain constant in this technique. In this technique phase is changed for different binary data and the amplitude and frequency remains constant. So you can see in this mathematical module that is here this is the amplitude. This is constant for both the binary 1 and binary 0. Next is frequency that is also common for both the binary 1 and binary 0. Here that phase is changed you can see the T, T plus pi. Here the phase is changed by pi that pi is 180 degree in our waveform. So that is while transmitting 1, if it is starting assume that the 1 is starting from 0. While transmitting 0s that the sine wave is shifted by 180 while transmitting the data. Now we can see assume that we are transmitting this binary data 1 0 1 1 0. This is the carrier that original carrier signal. So in original carrier signal we can see that the waveform is continuous. There is nothing changed in any frequency, amplitude or phase. So this is the modulated signal while transmitting 1 assume that this is starting from 0s. So here the direction is changed by pi while transmitting data from 1 to 0. Here the 1 is transmitting it is continuous. Here the 0 need to be transmitted that is why it is shifted by 180 degree. So here you can see this is the original one. So we are already familiar with these waveforms. This is 0 degree, this is 90, this is 180, this is 270 and this is 360. This completes one cycle. So this is the 180 means this is pi. So while transmitting 1 it is continuous form whenever 0 need to be transmitted this wave is shifted instead of continuing in the same direction it is shifted by 180 degree. So this is started from here and this is continued. Again the 1 need to be transmitted again it need to be shifted by pi. So 1 is transmitted. So here the next data 1 to be transmitted so there is no need to change the phase at this stage. It will be continued. Again 0 need to be transmitted so that is why it is shifted by 180 degree. So this is the short summary that briefly represented the modulated, modulated signals and these are the some important points about the 3 techniques. These are the references. Thank you.