8-PSK(Digital Communication Technique)

It contains the introduction, modulation, demodulation, phasor diagram, constellation diagram,time-domain diagram, signal space diagram, power spectral diagram, spectral diagram, bandwidth, spectral efficiency, uses, advantages, and disadvantages.

1. 8 - PSK

2. Phase-shift keying (PSK) is a digital modulation technique in which the phase of carrier signal is changed by varying the sine and cosine inputs at a particular time. It enables data to be carried on a radio communications signal in more efficient way compared to Frequency Shift Keying (FSK). There are different forms of PSK - BPSK, QPSK, MPSK etc. 8 PSK is a form of multiple level PSK or MPSK. In 8 PSK, there are 8 different phase changes defined, each phase change represents the transmission of 3 bits. The phase changes are -112.5, -157.5, -67.5, -22.5, 112.5, 157.5, 67.5 and 22.5 degrees. Introduction

3. In 8 PSK 3 bits are transmitted in a single modulation symbol. I and Q bits determine the polarity of the QAM signal, and the C channel determine the magnitude. Modulation 8 PSK MODULATOR

4. So, for I=0, Q=0, and C=0 The two inputs to the I channel product modulator are -0.541 and Sin ( ωct ) Then we get , I= -0.541 Sin( ωct ) The two inputs to the Q channel product modulator are -1.307 and Cos ( ωct ) We get, Q= -1.307 Cos ( ωct ) The linear summer output is -0.541 Sin ( ωct ) - 1.307 Cos ( ωct ) =1.41 Sin(ωct-112.5) Therefore, for the binary 000, the output phase for 8 PSK is -112.5 Similarly for the remaining tri bit codes, the procedure is same

5. Demodulation In 8 PSK the orthogonal coherent demodulation is used. 8 PSK DEMODULATOR

6. Here, in the demodulator, the carrier signal is recovered from the modulated signal itself so when the modulated signal (8 PSK) is taken as the input then at first the power of the signal is raised by the factor of M. After then the signal is passed through the Band Pass Filter (frequency as Mfb ) where all the higher and lower-level frequencies is being rejected. Then the signal is being divided by the factor of M for getting the sin( wct ) and cos( wct ) signals. Now, the sin( wct ) signal is multiplied with the product modulator and passes through the low pass filter which has the limit from 0 to 2 MTb , and similarly, the cos( wct ) signal is also multiplied with the product modulator and passes through the low pass filter which has the limit from (2M-1)Tb to (2M+1)Tb. Then finally both the signals are combined in the MUX and hence, with the help of the regenerator, we regenerate the demodulated output.

7. A constellation diagram is a representation of a signal modulated by a digital modulation scheme such as quadrature amplitude modulation or phase-shift keying. The angle of a point, measured counterclockwise from the horizontal axis, represents the phase shift of the carrier wave from a reference phase. The distance of a point from the origin represents a measure of the amplitude or power of the signal. In a digital modulation system, information is transmitted as a series of samples, each occupying a uniform time slot. During each sample, the carrier wave has a constant amplitude and phase, which is restricted to one of a finite number of values. So, each sample encodes one of a finite number of "symbols", which in turn represent one or more binary digits (bits) of information. Each symbol is encoded as a different combination of amplitude and phase of the carrier, so each symbol is represented by a point on the constellation diagram, called a constellation point. Constellation Diagram

8. Phasor Diagram is a graphical representation of the relation between two or more alternating quantities in terms of magnitude and direction. In other words, it depicts the phase relationship between two or more sinusoidal waveforms having the same frequency. Phasor Diagram and Truth Table Phasor Diagram Truth Table

9. A time-domain graph shows how a signal changes with time. The figure attached below shows the time domain diagram and how the phases are changing according to the message bit signal. Time domain diagram

10. Suppose the message bit is 101111100001110 In 8-PSK , 8 no. of symbols are transmitted along carrier (phase, frequency and amplitude) n = no. of bits/symbol = = = 3 Then we have to break the message bit in pairs of 3 for drawing the time domain diagram. 101 111 100 001 110 Now we can draw the time domain diagram and observe the phase change as shown in the diagram.

11. Power Spectral Density Power spectral density is the measure of signal’s power content versus frequency. The amplitude of PSD is normalized by spectral resolution employed to digitize signal. The PSD of 8-PSK signal or any other MPSK using rectangular data pulses is given by: For a given symbol rate, the bit rate for 8-PSK is 3/2 times the bit rate of QPSK and that of 16-PSK is 4/3 times bit rate of 8 PSK. The PSDs for m-PSK signals are typically compared on the basis of constant bit rate.

12. A 'signal space diagram' is an ideal constellation diagram showing the correct position of the point representing each symbol. The signal space diagram of 8-psk is shown : Signal Space Diagram for 8-PSK

13. Spectral efficiency = fb/ (2fb/n) = n/2 = /2 = 1.5 8-PSK Spectral diagram and Spectral efficiency

14. With 8PSK, because the input data are divided into Three channels, the bit rate in either the I ,Q or the C channel is equal to one-Third of the input data rate (fb /3). Baud Rate= Bit rate/n = Rb /3 Bandwidth considerations of 8PSK

15. Applications

16. Advantages

17. Disadvantages

18. In this presentation we have learnt the basic characteristics of 8 PSK, its modulation and demodulation process and how it differs from the other types of modulation techniques. We have come across various applications ( like broadcast video systems, aircraft and satellite systems etc.), advantage and disadvantage of 8 PSK signal. Conclusion

19. THANK YOU!