Phase Shift Keying
In Phase Shift Keying (PSK), each symbol in the message signal gives a unique phase shift to the carrier wave. There are two types of PSK, Binary and M-ary. In Binary PSK, logic 1 is associated with certain phase shift of carrier wave e.g. 90° and logic 0 is associated with different phase shift other than 90° e.g. 0°. In M-ary PSK, a group of log2M bits are considered together rather than 1 bit at a time and the phase shift is associated with this group of bits.
For example, in 16-ary PSK, a group of 4 bits are considered and are given a respective phase shift. Since there are 16 possible 4 bit binary numbers (24), 16 different phase shifts are required for modulation. If all such phase shifts are created using a single carrier wave, then it is called as coherent PSK. If multiple carrier wave each with different phase shifts are used for modulation then it is called as non-coherent PSK.
Block Diagram of Phase Shift Keying
Given Below is the Block Diagram of Phase Shift Keying
The analog message signal is converted to digital signal using Analog to Digital Converter. This digital signal is then passed to two multipliers which takes two inputs each. A sine wave with phase shift p1 is considered as carrier signal for logic 1 and a sine wave with phase shift p2 is considered as carrier signal for logic 0. These carrier waves are multiplied with the digital message signal. When logic 1 present in the digital signal gets multiplied with the carrier Asin(2πft+p1) it results in Asin(2πft+p1) only since the other multiplier gets logic 0 as input since it is passed through a NOT gate.
When logic 0 present in the digital signal gets multiplied with the carrier Asin(2πft+p2) it results in Asin(2πft+p2) only since the multiplier gets logic 1 as input since it is passed through a NOT gate. Both this signals are added to form PSK wave A[sin(2πft+p1)+sin(2πft+p2)]. However this PSK wave contains abrupt changes in phases which causes unnecessary high bandwidth usage. Hence this signal is passed through Band Pass Filter which limits the bandwidth usage.
For demodulating, the PSK wave is passed through two multipliers again where their respective carrier waves are multiplied again. This signal is passed through two Band Pass Filters out of which the top BPF allows the signal with phase shift p1 to pass if logic is 1 and the bottom allows the signal with phase shift p2 to pass if logic is 0. The output of both BPF is compared with each other where the output of the comparator is high if output of BPF1 is greater than output of BPF2 and is low if output of BPF2 is greater than output of BPF1. Hence a digital signal is received at the output of the comparator. This digital signal is converted to analog wave using Digital to Analog Converter.
Digital Modulation Techniques
Modulation is the Fundamental Process in Communication Systems, In Modulation Low-Frequency Message Signal Blends with High-Frequency Carrier Frequency to Enable Efficient Transfer of the Signal. In this article, we will be going through Digital Modulation Techniques, First we will start our Article by Defining Modulation, Then we will go through the Three types of Digital Modulation techniques with Their Wave, At Last we will conclude our Article With their Application, Advantages, Disadvantages and Some FAQs.
Table of Content
- Modulation
- Digital Modulation Techniques
- Amplitude Shift Keying
- Frequency Shift Keying
- Phase Shift Keying
- M-ary Encoding
- Applications
- Advantages
- Disadvantages
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