Shift sssssssssssssssssssssssKeyings.pptx

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1. Shift Keyings

2. Definition Shift Keying is a digital modulation technique used in telecommunications to transmit digital data (bits) by altering one of the characteristics of a carrier wave, such as its amplitude, frequency, or phase Digital to Analog Modulation

3. How it Works 1.  Digital Input : Digital data (a sequence of 0s and 1s) is fed into the transmitter.  2.  Modulation : A carrier wave is generated, and its amplitude, frequency, or phase is then adjusted in steps according to the incoming digital data.  3.  Transmission : The modulated analog signal is transmitted through the communication channel (like a telephone line or optical fiber).  4.  Demodulation : At the receiving end, a demodulator detects the changes in the carrier wave's property and converts them back into the original digital bits. 

4. Types of Shift Keying Amplitude Shift Keying (ASK) Frequency Shift Keying (FSK) Phase Shift Keying (PSK)

5. Amplitude Shift Keying (ASK) Amplitude of the carrier signal is changed to represent a data A high-frequency carrier wave is used (e.g., a sine wave). Types of ASK: i ) Binary Amplitude Shift Keying (BASK) ii) Multilevel Amplitude Shift Keying (MASK)

6. Binary Amplitude Shift Keying (BASK) Implemented using only 2 levels bit 0  0 voltage bit 1  + ve voltage Also know as on-off Keying

7. Multilevel ASK More than two different Amplitude levels ( ie ) not just 0 or 1, but multiple combinations. Example: 4-Level ASK (4-ASK) In 4-ASK , each symbol can carry 2 bits of data: General Formula: M=2^n Bits Amplitude Level 00 A₁ 01 A₂ 10 A₃ 11 A₄ where M is no of levels Where n is no of bits

8. Frequency Shift Keying (FSK) Frequency Shift Keying (FSK) is a digital modulation technique used to transmit digital data over analog communication channels by varying the frequency of the carrier signal. More resistant to noise compared to Amplitude Shift Keying (ASK) Phase and Amplitude remains constant The types are: i ) Binary FSK ii) Multilevel FSK

9. Binary FSK Carrier Frequency first carrier freq  bit 0 second carrier freq  bit 1 Digital Input A binary stream (e.g., 0 1 0 1 0) Carrier Frequency The base frequency of the signal f₀ Frequency representing binary f₁ Frequency representing binary 1

10. Multileval FSK Multilevel Frequency Shift Keying (MFSK) is an extension of BFSK where more than two frequencies are used to represent multiple bits per symbol — not just 0 or 1. Instead of encoding 1 bit per symbol like in BFSK, MFSK uses: M different frequencies (M > 2) M (Frequencies) Bits per symbol 4 2 bits 8 3 bits 16 4 bits ... ...

11. Phase Shift Keying (PSK) Phase Shift Keying (PSK) is a digital modulation technique where the phase of a carrier wave is changed to represent digital data (bits). Unlike FSK (which varies frequency) or ASK (which varies amplitude), PSK keeps the frequency and amplitude constant but shifts the phase of the signal.

12. Binary PSK (BPSK) Only 2 signal elements i ) One – in phase (0 degree) ii) Other – in phase (180 degree) Less affected by Noise

13. Quadrature PSK (QPSK) 4 phases: 0°, 90°, 180°, 270° Each symbol encodes 2 bits : Bits Phase 00 0° 01 90° 11 180° 10 270°