Coherent and Non-coherent detection of ASK, FSK AND QASK

Coherent and Noncoherent detection of ASK, FSK AND QASK by Naimish Patel(E&C Engineer)

1. DIGITAL COMMUNICATION Coherent and Non-coherent detection of ASK, FSK AND QASK NAIMISH M. PATEL (140053111017)

2. Detection Coherent detection Non-coherent detection

3. Coherent Detection An estimate of the channel phase and attenuation is recovered. It is then possible to reproduce the transmitted signal and demodulate. Requires a replica carrier wave of the same frequency and phase at the receiver. The received signal and replica carrier are cross-correlated using information contained in their amplitudes and phases. Also known as synchronous detection

4. Applicable to Phase Shift Keying (PSK) Frequency Shift Keying (FSK) Amplitude Shift Keying (ASK)

5. Non-Coherent Detection Requires no reference wave; does not exploit phase reference information (envelope detection) Differential Phase Shift Keying (DPSK) Frequency Shift Keying (FSK) Amplitude Shift Keying (ASK) Non coherent detection is less complex than coherent detection ( easier to implement), but has worse performance .

6. Amplitude Shift Keying (ASK) Baseband Data ASK modulated signal 1 1 Acos( t) Acos( t) Pulse shaping can be employed to remove spectral spreading ASK demonstrates poor performance, as it is heavily affected by noise, fading, and interference

7. COHERENT DETECTION OF ASK ASK+Noise Integrator Sample And Hold Synchronous carrier Comparator Binary Signal Reference Voltage V Bit sync Coherent ASK receiver

8. NON-COHERENT DETECTION OF ASK BPF Envelope detector Regenerator ASK + Noise Original Binary Output Bit Sync V Non-coherent ASK receiver

9. Bandpass Filter Envelope Detector Regenerator

10. Frequency Shift Keying (FSK) Baseband Data BFSK modulated signal where f =Acos(  c -)t and f 1 =Acos(  c +)t f f f 1 f 1 1 1

11. COHERENT DETECTION OF FSK ∫ Tb dt Threshold of 0 volts Decision Device ∫ Tb dt + X X O/P X 1 X 2 X 3 X(t) Received BFSK signal Correlator 1 Correlator 2 U 1 (t) or ɸ 1 (t) U 2 (t) or ɸ 2 (t) + - Coherent BFSK receiver

12. Multiplier Integrator Sample and Hold Comparator If, o/p < V , then signal is 0. o/p > V , then signal is 1.

13. U 1 (t) or ɸ 1 (t)= √2/T b cos ω H t or U 2 (t) or ɸ 2 (t)= √2/T b cos ω L t f H = m f b f L = n f b U 1 (t) = √2/T b cos(2 π m f b t) U 2 (t) = √2/T b sin(2 π n f b t)

14. s H (t) = √P s T b √2/T b cos(2 π m f b t) s L (t) = √P s T b √2/T b sin(2 π n f b t) where, 2 π m f b = ω H 2 π n f b = ω L s H (t) = √P s T b X U 1 (t) s L (t) = √P s T b X U 2 (t)

15. NON-COHERENT DETECTION OF FSK Filter Matched To √2/T b cos(2 π f L t) X(t) Comp- rator Envelope detector Filter Matched To √2/T b cos(2 π f H t) Envelope detector Received BFSK signal X 2 X 1 Sample at t=T b Sample at t=T b output Non-coherent BFSK receiver

16. QASK Receiver Raise i/p to 4 th power Band- Pass Filter 4f c Frequ-ency divider ÷4 ∫ Ts dt ∫ Ts dt A/D conv A/D conv Parallel To Serial converter X X b 3 b 2 b 1 b Bit Sequence b(t) A e (t) A o (t) cos ω c t sin ω c t V QASK (t)=√P s A e (t) cos ω c t+√P s A o (t) sin ω c t QASK Receiver Carrier Recovery circuit