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Coherent and Non-coherent detection of ASK, FSK AND QASK
- 1. DIGITAL COMMUNICATION • Coherent and Non-coherent detection of ASK, FSK AND QASK NAIMISH M. PATEL (140053111017)
- 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 10 0 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 f0 =Acos(c-)t and f1 =Acos(c+)t f0 f0f1 f1 1 10 0
- 11. COHERENT DETECTION OF FSK 0 ∫ Tb dt Threshold of 0 volts Decision Device 0 ∫ Tb dt + X X O/P X1 X2 X3 X(t) Received BFSK signal Correlator 1 Correlator 2 U1(t) or ɸ1(t) U2(t) or ɸ2(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. • U1(t) or ɸ1(t)= √2/Tb cosωHt or • U2(t) or ɸ2(t)= √2/Tb cosωLt • fH = m fb • fL = n fb • U1(t) = √2/Tb cos(2πm fb t) • U2(t) = √2/Tb sin(2πn fb t)
- 14. • sH(t) = √PsTb √2/Tb cos(2πm fb t) • sL(t) = √PsTb √2/Tb sin(2πn fb t) where, 2πm fb =ωH 2πn fb =ωL sH(t) = √PsTb X U1(t) sL(t) = √PsTb X U2(t)
- 15. NON-COHERENT DETECTION OF FSK Filter Matched To √2/Tb cos(2πfLt) X(t) Comp- rator Envelope detector Filter Matched To √2/Tb cos(2πfHt) Envelope detector Received BFSK signal X2 X1 Sample at t=Tb Sample at t=Tb output Non-coherent BFSK receiver
- 16. QASK Receiver Raise i/p to 4th power Band- Pass Filter 4fc Frequ- ency divider ÷4 0∫Tsdt 0∫Tsdt A/D conv A/D conv Parallel To Serial converter X X b3 b2 b1 b0 Bit Sequence b(t) Ae(t) Ao(t) cos ωc t sin ωc t VQASK(t)=√PsAe(t) cosωc t+√PsAo(t) sinωc t QASK Receiver Carrier Recovery circuit