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 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