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ASK, FSK, and PSK



ASK or OFF ON Keying

ASK is a simple (less complex) Digital Modulation Scheme where we vary the modulation signal's amplitude or voltage by the message signal's amplitude or voltage. We select two levels (two different voltage levels) for transmitting modulated message signals. For example, "+5 Volt" (upper level) and "0 Volt" (lower level). To transmit binary bit "1", the transmitter sends "+5 Volts", and for bit "0", it sends no power. The receiver uses filters to detect whether a binary "1" or "0" was transmitted.

Output of ASK, FSK, and PSK modulation using MATLAB
Fig 1: Output of ASK, FSK, and PSK modulation using MATLAB for a data stream "1 1 0 0 1 0 1 0" (Get MATLAB Code)

FSK

In Frequency Shift Keying (FSK), the message signal is modulated using a high-frequency carrier. Binary "1" and "0" are represented by two different frequencies close to the carrier frequency.

For example, using two frequencies f1 and f2 (where f1 > f2), binary "1" is modulated with f1 and binary "0" with f2. 

S₁(t) = A cos(2Ï€fc1t)      for binary 1
S₂(t) = A cos(2Ï€fc2t)      for binary 0

Here, fc1 is different from fc2.


PSK

In Phase Shift Keying (PSK), the phase of the carrier signal is changed to represent data bits. Binary "1" is transmitted by shifting the signal’s phase by 180°, while binary "0" keeps the same phase. 

s(t) = A cos(2πfct + π)        for binary 1
s(t) = A cos(2Ï€fct)            for binary 0

Which Modulation Technique Achieves Higher Bit Rates?

PSK (Phase Shift Keying)

PSK can use various phase shifts to encode more bits per symbol. For example, QPSK doubles the data rate of BPSK. Higher-order PSK (like 8-PSK, 16-PSK) further increases bit rate.

FSK (Frequency Shift Keying)

FSK generally requires more bandwidth, and symbol separation makes it less bit-efficient than PSK.

ASK (Amplitude Shift Keying)

ASK is more susceptible to noise and less bit-efficient. While higher-order schemes (like QAM) can help, pure ASK is typically less effective than PSK.

Conclusion: PSK can achieve the highest bit rates, especially using higher-order modulation techniques.


Simulator for Binary ASK, FSK, and PSK Modulation

Further Reading

  1. Amplitude, Frequency, and Phase Modulation
  2. Online Simulator for AM
  3. Digital Communication System Simulator
  4. Comparison of ASK, PSK, and FSK
  5. Simulation of ASK, FSK, and PSK
  6. MATLAB Code for ASK, FSK, and PSK
  7. Constellation Diagrams of ASK, PSK, and FSK
  8. BER vs. SNR for ASK, FSK, and PSK
  9. MATLAB Code for Constellation Diagrams

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