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Non-coherent detection is generally not possible for which type(s) of digital modulation?

Difficulty: Medium

Correct Answer: PSK

Explanation:


Introduction / Context:
Detection techniques are classified as coherent (requires carrier phase reference) or non-coherent (does not require carrier phase reference). Different modulation schemes have different requirements.


Given Data / Assumptions:

  • ASK = Amplitude Shift Keying.
  • FSK = Frequency Shift Keying.
  • PSK = Phase Shift Keying.


Concept / Approach:
PSK encodes data in the phase of a carrier wave. Phase can only be correctly interpreted if the receiver has a reference to the carrier's phase, requiring coherent detection.


Step-by-Step Solution:

ASK can use envelope detectors (non-coherent).FSK can use frequency discriminators (non-coherent).PSK cannot be decoded without phase synchronization.


Verification / Alternative check:
Digital communication textbooks confirm that BPSK and QPSK require coherent detection, while non-coherent detection works for ASK/FSK.


Why Other Options Are Wrong:

ASK: envelope detection works.FSK: slope/energy detectors allow non-coherent decoding.Both (a) and (c): wrong because only (a) strictly requires coherent detection.


Common Pitfalls:

Assuming FSK also strictly requires coherent detection.


Final Answer:

PSK
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