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JEE Physics · Hard

Principles of Communication: Mobile Communication MCQ

Solve this quality-checked JEE multiple-choice question, then review the correct answer and explanation.

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Mobile CommunicationHardQuestion 20300

Question

In OFDM (used in 4G/5G), the cyclic prefix serves to:
  1. A
    Carry error correction data
  2. B
    Prevent inter-symbol interference (ISI) caused by multipath propagation
    Correct
  3. C
    Add pilot tones for channel estimation
  4. D
    Control transmit power

Correct answer

Prevent inter-symbol interference (ISI) caused by multipath propagation

Explanation

The cyclic prefix (CP) is a copy of the last N_cp samples of each OFDM symbol prepended at the start. In time domain, multipath delays up to CP length appear as a circular convolution, which is easily equalized per-subcarrier after FFT. CP must be ≥ maximum multipath delay spread. LTE uses CP of 4.7 μs (normal) or 16.7 μs (extended).

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