Radio frequency mainly adopts spread spectrum technology. Which of the following technologies belong to spread spectrum technology? (Multiple choice)

Question

Options

• AFHSS
• BDSSS
• CQPSK
• DOFDM

• A
  74% (23)
• C
  16% (5)
• D
  10% (3)

Explanation

FHSS (Frequency Hopping Spread Spectrum) and DSSS (Direct Sequence Spread Spectrum) are the two classical spread spectrum techniques: FHSS spreads a signal by rapidly hopping across frequencies in a pseudo-random sequence, while DSSS multiplies the signal with a high-rate pseudo-random chipping code, spreading it across a much wider bandwidth than the data requires. Both techniques were designed specifically to resist interference and interception, which is the defining purpose of spread spectrum.

QPSK (Quadrature Phase Shift Keying) is a modulation scheme - it encodes bits by shifting the carrier's phase into one of four states, but it does not spread the signal across a broader frequency band. OFDM (Orthogonal Frequency Division Multiplexing) is a multiplexing/modulation technique that divides bandwidth into narrow orthogonal subcarriers for efficient transmission (used in Wi-Fi and LTE), but it is not classified as spread spectrum because its goal is spectral efficiency, not deliberate bandwidth spreading for interference resistance.

Memory tip: Look for the letters "SS" - both correct answers end in SS (FHSS, DSSS), which directly stands for Spread Spectrum. QPSK and OFDM lack those letters because they belong to different technology families (modulation and multiplexing, respectively).

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