Which spread-spectrum technique uses carrier frequency hopping?

• A. Uses PN code to spread data
• B. FHSS
• C. Uses OFDM
• D. Uses fixed carrier frequency

Answer: (B)

Frequency hopping is the hallmark of a spread-spectrum method that changes the carrier frequency rapidly according to a pseudorandom sequence shared by transmitter and receiver. By hopping across different frequencies within the available band, the signal’s energy is spread in time and across a broad spectrum, which helps avoid interference on any one frequency and improves security because an unintended listener would need to know the hopping pattern to follow the signal.

This approach is distinct from spreading data with a pseudonoise code (which expands bandwidth without changing the carrier frequency), from using multiple subcarriers simultaneously (OFDM), or from staying on a fixed carrier frequency (which does not spread the signal at all). Therefore, the technique that uses carrier frequency hopping is the Frequency-Hopping Spread Spectrum.