In a frequency-hopping spread spectrum (FHSS) system that uses 10 frequencies across a 12 megahertz (MHz) frequency band, what happens if narrowband interference occurs at only one of the 10 frequencies?

In a frequency-hopping spread spectrum (FHSS) system that uses 10 frequencies across a 12 megahertz (MHz) frequency band, what happens if narrowband interference occurs at only one of the 10 frequencies?

• A. The data on the interfered frequency is lost and cannot be recovered.
• B. Interference causes the whole signal to be discarded.
• C. The spread spectrum signal remains intact; data on the interfered frequency is retransmitted on one of the other nine frequencies.
• D. The system switches to a different spread spectrum technique.

Answer: (C)

FHSS spreads a transmission across multiple frequencies, switching (hopping) through them in a known pattern. If narrowband interference hits just one of those frequencies, only the data being sent on that particular hop is affected. The rest of the hops arrive cleanly, so the overall communication can continue. In practice, the data that would have ridden the interfered frequency can be carried again on a different hop when that frequency is used again, effectively retransmitting on one of the other nine frequencies. This is why the spread-spectrum signal stays intact despite a single-frequency interference. The other possibilities imply losing the entire signal, discarding the transmission, or switching to a different communication technique, which is not how FHSS handles localized interference.

FHSS spreads a transmission across multiple frequencies, switching (hopping) through them in a known pattern. If narrowband interference hits just one of those frequencies, only the data being sent on that particular hop is affected. The rest of the hops arrive cleanly, so the overall communication can continue. In practice, the data that would have ridden the interfered frequency can be carried again on a different hop when that frequency is used again, effectively retransmitting on one of the other nine frequencies. This is why the spread-spectrum signal stays intact despite a single-frequency interference.

The other possibilities imply losing the entire signal, discarding the transmission, or switching to a different communication technique, which is not how FHSS handles localized interference.