Which modulation type can involve frequency hopping of a single carrier or multiple simultaneous carriers?

• A. SSB
• B. FM
• C. OFSK
• D. Spread spectrum

Answer: (D)

Spread spectrum modulation spreads a signal over a wider bandwidth than the minimum needed, and frequency hopping is a common way to do that. In frequency hopping, the carrier frequency changes according to a pseudorandom sequence, and you can have just one carrier hopping or several carriers hopping in parallel, producing multiple simultaneous channels. This approach provides resilience to interference and eavesdropping and allows multiple users to share the spectrum.

The other options are standard modulations without intentional hopping across the spectrum: single sideband is a refined AM technique that preserves one sideband; frequency modulation varies the frequency to convey audio but doesn’t hop across frequencies to spread the signal; offset frequency shift keying uses multiple fixed tones to represent data, not a hopping spread-spectrum approach.

So, the modulation type that can involve frequency hopping of a single carrier or multiple simultaneous carriers is spread spectrum.