What modulation type involves frequency hopping of one carrier or multiple simultaneous carriers?

The correct choice involves spread spectrum modulation, which is characterized by the technique of frequency hopping. In this form of modulation, the signal's carrier frequency changes rapidly over time, which can occur in either a single carrier or multiple carriers simultaneously. This hopping spreads the signal over a wider bandwidth than the minimum necessary bandwidth for the information signal, enhancing the system's resistance to interference and jamming.

Spread spectrum is particularly useful in scenarios like wireless networks and cellular communications, where multiple users may need to operate in the same frequency band without interfering with each other. By hopping frequencies according to predefined algorithms, devices can transmit data securely and reliably.

Other modulation types mentioned do not incorporate the concept of frequency hopping. For instance, analog modulation refers to variations in amplitude, frequency, or phase of a single carrier signal based on the information being transmitted but lacks the dynamic frequency changes characteristic of spread spectrum techniques. Similarly, pulsed modulation is a method that concerns the structure of signal pulses rather than frequency variation and phase modulation, which entails changing the phase of the carrier to convey information but does not involve hopping between frequencies.