Which term describes a communications system where the RF carrier changes based on a pre-determined sequence?

The term that describes a communications system where the RF carrier changes based on a pre-determined sequence is known as spread-spectrum communication. This technique disperses the signal over a wide frequency range, which enhances the robustness of the transmission against interference and eavesdropping.

In spread-spectrum communication, this spreading of the signal is done using techniques like frequency hopping or direct-sequence spread spectrum. In frequency hopping, the carrier frequency changes in a specific sequence that is known to both the transmitter and receiver, allowing them to remain synchronized. This adds an additional layer of security and reliability to the communication system, as the transmission can hop to different frequencies to avoid interference.

Other modulation techniques mentioned, such as amplitude modulation and frequency modulation, involve changing specific characteristics of a single carrier wave (amplitude or frequency) to convey information but do not inherently involve changing the carrier frequency in a predetermined sequence like spread-spectrum does. Continuous wave transmission refers to a constant signal without modulation, focusing on transmitting information continuously rather than with a changing carrier.