Which variable is NOT required to frequency hop in radio communication?

In frequency hopping radio communication, the goal is to enhance security and reduce interference by rapidly switching the transmission frequency among a set of predetermined frequencies, known as a hopset. The hopset is essential because it defines the available frequency channels that the communication can utilize. The Transmission Security Key (TSK) is also critical as it serves to encode the sequence of frequency hops, ensuring that only authorized users can understand the transmission.

Time is a necessary variable because it dictates the duration for which each frequency is used before the system switches to the next one in the hopset. This timing must be precisely controlled to maintain synchronization between the transmitter and receiver.

On the other hand, the Frequency Modulation Index, which relates to the level of modulation applied to the carrier signal, is not required for frequency hopping itself. While it may affect the quality of the signal and how data is encoded, it does not play a role in the mechanism of frequency hopping. Therefore, the correct choice is that the Frequency Modulation Index is not a required variable for the frequency hopping process in radio communication.