Which radio system monitors frequency loads and reassigns transmissions to unused frequencies?

The trunked radio system is designed to optimize the use of available radio frequencies by monitoring frequency loads and reallocating transmissions to less-used frequencies, which greatly enhances communication efficiency. This system functions as a dynamic network, where multiple users share a smaller number of channels by automatically assigning the appropriate frequencies as needed. This capability is particularly beneficial in emergency situations where clear, reliable communication is essential, as it reduces the chances of congestion and communication failures.

The other options do not possess this specific functionality. Digital input/digital output (DIDO) is more about the processing and transmission of digital signals rather than managing frequency loads. Interoperability refers to the ability of different communication systems to work together, rather than how frequencies are assigned or monitored. Multiplexing involves combining multiple signals into one for transmission over a single medium, which does not inherently include monitoring and reallocating frequencies in response to usage.