(you are, aren't you?) then efficiency is the time-frequency product.
- Usage of spectrum is equivalent to a time-freq-power product.
- Assuming that all users are utilizing minimum necessary power
Spread-spectrum (and trunking) radio systems allow efficient sharing of idle times and idle frequencies.
Non spread systems partition users to channels in a static fashion, and share idle time with static users on a channel-by-channel basis.
Probability theory shows one-by-one sharing to be much inferior to sharing idle time across all channels and all users simultaneously.