The use of frequency-hopping radios or devices to reduce the
effect of jamming and complicate listening in on communications. Examples
include spread-spectrum portable telephones now available in for homes and
spread spectrum radios used in the military.
Complexity: The basic issues in spread spectrum are how to rapidly change
frequencies and how to schedule frequency sequences so as to make jamming
and listening difficult. The former is an electronics problem that has been
largely solved even for low-cost units, while the latter is a cryptographic
problem equivalent to other cryptographic problems.