•In traditional analog
communication each channel (radio station, phone call) gets
its own piece of the available frequency band
•Most modern digital
signals (internet, telephone calls) allocate different
time-slices to achieve multiple logical channels over
each physical channel (TDMA)
•Newest approaches
function well even in very low signal-to-noise ratio
environments via modulation that codes each bit into many
“chips” of a unique “pseudorandom code” that is assigned to each channel
(spread-spectrum, CDMA)