In the 20th-century analog world, you needed separate devices for separate communication functions, and you needed to transmit the signals on exclusive channels. Only radios picked up broadcast radio signals. Only TVs picked up television signals. In the 21st-century digital world, data, sound, and video will have been reduced to the same binary bits, which can be picked up by a variety of devices and transmitted in any order over similar territory in the spectrum. This technological change has sent a chain reaction reverberating through the world of wireless communications.
Digitization expands the amount of space available in the spectrum in two ways.
Externally, advances in digital technology promise to push the boundaries into parts of the spectrum once considered useless. However, along with the new space come new applications and services that push up demand. The more space we gain, the more crowded we get. Everyone thought in terms of analog devices when the spectrum was doled out. Now we're watching the first big digital projects being launched and facing up to the idea that everything eventually will go digital.