Multiplex

A multiplex is a piece of hardware or a function in software that is used to combine diferent input signals into a single signal. These input signals can be e.g. the telephone calls for different users that are combined at the base station to send them to the users or e.g. the audio- and videosignal that are combined into one single movie stream.

The different signals can be seperated in three different manners:

1. Frequency
   The total available bandwidth can be divided in a number of channels. Each signal gets its own channel.
2. Time
   The available time can be divided in different slots. Each signals gets periodically its own slot.
3. Code
   Each signal can use the whole bandwidth. Each signal is multiplied with its own code to be able to differentiate the signals at the receiving end.

The multiplex in digital broadcasting

In analogue broadcasting each radio- and television channel has it's own transmitter. This relationship between a radio channel (such as BBC1) and it's own transmitter is abandoned in digital broadcasting. In digital video broadcasting (DVB) and digital audio broadcasting (DAB are different television- and/or radiochannels combined into a single transport stream. The transport stream also contains Service Information which gives details of the programmes being broadcast.

This is illustrated in the following figures.

An 'old' analogue broadcasting station.

A digital broadcasting station.