TABLE OF CONTENTS Today, digital multiplexers are part of every microwave system, whether they are part of the microwave radio equipment or added as an external piece of equipment. Multiplexing is a process in which multiple data channels are combined into a single data or physical channel at the source; conversely, demultiplexing is the process of separating multiplexed data channels at the destination. An example of multiplexing is when data from multiple devices is combined into a single physical channel. Some methods used for multiplexing data are time-division multiplexing (TDM), asynchronous time-division multiplexing (ATDM), frequency-division multiplexing (FDM), and statistical multiplexing.
One method (FDM) involves splitting the frequency band transmitted by the channel into narrower bands. Each of these narrow bands is used to create a distinct channel. In FDM, information from each data channel is allocated bandwidth based on the signal frequency of the traffic, and multiple channels are combined onto a single aggregate signal for transmission. The channels are separated by their frequency. FDM was the first multiplexing scheme to be widely used, and such systems are still in use. However, TDM is the preferred approach today. In TDM, information from each data channel is allocated bandwidth based on preassigned time slots, regardless of whether there is data to transmit. In ATDM, information from data channels is allocated bandwidth as needed, using dynamically assigned time slots. In statistical multiplexing, bandwidth is dynamically allocated to any data channels that have information to transmit.
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