Multiplexing

Multiplexing is a set of techniques that allows the simultaneous transmission of multiple signals across a single link. It is much more convenient to use a single wire to carry several signals than to install a wire for every signal. Multiplexing increases the channel utilization, which means that, if the bandwidth of the channel that link two devices is grater than the bandwidth requirements, then some portion of the channel is wasted.  For multiplexing, we use two components: multiplexer and demultiplexer.  A multiplexer takes n-inputs and after combining it produces one output (many-to-one). The demultiplexer separates the combined signal into individual signals as they input to the multiplier (one-to-many).

Multiplexing

Here we discuss three types of multiplexing techniques: frequency-division multiplexing (analog signal), wavelength-division multiplexing (analog signal), and time-division multiplexing (digital signal).

Frequency Division Multiplexing

In Frequency division multiplexing, modulate input signals that are generated by sending devices into different carrier frequencies. These modulated signals are then combined into a single composite signal. The composite signal is send over the carrier link.  Guard bands are used to separate signals from overlapping.

Wavelength Division Multiplexing (WDM)

Wavelength division multiplexing is used explore highest data rate of the optical fiber cable. WDM is an analog multiplexing technique. Here we combine the signals with high frequency into a single composite signal at the sender and demultiplex them at the receiving end. WDM is logically same as the FDM, the difference is that WDM uses high frequency signals.

Wavelength division multiplexing

Time Division Multiplexing

In time division multiplexing, several connections share the high bandwidth of a channel. The difference between FDM and TDM is that, Instead of sharing a portion of the bandwidth as in FDM, TDM share the time.

TDM is a digital multiplexing technique.

Time division multiplexing

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