4.3 Multiplexing Outlines FDM TDM

Introduction Or Or Definition of Multiplexing 1. The transmission of information from one or more source to one or more destination over the same medium. 2. The process which two or more signals are combined for transmission over a single communications path. Or 3. A process where multiple analog message signals or digital data streams are combined into one signal with the aim is to share an expensive resource. http://en.wikipedia.org/wiki/Multiplexing

Cont’d... Make the communications very economical by transmitting thousands of independent signals over a single transmission line. Three predominant ways to multiplex Frequency Division Multiplexing (FDM) Time Division Multiplexing (TDM) Wavelength Division Multiplexing (WDM)

Cont’d... Multiplexing allows several analog signals to be processed by one analog-to-digital converter (ADC) E.g. Several phone calls may be transferred using one wire. The multiplexed signal is transmitted over a communication channel which may be a physical transmission medium.

Cont’d... The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred. A reverse process, known as demultiplexing, can extract the original channels on the receiver side.

Cont’d... A multiplexing technique may be further extended into a multiple access method or channel access method. E.g. Time Division Multiple Access (TDMA) Multiple access method makes it possible for several transmitters connected to the same physical medium to share its capacity.

Cont’d... Concept of multiplexing

Frequency Division Multiplexing (FDM) Predominantly used in analog communications. Widely used in FM stereo broadcast. Compatibility with mono-receivers. Requires only a slight increase in BW. Great advantage in increasing system capacity.

Cont’d... Transmitting end of an FDM System

Cont’d... Process Each signal assigned s different carrier frequency. Modulated carrier frequencies are combined for transmission over a single line by MUX. At Rx, a DEMUX separates channels by their frequencies & routes them to the proper end users.

Time Division Multiplexing (TDM) Offers greater system improvement. Capable of combining various protocols & different types of signals onto a single high speed transmission link. E.g. voice and data More efficient than FDM

Cont’d... Process The transmission must be digital in nature. To transmit telephone conversations (voice is analog signal) Analog signal is converted to digital and transmitted Reconverted into analog at the Rx telephone.

Cont’d... Drawbacks Greater complexity. Greater transmission BW required.

Wavelength Division Multiplexing (WDM) Cost effective way to increase the capacity of fiber optic communications. Make use of the optical fiber’s available BW by multiplexing many wavelengths along a single mode optical fiber channel. Each wavelength of light can transmit encoded information at the optimum data rate.

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