ENVS 1200 Chapter Notes - Chapter 9: Wavelength-Division Multiplexing, Frequency-Division Multiplexing, Bit Rate
13 May 2018
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ENVS 1200 Chapter 9 Notes – Summary
Introduction
• It can be used to carry several phone conversations on long-distance phone lines, for
example, or to provide multiple channels for wireless Ethernet (Wi-Fi).
• Ultimately it uses the bandwidth more effectively to increase the capacity of the
channel.
• An Illustration of FDM is shown
• The same technique can be applied to the light transmitted through a fiber-optic cable.
• Light of different colors have different frequencies.
• Viewed from the perspective of ASK analog signaling, it is possible to increase the bit
rate of data transmitted optically by combining lights of different color, with filters on
the receiving end of the cable to separate the different color signals.
• This procedure is essentially identical to that of frequency division multiplexing,
although the implementation is actually somewhat easier.
• To differentiate optical multiplexing from lower frequency radio multiplexing, we give
the process a different name
• Wavelength division multiplexing (WDM)
• This name reflects the fact that light is usually identified by its wavelength, rather than
by its frequency.
• As of this writing, there are claims that current optic technology can support bit rates of
8 Tbps over distances of 2500 km using a dense form of WDM called DWDM.
• As we noted earlier, most users think of the signals in fiber-optic cables as digital.
• Both wired and wireless analog signals are particularly susceptible to noise and
attenuation and other forms of distortion in a channel because the distortion created
cannot be detected and reversed.
• There is also interference from other signals operating nearby in the same spectrum.
• Attenuation, or signal loss, is the reduction of a signal that occurs in a medium as a
function of the physical length of the channel.
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