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Digital Communication
10 questions By Tony R. Kuphaldt
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Question 10 of 10
In Claude Shannon’s famous 1948 paper entitled A Mathematical Theory of Communication, he opens with the following statement:
- “The recent development of various methods of modulation such as PCM and PPM which exchange bandwidth for signal-to-noise ratio has intensified the interest in a general theory of communication.”
Explain what Shannon was referring to when he said, “exchange bandwidth for signal-to-noise ratio”. In many cases, the superior signal-to-noise ratio of digital communication over analog communication is the primary reason justifying the much greater complexity of digital communications equipment. Also, elaborate on how bandwidth becomes sacrificed in order to achieve relatively noiseless signal transmission.
Reveal answerDigital signals are highly resistant to corruption from noise, because they are composed of discrete (“high” and “low”) states rather than continuously-variable quantities as analog signals are. However, in order to communicate any significant measure of digital information in serial form, many pulses are needed. This requires a high-bandwidth data path to be comparable in speed to analog.
Notes:Shannon’s language is perhaps a bit above the norm for technician-level education, but it nevertheless captures an important quality of digital communication: that the noise immunity enjoyed by digital communication comes at a price: high bandwidth. Without a high-bandwidth medium in which to exchange digital information, communication is either slow or completely impractical.
