A11 Electronic Communications

Topic

Electronic communications transmit information by encoding it onto electromagnetic waves or electrical signals guided by cables. Classic analog modulation techniques encode information by varying the amplitude (AM) or frequency (FM) of a carrier wave; frequency modulation is generally more robust against noise—a characteristic previously described in this catalog—than amplitude modulation.

Modern digital communications employ more sophisticated modulation schemes that encode multiple bits of information into each transmitted symbol, packing more data into the same available bandwidth at the cost of requiring a higher signal-to-noise ratio for correct decoding: the more information squeezed from a given bandwidth, the less margin remains against noise. The Orthogonal Frequency-Division Multiplexing (OFDM) scheme, used in home wireless networks and modern mobile networks, divides the available channel into thousands of non-interfering subcarriers, making it particularly robust against the distortion caused by environments with multiple signal reflections.

Information theory establishes a fundamental theoretical limit on the maximum amount of information that can be reliably transmitted over a given channel, based on its available bandwidth and the aforementioned signal-to-noise ratio; no modulation scheme, however sophisticated, can exceed this limit. Finally, the power actually reaching a radio receiver decreases much more rapidly than the distance traveled between transmitter and receiver, and it also decreases as the frequency of the transmitted signal increases. That is why this module—which opens by encoding information onto a wave—concludes by showing that every communication scheme (whether analog or digital, narrowband or multi-subcarrier) ultimately competes against the same limit imposed by available bandwidth and the signal-to-noise ratio; no level of modulation sophistication can circumvent that limit—only bring us closer to it.

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