What frogs have to do with mobile and wireless networks
Have a look at the cover illustration for Uyless D. Black’s latest book, Mobile and Wireless Networks. It has pictures of frogs. What on earth do frogs have to do with mobile and wireless networks? Frog pictures belong on a biology textbook, sure_but on a book with chapters such as “Fundamentals of Cellular Systems,” “Data Over the Mobile Link” and “Network Management”?
Black explains that the science of telecommunications imitates nature_in this case, the communication skills of the frog species of coqui, 36mm in length. Quoting Black:
“In the tropical rain forests of Puerto Rico, where the coqui makes its home, there are many frogs in each part of the forest. Because of this population density, the coqui must share the audible frequency spectrum with other frogs. To ensure that a frog communicates effectively with another, each frog uses a variety of different frequencies when it croaks to its intended listener. In the technical words of the telecommunications industry, this little animal is capable of spectrum sharing and frequency division multiplexing. The listener is capable of filtering the extraneous signals and processing those signals that are relevant to the communications.
“What is equally extraordinary, these frogs exhibit time-division multiplexing capabilities. Different species ‘place calls’ (emit croaks) at particular times of the day to make better use of the limited frequency spectrum and to reduce ‘co-channel interference.’
“The coqui uses these time slots not only during a particular time of day, but during each moment of the day. Each frog knows when (and when not) to croak to reduce or eliminate possible interference with a neighbor in the same area of the forest. In mobile and wireless jargon, this capability is called a talk spurt. Perhaps we can dub the time-division multiplexing capabilities of these frogs as croak spurts.
“In an array of experiments, scientists have used machines to simulate (in a random fashion) the sending of frog croaks within an area of the rain forest. During these experiments, it was discovered that the coqui can avoid transmitting its call when certain tones are generated by the machine. The frog dynamically adjusts its croaking rate to randomized periods of silence and nonsilence and sends its messages in the silent periods only. If only humans were so polite!
“As if this adjustment to potential bandwidth ‘hogging’ were not amazing enough, some frogs add redundancy to their transmissions just as we do in some wireless systems. Certain species of frogs can produce a ‘periodic stereotyped’ call that exhibits redundancy in the ‘signals.’ The result of this redundancy is that if certain frogs happen to be interfering with other croaks, extra information is provided in the signal to help the listener figure out the information contained in the croak.
“Finally, certain frogs, such as the coqui, are tuned to the tone and characteristic periods of a specific croak. In case some frog is croaking at the same time as its neighbor, the listener can discern the desired signal from the undesired signal. In other words, these little animals have selective coders and decoders so they can glean the relevant information in a composite accumulation of croaks.
“If we pause and think for a moment about my description of this frog’s communications abilities, its capabilities can be rather humbling. Our society has invested extensive research and committed an immense amount of money in developing the sophisticated technology called mobile wireless communications. Yet, in the reaches of a primitive rain forest, we find that the frog has been developing and refining these communications capabilities for millions of years.”
A lot of people benefit from what Black has to say about frogs.
The scientists who study frogs and who sometimes receive criticism from people who think their studies are silly can cite Black’s book and say, “Ah-hah!”
People who think engineers charge too much to design communications networks can cite Black’s book and say, “A frog can do it cheaper!”
At Prentice Hall, they can say, “Look at the ink it got us!”
Uninspired magazine editors who nevertheless must deliver a commentary about telecommunications can quote Black’s comments about frogs extensively. And I think that’s about as far as I can carry this one. So, if you now would like to have the book, it can be ordered by your book dealer by ISBN 0-13-440546-3, or call the publisher at 201-236-7000. _Don Bishop