IEEE Awards Booklet - 2016 - 19

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powerful but less computationally complex algorithm.
Forney showed that this approach,
dubbed concatenation, could achieve
a much better trade-off between data
rates and computational complexity,
and that it would in principle let existing modems transmit and receive all
the way up to Shannon's limit. "Today,
almost every coding scheme for transmission is in some form a concatenated
scheme," says colleague Gottfried
Ungerboeck. "You can transmit information faster and more reliably with
the same power and bandwidth."
Coming out of graduate school in
1965, Forney recalls that information
theory was a field brimming with ideas
and yet-to-be-realized applications.
Any such IT f ield today might have
launched a dozen startups, with angel
investors hovering to pounce on possible secondary spin-off opportunities.
But at the time, startups weren't really
part of the culture, Forney says. Smart
and capable grads who didn't intend to
stay in academia typically sought out
big companies.
Forney submitted applications to
some of the usual suspects-IBM and
Bell Labs. But on the advice of Gallager,
Forney also applied to the recently
formed Codex Corp. The Massachusetts-based company gave Forney the
lowest offer. But he was sold. "They
were in business to try to make information theory practical, to make coding practical. Nobody else was doing
that," he says.
Forney became the 13th employee in
the company, which would be bought
by Motorola in 1977 and ultimately
employ thousands. One of his first projects was a communications contract for
NASA, creating coding and decoding
algorithms for some of the agency's
Pioneer spacecraft.
But the project that put Codex-and
Forney-on the map was a 9,600-bitper-second modem that became the
basis of the company's commercial success. The company had devised the first
such modem in 1968, Forney says, and
it sold for more than US $20,000 to
big firms with international data networks, such as banks and airlines. But,
like its competitors, the modem turned

out to be unreliable owing to a previously unrecognized problem with the
telephone networks that added "phase
jitter"-random variation in the phase
of the signal-carrying waves traveling
across them.
Following up on a suggestion made
by Gallager, Forney designed a family of modems that used a modulation
scheme called quadrature amplitude
modulation. This approach, which
could better handle phase shifts, produced a more reliable and successful
modem. The design eventually became
the basis of the international V.29
9,600-bit-per-second modem standard.
But this early practical success didn't
lure Forney away from the fundamentals. After his modem work in 1970 and
1971, he spent a sabbatical year at Stanford. And when he returned, he set out
to write up some thoughts he'd had on
how an algorithm proposed in 1967 by
Andrew Viterbi might be applied to
signal decoding.
The result was a landmark 1973 paper
in the Proceedings of the IEEE that
popularized the Viterbi algorithm by
introducing a visualization technique
called the "trellis diagram." The algorithm can be used to recover data from
a patchy or noisy signal. Today, it is
used in an extraordinary range of disparate technologies, including modems,
wireless communications, and voice
and handwriting recognition, as well
as DNA sequencing.
To explain how the Viterbi algorithm works, Forney gives a handw r it ing recog n it ion exa mple.
Reading in the letters for the word
"hand," the computer might initially
determine that the second letter looks
more like a q than an a. But a recognizer running the Viterbi algorithm
will also factor in the fact that "hand"
is a much more likely English word
than "hqnd." "It finds the most likely
sequences, taking into account both
raw likelihood and sequence constraints," Forney says.
Viterbi-algorithm decision trees
can be plotted in a latticelike trellis
diagram, an approach Forney and his
colleagues say is much simpler than
writing out formulas and logical ifthen statements. Trellis diagrams "laid

things out graphically, which appeals
to people more than just a collection of
equations [does]," says Stanford's Kailath. "They provided a tool for engineers to appreciate what the Viterbi
algorithm could do and make extensions of it."
From 1975 to 1985, Forney served
as an R&D executive for Codex and
then Motorola, after the company's
acquisition. In the 1980s, Forney was
inspired by trellis-coded modulation,
a new signaling scheme developed by
Ungerboeck that was rapidly adopted
in modems, and he was drawn back
into research. In the decades since, he
has worked extensively on codes, with
an eye toward continuing to raise the
efficiency of data transmission. A number of his papers, as with his work on
trellis diagrams, reintroduced key concepts into the field that other researchers could then apply.
Forney retired from Motorola in
1999. He has been an adjunct professor
in the department of electrical engineering and computer science and the
Laboratory for Information and Decision Systems at MIT since 1996.
Regarding his contributions, Forney says modestly, "I'm just the guy
who comes along at the end of the
circus parade." After a discovery has
been made, he'll add to it, he says. In
a sentence he sums up these insights:
"You know, the right mathematical
language to talk about this invention
is this."
Filling out the framework around
a new theory or algorithm might not
be the kind of work that garners headlines, but it's still critical to progress,
Gallager says. "Researchers 'keep score'
by counting inventions and weighting
them by their popularity," he says, but
"what makes a research field grow and
evolve is the context, relations, and
connection to reality." Forney has created this "context in the information
theory and communication technology
fields to a greater extent than almost
anyone else," Gallager says.
And in the ever-evolving world of
engineering, the ability to draw from
theory to push the limits of what's practical is one skill that will never go out
of style.



Table of Contents for the Digital Edition of IEEE Awards Booklet - 2016

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