Digital communications systems can communicate under conditions where analog systems won’t work because digital systems can use error correction coding to improve system gain. The mathematical algorithm developed by Dr. Andrew Viterbi is the basis for the error correction systems used in digital TV transmission (satellite and terrestrial) and digital cell phones.
The magazine Dr. Dobb’s Journal posted an excellent article, “Andrew Viterbi and the Viterbi Algorithm” describing Dr. Viterbi’s work at the Jet Propulsion Laboratory in Pasadena on satellite telemetry equipment through his retirement from Qualcomm in 2000.
In addition to his success in the commercial world — in 2000 Forbes ranked him one of the 400 richest Americans — he continued lecturing at University of California, becoming a UCSD professor emeritus in 1994.
Dr. Dobb’s Journal summarized the Viterbi algorithm this way:
it is essentially just a fast way of eliminating dead ends in the communication. The principle is simple, but the algorithm itself requires considerable computing power. Each bit in the digital information — 0 or 1 — has to be represented by four, eight or more code symbols. So, additional “redundant” information is added at the transmitter, in a process called error correction coding. The result coming into a receiver is a pulsing, miscellaneous stream of bits, ones and zeros.