Lloyd Welch, an esteemed mathematician and electrical engineer, whose research career has had a profound impact on digital communications, coding theory, and signal processing, passed away on December 28, 2023, at the age of 96.
His seminal research contributions include the celebrated Baum-Welch algorithm that is used to find unknown parameters of a hidden Markov model, and which has found widespread application in many fields including speech processing, cryptanalysis, and bioinformatics; the Berlekamp-Welch algorithm used to efficiently decode Reed-Solomon codes; the McEliece-Rodemich-Rumsey-Welch best asymptotic upper bound on the rate of a binary code; the Welch lower bound on the maximum cross-correlation of signals; and the family of Gordon-Mills-Welch sequences having ideal autocorrelation and large linear span.
Dr. Welch worked at the Jet Propulsion Lab, the Institute for Defense Analysis, and as a professor at the USC Ming Hsieh Department of Electrical and Computer Engineering. He was named an IEEE Fellow, elected to the National Academy of Engineering, and was awarded the 2003 Claude E. Shannon Award.