Mathematics of Information Seminar

When a sender transmits a message as a ''codeword'' over a noisy channel, the receiver's optimal ''decoding'' of the possibly garbled channel output is to identify the message that has most likely been sent. We extend this standard approach by asking if the sender's action is also optimal. That is, given the receiver's decoding strategy, is the sender most likely understood correctly by transmitting the original codeword, rather than any other channel input? A ''Nash code'' has this desirable stability property, where encoding and decoding define a Nash equilibrium in this sender-receiver game with fully aligned interests of the players. We study this concept with examples, and show two sufficient conditions for Nash codes: receiver-optimal codes, and, somewhat surprisingly, _arbitrary_ codes for the classic binary channel (if the receiver breaks ties ''monotonically,'' which holds for generic priors or payoffs). Joint work with Penelope Hernandez (Valencia).