Dialing for documents: an experiment in information theory

Abstract

Standard telephone keypads are labeled with letters of the alphabet, enabling users to enter textual data for a variety of possible applications. However, the overloading of three letters on a single key creates a potential ambiguity as to which character was intended, which must be resolved for unambiguous text entry. Existing systems all use pairs of keypresses to spell out single key letters, but are extremely cumbersome and frustrating to use. Instead, we propose single-stroke text entry on telephone keypads, with the ambiguity resolved by exploiting information-theoretic constraints. We develop algorithms capable of correctly identifying up to 99% of the characters in typical English text, sufficient for such applications as telephones for the hearing impaired, E-mail without a terminal, and advanced voice-response systems.