Character Pattern Recognition for a Telecommunication Aid for the Deaf

To communicate via the telephone with the hearing impaired, systems that transmit characters that appear on standard telephone keypads to aids that decode telephone audio tones representing characters (dual tone multiple frequency (DTMF) systems) have been used. However, due to the existence of three letters on each key, several keystrokes are required to represent the desired character without ambiguity. This paper describes an improved alternative to systems that require multiple keystrokes. Our investigations have shown that a large percentage of English words have a unique word code (the keystroke sequence required to enter the letters of the word). Techniques were developed to recognize the pattern of characters entered to allow for one keystroke per character. Further economization, achieved by recognizing syllable-like letter groups (SLLG) is described. A microprocessor-based, portable device was developed to enable telecommunication with special equipment only on the hearing impaired side of the communication channel. The device currently has 1200 SLLG´s, which allows recognition of more than 2000 of the most common words.