Bandwidth Reduction For The Transmission Of Sign Language Over Telephone Lines

Bandwidth reduction for the transmission of sign language over telephone linesMansouria BoubekkerTufts University/New England Medical Center750 Washington Street, Boston, Massachusetts 02111ABSTRACTThis paper describes a system for the transmission of American Sign Language (ASL) over standard telephone lines. Videoquality digital images require a transmission bandwidth at least 4000 times wider than that allowable by the standard voicetelephone network. This study presents compression, segmentation and coding techniques that reduce the information contentof visual images while preserving the meaning of the transmitted message.The resulting processed information can be transmitted at digital rates within the range of the commercially available 9600baud modems. The simulated real -time animations of the decoded cartoon images used for the experimental data representASL and finger spelling with an intelligibility approximating 85 %. This result is within the range of the intelligibilityprovided by speech communication over telephone lines.1. INTRODUCTIONThe deaf individual is vastly isolated not only from the rest of the society but also from other members of the deafcommunity because of the difficulty to communicate at a distance. He or she can not benefit from the telephone network,widely and extensively used by the hearing society. Even special telephones with amplifiers, available to the hard of hearing,can not be used by profoundly deaf individuals. The primary form of communication used among individuals of the deafcommunity is American Sign Language. ASL is a visual /gestural language comparable to spoken languages in the sense thatit has its own structure, morphology and syntax[1,2,3]. However, it is an independent language that uses movements of thehands and arms as well as facial expressions instead of sounds.While different means of communication at a distance can be used by deaf individuals, they all present some majordrawbacks:- High resolution video telecommunication systems, the ideal means of communication for the transmission ofvisual images, are limited by the high video bandwidth requirement[4].- Video conferencing, provides a high quality means of communication for the deaf but its use is limited because ofits incompatibility with the actual public switched telephone network and its restriction to the immediate institu-tion[5].- Teletypewriters (TTY), the most common means of communication at a distance, for the deaf individual, limit thesystem by the slow rate of typed messages and the unnatural use of English as a mean of communication.An ideal telecommunication system for the deaf would be one that allows the transmission of visual images through the useof the switched telephone network. The transmission of visual images, rather than auditory signals using the standardtelephone system is difficult because of the large bandwidth requirement of a video quality image. However, digitaltransmission, through the use of commonly available modems, can be accomplished over audio telephone lines at a datarate of 9600 bits /s. A compression factor of at least 4000 is required for the transmission of visual images over digitalchannels.