BAM, Lucent Collaborate on Service for Hearing, Speech Impaired
The innovation pioneered by Bell Labs researchers was prompted by BAM's priority in meeting the needs of speech and hearing-impaired customers, especially in emergency situations. Lucent is informing the FCC and industry organizations that it is making the patents and technology available royalty-free to wireless carriers and manufacturers serving TTY customers, subject to certain conditions.
The FCC has mandated that wireless service carriers provide TTY users access to 911 emergency services. Carriers deploying digital wireless systems have so far been unable to meet the FCC requirement, however, because existing digital wireless systems cannot accurately pass the specially encoded audio tones produced by TTY devices.
The Technology
The solution, developed by Steven Benno and Michael Recchione of the Bell Labs Speech and Audio Processing Technologies group, offers TTY users essentially error-free digital transmission, even in areas with extremely poor reception. The technology involves upgrading software both in the network and in the digital handset yet retains compatibility with existing digital wireless network standards. The Telecommunications Industry Association (TIA) has adopted the Bell Labs solution as a TTY solution that is compatible with the ANSI-41 standard for CDMA and TDMA wireless systems.
How It Works
Digital wireless transmissions inherently contain errors, but error-correction techniques can mitigate the problem by reconstructing speech to keep it intelligible on the receiving end. However, digital networks are less forgiving in the case of the tones generated by TTY devices, and the transmission errors can cause characters to be missed or changed on the receiving end, resulting in unintelligible messages.
Lucent's solution to this problem is to detect the TTY characters being sent and to transmit those characters to the receiving end repeatedly. The repetition allows the receiving end to correctly regenerate the tones corresponding to those characters despite over-the-air errors.
The solution treats TTY calls as data transmissions that also permit voice conversation over the same connection. Typically, people with speech impediments and hearing-impaired people who can speak require TTY capability in one direction and speech transmission in the other direction. Although data-only calls have a built-in capability for error correction, they do not allow a TTY user to switch between voice and TTY. This method treats TTY calls the same as voice calls—a feature called voice carryover/hearing carryover—that cannot currently be supported by treating TTY as a data call.