Telephonic communications – Having light wave or ultrasonic link for speech or paging... – Including fiber optic link within telephone network
Patent
1985-09-03
1988-04-12
Lev, Robert
Telephonic communications
Having light wave or ultrasonic link for speech or paging...
Including fiber optic link within telephone network
379 63, 379 89, 381 46, H04B 140
Patent
active
047379766
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENITON
The present invention relates generally to speech recognition control systems, and more particularly to a hands-free telephone control and dialing system especially suited for use in a noisy environment such as encountered in a vehicular radiotelephone application.
In both radio and landline telephone systems, the user typically communicates by means of a handset that includes a speaker at one end which is placed close to the user's ear, and a microphone at the other end which is held close to the user's mouth. In operation, one hand of the user is occupied holding the telephone handset in its proper orientation, thereby leaving the user's only free hand to accomplish tasks such as driving a vehicle. In order to provide a greater degree of freedom for the user, speakerphones have commonly been used in landline telephone systems. Recently, vehicular speakerphones (VSP's) have been developed for use in automobiles. For example, U.S. Pat. No. 4,378,603 by Eastmond and U.S. Pat. No. 4,400,584 by Vilmur, both assigned to the same Assignee as the present invention, describe vehicular speakerphones with hands-free operation.
Hands-free control systems which are responsive to human voice are disclosed in a number of U.S. patents. U.S. Pat. No. 4,520,576 by Vander Molen discloses a conversational voice command control system for a home appliance such as a clothes dryer. The control system recognizes voice commands and emits synthesized speech sounds, in an interaction with the user, to obtain the information necessary for setting the operating parameters. Speech recognition and speech synthesis have also been applied to radio transceiver control functions (on/off, transmit/receive, volume and squelch control, etc.) in U.S. Pat. No. 4,426,733 by Brenig. Additionally, U.S. Pat. No. 4,348,550 by Pirz et al. discloses a repertory dialing circuit for a telephone system which is controlled by the user's spoken word.
However, the application of hands-free control to a vehicular speech communications system, such as a mobile radiotelephone, introduces several significant obstacles. When speech recognition is utilized in a vehicular environment, the high degree of ambient noise inherent in a vehicle presents a considerable problem to reliable voice control. Furthermore, a vehicular speakerphone typically has a microphone that is distant from the user's mouth, such as being mounted overhead on the automobile sun visor. Consequently, the required high microphone sensitivity causes a large increase in the amount of environmental background noise being applied to the speech recognizer, as well as being transmitted to the landline party.
Numerous approaches to this noisy speech problem have been attempted, with only limited success. For example, it is well known that speech may be enhanced in an aircraft through the use of a separate microphone, located at a distance away from the user's first microphone, such that it picks up only background noise. The general characteristics of the background noise can then be removed by subtracting an estimate of the background noise from the desired signal. This technique has been shown to provide a limited improvement in signal-to-noise ratio (SNR). However, it is very difficult to achieve the required isolation of the second microphone from the speech source while at the same time attempting to pick up the same background noise environment as the first microphone.
A simple high-pass filter is often used, perhaps in a microphone preamplifier, to reduce low frequency background noise. This may generally be perceived as an improvement in voice quality, but does little to improve the speech recognition process. Another approach, that of spectral subtraction noise suppression, has typically been used as a noise pre-processor to enhance the noise-degraded speech in preparation for further processing by a bandwidth compression system such as a vocoder.
Although the aforementioned prior art techniques may perform adequately under nominal background noise conditions, th
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Borth David E.
Gerson Ira A.
Vilmur Richard J.
Boehm Douglas A.
Lev Robert
Motorola Inc.
Sarli, Jr. Anthony J.
Warren Charles L.
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