Bell Communications Research, Inc.

Bell Telephone Laboratories

Eric J Addeo

Gennady Shtirmer

Thomas Helm Judd

John D Robbins

Michael H Bianchi

Henri E Tohme

Joseph J Desmarias

Joseph J Desmarais

An audio processing system for use in teleconferencing systems having high and low transmission delays. The audio processing system utilizes complementary comb filters in combination with auxiliary echo suppressors, a frequency scaler, expander/gates and automatic level controlling devices to substantially improve acoustic stability margin and reduce far-end talker echo.

Audio processing system for teleconferencing with high and low

A teleconferencing system 100 is disclosed having a video camera for generating a video signal representative of a video image of a first station B. A microphone array 150, 160 is also provided in the first station for receiving a sound from one or more fixed non-overlapping volume zones 151, 152, 153, 154, 155, 156, 157, 158, 159, into which the first station is divided. The microphone array is also provided for generating a monochannel audio signal 170 representative of the received sound and a direction signal indicating, based on the sound received from each zone, from which of the volume zones the sound originated. The teleconferencing system also includes a display device 120A at a second station A for displaying a video image of the first station. A loudspeaker control device 140 is also provided at the second station for selecting a virtual location 121 on the displayed video image depending on the direction signal, and for generating stereo sound from the monochannel audio signal which stereo sound emanates from the virtual location on the displayed video image.

Sound localization system for teleconferencing using self-steering

A teleconferencing system (100, 100') provides a wide aspect ratio view at each site utilizing a single NTSC camera (250, 350) and projector (260,360). At the transmitting end of a teleconference, a transformation element (280, 380, 510, 610) maps a wide aspect ratio field of view into the field of view of an NTSC camera. The transformation is reversed at the receiving end of the teleconferencing system.

Video teleconferencing system employing aspect ratio transformation

An audio processing system (100) for use in a teleconferencing system (10) utilizes complementary comb filters (42, 52, 220, 320) in combination with an echo suppressor (210, 310) and/or a frequency scaler (60, 120) to substantially improve acoustic stability margin and reduce far-end talker echo.

Audio processing system for teleconferencing system

A method and apparatus for reducing the bit error probability of data transmitted over a Rayleigh fading channel are disclosed. A relatively high bit rate serial stream of data is divided into N parallel relatively low bit rate streams of data. A controlled amount of intersymbol interference is introduced in the parallel streams. The N parallel streams are then transmitted simultaneously over the Rayleigh fading channel. Each bit in the N parallel stream of data has a duration longer than the duration of the typical Rayleigh fade. Thus there is a reduced probability that a Rayleigh fade will cause a bit error.

Method for improving the reliability of data transmission over Rayleigh

A data signal stream includes, in a noisy signal channel, periodic word synchronization characters, and each such stream is preceded by a burst of predetermined bit rate information. An approximate bit rate timing signal is derived from the data stream and utilized for producing an initialization pulse when the predetermined bit rate information is detected. In addition, the approximate bit rate timing signal drives a digital phase-locked loop which is preset by the initialization pulse to a digital circuit state defining operation at the nominal frequency of the approximate bit rate timing signal. A stable bit clock signal provided by the phase-locked loop controls the operation of further circuits which are responsive to the baseband data stream for providing an indicator pulse each time that a synchronizing character appears in the data stream. The bit rate clock and the character indicator pulses are employed to operate a timing chain that yields word synchronization pulses in synchronism with the indicator pulses and having an extraordinarily low false-pulse rate as well as evidencing a flywheel effect to maintain word synchronization in the event that a small number of character indicating pulses are missed. If more such pulses are missed, the timing chain is resynchronized.

Digital synchronizing signal recovery circuits for a data receiver

In a radio communication system of the cellular type wherein sets of communication channels are reused in different adjacent sets of cell areas within a common mobile communication service area, each cell base station utilizing a given set of channels in common with other base stations is assigned a different supervisory tone to be modulated on all of its channels. Any mobile unit receiving such channel transponds the modulated supervisory tone and sends it back to the base station. At each base station the transmitted and received supervisory tones for any given channel are compared to produce an indication of whether or not the sending mobile unit is actually communicating on the transmitted channel of the same base station. At each mobile unit, reference tones are generated which are spectrally located between adjacent ones of the possible supervisory tones for the mobile communication area, and the spectral position of a received tone with respect to the reference tones is determined. Signals representing that determination are translated into a digital character corresponding to the name of the received tone, and that name is compared with the name of the tone for the mobile unit's assigned channel. A name mismatch is utilized to quiet the mobile unit receiver for the duration of the mismatch. In addition, if that duration exceeds a predetermined interval, the mobile unit controller is actuated to initiate the dropping of communication on the assigned channel.

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Long Valley, NJ, United States of America

Eric J Addeo