Half-duplex speakerphone

Details Half-duplex speakerphone Half-duplex speakerphone

1988-10-12

1989-11-07

Dwyer, James L.

Telephonic communications

Supervisory or control line signaling

Using line or loop condition detection

379390, H04M 160

Patent

active

048797456

ABSTRACT:
A half-duplex digital speakerphone includes a control state machine which controls the selection of either a transmit or a receive audio path based upon a present state of the speakerphone and the magnitudes of three signal related variables associated with each path. The three variables for each path includes a signal power variable, a noise power variable and a worst-case echo variable. A change of state of the state machine results in the value of a variable gain within each of the paths being adjusted to optimize the transition time from the receive to the transmit state or from the transmit to the receive state. Also optimized is a change of state from an idle state to a transmit or receive state or from a transmit or receive state to the idle state. A change of state is accomplished in accordance with a smoothly varying, substantially Gaussian switching waveform which is selected to optimize the transition time between states while simultaneously minimizing audible side effects.

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"Digital Speakerphones: Is Full-Duplex Possible" by Gary Kloesz, Business Communications, Jul. 13, 1987, pp. 36 & 40.

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