Abstract: A portable communication device (104), such as a cellular telephone, is operable in a speakerphone mode. The communication device uses a digital communication scheme, and both receives and generates vocoded signals. The speakerphone provides half duplex operation to eliminate echo. When voice activity is detected, the device activates a speaker and mutes a microphone to avoid echo. When no voice activity is detected in the received signal, the speaker is muted and the microphone activated. To determine when speech activity is present in the received signal, a novel voice activity detection (VAD) algorithm is used which takes advantage of parameters provided as part of the received vocoded signal. The new voice activity algorithm includes calculating a staggered average of the frame energy value for a sequence of received frames, and determining if the staggered average value exceeds a threshold.

Abstract: A digital signal processor (100) receives a digitally vocoded signal (102), and calculates a staggered average value (404) from the frame energy of each received frame, or the product of the frame energy and a voicing value. While the staggered average value is above a threshold voice indicator value, speech is declared present.

Abstract: In a portable communication device (104) that is able to operate in a speakerphone mode, a user interface such as a keypad (120) and display (122) are provided to allow the user to select (1104) an enhanced mode so that leading fricatives of speech are more likely to be detected as speech, and played over a speaker (214). Upon selecting the enhanced mode of operation, the voicing value of each frame of vocoded speech received is increased, thus making it more likely for energetic fricative frames to be detected as speech.

Abstract: An apparatus (800) processes a data stream of convolutionally encoded information and generates decoded information using a series of symbol selections that potentially correspond to at least a portion of the data stream (610, 620). A first reliability indication is obtained for a particular decision made for a symbol selection (630). When the reliability indicator does not satisfy a particular criteria, a traceback is performed along the series of symbol selections to develop a second reliability indication based on whether, after adjusting for allowable error patterns, an alternative set of symbol selections yields the decoded information within a predetermined number of symbol selections (635, 640, 645, 650, 655, 660, 665). An action is taken based on the second reliability indication (670).