Abstract: A voice activity detector (VAD) which determines whether received voice signal samples contain speech by deriving parameters measuring short term time domain characteristics of the input signal, including the average signal level and the absolute value of any change in average signal level, and comparing the derived parameter values with corresponding thresholds, which are periodically monitored and updated to reflect changes in the level of background noise, thereby minimizing clipping and false alarms.

Abstract: Noise is suppressed during pauses and silent periods in conversation, and voiced signals are freely passed in a mobile communications system thereby improving the quality of the transmitted speech. Noise suppression is implemented in such a way that a low level of noise is still allowed to pass to provide presence of the remote speaker; that is, the line is not made completely silent as this may falsely indicate that the connection has been interrupted. The noise suppression has an added feature of decreasing the background noise fractionally when voice is no longer detected. This provides perceptually improved quality of the communication.

Abstract: A voice activity detector (VAD) which determines whether an input signal contains speech by deriving parameters measuring short term time domain characteristics of the input signal, including the average signal level and the absolute value of any change in average signal level, and comparing the derived parameter values with corresponding predetermined threshold values. In order to further minimize clipping and false alarms, the VAD periodically monitors and updates the threshold values to reflect changes in the level of background noise.

Abstract: TDMA timing is maintained by the use of visibility information transmitted among the stations in a conference. Each station monitors the identity of stations from which bursts are received. A station also receives visibility information from other stations. The station combines the information to maintain a two-dimensional Visibility Designator Byte matrix or array. A station participates in the process by periodically transmitting its own VDB array to other stations. The stations then, independently, identify a prime station by using the collected and processed information. Using the same information, a station also identifies the manner in which it will lock to the timing of the prime station.