An experimental investigation of the active-idle pattern of speech over land mobile radio telephone channels

Two methods of speech detection at the syllabic level of voice traffic over land mobile radio telephone channels are presented. Both methods are based on the periodic comparison of the audio signal level with a threshold and provide an ON-OFF pattern of active-idle periods on the channel at a rate equal to 100 to 200 samples per second. One method is entirely digital whereas the other method uses an analog detector followed by digital processing. Results of the analysis show that during a conversation more than 50 percent of the time the channel is idle, with an average duration of the silences larger than 300 ms. These results and those concerning other parameters of interest indicate that even during a conversation many useful idle periods do occur. These silences could indeed be exploited by making them available to additional users and hence improve both the efficiency of the channels and their congestion.