Digital speech interpolation trunk priority rotator

Abstract

In a digital speech interpolation system, speech inactivity time is utilized to reduce the bit rate on a link between transmitter and receiver by compressing digital characters from a plurality of trunks onto a lesser plurality of channels. If the number of trunks having active speech samples exceeds the number of channels, an overload may exist. To mitigate overload, it is common to truncate one or more bits from a transmitted character. However, bit truncation leads to signal degradation. Of course, it is desirable to abate the degradation consistent with mitigating the overload. Unfortunately, the number of bits truncated from a character on a first trunk is typically more or less than the number of bits truncated from a character on a second trunk. As a result, the signal degradation may not be uniform. To obtain a more uniform signal degradation, the instant priority rotation arrangement rotates the starting point for assigning bits to a digital frame responsive to the activity status of the trunks. Specifically, an active trunk is assigned to one of a plurality of groups of trunks. The starting point is taken from a different group for each output frame. Thereby, the starting point is adaptively adjusted on a frame-by-frame basis according to which trunks are active during the frame. By so rotating the starting point among active trunks rather than among all trunks, the instant arrangement achieves a more uniform signal degradation during periods of overload than was obtained with the prior art.