Time-assignment speech interpolation in time-compression-multiplex transmission

Abstract

In time-compression multiplex (t.c.m.) transmission, the signals of the channels are scanned and the samples are stored before being transmitted at high speed. In this way, the signals of a large number of channels can be sent over a single transmission path. The number of telephone channels that can be transmitted can be at least doubled by the process called time-assignment speech interpolation (t.a.s.i.). This exploits the fact that, on average, each channel in a multiplex telephone system is transmitting speech for less than half the time. The addition of t.a.s.i. facilities to a t.c.m. system is relatively simple because the main t.a.s.i. requirement (switching of all speech signals) already exists as an inherent part of any t.c.m. system. Furthermore, the extra information which has to be transmitted (the channel identification information) can be incorporated in the standard t.c.m. signal with very little change in the bandwidth requirements. The simplest t.a.s.i. systems favour the lower-numbered channels, so that, in the event of more channels being active than there are transmission slots available, the same higher-numbered channels are always `frozen out?. In order to overcome this difficulty, a queue-control system is necessary. It can be made to balance the overload conditions such that the queuing channels always accept the back of the queue in time rotation. A queue controller for a t.c.m.-t.a.s.i. system consists of a logical array of conventional binary stores, gates and shift registers.