Multirate sub-band coding applied to digital speech interpolation

This paper discusses the application of sub-band coding to digital speech interpolation (DSI). The optimum allocation of bits for the single port coder and its extension to the multiport case are reviewed. The output of the multiport coder has an embedded bit stream; this property is of great importance in a digital communication network, since it allows any overloaded node to simply flag and drop appropriate bits from the bit stream, without tandeming of encode/decode operations, and without freeze-out. A strategy for bit rate allocation among a number of channels is defined, and a performance analysis is outlined using queueing models for the arrival and departure of calls and talkspurts. This analysis is applied to a configuration in which 96 PCM channels at 64Kbps each are concentrated on a single 1544Kbps T-1 link. The application of multi-rate sub-band coding is shown to be extremely efficient, since toll quality speech transmission is provided in this system even at the full 4-to-1 compression ratio, with no freeze out.