Subsampling of a DPCM Speech Channel to Provide Two “Self-Contained” Half-Rate Channels
Nikil S. Jayant · Bell System Technical Journal · 1981
We consider the following channel-splitting problem: it is required to split a B-bits/s speech-code sequence into two “self-contained” B/2-bits/s components, either of which can be used to reproduce acceptable speech; also, if both components are available at a receiver, it must be possible to reproduce speech with full B-bits/s quality. We propose a solution where for interesting values of B, the speech quality resulting from half-rate receptions approximately equals that from conventional full-rate receptions at B/2 bits/s. In the proposed solution, 3.2kHz speech is sampled at 12 kHz and coded using PCM or differential PCM. The output sequence of code-words is split into odd- and even-word sequences. A full-rate receiver with access to both of the subchannels simply reconstitutes the output sequence prior to decoding, while a half-rate receiver with only the odd (or even) subchannel estimates the even (or odd) components by nearest-neighbor interpolation.