A method and apparatus for performing multiple descriptive source coding
in which a plurality of homogeneous encoders are advantageously employed
in combination with a corresponding plurality of advantageously
substantially identical decoders. In particular, diversity is provided to
the multiple encoders by modifying the quantization process in at least
one of the encoders such that the modified quantization process is based
at least on a quantization error resulting from the quantization process
of another one of the encoders. In this manner, diversity among the
multiple bit streams is obtained, and in particular, the quality of a
reconstructed signal based on a combination of multiple decoded bit
streams at the receiver is advantageously superior to that based on any
one of the decoded bit streams. In accordance with a first illustrative
embodiment of the present invention, two Pulse Code Modulation (PCM)
coders are employed. In accordance with a second illustrative embodiment
of the present invention, two Adaptive Differential Pulse Code Modulation
(ADPCM) coders are employed. And in accordance with a third illustrative
embodiment of the present invention, two Low-Delay Code Excited Linear
Prediction (LD-CELP) coders are employed. In each case, diversity is
ensured by an appropriate modification to the quantization process of at
least one of the encoders, and the total error may be advantageously
reduced when decoded bit streams from both coders are combined at the
receiver.