Principles of MDC - Distributed Multiple Description Coding - page 23

the code rate of a single description, equivalent to transmit the single description
through the different channel twice. There is no independent information among the
various descriptions, it fails to achieve complementary enhanced, center decoding
equivalent to the single-channel decoding effect of using only one description.
Therefore, to coordinate the independence and correlation among descriptions is
the key to MDC.

2.3 Review of MDC

2.3.1 Subsampling-Based MDC

The MDC based on subsampling [ 8 - 19 ] divides the original signal into several
subsets on space domain, time domain, or frequency domain; each subset is
transmitted as different descriptions. The MDC method based on subsampling
mainly takes advantage of the smoothing characteristic of image or video signals,
that is, apart from the border area. The adjacent pixel values in space or time are
related or change smoothly. Therefore, a description can be estimated by others.
In the early research of Bell Labs [ 20 ], they used the method of parity sampling
for video source to realize the separation of signal channels, generating two
descriptions, as shown in Fig. 2.2 .
Representative algorithms include: frame sampling in time domain [ 9 , 10 ], the
space-pixel-mixed algorithm applied to image sampling points [ 11 , 17 ]ormotion
vector [ 14 ] and mixed algorithm of transform coefficients [ 12 , 13 , 19 ].
In the simplest time domain subsampling method [ 9 ], according to the odd-even
frame, the input video sequence was sampled to two subsequences to transmit, and
each subsequence can decode independently. Wenger [ 10 ] proposed the algorithm
of VRC, and was supported by H.263C and recommended by ITU-T.
Franchi et al. [ 17 ] designed two structures of multiple-description coding -
these two structures are all prediction loop based on motion compensation - and
used polyphase down-sampling technique to produce a description of each other

Fig. 2.2 Speech coding for channel splitting as proposed by Jayant [ 20 ]