| Summary: | 碩士 === 國立交通大學 === 電信研究所 === 81 === Traditionally,digital broadcast system uses single resolution
strategy.Due to the propagation loss, the channel capacity
decreases monotonically with increased distance from the
transmitter. The picture quality will degrade abruptly. This is
so called threshold effect. A better video broadcast system can
be designed by the multiresolution strategy. Joint
consideration for signal bit stream priority in source coding
and the Euclidean distance between signal points in modulation
achieves stepwise degradation in the picture quality. In this
multiresolution strategy, system performance is affected by the
way how the original images are decomposed, and how many signal
levels are used in modulation. With the 1:2 ratio of bit-rates
between two components in multiresolution 64 QAM transmission,
we investigate that subband coder, pyramid coder, and
decomposed DCT coder in multiresolution source coding. Optimum
quantization is employed with nonuniform quantizer matched to
Laplacian distribution in several different bit-rates. To
increase full resolution coverage,trellis code that matched to
multiresolution 64 QAM modulator is established in AWGN
channel. Simulation reveals that decomposed DCT coder is a
better candidate for multiresolution transmission, which has
the advantages that source coder is simple and not sensitive to
bit ratio variation,bit allocation is efficient, and more
flexible for system design.
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