12-04-2012, 12:53 PM
An Unequal Power Allocation Scheme for JPEG Image Transmission
mfs-2004-CCCT-uneq-power-jpeg.pdf (Size: 67.68 KB / Downloads: 31)
INTRODUCTION
Real-time image and video communication is becoming
common in the 3rd generation (3G) wireless systems
with the introduction of high data rates. These
sources are very sensitive to channel errors and even
a small number of channel errors have the potential
to introduce significant amounts of perceptual distortion
in the reconstructed source. There are many
different methods of protecting these sources against
channel errors. Channel coding (also known as error
protection) and an increase in the transmit power
are amongst the most commonly used methods for
protecting the transmitted data against channel errors.
The Source Coding Model
In our JPEG encoding, we use the progressive discrete
cosine transform (DCT) based mode of operation
with spectral-selection [14]. In the progressive
DCT mode, the data is arranged in different quality
layers in such a way that the quality of the decoded
image is increased progressively as more and more
layers are decoded.
The Channel Model
We transmit the JPEG compressed bitstream using
4-quadrature amplitude modulation (4-QAM) over a
quasi-static Rayleigh flat fading channel [15]. We assume
that the headers and the markers are transmitted
error free, which is a valid assumption since powerful
channel codes can be used to transmit the headers
and markers (which constitute a small fraction of the
total bitstream).
The Distortion Model
We use mean squared error (MSE) as our distortion
metric. MSE is converted to PSNR assuming 8 bit unsigned
representation for unquantized pixel values using
the simple relation PSNR = 10 log10
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MSE, since
PSNR is commonly used for image quality assessment.
UNEQUAL POWER ALLOCATION
Since different coefficients contribute to total distortion
in an unequal manner, it is a natural choice to
transmit these different coefficients with different levels
of error protection and/or transmit power. Using
this idea, in this section, we present an unequal
power allocation scheme for transmission of progressive
JPEG coded images over Rayleigh flat fading
channels.
CONCLUSION
In this paper, we presented an unequal power allocation
scheme for transmission of progressive JPEG
compressed images over Rayleigh fading channels.
Different layers in the JPEG image are transmitted
using different power levels, where as the total power
transmitted over the length of the bitstream is kept
constant, such that the total distortion in the reconstructed
image is minimized.