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4.7 Simulation of Streaming PFGS Video over Wireless Channels 85
encoding even frames. On the other hand, if allocating a fixed bit rate for all pictures,
for example, at a bit rate where the third enhancement layer in an even picture is
partially decoded, the previous odd picture may be only decoded up to the second
enhancement layer due to the fact that its bitstream is longer. In turn, the quality
of even pictures may be limited since its higher layer reference (third enhancement
layer) in odd pictures is not available. This will not only cause the fluctuation of
PSNR in adjacent pictures, but also affect the overall coding efficiency of the video
sequence. Fortunately, the PFGS scheme provides an embedded and fully scalable
bitstream, so