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17.5 Evaluation 389
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Receiver SNR (dB)
PSNR (dB)
Cactus
SoftCast
BPSK 1/2
QPSK 1/2
QPSK 3/4
16-QAM 1/2
Figure 17.14 Compare Cactus against two reference schemes for a CIF sequence in a multicast
session when bandwidth ratio ρ = 1.
and average video PSNR across sequences. To plot the video PSNR as a function
of receiver SNR, we divide the receiver SNR range into 1 dB bins, and average all
the (receiver SNR, PSNR) pairs whose receiver SNR fall into the same bin. Results
show that although both Cactus and SoftCast achieve graceful rate adaptation, Cac-
tus consistently outperforms SoftCast in video PSNR, and