Yubing Wang's PhD
August 2008
The CS department is very pleased to be able to announce that Yubing Wang successfully defended his Ph.D. Dissertation on Wednesday, August 27, 2008.
The title of his dissertation is "Modeling and Evaluating Feedback-Based Error Control for Video Transfer".
His advisors were Mark Claypool and Robert E. Kinicki. The committee members were Dan Dougherty (WPI CS) and Ketan Mayer-Patel (University of North Carolina at Chapel Hill).
The abstract for the Dissertation is as follows:
Packet loss can be detrimental to real-time interactive video over lossy
networks because one lost video packet can propagate errors to many
subsequent video frames due to the encoding dependency between frames.
Feedback-based error control techniques use feedback information from the
decoder to adjust coding parameters at the encoder or retransmit lost
packets to reduce the error propagation due to data loss. Feedback-based
error control techniques have been shown to be more effective than trying to
conceal the error at the encoder or decoder alone since they allow the
encoder and decoder to cooperate in the error control process. However,
there has been no systematic exploration of the impact of video content and
network conditions on the performance of feedback-based error control
techniques. In particular, the impact of packet loss, round-trip delay,
network capacity constraint, video motion and reference distance on the
quality of videos using feedback-based error control techniques have not
been systematically studied.
This thesis presents analytical models for the major feedback-based error
control techniques: Retransmission, Reference Picture Selection (both NACK
and ACK modes) and Intra Update. These feedback-based error control
techniques have been included in H.263/H.264 and MPEG4, the state of the art
video in compression standards. Given a round-trip time, packet loss rate,
network capacity constraint, our models can predict the quality for a
streaming video with retransmission, Intra Update and RPS over a lossy
network. In order to exploit our analytical models, a series of studies has
been conducted to explore the effect of reference distance, capacity
constraint and Intra coding on video quality. The accuracy of our analytical
models in predicting the video quality under different network conditions is
validated through simulations. These models are used to examine the behavior
of feedback-based error control schemes under a variety of network
conditions and video content through a series of analytic experiments.
Analysis shows that the performance of feedback-based error control
techniques is affected by a variety of factors including round-trip time,
loss rate, video content and the Group of Pictures (GOP) length. In
particular: 1) RPS NACK achieves the best performance when loss rate is low
while RPS ACK outperforms other repair techniques when loss rate is high.
However RPS ACK performs the worst when loss rate is low. Retransmission
performs the worst when the loss rate is high; 2) for a given round-trip
time, the loss rate where RPS NACK performs worse than RPS ACK is higher for
low motion videos than it is for high motion videos; 3) Videos with RPS NACK
always perform the same or better than videos without repair. However, when
small GOP sizes are used, videos without repair perform better than videos
with RPS ACK; 4) RPS NACK outperform Intra Update for low-motion videos.
However, the performance gap between RPS NACK and Intra Update drops when
the round-trip time or the intensity of video motion increases. 5) Although
the above trends hold for both VQM and PSNR, when VQM is the video quality
metric the performance results are much more sensitive to network loss. 6)
Retransmission is effective only when the round-trip time is low. When the
round-trip time is high, Partial Retransmission achieves almost the same
performance as Full Retransmission. These insights derived from our models
can help determine appropriate choices for feedback-based error control
techniques under various network conditions and video content.
Last modified: August 28, 2008 19:15:32