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Reduce Latency: The Key to Successful Interactive Remote Rendering Systems
Shu Shi
Department of Computer Science
University of Illinois at Urbana-Champaign
Urbana, IL, United States
Abstract—Remote rendering is considered as a general andeffective approach to collaborate mobile devices and cloudcomputing services and deliver computation or network band-width intensive media content (e.g., 3D games, 3D video)to mobile devices. In this abstract, I propose my doctoralthesis research on interaction latency reduction for remoterendering systems. My work mainly focuses on how imagebased rendering techniques can be appropriately applied toreduce the interaction latency which is originally caused bynetwork delay.
Keywords-Remote rendering, interaction latency, 3D video
I. INTRODUCTION
The recent explosion of mobile devices is changing peo-
ple’s computing behaviors and more and more applications
are ported to mobile platforms. However, some applications
(e.g., 3D games, multi-view multi-stream 3D video based
tele-immersive applications [1]) that require intensive com-
putation or network bandwidth are not capable of running
on mobile platforms yet. Remote rendering is considered
as a general and effective approach to deliver computation
or network bandwidth intensive media content to mobile
devices. According to Figure 1, a workstation with enough
computation and network bandwidth resources (e.g., cloud
server) is served as the rendering server. It receives and
renders the source media content (e.g., 3D graphic or 3D
video), and sends the rendering results (2D images) to
one or multiple mobile clients. The mobile client simply
receives and displays the result images. 2D images can be
efficiently compressed with existing video coding tools to
save transmission bandwidth between the rendering server
and mobile clients.
A well known problem of remote rendering is the latency
for the view-change user interaction on mobile clients. If
the mobile user tries to change the rendering viewpoint,
the mobile client needs to send the interaction request
back to the rendering server, and wait for the server to
send back the scene rendered with the updated rendering
viewpoint. Figure 1 shows an illustration of this procedure
with the red dash line. We define the interaction latency
as the time from the generation of interaction request till
the appearance of updated image. Obviously, the interaction
latency takes at least a roundtrip network transmission time
between the mobile client and the rendering server. Given the
Figure 1. Remote Rendering System Framework
unreliable nature of wireless networks, the latency can vary
significantly from time to time and kill the user experience
in many latency-sensitive applications [2].
Therefore, my doctoral thesis research intends to reduce
the interaction latency for remote rendering systems. Ac-
cording to Figure 1, the goal is to reduce the interaction
latency when the mobile client receives a interaction request
that changes the current rendering viewpoint v to v+. If the
mobile client can directly generate the new image I+ (I+
denotes the result image of rendering 3D scene with new
viewpoint v+) in high quality only from the received R
(R denotes the reference frame generated on the rendering
server with old viewpoint v), which is indicated by the
green dash line path, our goal is achieved. Obviously, it
is not enough for the rendering server to simply send the
2D rendering result image. Inspired by previous work in [3]
which suggested using 3D image warping to compensate
latency in remote rendering static 3D models, we apply
image based rendering techniques in our system for dynamic
content rendering. The rendering server is expected to gen-
erate and send auxiliary information (e.g., depth images) as
long as the 2D result image in one reference frame to mobile
clients. The mobile client can use image based rendering
techniques to generate images at the new viewpoint if
any user interaction happens. Compared with static model
rendering in [3], there are more challenges in our research
on rendering dynamic content because all operations should
be finished before the data frame expires. My research will
focus on what reference frames should be selected to support
high quality rendering on mobile side and how reference
frames can be efficiently generated to meet the deadline of
each dynamic data frame.
Fourth Annual PhD Forum on Pervasive Computing and Communications
978-1-4244-9529-0/11/$26.00 ©2011 IEEE 391
My thesis research is novel in two aspects. First, we study
the remote rendering system from a new perspective and
transform the network related interaction latency problem
to a content based reference selection problem. Second, we
try to find a computation efficient method to create an image
based representation for any complex graphic models. The
image based representation is sufficient to support high-
quality rendering of the original model in a limited viewpoint
range. The contribution of my thesis is expected to find
a system solution that integrates image based rendering,
network streaming, cloud computing services, and human
behaviors all together to reduce the interaction latency of
remote rendering systems. In the rest of this abstract, we
discuss the thesis research topics and briefly introduce the
current research status.
II. RESEARCH TOPICS
My thesis research has two general topics. The first topic
is latency reduction. We try to answer four questions:
1) What auxiliary information (reference frame) should
the rendering server generate in order to reduce la-
tency?
2) How does the rendering server generate the reference
frame efficiently?
3) What should the mobile client do if the auxiliary
information is not available?
4) How to scale the system up if one rendering server
needs to serve more than one mobile client?
The second topic is how to evaluate the performance of
latency reduction. In our system, the latency should be
determined by both time and quality of image based ren-
dering. Besides, source content with various motion and
subjective opinions from different individuals can also affect
the evaluation. Thus, we consider the study of latency
reduction evaluation an important topic to understand both
system and human behaviors.
III. STATE OF RESEARCH
We have taken a survey on different previous remote
rendering systems before this thesis proposal. The survey
analyzes the interaction latency of each remote rendering
system design and the details are summarized in [4]. Our
work on 3D video rendering [4][5] answers the question
(1) and (2) as shown above. For each 3D video frame,
two or more depth images are generated on the rendering
server as the reference frame. The mobile client runs the
3D image warping algorithm for every depth image in the
reference frame to generate the image at the target viewpoint
so that the exposure errors caused by single warping are
fixed. Different algorithms on how reference frame should
be selected have been proposed in [4][5]. We also studied
how to use GPU to accelerate search based algorithms in
[6]. For the next stage, we plan to extend our current
Figure 2. Prototype Platform: iPhone Client
research to answer two remaining questions and design more
experiments to better evaluate our system and algorithms.
In addition, we have also built a remote rendering system
prototype (Figure 2) which can render both dynamic 3D
graphics and 3D video for mobile devices. The prototype
provides a good platform to test new ideas on latency
reduction in the future.
IV. ACKNOWLEDGMENTS
I want to thank my adviser Prof. Roy Campbell and co-
adviser Prof. Klara Nahrstedt for their guidance and support.
This research has been supported by the National Science
Foundation under Grant CNS 05-20182 and CNS 07-20702.
REFERENCES
[1] Z. Yang, K. Nahrstedt, Y. Cui, B. Yu, J. Liang, S.-H. Jung, andR. Bajcsy, “Teeve: The next generation architecture for tele-immersive environment,” in ISM. IEEE Computer Society,2005, pp. 112–119.
[2] M. Claypool and K. Claypool, “Latency can kill: precision anddeadline in online games,” in MMSys ’10: Proceedings of thefirst annual ACM SIGMM conference on Multimedia systems.New York, NY, USA: ACM, 2010, pp. 215–222.
[3] W. R. Mark, G. Bishop, and L. McMillan, “Post-renderingimage warping for latency compensation,” Chapel Hill, NC,USA, Tech. Rep., 1996.
[4] S. Shi, M. Kamali, J. C. Hart, K. Nahrstedt, and R. H.Campbell, “A high-quality low-delay remote rendering systemfor 3d video,” in MM ’10: Proceedings of the eighteen ACMinternational conference on Multimedia. New York, NY, USA:ACM, 2010.
[5] S. Shi, W. J. Jeon, K. Nahrstedt, and R. H. Campbell, “Real-time remote rendering of 3d video for mobile devices,” inMM ’09: Proceedings of the seventeen ACM internationalconference on Multimedia. New York, NY, USA: ACM, 2009,pp. 391–400.
[6] W. Yoo, S. Shi, W. J. Jeon, K. Nahrstedt, and R. H. Campbell,“Real-time parallel remote rendering for mobile devices usinggraphics processing units,” in ICME. IEEE, 2010, pp. 902–907.
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