mandatory component on the devices.
For any application targeted at mobile devices, reducing
power consumption is perennially one of the major concerns
and challenges. Flinn et al. [14] exploit collaborations between
the mobile OS and the mobile applications to balance the
energy conservation and application performance. Yuan et al.
[15] investigate mobile multimedia streaming, similar to most
of the other work, by adjusting the CPU power for energy
saving; however, according to the recent measurement work
of Carroll et al. [6], the display and the wireless network card
(including the cellular module) and not the CPU consume more
than half of the overall power consumption in smart phones nowadays. Our work is able to achieve a significant (about
30%) power saving, by opportunistically switching the device
between high-power and low-power transmission modes during
streaming. Some existing work (e.g., Anastasi et al. [16]) have
provided valuable guidelines for energy saving over WiFi
transmissions; our work focuses on 3G cellular transmissions
which have significantly different power models; 3G is a more
practical wireless connection technology for mobile TVs on
the go at the present time.
Cloud computing had its debut with much fanfare and is now
deemed a most powerful hosting platform in many areas includingmobile
computing. Satyanarayanan et al. [1] suggest offloading
mobile devices’ computation workload to a nearby resource-
rich infrastructure (i.e., Cloudlets) by dynamic VM synthesis.
Kosta et al. [2] propose a virtualization framework for
mobile code offloading to the cloud. Zhang et al. [17] introduce
an elastic mobile application model by offloading part of the
applications (weblets) to an IaaS cloud. All these work target
at computational job offloading. Recently, attentions have been
drawn to enabling media applications using the cloud, for both
media storage [18] and processing [19]. We are aware of a recent
work by Huang et al. [3] which, in resemblance to ours,
also leverages cloud resources for video transcoding. But they
advocate scalable video coding (SVC) using multiple cluster
nodes, which is not suitable in a mobile social TV scenario
due to the encoding complexity of SVC (hence leading to intolerable
delays), when realtime video retrievals and social interactions
via mobile devices are desired. We instead advocate
non-layered coding in such delay-sensitive mobile applications,
although the detailed transcoding algorithm designs are out of
the scope of this work. In addition, we novelly employ a surrogate
for each mobile user in the cloud rather than relying on
a dedicated cluster, which can be more easily implemented in
practice. Liu et al. [20] build a mobile-based social interaction
framework on top of the Google App Engine and offer an iOS
implementation. We set out to design a portable, generic, and
robust framework to enable realtime streaming and social interaction
concurrently, which is not bound to any specific cloud
platform. Although our prototype is implemented on only two
public clouds, i.e., Amazon EC2 and Google App Engine, it can
be easily ported to other cloud systems as long as the targeted
cloud platforms conform to the unified standard.
A recent work by Zhang et al. [21] investigates the media
caching management problem under HTTP adaptive bit rate
streaming over a wireless network environment, which can
complement our work when video streams are required to be
transcoded into multiple bit rates.
Finally, we are aware of the lack of a richly-featured cloudbased
mobile social TV system in real life. The only system
coming close to ours is Live Stream [22] on the iOS platform.
This iOS-locked application only supports live video channels,
and all its social functions are bound to Facebook open APIs.
Conversely, the prototype we implement is browser-based and
platform independent; it supports both live channels, VoD channels
and even personal channels hosted by any user, with wider
usage ranges and flexible extensibility. The framework we propose
can be readily applied to other cloud-assistedmobile media
applications as well.