  This paper explores caching of fractions of a video content, not caching of
an entire content, to increase the expected video quality. We first show that
the highest-quality content is better to be cached and propose the caching
policy of video chunks having different qualities. Our caching policy utilizes
the characteristics of video contents that video files can be encoded into
multiple versions with different qualities, each file consists of many chunks,
and chunks can have different qualities. Extensive performance evaluations are
conducted to show that caching of content fractions, rather than an entire
content, can improve the expected video quality especially when the channel
conditions is sufficiently good to cooperate with nearby BS or helpers.
