  The recent surge of applications involving the use of $360^o$ video
challenges mobile networks infrastructure, as $360^o$ video files are of
significant size, and current delivery and edge caching architectures are
unable to guarantee their timely delivery. In this paper, we investigate the
problem of joint collaborative content-aware caching and delivery of $360^o$
videos in a video on demand setting. The proposed scheme takes advantage of
$360^o$ video encoding in multiple tiles and layers to make fine-grained
decisions regarding which tiles to cache in each Small Base Station (SBS), and
where to deliver them from to the end users, as users may reside in the
coverage area of multiple SBSs. This permits to cache the most popular tiles in
the SBSs, while the remaining tiles may be obtained through the backhaul. In
addition, we explicitly consider the time delivery constraints to ensure
continuous video playback. To reduce the computational complexity of the
optimization problem, we simplify it by introducing a fairness constraint. This
allows us to split the original problem into subproblems corresponding to
Groups of Pictures (GoP). Each of the subproblems is then solved with the
method of Lagrange partial relaxation. Finally, we evaluate the performance of
the proposed method for various system parameters and compare it with schemes
that do not consider $360^o$ video encoding into multiple tiles and quality
layers, as well as with two variants of the proposed method one that considers
layered encoding and SBSs collaboration and another that uses tiles encoding
but with no SBSs collaboration. The results showcase the benefits coming from
caching and delivery decisions on per tile basis and the importance of
exploiting SBSs collaboration.
