  Caching at the wireless edge can be used to keep up with the increasing
demand for high-definition wireless video streaming. By prefetching popular
content into memory at wireless access points or end-user devices, requests can
be served locally, relieving strain on expensive backhaul. In addition, using
network coding allows the simultaneous serving of distinct cache misses via
common coded multicast transmissions, resulting in significantly larger load
reductions compared to those achieved with traditional delivery schemes. Most
prior works simply treat video content as fixed-size files that users would
like to fully download. This work is motivated by the fact that video can be
coded in a scalable fashion and that the decoded video quality depends on the
number of layers a user receives in sequence. Using a Gaussian source model,
caching and coded delivery methods are designed to minimize the squared error
distortion at end-user devices in a rate-limited caching network. The framework
is very general and accounts for heterogeneous cache sizes, video popularities
and user-file play-back qualities. As part of the solution, a new decentralized
scheme for lossy cache-aided delivery subject to preset user distortion targets
is proposed, which further generalizes prior literature to a setting with file
heterogeneity.
