  Pushing popular content to cheap "helper" nodes (e.g., small cells) during
off-peak hours has recently been proposed to cope with the increase in mobile
data traffic. User requests can be served locally from these helper nodes, if
the requested content is available in at least one of the nearby helpers.
Nevertheless, the collective storage of a few nearby helper nodes does not
usually suffice to achieve a high enough hit rate in practice. We propose to
depart from the assumption of hard cache hits, common in existing works, and
consider "soft" cache hits, where if the original content is not available,
some related contents that are locally cached can be recommended instead. Given
that Internet content consumption is entertainment-oriented, we argue that
there exist scenarios where a user might accept an alternative content (e.g.,
better download rate for alternative content, low rate plans, etc.), thus
avoiding to access expensive/congested links. We formulate the problem of
optimal edge caching with soft cache hits in a relatively generic setup,
propose efficient algorithms, and analyze the expected gains. We then show
using synthetic and real datasets of related video contents that promising
caching gains could be achieved in practice.
