  A cache-aided broadcast network is studied, in which a server delivers
contents to a group of receivers over a packet erasure broadcast channel (BC).
The receivers are divided into two sets with regards to their channel
qualities: the weak and strong receivers, where all the weak receivers have
statistically worse channel qualities than all the strong receivers. The weak
receivers, in order to compensate for the high erasure probability they
encounter over the channel, are equipped with cache memories of equal size,
while the receivers in the strong set have no caches. Data can be pre-delivered
to weak receivers' caches over the off-peak traffic period before the receivers
reveal their demands. Allowing arbitrary erasure probabilities for the weak and
strong receivers, a joint caching and channel coding scheme, which divides each
file into several subfiles, and applies a different caching and delivery scheme
for each subfile, is proposed. It is shown that all the receivers, even those
without any cache memories, benefit from the presence of caches across the
network. An information theoretic trade-off between the cache size and the
achievable rate is formulated. It is shown that the proposed scheme improves
upon the state-of-the-art in terms of the achievable trade-off.
