Secure joint cache-channel coding over erasure broadcast channels

We derive upper and lower bounds on the secure capacity-memory tradeoff of the two-user wiretap erasure BC with cache memory at the weaker receiver. The bounds coincide when the cache memory exceeds a given threshold. The lower bound also exhibits that cache memories provide larger gains under a secrecy constraint than without such a constraint. Moreover, for a large set of parameters the capacity-memory tradeoff is larger if only the weaker receiver has cache memory than when this cache memory is split equally among the receivers. The lower bound is based on a joint cache-channel coding scheme that simultaneously exploits the cache contents and the channel statistics. Such a joint design yields significant gains over a separation-based design.