Reduce Transmission Delay for Caching-Aided Two-Layer Networks

In this paper, we consider a two-layer caching-aided network, where a single server consisting of a library of N files connects with multiple relays, each equipped with a cache memory of M
₁
files and each relay connects with a distinct set of users, each equipped with a cache memory of M
₂
files. We design a caching scheme that exploits the spared transmission time resource by constructing a concurrent transmission between the two layers. It is shown that the caching scheme is order optimal and achieves an additive parallel gain compared to the previously known caching scheme. Also, we show that for the two-relay case, if each relay's caching size M
₁
equals to 0.382N, our scheme achieves the optimal delay as M
₁
= N, implying that increasing the relay's cache size will not always reduce the transmission delay.