Reduce Transmission Delay for Cache-Aided Two-Layer Network

In this paper, we consider a two-layer caching-aided network, where a single server consisting a library of N files connects with multiple relays through a shared noiseless link, and each relay connects with multiple users through a shared noiseless link. Each relay and user are equipped with a cache memory of M1 and M2 files, respectively. We design a caching scheme that exploits the spared transmission time resource by allowing the concurrent transmission between the two layers. It is shown that the caching scheme is order optimal and can further reduce the transmission delay compared to the previously known caching scheme. Also, we show that for the two-relay case, if each relay's caching size M1 equals to 0.382N, our scheme achieves the same delay as M1 = N, which implies that increasing M1 will not always reduce the transmission delay