  Content-centric mobile hybrid Internet-of-Things (IoT) networks consisting of
mobile devices and static femto access points (FAPs) are studied, where each
device moves according to the random walk mobility model and requests a content
object from the library independently at random according to a Zipf popularity
distribution. Instead of allowing access to content objects at macro base
stations via costly backhaul providing connection to the core network, we
consider a more practical scenario where mobile devices and static FAPs, each
having a finite-size cache space, are able to cache a subset of content objects
so that each request is served by other mobile devices or static FAPs. Under a
general multihop-based content delivery protocol, we analyze the order-optimal
throughput--delay trade-off by presenting a new cache allocation strategy. In
particular, under a given caching strategy, we first characterize a
throughput--delay trade-off in terms of scaling laws along with the general
content delivery multihop routing protocol. Then, the order-optimal
throughput--delay trade-off is characterized by presenting the order-optimal
cache allocation strategy, which jointly finds the replication sets at mobile
devices and static FAPs via a novel variable decoupling approach. In our mobile
IoT network, an interesting observation is that highly popular content objects
are mainly served by mobile devices while the rest of content objects are
served by static FAPs. We perform numerical evaluation to validate our
analytical results. We also show that the order-optimal strategy strictly
outperforms a baseline approach, where the replication sets at mobile devices
and static FAPs are optimized separately.
