20 research outputs found
Mobility Increases the Data Offloading Ratio in D2D Caching Networks
Caching at mobile devices, accompanied by device-to-device (D2D)
communications, is one promising technique to accommodate the exponentially
increasing mobile data traffic. While most previous works ignored user
mobility, there are some recent works taking it into account. However, the
duration of user contact times has been ignored, making it difficult to
explicitly characterize the effect of mobility. In this paper, we adopt the
alternating renewal process to model the duration of both the contact and
inter-contact times, and investigate how the caching performance is affected by
mobility. The data offloading ratio, i.e., the proportion of requested data
that can be delivered via D2D links, is taken as the performance metric. We
first approximate the distribution of the communication time for a given user
by beta distribution through moment matching. With this approximation, an
accurate expression of the data offloading ratio is derived. For the
homogeneous case where the average contact and inter-contact times of different
user pairs are identical, we prove that the data offloading ratio increases
with the user moving speed, assuming that the transmission rate remains the
same. Simulation results are provided to show the accuracy of the approximate
result, and also validate the effect of user mobility.Comment: 6 pages, 5 figures, accepted to IEEE Int. Conf. Commun. (ICC), Paris,
France, May 201
Dynamic Coded Caching in Wireless Networks
We consider distributed and dynamic caching of coded content at small base
stations (SBSs) in an area served by a macro base station (MBS). Specifically,
content is encoded using a maximum distance separable code and cached according
to a time-to-live (TTL) cache eviction policy, which allows coded packets to be
removed from the caches at periodic times. Mobile users requesting a particular
content download coded packets from SBSs within communication range. If
additional packets are required to decode the file, these are downloaded from
the MBS. We formulate an optimization problem that is efficiently solved
numerically, providing TTL caching policies minimizing the overall network
load. We demonstrate that distributed coded caching using TTL caching policies
can offer significant reductions in terms of network load when request arrivals
are bursty. We show how the distributed coded caching problem utilizing TTL
caching policies can be analyzed as a specific single cache, convex
optimization problem. Our problem encompasses static caching and the single
cache as special cases. We prove that, interestingly, static caching is optimal
under a Poisson request process, and that for a single cache the optimization
problem has a surprisingly simple solution.Comment: To appear in IEEE Transactions on Communication