15,174 research outputs found
Cooperative Caching and Transmission Design in Cluster-Centric Small Cell Networks
Wireless content caching in small cell networks (SCNs) has recently been
considered as an efficient way to reduce the traffic and the energy consumption
of the backhaul in emerging heterogeneous cellular networks (HetNets). In this
paper, we consider a cluster-centric SCN with combined design of cooperative
caching and transmission policy. Small base stations (SBSs) are grouped into
disjoint clusters, in which in-cluster cache space is utilized as an entity. We
propose a combined caching scheme where part of the available cache space is
reserved for caching the most popular content in every SBS, while the remaining
is used for cooperatively caching different partitions of the less popular
content in different SBSs, as a means to increase local content diversity.
Depending on the availability and placement of the requested content,
coordinated multipoint (CoMP) technique with either joint transmission (JT) or
parallel transmission (PT) is used to deliver content to the served user. Using
Poisson point process (PPP) for the SBS location distribution and a hexagonal
grid model for the clusters, we provide analytical results on the successful
content delivery probability of both transmission schemes for a user located at
the cluster center. Our analysis shows an inherent tradeoff between
transmission diversity and content diversity in our combined
caching-transmission design. We also study optimal cache space assignment for
two objective functions: maximization of the cache service performance and the
energy efficiency. Simulation results show that the proposed scheme achieves
performance gain by leveraging cache-level and signal-level cooperation and
adapting to the network environment and user QoS requirements.Comment: 13 pages, 10 figures, submitted for possible journal publicatio
How migrating 0.0001% of address space saves 12% of energy in hybrid storage
We present a simple, operating-\ud
system independent method to reduce the num-\ud
ber of seek operations and consequently reduce\ud
the energy consumption of a hybrid storage\ud
device consisting of a hard disk and a flash\ud
memory. Trace-driven simulations show that\ud
migrating a tiny amount of the address space\ud
(0.0001%) from disk to flash already results\ud
in a significant storage energy reduction (12%)\ud
at virtually no extra cost. We show that the\ud
amount of energy saving depends on which part\ud
of the address space is migrated, and we present\ud
two indicators for this, namely sequentiality and\ud
request frequency. Our simulations show that\ud
both are suitable as criterion for energy-saving\ud
file placement methods in hybrid storage. We\ud
address potential wear problems in the flash\ud
subsystem by presenting a simple way to pro-\ud
long its expected lifetime.\u
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