4,603 research outputs found
Fundamental Limits of Cloud and Cache-Aided Interference Management with Multi-Antenna Edge Nodes
In fog-aided cellular systems, content delivery latency can be minimized by
jointly optimizing edge caching and transmission strategies. In order to
account for the cache capacity limitations at the Edge Nodes (ENs),
transmission generally involves both fronthaul transfer from a cloud processor
with access to the content library to the ENs, as well as wireless delivery
from the ENs to the users. In this paper, the resulting problem is studied from
an information-theoretic viewpoint by making the following practically relevant
assumptions: 1) the ENs have multiple antennas; 2) only uncoded fractional
caching is allowed; 3) the fronthaul links are used to send fractions of
contents; and 4) the ENs are constrained to use one-shot linear precoding on
the wireless channel. Assuming offline proactive caching and focusing on a high
signal-to-noise ratio (SNR) latency metric, the optimal information-theoretic
performance is investigated under both serial and pipelined fronthaul-edge
transmission modes. The analysis characterizes the minimum high-SNR latency in
terms of Normalized Delivery Time (NDT) for worst-case users' demands. The
characterization is exact for a subset of system parameters, and is generally
optimal within a multiplicative factor of 3/2 for the serial case and of 2 for
the pipelined case. The results bring insights into the optimal interplay
between edge and cloud processing in fog-aided wireless networks as a function
of system resources, including the number of antennas at the ENs, the ENs'
cache capacity and the fronthaul capacity.Comment: 34 pages, 15 figures, submitte
Delivery Time Minimization in Edge Caching: Synergistic Benefits of Subspace Alignment and Zero Forcing
An emerging trend of next generation communication systems is to provide
network edges with additional capabilities such as additional storage resources
in the form of caches to reduce file delivery latency. To investigate this
aspect, we study the fundamental limits of a cache-aided wireless network
consisting of one central base station, transceivers and receivers from
a latency-centric perspective. We use the normalized delivery time (NDT) to
capture the per-bit latency for the worst-case file request pattern at high
signal-to-noise ratios (SNR), normalized with respect to a reference
interference-free system with unlimited transceiver cache capabilities. For
various special cases with and that satisfy , we establish the optimal tradeoff between cache storage and latency. This
is facilitated through establishing a novel converse (for arbitrary and
) and an achievability scheme on the NDT. Our achievability scheme is a
synergistic combination of multicasting, zero-forcing beamforming and
interference alignment.Comment: submitted to ICC 2018; fixed some typo
How Much Can D2D Communication Reduce Content Delivery Latency in Fog Networks with Edge Caching?
A Fog-Radio Access Network (F-RAN) is studied in which cache-enabled Edge
Nodes (ENs) with dedicated fronthaul connections to the cloud aim at delivering
contents to mobile users. Using an information-theoretic approach, this work
tackles the problem of quantifying the potential latency reduction that can be
obtained by enabling Device-to-Device (D2D) communication over out-of-band
broadcast links. Following prior work, the Normalized Delivery Time (NDT) --- a
metric that captures the high signal-to-noise ratio worst-case latency --- is
adopted as the performance criterion of interest. Joint edge caching, downlink
transmission, and D2D communication policies based on compress-and-forward are
proposed that are shown to be information-theoretically optimal to within a
constant multiplicative factor of two for all values of the problem parameters,
and to achieve the minimum NDT for a number of special cases. The analysis
provides insights on the role of D2D cooperation in improving the delivery
latency.Comment: Submitted to the IEEE Transactions on Communication
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