4,421 research outputs found
Age Minimization in Energy Harvesting Communications: Energy-Controlled Delays
We consider an energy harvesting source that is collecting measurements from
a physical phenomenon and sending updates to a destination within a
communication session time. Updates incur transmission delays that are function
of the energy used in their transmission. The more transmission energy used per
update, the faster it reaches the destination. The goal is to transmit updates
in a timely manner, namely, such that the total age of information is minimized
by the end of the communication session, subject to energy causality
constraints. We consider two variations of this problem. In the first setting,
the source controls the number of measurement updates, their transmission
times, and the amounts of energy used in their transmission (which govern their
delays, or service times, incurred). In the second setting, measurement updates
externally arrive over time, and therefore the number of updates becomes fixed,
at the expense of adding data causality constraints to the problem. We
characterize age-minimal policies in the two settings, and discuss the
relationship of the age of information metric to other metrics used in the
energy harvesting literature.Comment: Appeared in Asilomar 201
Optimal Status Updating with a Finite-Battery Energy Harvesting Source
We consider an energy harvesting source equipped with a finite battery, which
needs to send timely status updates to a remote destination. The timeliness of
status updates is measured by a non-decreasing penalty function of the Age of
Information (AoI). The problem is to find a policy for generating updates that
achieves the lowest possible time-average expected age penalty among all online
policies. We prove that one optimal solution of this problem is a monotone
threshold policy, which satisfies (i) each new update is sent out only when the
age is higher than a threshold and (ii) the threshold is a non-increasing
function of the instantaneous battery level. Let denote the optimal
threshold corresponding to the full battery level , and denote
the age-penalty function, then we can show that is equal to the
optimum objective value, i.e., the minimum achievable time-average expected age
penalty. These structural properties are used to develop an algorithm to
compute the optimal thresholds. Our numerical analysis indicates that the
improvement in average age with added battery capacity is largest at small
battery sizes; specifically, more than half the total possible reduction in age
is attained when battery storage increases from one transmission's worth of
energy to two. This encourages further study of status update policies for
sensors with small battery storage.Comment: 15 pages, 6 figure
Age-Minimal Transmission in Energy Harvesting Two-hop Networks
We consider an energy harvesting two-hop network where a source is
communicating to a destination through a relay. During a given communication
session time, the source collects measurement updates from a physical
phenomenon and sends them to the relay, which then forwards them to the
destination. The objective is to send these updates to the destination as
timely as possible; namely, such that the total age of information is minimized
by the end of the communication session, subject to energy causality
constraints at the source and the relay, and data causality constraints at the
relay. Both the source and the relay use fixed, yet possibly different,
transmission rates. Hence, each update packet incurs fixed non-zero
transmission delays. We first solve the single-hop version of this problem, and
then show that the two-hop problem is solved by treating the source and relay
nodes as one combined node, with some parameter transformations, and solving a
single-hop problem between that combined node and the destination.Comment: Appeared in IEEE Globecom 201
Age of Information in Multicast Networks with Multiple Update Streams
We consider the age of information in a multicast network where there is a
single source node that sends time-sensitive updates to receiver nodes.
Each status update is one of two kinds: type I or type II. To study the age of
information experienced by the receiver nodes for both types of updates, we
consider two cases: update streams are generated by the source node at-will and
update streams arrive exogenously to the source node. We show that using an
earliest and transmission scheme for type I and type II updates,
respectively, the age of information of both update streams at the receiver
nodes can be made a constant independent of . In particular, the source node
transmits each type I update packet to the earliest and each type II
update packet to the earliest of receiver nodes. We determine the
optimum and stopping thresholds for arbitrary shifted exponential
link delays to individually and jointly minimize the average age of both update
streams and characterize the pareto optimal curve for the two ages
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