3,631 research outputs found
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
Optimizing Information Freshness in a Multiple Access Channel with Heterogeneous Devices
In this work, we study age-optimal scheduling with stability constraints in a
multiple access channel with two heterogeneous source nodes transmitting to a
common destination. The first node is connected to a power grid and it has
randomly arriving data packets. Another energy harvesting (EH) sensor monitors
a stochastic process and sends status updates to the destination. We formulate
an optimization problem that aims at minimizing the average age of information
(AoI) of the EH node subject to the queue stability condition of the
grid-connected node. First, we consider a Probabilistic Random Access (PRA)
policy where both nodes make independent transmission decisions based on some
fixed probability distributions. We show that with this policy, the average AoI
is equal to the average peak AoI, if the EH node only sends freshly generated
samples. In addition, we derive the optimal solution in closed form, which
reveals some interesting properties of the considered system. Furthermore, we
consider a Drift-Plus-Penalty (DPP) policy and develop AoI-optimal and
peak-AoI-optimal scheduling algorithms using the Lyapunov optimization theory.
Simulation results show that the DPP policy outperforms the PRA policy in
various scenarios, especially when the destination node has low multi-packet
reception capabilities.Comment: 13 pages, 8 figures, accepted for publication in IEEE Open Journal of
the Communications Societ
Energy Harvesting Wireless Sensor Networks: Delay Analysis Considering Energy Costs of Sensing and Transmission
Energy harvesting (EH) provides a means of greatly enhancing the lifetime of
wireless sensor nodes. However, the randomness inherent in the EH process may
cause significant delay for performing sensing operation and transmitting the
sensed information to the sink. Unlike most existing studies on the delay
performance of EH sensor networks, where only the energy consumption of
transmission is considered, we consider the energy costs of both sensing and
transmission. Specifically, we consider an EH sensor that monitors some status
environmental property and adopts a harvest-then-use protocol to perform
sensing and transmission. To comprehensively study the delay performance, we
consider two complementary metrics and analytically derive their statistics:
(i) update age - measuring the time taken from when information is obtained by
the sensor to when the sensed information is successfully transmitted to the
sink, i.e., how timely the updated information at the sink is, and (ii) update
cycle - measuring the time duration between two consecutive successful
transmissions, i.e., how frequently the information at the sink is updated. Our
results show that the consideration of sensing energy cost leads to an
important tradeoff between the two metrics: more frequent updates result in
less timely information available at the sink.Comment: submitted for possible journal publicatio
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