28 research outputs found
Using Erasure Feedback for Online Timely Updating with an Energy Harvesting Sensor
A real-time status updating system is considered, in which an energy
harvesting sensor is acquiring measurements regarding some physical phenomenon
and sending them to a destination through an erasure channel. The setting is
online, in which energy arrives in units according to a Poisson process with
unit rate, with arrival times being revealed causally over time. Energy is
saved in a unit-sized battery. The sensor is notified by the destination of
whether updates were erased via feedback. Updates need to reach the destination
successfully in a timely fashion, namely, such that the long term average age
of information, defined as the time elapsed since the latest successful update
has reached the destination, is minimized. First, it is shown that the optimal
status update policy has a renewal structure: successful update times should
constitute a renewal process. Then, threshold-greedy policies are investigated:
a new update is transmitted, following a successful one, only if the age of
information grows above a certain threshold; and if it is erased, then all
subsequent update attempts are greedily scheduled whenever energy is available.
The optimal threshold-greedy policy is then analytically derived.Comment: To appear in the 2019 IEEE International Symposium on Information
Theor
Age of Information in a Multiple Access Channel with Heterogeneous Traffic and an Energy Harvesting Node
Age of Information (AoI) is a newly appeared concept and metric to
characterize the freshness of data. In this work, we study the delay and AoI in
a multiple access channel (MAC) with two source nodes transmitting different
types of data to a common destination. The first node is grid-connected and its
data packets arrive in a bursty manner, and at each time slot it transmits one
packet with some probability. Another energy harvesting (EH) sensor node
generates a new status update with a certain probability whenever it is
charged. We derive the delay of the grid-connected node and the AoI of the EH
sensor as functions of different parameters in the system. The results show
that the mutual interference has a non-trivial impact on the delay and age
performance of the two nodes.Comment: 2nd Age of Information Workshop, IEEE INFOCOM Workshops 201
Online Timely Status Updates with Erasures for Energy Harvesting Sensors
An energy harvesting sensor that is sending status updates to a destination
through an erasure channel is considered, in which transmissions are prone to
being erased with some probability , independently from other transmissions.
The sensor, however, is unaware of erasure events due to lack of feedback from
the destination. Energy expenditure is normalized in the sense that one
transmission consumes one unit of energy. The sensor is equipped with a
unit-sized battery to save its incoming energy, which arrives according to a
Poisson process of unit rate. The setting is online, in which energy arrival
times are only revealed causally after being harvested, and the goal is to
design transmission times such that the long term average age of information
(AoI), defined as the time elapsed since the latest update has reached the
destination successfully, is minimized. The optimal status update policy is
first shown to have a renewal structure, in which the time instants at which
the destination receives an update successfully constitute a renewal process.
Then, for , the optimal renewal policy is shown to have a
threshold structure, in which a new status update is transmitted only if the
AoI grows above a certain threshold, that is shown to be a decreasing function
of . While for , the optimal renewal policy is shown to be
greedy, in which a new status update is transmitted whenever energy is
available.Comment: Appeared at Allerton 201
Optimal Transmission Policies for Energy Harvesting Age of Information Systems with Battery Recovery
We consider an energy harvesting information update system where a sensor is
allowed to choose a transmission mode for each transmission, where each mode
consists of a transmission power-error pair. We also incorporate the battery
phenomenon called battery recovery effect where a battery replenishes the
deliverable energy if kept idle after discharge. For an energy-limited age of
information (AoI) system, this phenomenon gives rise to the interesting
trade-off of recovering energy after transmissions, at the cost of increased
AoI. Considering two metrics, namely peak-age hitting probability and average
age as the worst-case and average performance indicators, respectively, we
propose a framework that formulates the optimal transmission scheme selection
problem as a Markov Decision Process (MDP). We show that the gains obtained by
considering both battery dynamics and adjustable transmission power together
are much higher than the sum gain achieved if they are considered separately.
We also propose a simple methodology to optimize the system performance taking
into account worst-case and average performances jointly.Comment: Submitted for publicatio
On Age and Value of Information in Status Update Systems
Motivated by the inherent value of packets arising in many cyber-physical
applications (e.g., due to precision of the information content or an alarm
message), we consider status update systems with update packets carrying values
as well as their generation time stamps. Once generated, a status update packet
has a random initial value and a deterministic deadline after which it is not
useful (ultimate staleness). In our model, value of a packet decreases in time
(even after reception) starting from its generation to ultimate staleness when
it vanishes. The value of information (VoI) at the receiver is additive in that
the VoI is the sum of the current values of all packets held by the receiver.
We investigate various queuing disciplines under potential dependence between
value and service time and provide closed form expressions for average VoI at
the receiver. Numerical results illustrate the average VoI for different
scenarios and the contrast between average age of information (AoI) and average
VoI
Who Should Google Scholar Update More Often?
We consider a resource-constrained updater, such as Google Scholar, which
wishes to update the citation records of a group of researchers, who have
different mean citation rates (and optionally, different importance
coefficients), in such a way to keep the overall citation index as up to date
as possible. The updater is resource-constrained and cannot update citations of
all researchers all the time. In particular, it is subject to a total update
rate constraint that it needs to distribute among individual researchers. We
use a metric similar to the age of information: the long-term average
difference between the actual citation numbers and the citation numbers
according to the latest updates. We show that, in order to minimize this
difference metric, the updater should allocate its total update capacity to
researchers proportional to the of their mean citation rates.
That is, more prolific researchers should be updated more often, but there are
diminishing returns due to the concavity of the square root function. More
generally, our paper addresses the problem of optimal operation of a
resource-constrained sampler that wishes to track multiple independent counting
processes in a way that is as up to date as possible
Partial Updates: Losing Information for Freshness
We consider an information updating system where a source produces updates as
requested by a transmitter. The transmitter further processes these updates in
order to generate , which have smaller information compared
to the original updates, to be sent to a receiver. We study the problem of
generating partial updates, and finding their corresponding real-valued
codeword lengths, in order to minimize the average age experienced by the
receiver, while maintaining a desired level of mutual information between the
original and partial updates. This problem is NP hard. We relax the problem and
develop an alternating minimization based iterative algorithm that generates a
pmf for the partial updates, and the corresponding age-optimal real-valued
codeword length for each update. We observe that there is a tradeoff between
the attained average age and the mutual information between the original and
partial updates
Timely Group Updating
We consider two closely related problems: anomaly detection in sensor
networks and testing for infections in human populations. In both problems, we
have nodes (sensors, humans), and each node exhibits an event of interest
(anomaly, infection) with probability . We want to keep track of the
anomaly/infection status of all nodes at a central location. We develop a
scheme, akin to group testing, which updates a central
location about the status of each member of the population by appropriately
grouping their individual status. Unlike group testing, which uses the expected
number of tests as a metric, in group updating, we use the expected age of
information at the central location as a metric. We determine the optimal group
size to minimize the age of information. We show that, when is small, the
proposed group updating policy yields smaller age compared to a sequential
updating policy
ACP: An End-to-End Transport Protocol for Delivering Fresh Updates in the Internet-of-Things
The next generation of networks must support billions of connected devices in
the Internet-of-Things (IoT). To support IoT applications, sources sense and
send their measurement updates over the Internet to a monitor (control station)
for real-time monitoring and actuation. Ideally, these updates would be
delivered at a high rate, only constrained by the sensing rate supported by the
sources. However, given network constraints, such a rate may lead to delays in
delivery of updates at the monitor that make the freshest update at the monitor
unacceptably old for the application.
We propose a novel transport layer protocol, namely the Age Control Protocol
(ACP), that enables timely delivery of such updates to monitors, in a
network-transparent manner. ACP allows the source to adapt its rate of updates
to dynamic network conditions such that the average age of the sensed
information at the monitor is minimized. We detail the protocol and the
proposed control algorithm. We demonstrate its efficacy using extensive
simulations and real-world experiments, which have a source send its updates
over the Internet to a monitor on another continent.Comment: This is an extended version of paper accepted in the Proceedings of
20th IEEE International Conference on the World of Wireless, Mobile and
Multimedia Networks (IEEE WoWMoM 2019). A short version of this work is
published as a poster in ACM MobiCom 2018 proceedings. The poster proceedings
are available at: https://dl.acm.org/citation.cfm?id=326774
Active Status Update Packet Drop Control in an Energy Harvesting Node
This paper considers an energy harvesting sensor node with battery size
that recharges its battery through an incremental energy harvesting
process and receives updates from a single information source in slotted time.
The node actively decides to power down (OFF) or up (ON) the communication
circuitry for a portion of its operation time in order to maintain energy
efficiency. Update packets arriving in ON (OFF) periods are received
(discarded). A deterministic energy cost per time is paid during ON periods.
The power down decision can be in partial or full nature, yielding various
options for deciding ON-OFF intervals. We develop age-threshold based power
ON-OFF schemes to minimize age of information at the node subject to energy
harvesting constraints with partial and full power down options for
and cases