57 research outputs found
Broadcasting with an Energy Harvesting Rechargeable Transmitter
In this paper, we investigate the transmission completion time minimization
problem in a two-user additive white Gaussian noise (AWGN) broadcast channel,
where the transmitter is able to harvest energy from the nature, using a
rechargeable battery. The harvested energy is modeled to arrive at the
transmitter randomly during the course of transmissions. The transmitter has a
fixed number of packets to be delivered to each receiver. Our goal is to
minimize the time by which all of the packets for both users are delivered to
their respective destinations. To this end, we optimize the transmit powers and
transmission rates intended for both users. We first analyze the structural
properties of the optimal transmission policy. We prove that the optimal total
transmit power has the same structure as the optimal single-user transmit
power. We also prove that there exists a cut-off power level for the stronger
user. If the optimal total transmit power is lower than this cut-off level, all
transmit power is allocated to the stronger user, and when the optimal total
transmit power is larger than this cut-off level, all transmit power above this
level is allocated to the weaker user. Based on these structural properties of
the optimal policy, we propose an algorithm that yields the globally optimal
off-line scheduling policy. Our algorithm is based on the idea of reducing the
two-user broadcast channel problem into a single-user problem as much as
possible.Comment: Submitted to IEEE Transactions on Wireless Communications, October
201
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
Energy Harvesting Networks with General Utility Functions: Near Optimal Online Policies
We consider online scheduling policies for single-user energy harvesting
communication systems, where the goal is to characterize online policies that
maximize the long term average utility, for some general concave and
monotonically increasing utility function. In our setting, the transmitter
relies on energy harvested from nature to send its messages to the receiver,
and is equipped with a finite-sized battery to store its energy. Energy packets
are independent and identically distributed (i.i.d.) over time slots, and are
revealed causally to the transmitter. Only the average arrival rate is known a
priori. We first characterize the optimal solution for the case of Bernoulli
arrivals. Then, for general i.i.d. arrivals, we first show that fixed fraction
policies [Shaviv-Ozgur] are within a constant multiplicative gap from the
optimal solution for all energy arrivals and battery sizes. We then derive a
set of sufficient conditions on the utility function to guarantee that fixed
fraction policies are within a constant additive gap as well from the optimal
solution.Comment: To appear in the 2017 IEEE International Symposium on Information
Theory. arXiv admin note: text overlap with arXiv:1705.1030
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
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