392 research outputs found
Can Feedback Increase the Capacity of the Energy Harvesting Channel?
We investigate if feedback can increase the capacity of an energy harvesting
communication channel where a transmitter powered by an exogenous energy
arrival process and equipped with a finite battery communicates to a receiver
over a memoryless channel. For a simple special case where the energy arrival
process is deterministic and the channel is a BEC, we explicitly compute the
feed-forward and feedback capacities and show that feedback can strictly
increase the capacity of this channel. Building on this example, we also show
that feedback can increase the capacity when the energy arrivals are i.i.d.
known noncausally at the transmitter and the receiver
The Binary Energy Harvesting Channel with a Unit-Sized Battery
We consider a binary energy harvesting communication channel with a
finite-sized battery at the transmitter. In this model, the channel input is
constrained by the available energy at each channel use, which is driven by an
external energy harvesting process, the size of the battery, and the previous
channel inputs. We consider an abstraction where energy is harvested in binary
units and stored in a battery with the capacity of a single unit, and the
channel inputs are binary. Viewing the available energy in the battery as a
state, this is a state-dependent channel with input-dependent states, memory in
the states, and causal state information available at the transmitter only. We
find an equivalent representation for this channel based on the timings of the
symbols, and determine the capacity of the resulting equivalent timing channel
via an auxiliary random variable. We give achievable rates based on certain
selections of this auxiliary random variable which resemble lattice coding for
the timing channel. We develop upper bounds for the capacity by using a
genie-aided method, and also by quantifying the leakage of the state
information to the receiver. We show that the proposed achievable rates are
asymptotically capacity achieving for small energy harvesting rates. We extend
the results to the case of ternary channel inputs. Our achievable rates give
the capacity of the binary channel within 0.03 bits/channel use, the ternary
channel within 0.05 bits/channel use, and outperform basic Shannon strategies
that only consider instantaneous battery states, for all parameter values.Comment: Submitted to IEEE Transactions on Information Theory, August 201
On the Capacity of SWIPT Systems with a Nonlinear Energy Harvesting Circuit
In this paper, we study information-theoretic limits for simultaneous
wireless information and power transfer (SWIPT) systems employing a practical
nonlinear radio frequency (RF) energy harvesting (EH) receiver. In particular,
we consider a three-node system with one transmitter that broadcasts a common
signal to separated information decoding (ID) and EH receivers. Owing to the
nonlinearity of the EH receiver circuit, the efficiency of wireless power
transfer depends significantly on the waveform of the transmitted signal. In
this paper, we aim to answer the following fundamental question: What is the
optimal input distribution of the transmit waveform that maximizes the rate of
the ID receiver for a given required harvested power at the EH receiver? In
particular, we study the capacity of a SWIPT system impaired by additive white
Gaussian noise (AWGN) under average-power (AP) and peak-power (PP) constraints
at the transmitter and an EH constraint at the EH receiver. Using Hermite
polynomial bases, we prove that the optimal capacity-achieving input
distribution that maximizes the rate-energy region is unique and discrete with
a finite number of mass points. Furthermore, we show that the optimal input
distribution for the same problem without PP constraint is discrete whenever
the EH constraint is active and continuous zero-mean Gaussian, otherwise. Our
numerical results show that the rate-energy region is enlarged for a larger PP
constraint and that the rate loss of the considered SWIPT system compared to
the AWGN channel without EH receiver is reduced by increasing the AP budget.Comment: 7 pages, 4 figures, submitted for possible conference publicatio
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