22 research outputs found
Universally Near Optimal Online Power Control for Energy Harvesting Nodes
We consider online power control for an energy harvesting system with random
i.i.d. energy arrivals and a finite size battery. We propose a simple online
power control policy for this channel that requires minimal information
regarding the distribution of the energy arrivals and prove that it is
universally near-optimal for all parameter values. In particular, the policy
depends on the distribution of the energy arrival process only through its mean
and it achieves the optimal long-term average throughput of the channel within
both constant additive and multiplicative gaps. Existing heuristics for online
power control fail to achieve such universal performance. This result also
allows us to approximate the long-term average throughput of the system with a
simple formula, which sheds some light on the qualitative behavior of the
throughput, namely how it depends on the distribution of the energy arrivals
and the size of the battery.Comment: the proposed scheme is shown to be optimal both within constant
additive and multiplicative gaps; submitted to Journal on Selected Areas in
Communications - Series on Green Communications and Networking (Issue 3);
revised following reviewers' comment
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
Energy Harvesting Communication System with SOC-Dependent Energy Storage Losses
The popularity of Energy Harvesting Devices (EHDs) has grown in the past few
years, thanks to their capability of prolonging the network lifetime. In
reality, EHDs are affected by several inefficiencies, e.g., energy leakage,
battery degradation or storage losses. In this work we consider an energy
harvesting transmitter with storage inefficiencies. In particular, we assume
that when new energy has to be stored in the battery, part of this is wasted
and the losses depend upon the current state of charge of the device. This is a
practical realistic assumption, e.g., for a capacitor, that changes the
structure of the optimal transmission policy. We analyze the throughput
maximization problem with a dynamic programming approach and prove that, given
the battery status and the channel gain, the optimal transmission policy is
deterministic. We derive numerical results for the energy losses in a capacitor
and show the presence of a \emph{loop effect} that degrades the system
performance if the optimal policy is not considered.Comment: In Proc. IEEE Twelfth Int. Symposium on Wireless Communication
Systems (ISWCS), pp. 406-410, Aug. 201
On Optimal Power Control for Energy Harvesting Communications with Lookahead
Consider the problem of power control for an energy harvesting communication
system, where the transmitter is equipped with a finite-sized rechargeable
battery and is able to look ahead to observe a fixed number of future energy
arrivals. An implicit characterization of the maximum average throughput over
an additive white Gaussian noise channel and the associated optimal power
control policy is provided via the Bellman equation under the assumption that
the energy arrival process is stationary and memoryless. A more explicit
characterization is obtained for the case of Bernoulli energy arrivals by means
of asymptotically tight upper and lower bounds on both the maximum average
throughput and the optimal power control policy. Apart from their pivotal role
in deriving the desired analytical results, such bounds are highly valuable
from a numerical perspective as they can be efficiently computed using convex
optimization solvers.Comment: 25 pages, 5 figure
Maximum entropy based analysis of a DS/SSMA diversity system
D.Ing.This thesis sets out to propose and analyze a cellular Direct Sequence Spread Spectrum Multiple Access (DSjSSMA) system for the Indoor Wireless Communication (IWC) Nakagami fading channel. The up- and downlink of the system implement Differential Phase Shift Keying (DPSK) and Coherent Phase Shift Keying (CPSK) as modulation schemes respectively, and are analyzed using Maximum Entropy (MaxEnt) principles due to its reliability and accuracy. As a means to enhance system capacity and performance, different forms of diversity are investigated; for the up- and downlink, respectively, RAKE reception and Maximum Ratio Combining (MRC) diversity together with Forward Error Control (FEC) coding are assumed. Further, the validity of the Gaussian Assumption (GA) is quantified and investigated under fading and non-fading conditions by calculating the missing information, using Minimum Relative Entropy (MRE) principles between the Inter- User Interference (IUI) distribution and a Gaussian distribution of equal variance