14,599 research outputs found
Hybrid NOMA-TDMA for Multiple Access Channels with Non-Ideal Batteries and Circuit Cost
We consider a multiple-access channel where the users are powered from
batteries having non-negligible internal resistance. When power is drawn from
the battery, a variable fraction of the power, which is a function of the power
drawn from the battery, is lost across the internal resistance. Hence, the
power delivered to the load is less than the power drawn from the battery. The
users consume a constant power for the circuit operation during transmission
but do not consume any power when not transmitting. In this setting, we obtain
the maximum sum-rates and achievable rate regions under various cases. We show
that, unlike in the ideal battery case, the TDMA (time-division multiple
access) strategy, wherein the users transmit orthogonally in time, may not
always achieve the maximum sum-rate when the internal resistance is non-zero.
The users may need to adopt a hybrid NOMA-TDMA strategy which combines the
features of NOMA (non-orthogonal multiple access) and TDMA, wherein a set of
users are allocated fixed time windows for orthogonal single-user and
non-orthogonal joint transmissions, respectively. We also numerically show that
the maximum achievable rate regions in NOMA and TDMA strategies are contained
within the maximum achievable rate region of the hybrid NOMA-TDMA strategy
On Distributed Power Control for Uncoordinated Dual Energy Harvesting Links: Performance Bounds and Near-Optimal Policies
In this paper, we consider a point-to-point link between an energy harvesting
transmitter and receiver, where neither node has the information about the
battery state or energy availability at the other node. We consider a model
where data is successfully delivered only in slots where both nodes are active.
Energy loss occurs whenever one node turns on while the other node is in sleep
mode. In each slot, based on their own energy availability, the transmitter and
receiver need to independently decide whether or not to turn on, with the aim
of maximizing the long-term time-average throughput. We present an upper bound
on the throughput achievable by analyzing a genie-aided system that has
noncausal knowledge of the energy arrivals at both the nodes. Next, we propose
an online policy requiring an occasional one-bit feedback whose throughput is
within one bit of the upper bound, asymptotically in the battery size. In order
to further reduce the feedback required, we propose a time-dilated version of
the online policy. As the time dilation gets large, this policy does not
require any feedback and achieves the upper bound asymptotically in the battery
size. Inspired by this, we also propose a near-optimal fully uncoordinated
policy. We use Monte Carlo simulations to validate our theoretical results and
illustrate the performance of the proposed policies.Comment: 8 page
Using Battery Storage for Peak Shaving and Frequency Regulation: Joint Optimization for Superlinear Gains
We consider using a battery storage system simultaneously for peak shaving
and frequency regulation through a joint optimization framework which captures
battery degradation, operational constraints and uncertainties in customer load
and regulation signals. Under this framework, using real data we show the
electricity bill of users can be reduced by up to 15\%. Furthermore, we
demonstrate that the saving from joint optimization is often larger than the
sum of the optimal savings when the battery is used for the two individual
applications. A simple threshold real-time algorithm is proposed and achieves
this super-linear gain. Compared to prior works that focused on using battery
storage systems for single applications, our results suggest that batteries can
achieve much larger economic benefits than previously thought if they jointly
provide multiple services.Comment: To Appear in IEEE Transaction on Power System
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Unintended Effects of Residential Energy Storage on Emissions from the Electric Power System.
In many jurisdictions, policy-makers are seeking to decentralize the electric power system while also promoting deep reductions in the emission of greenhouse gases (GHG). We examine the potential roles for residential energy storage (RES), a technology thought to be at the epicenter of these twin revolutions. We model the impact of grid-connected RES operation on electricity costs and GHG emissions for households in 16 of the largest U.S. utility service territories under 3 plausible operational modes. Regardless of operation mode, RES mostly increases emissions when users seek to minimize their electricity cost. When operated with the goal of minimizing emissions, RES can reduce average household emissions by 2.2-6.4%, implying a cost equivalent of 5160 per metric ton of carbon dioxide avoided. While RES is costly compared with many other emission-control measures, tariffs that internalize the social cost of carbon would reduce emissions by 0.1-5.9% relative to cost-minimizing operation. Policy-makers should be careful about assuming that decentralization will clean the electric power system, especially if it proceeds without carbon-mindful tariff reforms
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