44 research outputs found
Optimal Paths in Large Deviations of Symmetric Reflected Brownian Motion in the Octant
We study the variational problem that arises from consideration of large
deviations for semimartingale reflected Brownian motion (SRBM) in the positive
octant. Due to the difficulty of the general problem, we consider the case in
which the SRBM has rotationally symmetric parameters. In this case, we are able
to obtain conditions under which the optimal solutions to the variational
problem are paths that are gradual (moving through faces of strictly increasing
dimension) or that spiral around the boundary of the octant. Furthermore, these
results allow us to provide an example for which it can be verified that a
spiral path is optimal. For rotationally symmetric SRBM's, our results
facilitate the simplification of computational methods for determining optimal
solutions to variational problems and give insight into large deviations
behavior of these processes
A two-stage stochastic programming model for electric substation flood mitigation prior to an imminent hurricane
We present a stochastic programming model for informing the deployment of
temporary flood mitigation measures to protect electrical substations prior to
an imminent and uncertain hurricane. The first stage captures the deployment of
a fixed number of mitigation resources, and the second stage captures grid
operation in response to a contingency. The primary objective is to minimize
expected load shed. We develop methods for simulating flooding induced by
extreme rainfall and construct two geographically realistic case studies, one
based on Tropical Storm Imelda and the other on Hurricane Harvey. Applying our
model to those case studies, we investigate the effect of the mitigation budget
on the optimal objective value and solutions. Our results highlight the
sensitivity of the optimal mitigation to the budget, a consequence of those
decisions being discrete. We additionally assess the value of having better
mitigation options and the spatial features of the optimal mitigation.Comment: 35 pages, 12 figure
Relay-Assisted User Scheduling in Wireless Networks with Hybrid-ARQ
This paper studies the problem of relay-assisted user scheduling for downlink
wireless transmission. The base station or access point employs hybrid
automatic-repeat-request (HARQ) with the assistance of a set of fixed relays to
serve a set of mobile users. By minimizing a cost function of the queue lengths
at the base station and the number of retransmissions of the head-of-line
packet for each user, the base station can schedule an appropriate user in each
time slot and an appropriate transmitter to serve it. It is shown that a
priority-index policy is optimal for a linear cost function with packets
arriving according to a Poisson process and for an increasing convex cost
function where packets must be drained from the queues at the base station.Comment: 14 pages, 5 figures, submitted to the IEEE Transactions on Vehicular
Technology in October 2008, revised in March 2009 and May 200
Two-stage models for flood mitigation of electrical substations
We compare stochastic programming and robust optimization decision models for
informing the deployment of temporary flood mitigation measures to protect
electrical substations prior to an imminent and uncertain hurricane. In our
models, the first stage captures the deployment of a fixed quantity of flood
mitigation resources, and the second stage captures the operation of a
potentially degraded power grid with the primary goal of minimizing load shed.
To model grid operation, we introduce novel adaptations of the DC and LPAC
power flow approximation models that feature relatively complete recourse by
way of a blackout indicator variable and relaxed model of power generation. We
apply our models to a pair of geographically realistic flooding case studies,
one based on Hurricane Harvey and the other on Tropical Storm Imelda. We
investigate the effect of the mitigation budget, the choice of power flow
model, and the uncertainty perspective on the optimal mitigation strategy. Our
results indicate the mitigation budget and uncertainty perspective are
impactful whereas the choice of power flow model is of little to no
consequence