27,141 research outputs found
Packet loss characteristics for M/G/1/N queueing systems
In this contribution we investigate higher-order loss characteristics for M/G/1/N queueing systems. We focus on the lengths of the loss and non-loss periods as well as on the number of arrivals during these periods. For the analysis, we extend the Markovian state of the queueing system with the time and number of admitted arrivals since the instant where the last loss occurred. By combining transform and matrix techniques, expressions for the various moments of these loss characteristics are found. The approach also yields expressions for the loss probability and the conditional loss probability. Some numerical examples then illustrate our results
Selection and Estimation for Mixed Graphical Models
We consider the problem of estimating the parameters in a pairwise graphical
model in which the distribution of each node, conditioned on the others, may
have a different parametric form. In particular, we assume that each node's
conditional distribution is in the exponential family. We identify restrictions
on the parameter space required for the existence of a well-defined joint
density, and establish the consistency of the neighbourhood selection approach
for graph reconstruction in high dimensions when the true underlying graph is
sparse. Motivated by our theoretical results, we investigate the selection of
edges between nodes whose conditional distributions take different parametric
forms, and show that efficiency can be gained if edge estimates obtained from
the regressions of particular nodes are used to reconstruct the graph. These
results are illustrated with examples of Gaussian, Bernoulli, Poisson and
exponential distributions. Our theoretical findings are corroborated by
evidence from simulation studies
Implementing Loss Distribution Approach for Operational Risk
To quantify the operational risk capital charge under the current regulatory
framework for banking supervision, referred to as Basel II, many banks adopt
the Loss Distribution Approach. There are many modeling issues that should be
resolved to use the approach in practice. In this paper we review the
quantitative methods suggested in literature for implementation of the
approach. In particular, the use of the Bayesian inference method that allows
to take expert judgement and parameter uncertainty into account, modeling
dependence and inclusion of insurance are discussed
Estimating the Propagation of Interdependent Cascading Outages with Multi-Type Branching Processes
In this paper, the multi-type branching process is applied to describe the
statistics and interdependencies of line outages, the load shed, and isolated
buses. The offspring mean matrix of the multi-type branching process is
estimated by the Expectation Maximization (EM) algorithm and can quantify the
extent of outage propagation. The joint distribution of two types of outages is
estimated by the multi-type branching process via the Lagrange-Good inversion.
The proposed model is tested with data generated by the AC OPA cascading
simulations on the IEEE 118-bus system. The largest eigenvalues of the
offspring mean matrix indicate that the system is closer to criticality when
considering the interdependence of different types of outages. Compared with
empirically estimating the joint distribution of the total outages, good
estimate is obtained by using the multitype branching process with a much
smaller number of cascades, thus greatly improving the efficiency. It is shown
that the multitype branching process can effectively predict the distribution
of the load shed and isolated buses and their conditional largest possible
total outages even when there are no data of them.Comment: Accepted by IEEE Transactions on Power System
HetHetNets: Heterogeneous Traffic Distribution in Heterogeneous Wireless Cellular Networks
A recent approach in modeling and analysis of the supply and demand in
heterogeneous wireless cellular networks has been the use of two independent
Poisson point processes (PPPs) for the locations of base stations (BSs) and
user equipments (UEs). This popular approach has two major shortcomings. First,
although the PPP model may be a fitting one for the BS locations, it is less
adequate for the UE locations mainly due to the fact that the model is not
adjustable (tunable) to represent the severity of the heterogeneity
(non-uniformity) in the UE locations. Besides, the independence assumption
between the two PPPs does not capture the often-observed correlation between
the UE and BS locations.
This paper presents a novel heterogeneous spatial traffic modeling which
allows statistical adjustment. Simple and non-parameterized, yet sufficiently
accurate, measures for capturing the traffic characteristics in space are
introduced. Only two statistical parameters related to the UE distribution,
namely, the coefficient of variation (the normalized second-moment), of an
appropriately defined inter-UE distance measure, and correlation coefficient
(the normalized cross-moment) between UE and BS locations, are adjusted to
control the degree of heterogeneity and the bias towards the BS locations,
respectively. This model is used in heterogeneous wireless cellular networks
(HetNets) to demonstrate the impact of heterogeneous and BS-correlated traffic
on the network performance. This network is called HetHetNet since it has two
types of heterogeneity: heterogeneity in the infrastructure (supply), and
heterogeneity in the spatial traffic distribution (demand).Comment: JSA
Statistical properties of determinantal point processes in high-dimensional Euclidean spaces
The goal of this paper is to quantitatively describe some statistical
properties of higher-dimensional determinantal point processes with a primary
focus on the nearest-neighbor distribution functions. Toward this end, we
express these functions as determinants of matrices and then
extrapolate to . This formulation allows for a quick and accurate
numerical evaluation of these quantities for point processes in Euclidean
spaces of dimension . We also implement an algorithm due to Hough \emph{et.
al.} \cite{hough2006dpa} for generating configurations of determinantal point
processes in arbitrary Euclidean spaces, and we utilize this algorithm in
conjunction with the aforementioned numerical results to characterize the
statistical properties of what we call the Fermi-sphere point process for to 4. This homogeneous, isotropic determinantal point process, discussed
also in a companion paper \cite{ToScZa08}, is the high-dimensional
generalization of the distribution of eigenvalues on the unit circle of a
random matrix from the circular unitary ensemble (CUE). In addition to the
nearest-neighbor probability distribution, we are able to calculate Voronoi
cells and nearest-neighbor extrema statistics for the Fermi-sphere point
process and discuss these as the dimension is varied. The results in this
paper accompany and complement analytical properties of higher-dimensional
determinantal point processes developed in \cite{ToScZa08}.Comment: 42 pages, 17 figure
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