757 research outputs found
A noncommutative extended de Finetti theorem
The extended de Finetti theorem characterizes exchangeable infinite random
sequences as conditionally i.i.d. and shows that the apparently weaker
distributional symmetry of spreadability is equivalent to exchangeability. Our
main result is a noncommutative version of this theorem.
In contrast to the classical result of Ryll-Nadzewski, exchangeability turns
out to be stronger than spreadability for infinite noncommutative random
sequences. Out of our investigations emerges noncommutative conditional
independence in terms of a von Neumann algebraic structure closely related to
Popa's notion of commuting squares and K\"ummerer's generalized Bernoulli
shifts. Our main result is applicable to classical probability, quantum
probability, in particular free probability, braid group representations and
Jones subfactors.Comment: 44 page
A Remote Interface for Live Interaction with OMNeT++ Simulations
Discrete event simulators, such as OMNeT++, provide fast and convenient
methods for the assessment of algorithms and protocols, especially in the
context of wired and wireless networks. Usually, simulation parameters such as
topology and traffic patterns are predefined to observe the behaviour
reproducibly. However, for learning about the dynamic behaviour of a system, a
live interaction that allows changing parameters on the fly is very helpful.
This is especially interesting for providing interactive demonstrations at
conferences and fairs. In this paper, we present a remote interface to OMNeT++
simulations that can be used to control the simulations while visualising
real-time data merged from multiple OMNeT++ instances. We explain the software
architecture behind our framework and how it can be used to build
demonstrations on the foundation of OMNeT++.Comment: Published in: A. Foerster, A. Udugama, A. Koensgen, A. Virdis, M.
Kirsche (Eds.), Proc. of the 4th OMNeT++ Community Summit, University of
Bremen - Germany - September 7-8, 201
Noncommutative Independence in the Infinite Braid and Symmetric Group
This is an introductory paper about our recent merge of a noncommutative de
Finetti type result with representations of the infinite braid and symmetric
group which allows to derive factorization properties from symmetries. We
explain some of the main ideas of this approach and work out a constructive
procedure to use in applications. Finally we illustrate the method by applying
it to the theory of group characters
Analysis of Static and Dynamic Configurability of Existing Group Communication Systems
Active replication following the state machine replication (SMR) approach is
a way to make existing systems and services more reliable and fault-tolerant.
The additional communication overhead has a negative impact on the system's
throughput and overall request latency. Today's systems should be highly
optimized to their execution environment and usage scenario in order to remedy
the performance loss introduced by such group communication systems (GCS). In
addition to that, systems should be able to adapt to changing environmental
conditions. This report analyzes the available configuration options of three
existing GCSs. Therefore, it explains the available configuration parameters
and describes the given reconfiguration mechanisms. The found parameters are
then classified in a parameter scheme.Comment: Technical Report (38 pages
On the structure of non-commutative white noises
We consider the concepts of continuous Bernoulli systems and non-commutative
white noises. We address the question of isomorphism of continuous Bernoulli
systems and show that for large classes of quantum L{\'e}vy processes one can
make quite precise statements about the time behaviour of their moments.Comment: 17 page
Tail algebras of quantum exchangeable random variables
We show that any countably generated von Neumann algebra with specified
normal faithful state can arise as the tail algebra of a quantum exchangeable
sequence of noncommutative random variables. We also characterize the cases
when the state corresponds to a limit of convex combinations of free products
states.Comment: The revised version includes more detailed exposition in section
Reliable Wireless Multi-Hop Networks with Decentralized Slot Management: An Analysis of IEEE 802.15.4 DSME
Wireless communication is a key element in the realization of the Industrial
Internet of Things for flexible and cost-efficient monitoring and control of
industrial processes. Wireless mesh networks using IEEE 802.15.4 have a high
potential for executing monitoring and control tasks with low energy
consumption and low costs for deployment and maintenance. However, conventional
medium access techniques based on carrier sensing cannot provide the required
reliability for industrial applications. Therefore, the standard was extended
with techniques for time-slotted medium access on multiple channels. In this
paper, we present openDSME, a comprehensive implementation of the Deterministic
and Synchronous Multi-channel Extension (DSME) and propose a method for
traffic-aware and decentralized slot scheduling to enable scalable wireless
industrial networks. The performance of DSME and our implementation is
demonstrated in the OMNeT++ simulator and on a physically deployed wireless
network in the FIT/IoT-LAB. It is shown that in the given scenarios, twice as
much traffic can be delivered reliably by using DSME instead of CSMA/CA and
that the energy consumption can be reduced significantly. The paper is
completed by presenting important trade-offs for parameter selection and by
uncovering open issues of the current specification that call for further
effort in research and standardization.Comment: 27 pages, 18 figure
Noncommutative continuous Bernoulli shifts
We introduce a non-commutative extension of Tsirelson-Vershik's noises,
called (non-commutative) continuous Bernoulli shifts. These shifts encode
stochastic independence in terms of commuting squares, as they are familiar in
subfactor theory. Such shifts are, in particular, capable of producing
Arveson's product system of type I and type II. We investigate the structure of
these shifts and prove that the von Neumann algebra of a (scalar-expected)
continuous Bernoulli shift is either finite or of type III.
The role of (`classical') stationary flows for Tsirelson-Vershik's noises is
now played by cocycles of continuous Bernoulli shifts. We show that these
cocycles provide an operator algebraic notion for Levy processes. They lead, in
particular, to units and `logarithms' of units in Arveson's product systems.
Furthermore, we introduce (non-commutative) white noises, which are operator
algebraic versions of Tsirelson's `classical' noises. We give examples coming
from probability, quantum probability and from Voiculescu's theory of free
probability.
Our main result is a bijective correspondence between additive and unital
shift cocycles. For the proof of the correspondence we develop tools which are
of interest on their own: non-commutative extensions of stochastic Ito
integration, stochastic logarithms and exponentials.Comment: 87 page
Semi-Cosimplicial Objects and Spreadability
To a semi-cosimplicial object (SCO) in a category we associate a system of
partial shifts on the inductive limit. We show how to produce an SCO from an
action of the infinite braid monoid and provide examples.
In categories of (noncommutative) probability spaces SCOs correspond to
spreadable sequences of random variables, hence SCOs can be considered as the
algebraic structure underlying spreadability.Comment: 20 pages, minor changes (1.2, 2.9, 4.3) in (v3), to be published in:
Rocky Mountain Journal of Mathematic
On Lehner's `free' noncommutative analogue of De Finetti's theorem
Inspired by Lehner's results on exchangeability systems we define `weak
conditional freeness' and `conditional freeness' for stationary processes in an
operator algebraic framework of noncommutative probability. We show that these
two properties are equivalent and thus the process embeds into a von Neumann
algebraic amalgamated free product over the fixed point algebra of the
stationary process.Comment: 9 page
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