1,156 research outputs found
Efficient parallel processing with optical interconnections
With the advances in VLSI technology, it is now possible to build chips which can each contain thousands of processors. The efficiency of such chips in executing parallel algorithms heavily depends on the interconnection topology of the processors. It is not possible to build a fully interconnected network of processors with constant fan-in/fan-out using electrical interconnections. Free space optics is a remedy to this limitation. Qualities exclusive to the optical medium are its ability to be directed for propagation in free space and the property that optical channels can cross in space without any interference. In this thesis, we present an electro-optical interconnected architecture named Optical Reconfigurable Mesh (ORM). It is based on an existing optical model of computation. There are two layers in the architecture. The processing layer is a reconfigurable mesh and the deflecting layer contains optical devices to deflect light beams. ORM provides three types of communication mechanisms. The first is for arbitrary planar connections among sets of locally connected processors using the reconfigurable mesh. The second is for arbitrary connections among N of the processors using the electrical buses on the processing layer and N2 fixed passive deflecting units on the deflection layer. The third is for arbitrary connections among any of the N2 processors using the N2 mechanically reconfigurable deflectors in the deflection layer. The third type of communication mechanisms is significantly slower than the other two. Therefore, it is desirable to avoid reconfiguring this type of communication during the execution of the algorithms. Instead, the optical reconfiguration can be done before the execution of each algorithm begins. Determining a right configuration that would be suitable for the entire configuration of a task execution is studied in this thesis. The basic data movements for each of the mechanisms are studied. Finally, to show the power of ORM, we use all three types of communication mechanisms in the first O(logN) time algorithm for finding the convex hulls of all figures in an N x N binary image presented in this thesis
Distributed Adaptive Fault-Tolerant Control of Uncertain Multi-Agent Systems
This paper presents an adaptive fault-tolerant control (FTC) scheme for a
class of nonlinear uncertain multi-agent systems. A local FTC scheme is
designed for each agent using local measurements and suitable information
exchanged between neighboring agents. Each local FTC scheme consists of a fault
diagnosis module and a reconfigurable controller module comprised of a baseline
controller and two adaptive fault-tolerant controllers activated after fault
detection and after fault isolation, respectively. Under certain assumptions,
the closed-loop system's stability and leader-follower consensus properties are
rigorously established under different modes of the FTC system, including the
time-period before possible fault detection, between fault detection and
possible isolation, and after fault isolation
Quantum Experiments and Graphs: Multiparty States as coherent superpositions of Perfect Matchings
We show a surprising link between experimental setups to realize
high-dimensional multipartite quantum states and Graph Theory. In these setups,
the paths of photons are identified such that the photon-source information is
never created. We find that each of these setups corresponds to an undirected
graph, and every undirected graph corresponds to an experimental setup. Every
term in the emerging quantum superposition corresponds to a perfect matching in
the graph. Calculating the final quantum state is in the complexity class
#P-complete, thus cannot be done efficiently. To strengthen the link further,
theorems from Graph Theory -- such as Hall's marriage problem -- are rephrased
in the language of pair creation in quantum experiments. We show explicitly how
this link allows to answer questions about quantum experiments (such as which
classes of entangled states can be created) with graph theoretical methods, and
potentially simulate properties of Graphs and Networks with quantum experiments
(such as critical exponents and phase transitions).Comment: 6+5 pages, 4+7 figure
Demand-Aware Network Design with Steiner Nodes and a Connection to Virtual Network Embedding
Emerging optical and virtualization technologies enable the design of more
flexible and demand-aware networked systems, in which resources can be
optimized toward the actual workload they serve. For example, in a demand-aware
datacenter network, frequently communicating nodes (e.g., two virtual machines
or a pair of racks in a datacenter) can be placed topologically closer,
reducing communication costs and hence improving the overall network
performance.
This paper revisits the bounded-degree network design problem underlying such
demand-aware networks. Namely, given a distribution over communicating server
pairs, we want to design a network with bounded maximum degree that minimizes
expected communication distance. In addition to this known problem, we
introduce and study a variant where we allow Steiner nodes (i.e., additional
routers) to be added to augment the network.
We improve the understanding of this problem domain in several ways. First,
we shed light on the complexity and hardness of the aforementioned problems,
and study a connection between them and the virtual networking embedding
problem. We then provide a constant-factor approximation algorithm for the
Steiner node version of the problem, and use it to improve over prior
state-of-the-art algorithms for the original version of the problem with sparse
communication distributions. Finally, we investigate various heuristic
approaches to bounded-degree network design problem, in particular providing a
reliable heuristic algorithm with good experimental performance.
We report on an extensive empirical evaluation, using several real-world
traffic traces from datacenters, and find that our approach results in improved
demand-aware network designs
On the Complexity of Parameterized Reachability in Reconfigurable Broadcast Networks
We investigate the impact of dynamic topology reconfiguration on the complexity of verification problems for models of protocols with broadcast communication. We first consider reachability of a configuration with a given set of control states and show that parameterized verification is decidable with polynomial time complexity. We then move to richer queries and show how the complexity changes when considering properties with negation or cardinality constraints
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