805 research outputs found
Link Delay Estimation via Expander Graphs
One of the purposes of network tomography is to infer the status of
parameters (e.g., delay) for the links inside a network through end-to-end
probing between (external) boundary nodes along predetermined routes. In this
work, we apply concepts from compressed sensing and expander graphs to the
delay estimation problem. We first show that a relative majority of network
topologies are not expanders for existing expansion criteria. Motivated by this
challenge, we then relax such criteria, enabling us to acquire simulation
evidence that link delays can be estimated for 30% more networks. That is, our
relaxation expands the list of identifiable networks with bounded estimation
error by 30%. We conduct a simulation performance analysis of delay estimation
and congestion detection on the basis of l1 minimization, demonstrating that
accurate estimation is feasible for an increasing proportion of networks
CLEX: Yet Another Supercomputer Architecture?
We propose the CLEX supercomputer topology and routing scheme. We prove that
CLEX can utilize a constant fraction of the total bandwidth for point-to-point
communication, at delays proportional to the sum of the number of intermediate
hops and the maximum physical distance between any two nodes. Moreover, %
applying an asymmetric bandwidth assignment to the links, all-to-all
communication can be realized -optimally both with regard to
bandwidth and delays. This is achieved at node degrees of ,
for an arbitrary small constant . In contrast, these
results are impossible in any network featuring constant or polylogarithmic
node degrees. Through simulation, we assess the benefits of an implementation
of the proposed communication strategy. Our results indicate that, for a
million processors, CLEX can increase bandwidth utilization and reduce average
routing path length by at least factors respectively in comparison to
a torus network. Furthermore, the CLEX communication scheme features several
other properties, such as deadlock-freedom, inherent fault-tolerance, and
canonical partition into smaller subsystems
Convex recovery from interferometric measurements
This note formulates a deterministic recovery result for vectors from
quadratic measurements of the form for some
left-invertible . Recovery is exact, or stable in the noisy case, when the
couples are chosen as edges of a well-connected graph. One possible way
of obtaining the solution is as a feasible point of a simple semidefinite
program. Furthermore, we show how the proportionality constant in the error
estimate depends on the spectral gap of a data-weighted graph Laplacian. Such
quadratic measurements have found applications in phase retrieval, angular
synchronization, and more recently interferometric waveform inversion
Analysis and design of a capsule landing system and surface vehicle control system for Mars exploration
Problems related to the design and control of a mobile planetary vehicle to implement a systematic plan for the exploration of Mars are reported. Problem areas include: vehicle configuration, control, dynamics, systems and propulsion; systems analysis, terrain modeling and path selection; and chemical analysis of specimens. These tasks are summarized: vehicle model design, mathematical model of vehicle dynamics, experimental vehicle dynamics, obstacle negotiation, electrochemical controls, remote control, collapsibility and deployment, construction of a wheel tester, wheel analysis, payload design, system design optimization, effect of design assumptions, accessory optimal design, on-board computer subsystem, laser range measurement, discrete obstacle detection, obstacle detection systems, terrain modeling, path selection system simulation and evaluation, gas chromatograph/mass spectrometer system concepts, and chromatograph model evaluation and improvement
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