27,510 research outputs found
Timely Updates over an Erasure Channel
Using an age of information (AoI) metric, we examine the transmission of
coded updates through a binary erasure channel to a monitor/receiver. We start
by deriving the average status update age of an infinite incremental redundancy
(IIR) system in which the transmission of a k-symbol update continuesuntil k
symbols are received. This system is then compared to a fixed redundancy (FR)
system in which each update is transmitted as an n symbol packet and the packet
is successfully received if and only if at least k symbols are received. If
fewer than k symbols are received, the update is discarded. Unlike the IIR
system, the FR system requires no feedback from the receiver. For a single
monitor system, we show that tuning the redundancy to the symbol erasure rate
enables the FR system to perform as well as the IIR system. As the number of
monitors is increased, the FR system outperforms the IIR system that guarantees
delivery of all updates to all monitors
Analyzing and Modeling the Performance of the HemeLB Lattice-Boltzmann Simulation Environment
We investigate the performance of the HemeLB lattice-Boltzmann simulator for
cerebrovascular blood flow, aimed at providing timely and clinically relevant
assistance to neurosurgeons. HemeLB is optimised for sparse geometries,
supports interactive use, and scales well to 32,768 cores for problems with ~81
million lattice sites. We obtain a maximum performance of 29.5 billion site
updates per second, with only an 11% slowdown for highly sparse problems (5%
fluid fraction). We present steering and visualisation performance measurements
and provide a model which allows users to predict the performance, thereby
determining how to run simulations with maximum accuracy within time
constraints.Comment: Accepted by the Journal of Computational Science. 33 pages, 16
figures, 7 table
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