5,654 research outputs found
The Pros and Cons of Compressive Sensing for Wideband Signal Acquisition: Noise Folding vs. Dynamic Range
Compressive sensing (CS) exploits the sparsity present in many signals to
reduce the number of measurements needed for digital acquisition. With this
reduction would come, in theory, commensurate reductions in the size, weight,
power consumption, and/or monetary cost of both signal sensors and any
associated communication links. This paper examines the use of CS in the design
of a wideband radio receiver in a noisy environment. We formulate the problem
statement for such a receiver and establish a reasonable set of requirements
that a receiver should meet to be practically useful. We then evaluate the
performance of a CS-based receiver in two ways: via a theoretical analysis of
its expected performance, with a particular emphasis on noise and dynamic
range, and via simulations that compare the CS receiver against the performance
expected from a conventional implementation. On the one hand, we show that
CS-based systems that aim to reduce the number of acquired measurements are
somewhat sensitive to signal noise, exhibiting a 3dB SNR loss per octave of
subsampling, which parallels the classic noise-folding phenomenon. On the other
hand, we demonstrate that since they sample at a lower rate, CS-based systems
can potentially attain a significantly larger dynamic range. Hence, we conclude
that while a CS-based system has inherent limitations that do impose some
restrictions on its potential applications, it also has attributes that make it
highly desirable in a number of important practical settings
Linking Unit Tests and Properties
QuickCheck allows us to verify software against particular proper- ties. A property can be regarded as an abstraction over many unit tests. QuickCheck uses generated random input data to test such properties. If a counterexample is found, it becomes immediately clear what we have tested. This is not the case when all tests pass, since we do not (and shall not) see the actual generated test cases. How can we be sure about what is tested? QuickCheck has the ability to gather statistics about the test cases, which is insightful. But still it does not tell us whether the particular unit test scenarios we have in mind are included. For this reason, we have developed a tool that can answer this question. It checks if a given unit test can be generated by a property, making it easier to judge the property’s quality. We have applied our tool to an industrial use case of testing the AUTOSAR basic software modules and shows that it can handle complex models and large unit tests
Tactics for Reasoning modulo AC in Coq
We present a set of tools for rewriting modulo associativity and
commutativity (AC) in Coq, solving a long-standing practical problem. We use
two building blocks: first, an extensible reflexive decision procedure for
equality modulo AC; second, an OCaml plug-in for pattern matching modulo AC. We
handle associative only operations, neutral elements, uninterpreted function
symbols, and user-defined equivalence relations. By relying on type-classes for
the reification phase, we can infer these properties automatically, so that
end-users do not need to specify which operation is A or AC, or which constant
is a neutral element.Comment: 16
Adapting to the Shifting Intent of Search Queries
Search engines today present results that are often oblivious to abrupt
shifts in intent. For example, the query `independence day' usually refers to a
US holiday, but the intent of this query abruptly changed during the release of
a major film by that name. While no studies exactly quantify the magnitude of
intent-shifting traffic, studies suggest that news events, seasonal topics, pop
culture, etc account for 50% of all search queries. This paper shows that the
signals a search engine receives can be used to both determine that a shift in
intent has happened, as well as find a result that is now more relevant. We
present a meta-algorithm that marries a classifier with a bandit algorithm to
achieve regret that depends logarithmically on the number of query impressions,
under certain assumptions. We provide strong evidence that this regret is close
to the best achievable. Finally, via a series of experiments, we demonstrate
that our algorithm outperforms prior approaches, particularly as the amount of
intent-shifting traffic increases.Comment: This is the full version of the paper in NIPS'0
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