7,744 research outputs found
Eigen-Based Transceivers for the MIMO Broadcast Channel with Semi-Orthogonal User Selection
This paper studies the sum rate performance of two low complexity
eigenmode-based transmission techniques for the MIMO broadcast channel,
employing greedy semi-orthogonal user selection (SUS). The first approach,
termed ZFDPC-SUS, is based on zero-forcing dirty paper coding; the second
approach, termed ZFBF-SUS, is based on zero-forcing beamforming. We first
employ new analytical methods to prove that as the number of users K grows
large, the ZFDPC-SUS approach can achieve the optimal sum rate scaling of the
MIMO broadcast channel. We also prove that the average sum rates of both
techniques converge to the average sum capacity of the MIMO broadcast channel
for large K. In addition to the asymptotic analysis, we investigate the sum
rates achieved by ZFDPC-SUS and ZFBF-SUS for finite K, and show that ZFDPC-SUS
has significant performance advantages. Our results also provide key insights
into the benefit of multiple receive antennas, and the effect of the SUS
algorithm. In particular, we show that whilst multiple receive antennas only
improves the asymptotic sum rate scaling via the second-order behavior of the
multi-user diversity gain; for finite K, the benefit can be very significant.
We also show the interesting result that the semi-orthogonality constraint
imposed by SUS, whilst facilitating a very low complexity user selection
procedure, asymptotically does not reduce the multi-user diversity gain in
either first (log K) or second-order (loglog K) terms.Comment: 35 pages, 3 figures, to appear in IEEE transactions on signal
processin
A failure of meiotic chromosome segregation in a fbh1Δ mutant correlates with persistent Rad51-DNA associations
Peer reviewedPublisher PD
Quantum Phase Imaging using Spatial Entanglement
Entangled photons have the remarkable ability to be more sensitive to signal
and less sensitive to noise than classical light. Joint photons can sample an
object collectively, resulting in faster phase accumulation and higher spatial
resolution, while common components of noise can be subtracted. Even more, they
can accomplish this while physically separate, due to the nonlocal properties
of quantum mechanics. Indeed, nearly all quantum optics experiments rely on
this separation, using individual point detectors that are scanned to measure
coincidence counts and correlations. Scanning, however, is tedious, time
consuming, and ill-suited for imaging. Moreover, the separation of beam paths
adds complexity to the system while reducing the number of photons available
for sampling, and the multiplicity of detectors does not scale well for greater
numbers of photons and higher orders of entanglement. We bypass all of these
problems here by directly imaging collinear photon pairs with an
electron-multiplying CCD camera. We show explicitly the benefits of quantum
nonlocality by engineering the spatial entanglement of the illuminating photons
and introduce a new method of correlation measurement by converting time-domain
coincidence counting into spatial-domain detection of selected pixels. We show
that classical transport-of-intensity methods are applicable in the quantum
domain and experimentally demonstrate nearly optimal (Heisenberg-limited) phase
measurement for the given quantum illumination. The methods show the power of
direct imaging and hold much potential for more general types of quantum
information processing and control
Pruning, Pushdown Exception-Flow Analysis
Statically reasoning in the presence of exceptions and about the effects of
exceptions is challenging: exception-flows are mutually determined by
traditional control-flow and points-to analyses. We tackle the challenge of
analyzing exception-flows from two angles. First, from the angle of pruning
control-flows (both normal and exceptional), we derive a pushdown framework for
an object-oriented language with full-featured exceptions. Unlike traditional
analyses, it allows precise matching of throwers to catchers. Second, from the
angle of pruning points-to information, we generalize abstract garbage
collection to object-oriented programs and enhance it with liveness analysis.
We then seamlessly weave the techniques into enhanced reachability computation,
yielding highly precise exception-flow analysis, without becoming intractable,
even for large applications. We evaluate our pruned, pushdown exception-flow
analysis, comparing it with an established analysis on large scale standard
Java benchmarks. The results show that our analysis significantly improves
analysis precision over traditional analysis within a reasonable analysis time.Comment: 14th IEEE International Working Conference on Source Code Analysis
and Manipulatio
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