291 research outputs found
Selective Fair Scheduling over Fading Channels
Imposing fairness in resource allocation incurs a loss of system throughput,
known as the Price of Fairness (). In wireless scheduling, increases
when serving users with very poor channel quality because the scheduler wastes
resources trying to be fair. This paper proposes a novel resource allocation
framework to rigorously address this issue. We introduce selective fairness:
being fair only to selected users, and improving by momentarily blocking
the rest. We study the associated admission control problem of finding the user
selection that minimizes subject to selective fairness, and show that
this combinatorial problem can be solved efficiently if the feasibility set
satisfies a condition; in our model it suffices that the wireless channels are
stochastically dominated. Exploiting selective fairness, we design a stochastic
framework where we minimize subject to an SLA, which ensures that an
ergodic subscriber is served frequently enough. In this context, we propose an
online policy that combines the drift-plus-penalty technique with
Gradient-Based Scheduling experts, and we prove it achieves the optimal .
Simulations show that our intelligent blocking outperforms by 40 in
throughput previous approaches which satisfy the SLA by blocking low-SNR users
Black-hole spectroscopy: quasinormal modes, ringdown stability and the pseudospectrum
Black-hole spectroscopy is a powerful tool to probe the Kerr nature of
astrophysical compact objects and their environment. The observation of
multiple ringdown modes in gravitational waveforms could soon lead to
high-precision gravitational-wave spectroscopy, thus it is critical to
understand if the quasinormal mode spectrum itself is affected by astrophysical
environments, quantum corrections, and other generic modifications. In this
chapter, we will review the black-hole spectroscopy program and its challenges
regarding quasinormal mode detection, the overtone status and the recent
evidence that supports the existence of nonlinearities in the spectrum of black
holes. We will then discuss a newly introduced non-modal tool in black-hole
physics, namely the pseudospectrum; a mathematical notion that can shed light
on the spectral stability of quasinormal modes, and discuss its novel
applications in black holes and exotic horizonless compact objects. We will
show that quasinormal modes generically suffer from spectral instabilities,
explore how such phenomena can further affect black-hole spectroscopy, and
discuss potential ringdown imprints and waveform stability issues in current
and future gravitational-wave detectors.Comment: 35 pages, 24 figures, Topical review presented on the 11th Aegean
Summer School, Syros, Greece, References adde
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