1,393 research outputs found
Analysis Framework for Opportunistic Spectrum OFDMA and its Application to the IEEE 802.22 Standard
We present an analytical model that enables throughput evaluation of
Opportunistic Spectrum Orthogonal Frequency Division Multiple Access (OS-OFDMA)
networks. The core feature of the model, based on a discrete time Markov chain,
is the consideration of different channel and subchannel allocation strategies
under different Primary and Secondary user types, traffic and priority levels.
The analytical model also assesses the impact of different spectrum sensing
strategies on the throughput of OS-OFDMA network. The analysis applies to the
IEEE 802.22 standard, to evaluate the impact of two-stage spectrum sensing
strategy and varying temporal activity of wireless microphones on the IEEE
802.22 throughput. Our study suggests that OS-OFDMA with subchannel notching
and channel bonding could provide almost ten times higher throughput compared
with the design without those options, when the activity and density of
wireless microphones is very high. Furthermore, we confirm that OS-OFDMA
implementation without subchannel notching, used in the IEEE 802.22, is able to
support real-time and non-real-time quality of service classes, provided that
wireless microphones temporal activity is moderate (with approximately one
wireless microphone per 3,000 inhabitants with light urban population density
and short duty cycles). Finally, two-stage spectrum sensing option improves
OS-OFDMA throughput, provided that the length of spectrum sensing at every
stage is optimized using our model
Packet Relaying Control in Sensing-based Spectrum Sharing Systems
Cognitive relaying has been introduced for opportunistic spectrum access
systems by which a secondary node forwards primary packets whenever the primary
link faces an outage condition. For spectrum sharing systems, cognitive
relaying is parametrized by an interference power constraint level imposed on
the transmit power of the secondary user. For sensing-based spectrum sharing,
the probability of detection is also involved in packet relaying control. This
paper considers the choice of these two parameters so as to maximize the
secondary nodes' throughput under certain constraints. The analysis leads to a
Markov decision process using dynamic programming approach. The problem is
solved using value iteration. Finally, the structural properties of the
resulting optimal control are highlighted
Automatic detection of alarm sounds in a noisy hospital environment using model and non-model based approaches
Article publicat sense revisió per parells a ArxivIn the noisy acoustic environment of a Neonatal Intensive Care Unit (NICU) there is a variety of alarms, which are frequently triggered by the biomedical equipment. In this paper different approaches for automatic detection of those sound alarms are presented and compared: 1) a non-model-based approach that employs signal processing techniques; 2) a model-based approach based on neural networks; and 3) an approach that combines both non-model and model-based approaches. The performance of the developed detection systems that follow each of those approaches is assessed, analysed and compared both at the frame level and at the event level by using an audio database recorded in a real-world hospital environment.Preprin
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