Wireless sensor networks (WSNs) provide the potential for effective and cost efficient remote and ubiquitous health care monitoring as they are easy to install, robust and secure. By their nature, these WSNs use async...
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ISBN:
(纸本)9780889866676
Wireless sensor networks (WSNs) provide the potential for effective and cost efficient remote and ubiquitous health care monitoring as they are easy to install, robust and secure. By their nature, these WSNs use asynchronous communications to reduce transmission power and improve efficiency. However this form of communication creates potential issues with the synchronization of the data received and stored by the telehealth system that they provide data to. This problem can be exacerbated if multiple sensors are employed, which is very likely due to the relatively low cost of such devices as well as the intended applications of these WSNs. Time synchronization is one essential component to maintain in the security of data transmission through wireless sensor networks (WSN). Each individual node in a WSN contains a crystal clock. Although the natural frequency of each crystal clock remains relatively constant, the quality of the crystal and environmental factors such as temperature cause the frequency to drift over time. In order to ensure that each node maintains and broadcasts the same global time within the micro-second range, a time synchronization protocol must be implemented. Several protocols have been developed;however, none has been developed with security in mind. It is easy for a system error or even a malicious third party to compromise a node, causing faulty time sync messages to be sent into the network. The Flooding Time Synchronization Protocol (FTSP) [5] is proposed to ensure time sychrony in the telehealh WSN. The FTSP is made up of several component modules written in nesC and has been implemented in the TinyOS [1] environment. TinyOS is an open source operating system developed specifically for network systems. In order to investigate the effects of injecting bad time synchronization messages into a WSN implemented with the FTSP, one or two nodes in a testbed of Telos motes (a mote being a remote wireless sensor) have been programmed to send fault
In cooperative networks using a decode-and-forward strategy, the multiple relays effectively transmit a distributed space-time code, the performance of which can be severely degraded when timing synchronization among ...
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In this work we theoretically model continuous and pulse wave propagation using the underlying dispersion relations. We also derive the dispersion relations of the underlying wave equations based on the real and imagi...
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ISBN:
(纸本)9780819468468
In this work we theoretically model continuous and pulse wave propagation using the underlying dispersion relations. We also derive the dispersion relations of the underlying wave equations based on the real and imaginary parts of the propagation constant which are related through Hubert transformation to ensure causality. Also, in this paper we show that by using a model of photorefractive two wave coupling, we can derive the dispersion relation for pulsed propagation and coupling in a diffusion dominated photorefractive material. We note that the dispersion relation we have found in photorefractive material also obeys the Hubert transform property. Finally, we show that the group velocity of light can be slowed down by means of phase coupling in the photorefractive two-wave mixing process.
Peripheral coupled waveguide (PCW) electro-absorption modulator (EAM) with different dimensions is studied. By incorporating a waveguide taper in the PCW to reduce the absorption at the input facet of the EAM, we show...
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We report on two-dimensional isothermal simulations of recessed gate and field-plated AlGaN-GaN HFETs with submicron gates. The optimization of the recessed gate shape allows us to reduce the electric field at the dra...
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In cooperative networks using a decode-and-forward strategy, the multiple relays effectively transmit a distributed space-time code, the performance of which can be severely degraded when timing synchronization among ...
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We report an experimental study of femtosecond near-infrared optically excited THz-emission from InN thin films grown by molecular beam epitaxy (MBE) on sapphire substrates. THz-emission was investigated as a function...
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ISBN:
(纸本)1424414385
We report an experimental study of femtosecond near-infrared optically excited THz-emission from InN thin films grown by molecular beam epitaxy (MBE) on sapphire substrates. THz-emission was investigated as a function of structural as well as electronic properties such as types of buffer layer, film thickness, electron mobilities, electron concentrations and doping of the InN with Si and Mg atoms. The THz-emission mechanism in InN has been analyzed. Ultrafast transient currents are identified as dominant THz-emission mechanisms. Ultrafast carrier recombination is identified as a limiting factor of THz-emission from n-type InN:Si.
Localized Surface Plasmon Resonance (LSPR) of metallic nanoparticles has been widely studied for sensing applications. We propose an ellipsometry-based configuration for sensing exploiting the polarization dependent L...
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Li and Xia have recently investigated the design of space-time codes that achieve full spatial diversity for asynchronous cooperative communications. They show that certain of the binary space-time trellis codes deriv...
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ISBN:
(纸本)1424424836
Li and Xia have recently investigated the design of space-time codes that achieve full spatial diversity for asynchronous cooperative communications. They show that certain of the binary space-time trellis codes derived from the Hammons-El Gamal stacking construction are delay tolerant and can be used in the multilevel code constructions by Lu and Kumar to produce delay tolerant space-time codes for PSK and QAM signaling. In prior work, the first author has developed generalizations of the Lu-Kumar construction for more general AM-PSK constellations that also preserve the delay tolerance of the underlying constituent codes and exhibited a new construction of short block codes that achieve significant levels of delay tolerance. This paper discusses how lattice decoding techniques can be adapted to perform decoding of such STBC for asynchronous diversity.
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