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Articles 1 - 11 of 11
Full-Text Articles in Systems and Communications
Collision-Tolerant Transmission With Narrow-Beam Antennas, Hong-Ning Dai, Kam-Wing Ng, Min-You Wu, Bo Li
Collision-Tolerant Transmission With Narrow-Beam Antennas, Hong-Ning Dai, Kam-Wing Ng, Min-You Wu, Bo Li
Hong-Ning Dai
The application of directional antennas in wireless ad hoc networks brings numerous benefits, such as increased spatial reuse and mitigated interference. Most MAC protocols with directional antennas are based on the RTS/CTS mechanism which works well in wireless ad hoc networks using omni-directional antennas. However, RTS/CTS frames cannot mitigate the interference completely. Besides, they also contribute a lot to the performance overhead. This paper studies the problem from a new perspective. We have found that the transmission success probability under directional transmission and directional reception is quite high when the antenna beamwidth is quite narrow. Motivated by the analytical results, …
Cut Part Count And Increase Dynamic Range In The Hybrid Coupled Attenuator, Chin-Leong Lim
Cut Part Count And Increase Dynamic Range In The Hybrid Coupled Attenuator, Chin-Leong Lim
Chin-Leong Lim
Modern digital modulation formats are generally phase-sensitive. Therefore, the variable attenuators in digital wireless equipment should exhibit minimal phase variation over attenuation. The hybrid coupled attenuator (HCA) has substantially less phase variation than the competing constant-impedance attenuators such as the Pi and the Bridged-T. At microwave frequencies, HCA implementations tend to suffer from reduced dynamic (attenuation) range due to component parasitics, especially when plastic-packaged PIN diodes are selected to lower cost. To maximize the dynamic range in a low-cost 1.9 GHz HCA , we first identified the critical components and then compensated for their deleterious effect. This paper describes the …
Design A Pin Diode Switch For High-Linearity Applications, Chin-Leong Lim
Design A Pin Diode Switch For High-Linearity Applications, Chin-Leong Lim
Chin-Leong Lim
This paper describes the semiconductor technology, packaging and characterization of a new PIN diode for switching WCDMA signal up to 10W. PIN semiconductor technology was picked as the basis for this switch because of the various performance and reliability advantages that can be had. A model for the PIN diode is generated based on the measured RF performance. How the various model parameters affect the RF performance is also discussed. This is followed by an application description of a 2.0 GHz switch based on the said model and a discussion of some circuit changes to further improve the performance. The …
Rf Applications Of Pin Diodes, Chin-Leong Lim
Rf Applications Of Pin Diodes, Chin-Leong Lim
Chin-Leong Lim
PIN diodes are the ubiquitous "nuts & screws" components that hold together RF equipment as varied as the television, radio, 2-way radios, WLAN equipment etc. This talk covers PIN diode characteristics and RF applications such as switches, attenuators and limiters. Performance improvement techniques will also be discussed.
Cut Loss In Low-Voltage, Wideband Pin Attenuators, Chin-Leong Lim
Cut Loss In Low-Voltage, Wideband Pin Attenuators, Chin-Leong Lim
Chin-Leong Lim
Many RF applications, including Cable and Satellite TV (CATV / SATV) networks, rely on voltage-variable attenuators (VVAs) for gain adjustment. VVAs consisting of PIN diodes arranged as a PI network are popular in CATV / SATV service owing to their constant impedance, high linearity, multi-decade bandwidth, low part count and compactness. When fabricated from thick bulk PIN diodes for high linearity, the PI VVA configuration typically requires a 0-15V control range. But modern equipment typically operates at 5V or less. Capping the control voltage at 5V adversely raises the VVA's minimum attenuation. To enable low voltage operation without degrading the …
Achieving Transparency With Plasmonic And Metamaterial Coatings, Andrea Alù, Nader Engheta
Achieving Transparency With Plasmonic And Metamaterial Coatings, Andrea Alù, Nader Engheta
Nader Engheta
The possibility of using plasmonic and metamaterial covers to drastically reduce the total scattering cross section of spherical and cylindrical objects is discussed. While it is intuitively expected that increasing the physical size of an object may lead to an increase in its overall scattering cross section, here we see how a proper design of these lossless metamaterial covers near their plasma resonance may induce a dramatic drop in the scattering cross section, making these objects nearly “invisible” or “transparent” to an outside observer—a phenomenon with obvious applications for low-observability and noninvasive probe design. Physical insights into this phenomenon and …
Achieving Transparency With Plasmonic And Metamaterial Coatings, Andrea Alù, Nader Engheta
Achieving Transparency With Plasmonic And Metamaterial Coatings, Andrea Alù, Nader Engheta
Andrea Alù
The possibility of using plasmonic and metamaterial covers to drastically reduce the total scattering cross section of spherical and cylindrical objects is discussed. While it is intuitively expected that increasing the physical size of an object may lead to an increase in its overall scattering cross section, here we see how a proper design of these lossless metamaterial covers near their plasma resonance may induce a dramatic drop in the scattering cross section, making these objects nearly “invisible” or “transparent” to an outside observer—a phenomenon with obvious applications for low-observability and noninvasive probe design. Physical insights into this phenomenon and …
A Framework For Evaluating Managerial Styles In Open Source Projects, Tony Wasserman, Eugenio Capra
A Framework For Evaluating Managerial Styles In Open Source Projects, Tony Wasserman, Eugenio Capra
Tony Wasserman
This paper presents the Software Project Governance Framework (SPGF) for characterizing management of software projects, based on mechanisms used for communication and collaboration, the organizational structure of projects, and testing and quality assurance procedures. The framework was developed and validated from interviews and surveys with leaders of more than 70 commercial and community based software projects, including both closed and open source projects.
On Collision-Tolerant Transmission With Directional Antennas, Hong-Ning Dai, Kam-Wing Ng, Min-You Wu
On Collision-Tolerant Transmission With Directional Antennas, Hong-Ning Dai, Kam-Wing Ng, Min-You Wu
Hong-Ning Dai
The application of directional antennas in wireless networks brings numerous benefits, such as increased spatial reuse and mitigated interferences. Most MAC protocols with directional antennas are based on the RTS/CTS mechanism which works well in wireless networks using omni-directional antennas. However, RTS/CTS frames cannot mitigate the interfering nodes completely. Besides, they also contribute a lot to the performance overhead. This paper studies the problem from a new perspective. We analyze the transmission success probability under directional transmission and directional reception when the antenna beamwidth is quite narrow. Motivated by the analytical results, we design a lightweight MAC protocol without RTS/CTS …
On The Capacity Of Multi-Channel Wireless Networks Using Directional Antennas, Hong-Ning Dai, Kam-Wing Ng, Raymond Chi-Wing Wong, Min-You Wu
On The Capacity Of Multi-Channel Wireless Networks Using Directional Antennas, Hong-Ning Dai, Kam-Wing Ng, Raymond Chi-Wing Wong, Min-You Wu
Hong-Ning Dai
The capacity of wireless ad hoc networks is affected by two key factors: the interference among concurrent transmissions and the number of simultaneous transmissions on a single interface. Recent studies found that using multiple channels can separate concurrent transmissions and greatly improve network throughput. However, those studies only consider that wireless nodes are equipped with only omnidirectional antennas, which cause high collisions. On the other hand, some researchers found that directional antennas bring more benefits such as reduced interference and increased spatial reuse compared with omnidirectional antennas. But, they only focused on a single-channel network which only allows finite concurrent …
Diagnosing Faults In Electrical Power Systems Of Spacecraft And Aircraft, Ole J. Mengshoel, Adnan Darwichse, Keith Cascio, Mark Chavira, Scott Poll, Serdar Uckun
Diagnosing Faults In Electrical Power Systems Of Spacecraft And Aircraft, Ole J. Mengshoel, Adnan Darwichse, Keith Cascio, Mark Chavira, Scott Poll, Serdar Uckun
Ole J Mengshoel
Electrical power systems play a critical role in spacecraft and aircraft. This paper discusses our development of a diagnostic capability for an electrical power system testbed, ADAPT, using probalistic techniques. In the context of ADAPT, we present two challenges, regarding modelling and real-time performance, often encountered in real-world diagnostic applications. To meet the modelling challenge, we discuss our novel high-level specification language which supports auto-generation of Bayesian networks. To meet the real-time challenge, we compile Bayesian networks intro arithmetic circuits. Arithmetic circuits typically have small footprints and are optimized for the real-time avionics systems found in spacecraft and aircraft. Using …