Articles

Broadband in school: Impact on student performance

Belo R., Ferreira P., Telang R.

Management Science

2014

Abstract:

This paper examines the effects of providing broadband to schools on students’ performance. We use a rich panel of data on broadband use and students’ grades from all middle schools in Portugal. Employing a first-differences specification to control for school-specific unobserved effects and instrumenting the quality of broadband to account for unobserved time-varying effects, we show that high levels of broadband use in schools were detrimental for grades on the ninth-grade national exams in Portugal. For the average broadband use in schools, grades reduced 0.78 of a standard deviation from 2005 to 2009. We also show that broadband has a negative impact on exam scores regardless of gender, subject, or school quality and that the way schools allow students to use the Internet affects their performance. In particular, students in schools that block access to websites such as YouTube perform relatively better.

Broadband in schools: Does it help or hurt student performance?

Belo R., Ferreira P., Telang R.

ICIS 2010 Proceedings - Thirty First International Conference on Information Systems

2010

Abstract:

This paper examines the effects of providing broadband to schools on students’ performance. We use a rich panel of data on broadband use and students’ grades from all middle schools in Portugal. Employing a first-differences specification to control for school-specific unobserved effects and instrumenting the quality of broadband to account for unobserved time-varying effects, we show that high levels of broadband use in schools were detrimental for grades on the ninth-grade national exams in Portugal. For the average broadband use in schools, grades reduced 0.78 of a standard deviation from 2005 to 2009. We also show that broadband has a negative impact on exam scores regardless of gender, subject, or school quality and that the way schools allow students to use the Internet affects their performance. In particular, students in schools that block access to websites such as YouTube perform relatively better.

Can a wind farm with CAES survive in the day-ahead market?

Mauch B., Carvalho P.M.S., Apt J.

Energy Policy

2012

Abstract:

We investigate the economic viability of coupling a wind farm with compressed air energy storage (CAES) to participate in the day-ahead electricity market at a time when renewable portfolio standards are not binding and wind competes freely in the marketplace. In our model, the CAES is used to reduce the risk of committing uncertain quantities of wind energy and to shift dispatch of wind generation to high price periods. Other sources of revenue (capacity markets, ancillary services, price arbitrage) are not included in the analysis. We present a model to calculate profit maximizing day-ahead dispatch schedules based on wind forecasts. Annual profits are determined with dispatch schedules and actual wind generation values. We find that annual income for the modeled wind–CAES system would not cover annualized capital costs using market prices from the years 2006 to 2009. We also estimate market prices with a carbon price of $20 and $50 per tonne CO2 and find that revenue would still not cover the capital costs. The implied cost per tonne of avoided CO2 to make a wind–CAES profitable from trading on the day-ahead market is roughly $100, with large variability due to electric power prices.

Capacity expansion in transmission networks using portfolios of real options

Loureiro M.V., Claro J., Pereira P.J.

International Journal of Electrical Power and Energy Systems

2015

Abstract:

We adopt in this paper a perspective of portfolios of real options, to propose a mixed integer linear programming model for multistage Transmission Network Expansion Planning. The model is then used to analyze three fundamental network building blocks – an independent design, a radial design, and a meshed design – seeking to develop network design insights, in particular regarding the joint value of postponement and other sources of operational flexibility. The results clearly point to the importance of explicitly incorporating uncertainty, adopting a multistage perspective, and addressing complex interactions between different sources of flexibility, in the design of transmission networks.

Capturing location-privacy preferences: quantifying accuracy and user-burden tradeoffs

Benisch M., Kelley P., Sadeh N., Cranor L.

Personal and Ubiquitous Computing

2010

Abstract:

We present a 3-week user study in which we tracked the locations of 27 subjects and asked them to rate when, where, and with whom they would have been comfortable sharing their locations. The results of analysis conducted on over 7,500 h of data suggest that the user population represented by our subjects has rich location-privacy preferences, with a number of critical dimensions, including time of day, day of week, and location. We describe a methodology for quantifying the effects, in terms of accuracy and amount of information shared, of privacy-setting types with differing levels of complexity (e.g., setting types that allow users to specify location- and/or time-based rules). Using the detailed preferences we collected, we identify the best possible policy (or collection of rules granting access to one’s location) for each subject and privacy-setting type. We measure the accuracy with which the resulting policies are able to capture our subjects’ preferences under a variety of assumptions about the sensitivity of the information and user-burden tolerance. One practical implication of our results is that today’s location-sharing applications may have failed to gain much traction due to their limited privacy settings, as they appear to be ineffective at capturing the preferences revealed by our study.

Catch-up TV analytics: statistical characterization and consumption patterns identification on a production service

Nogueira J., Guardalben L., Cardoso B., Sargento S.

Multimedia Systems

2016

Abstract:

Multimedia IP Television services, such as on-demand Catch-up TV, are in an active migration process towards Over-The-Top (OTT) delivery using state-of-the-art Content Delivery Networks (CDNs). Maintaining the same Quality-of-Experience (QoE) of managed IPTV networks is challenging and requires a thorough understanding of users’ behaviors and content demand characteristics. This article leverages Catch-up TV usage logs obtained from a Pay-TV operator’s live production IPTV service containing over 1 million subscribers to characterize and extract insights from service utilization at a scale and scope not yet addressed in the literature. A detailed analysis on the characteristics of users’ viewings is performed, with a study of when, where, and how often users access the service, along with how they behave during each viewing session. The results show that Catch-up TV consumption exhibits very high levels of utilization throughout the day, and is heavily polarized towards specific genres, recently aired programs, and content broadcasted during prime-time. The superstar effect is notorious. This analysis is complemented by a service optimization perspective, which shows that large gains are achievable by caching popular programs, and by loading content in advance to users’ Set-Top-Boxes (STBs). This comprehensive research study is supplemented by detailed statistical information tables, which highlight the feasibility of efficiently migrating Catch-up TV services to OTT-scenarios, and provide the foundations for future works able to explore these results.

Channel asymmetry in cellular OFDMA-TDD networks

Foutekova E., Agyapong P., Haas H.

Eurasip Journal on Wireless Communications and Networking

2008

Abstract:

his paper studies time division duplex- (TDD-) specific interference issues in orthogonal frequency division multiple access- (OFDMA-) TDD cellular networks arising from various uplink (UL)/downlink (DL) traffic asymmetries, considering both line-of-sight (LOS) and non-LOS (NLOS) conditions among base stations (BSs). The study explores aspects both of channel allocation and user scheduling. In particular, a comparison is drawn between the fixed slot allocation (FSA) technique and a dynamic channel allocation (DCA) technique for different UL/DL loads. For the latter, random time slot opposing (RTSO) is assumed due to its simplicity and its low signaling overhead. Both channel allocation techniques do not obviate the need for user scheduling algorithms, therefore, a greedy and a fair scheduling approach are applied to both the RTSO and the FSA. The systems are evaluated based on spectral efficiency, subcarrier utilization, and user outage. The results show that RTSO networks with DL-favored traffic asymmetries outperform FSA networks for all considered metrics and are robust to LOS between BSs. In addition, it is demonstrated that the greedy scheduling algorithm only offers a marginal increase in spectral efficiency as compared to the fair scheduling algorithm, while the latter exhibits up to ≈20% lower outage.

Channel Selection Relying on Probabilistic Adjacent Channel Interference Analysis and Pattern Recognition

Nogueira J., Sargento S.

Wireless Personal Communications

2016

Abstract:

The number of Wi-Fi devices and their requirements for bandwidth keep on increasing, along with their hunger for spectrum. This fact is mostly noticeable in dense urban scenarios where neighbors fight for bandwidth and their networks struggle to deliver the requested information. While the inherent limitations of Wi-Fi technologies cannot be overcome, they can be mitigated through configuration. Optimally selecting a wireless channel is a critical aspect of access point (AP) configuration, and a challenging task due to a broad range of factors affecting the wireless connection performance. This paper addresses the channel selection problem by relying on a time-varying dynamic approach capable of modeling its surrounding wireless networks with respect to their usage patterns, channel utilization and adjacent channel interference. This contextual data is used in a channel selection model, which combines utilization patterns and statistics with a probabilistic mathematical model to accurately estimate the impact of adjacent channel interference on the signal to interference plus noise ratio, hence effectively selecting a wireless channel whose optimal performance is exhibited when the users’ need it. The experimental results demonstrate that the proposed approach outperforms competing methods while closely tracking the simulation models, thus paving the way for smarter APs.

Characterization of the multiscale limit associated with bounded sequences in BV

Ferreira R., Fonseca I.

Journal of Convex Analysis

2012

Abstract:

The notion of two-scale convergence for sequences of Radon measures with finite total variation is generalized to the case of multiple periodic length scales of oscillations. The main result concerns the characterization of (n + 1)-scale limit pairs (u, U) of sequences {(u”LNb⌦, Du”b⌦)}”>0 ⇢ M(⌦; Rd) ⇥ M(⌦; Rd⇥N ) whenever {u”}”>0 is a bounded sequence in BV (⌦; Rd). This characterization is useful in the study of the asymptotic behavior of periodically oscillating functionals with linear growth, defined on the space BV of functions of bounded variation and described by n 2 N microscales, undertaken in [10].