Cross-layer Perceptual ARQ for Video Communications over 802.11e Wireless Networks

This work presents an application-level perceptual ARQ algorithm for video streaming over 802.11e wireless networks. A simple and effective formula is proposed to combine the perceptual and temporal importance of each packet into a single priority value, which is then used to drive the packet-selection process at each retransmission opportunity. Compared to the standard 802.11 MAC-layer ARQ scheme, the proposed technique delivers higher perceptual quality because it can retransmit only the most perceptually important packets reducing retransmission bandwidth waste. Video streaming of H.264 test sequences has been simulated with ns in a realistic 802.11e home scenario, in which the various kinds of traffic flows have been assigned to different 802.11e access categories according to the Wi-Fi alliance WMM specification. Extensive simulations show that the proposed method consistently outperforms the standard link-layer 802.11 retransmission scheme, delivering PSNR gains up to 12 dB while achieving low transmission delay and limited impact on concurrent traffic. Moreover, comparisons with a MAC-level ARQ scheme which adapts the retry limit to the type of frame contained in packets and with an application-level deadline-based priority retransmission scheme show that the PSNR gain offered by the proposed algorithm is significant, up to 5 dB. Additional results obtained in a scenario in which the transmission relies on an intermediate node (i.e., the access point) further confirms the consistency of the perceptual ARQ performance. Finally, results obtained by varying network conditions such as congestion and channel noise levels show the consistency of the improvements achieved by the proposed algorithm

Determinants of Life Expectancy at Birth A Longitudinal Study on OECD Countries

This paper analyses the influence of several determinants on life expectancy at birth in 36 OECD countries over the 1999–2018 period. We used a cross–country fixed-effects multiple regression analysis with year and country dummies and used dynamic models, backward stepwise selection, and Arellano-Bond estimators to treat potential endogeneity issues. The results show the relationship between per capita health–care expenditure, incidence of out-of-pocket expenditure, physician density, hospital bed density, social spending, GDP level, participation ratio to labour, prevalence of chronic respiratory diseases, temperature, and total size of the population and life expectancy at birth. In line with previous studies, this analysis confirms the positive correlation of both health care expenditure and health care system (physicians and hospital beds in our analysis) and a country’s population life expectancy. It also outlines the association of other factors related to population behaviour and social spending jointly considered on this outcome. Policy makers should carefully consider these mutual effects when allocating public funds, particularly after the COVID-19 pandemic period

Who should monitor job sick leave?

We use a large and unique administrative dataset from Italy, covering the period 2009-2014, to investigate opportunistic behavior (moral hazard) and the effectiveness of monitoring policies related to insurance against illness-related income losses. The analysis is based on the outcome of mandatory medical visits aimed at verifying the health status of employees during sickness spells. We find that employers are more effective than the public insurer in selecting sickness episodes to monitor. However, a reduction in the number and a better targeting of visits with the support of appropriate statistical tools may close the gap. We discuss the impact of using direct measures of health, such as the outcome of a medical visit, on the study of the determinants of opportunistic behavior and argue that simply looking at days of work lost, without appropriately controlling for health status, may lead to misleading conclusions if the goal is studying moral hazard

Job Sick Leave: Detecting Opportunistic Behavior

We utilize a large administrative dataset of sickness leave in Italy, i) to investigate whether private firms are more effective than the public insurer in choosing who to monitor, and ii) to study the correlation between potentially opportunistic behavior and the observable characteristics of the employee. We find that private employers are more likely to select into monitoring employees who are fit for work despite being on sick leave, if the public insurer is not supported by any data-driven tool. However, the use of a scoring mechanism, based on past records, allows the public insurer to be as effective as the employer. This result suggests that the application of machine learning to appropriate databases may improve the targeting of public monitoring to detect opportunistic behavior. Concerning the association between observable characteristics and potentially opportunistic behavior, we find that males, employees younger than 50, those on short leaves or without a history of illness are more likely to be found fit for work

Broadband internet access via multi-hop wireless mesh networks: design, protocol and experiments

While bandwidth for Internet access in urban areas is steadily increasing in recent years, many rural areas are still suffering from the effect of the digital divide. This paper presents a broadband Internet access paradigm developed in the context of the ADHOCSYS project, which was financed by the European Commission under the 6th Framework Program Information and Society Technologies, within the strategic objective of Broadband for All. Aiming at providing reliable Internet access in rural and mountainous regions where xDSL connections are not available due to coverage limit, the ADHOCSYS network provides a cost-effective solution based on multi-hop wireless mesh network technologies. Starting from a general description of the network architecture and application scenarios, this paper focuses on presenting the routing, QoS and network deployment aspects of the developed solution. Other aspects like reliability prediction, power supply, security and authentication, and auto-configuration, etc are discussed only briefly. In order to validate the developed broadband access solution, a real-life operational wireless mesh network has been deployed in a mountainous region in Northern Italy. The performance of the developed solution has been evaluated based on the deployed real-life network, and the obtained numerical experimental results, along with the practical lessons learnt through installations and experiments are also presented in this paper. © 2010 Springer Science+Business Media, LLC