Protocolo de Cooperación Adaptativo para Sistemas de Comunicaciones Opticas Atmosféricas

En concreto, se ha analizado un sistema de comunicaciones cooperativas formado por 3 enlaces FSO con retransmision DF usando IM/DD sobre canales con turbulencia atmosferica y desalineamiento entre el transmisor y el receptor. Se han evaluado las prestaciones de un protocolo de cooperacion adaptativo basado en la seleccion de camino óptico con mayor valor de irradiancia.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Converging Underwater and FSO Ground Communication Links

We propose a new combined underwater-atmospheric optical communication link for providing a high speed optical connectivity between onshore and sumerge systems. New average BER expressions are derived when assuming amplify-and-forward (AF) relay.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Evaluating pointing errors on ergodic capacity of DF relay-assisted FSO communication systems

Ergodic capacity of decode-and-forward (DF) relay-assisted free-space optical (FSO) communication systems when line of sight is available is analyzed over gamma-gamma fading channels with pointing errors. Novel closed-form approximate ergodic capacity expression is obtained in terms of the H-Fox function for a 3-way FSO communication system when the α-μ distribution to efficiently approximate the probability density function (PDF) of the sum of gamma-gamma with pointing errors variates is considered. Moreover, we present a novel asymptotic expression at high signal-to-noise ratio (SNR) for the ergodic capacity of DF relay-assisted FSO systems. The main contribution in this work lies in an in-depth analysis about the impact of pointing errors on the ergodic capacity for cooperative FSO systems. In order to maintain the same performance in terms of capacity, it is corroborated that the presence of pointing errors requires an increase in SNR, which is related to the fraction of the collected power at the receive aperture, i.e. A 0 . Simulation results are further demonstrated to confirm the accuracy and usefulness of the derived results.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. The authors wish to acknowledge the financial support given by Spanish MINECO Project TEC2012-32606

Disability, Human Resources and Behavioral Economics: The Labour Inclusion case of Ilunion Hotels of the Costa del Sol (Spain).

The situation of labour inclusion of people with disabilities in Spain is still too negative, in spite of the different efforts carried out by public and private sector. Previous research points to social discrimination as one of the main causes of the situation. Ilunion Hotels is one of the most important hotel companies in Spain focused on labour inclusion of people with disabilities. The objective of this paper is to explore the social inclusion case of Ilunion Hotels of the Costa del Sol, the actions that they have developed to improve the labour integration of this collective, based on a behavioral economics theoretical model (with a high relevance of the influence of social stigma, stress theories and coping to stress responses). We look into the specific situation of two of the three hotels developed as Special Employment Centres (sheltered employment contexts defined by Spanish legislation) and the possible impact of their Support Units for Professional Activity. Case study methodology is considered the most appropriate, according to the research objective, supported by semi-structured interviews with the hotel managers. The results show that, although Special Employment Centres are effective in improving labour integration in the short term and could contribute to change the long-term social perspectives about workers with disabilities, they could be also reinforcing the social stigma existing in the ordinary market

Special Employment Centres, Time Factor and Sustainable Human Resources Management in Spanish Hotel Industry: Can Corporate Social Marketing improve the labour situation of People With Disabilities?

Background: The hotel industry has long been known for offering low-quality jobs, long working hours, and difficult scheduling, which is even more challenging for people with disabilities (PWD). The COVID-19 crisis has further exacerbated these issues, particularly in terms of labor inclusion due to widespread discrimination against this group. In Spain, Special Employment Centres (SECs) have been established to provide protected employment for PWD. While SECs have shown short-term improvements, their long-term impact on sustainable employment remains uncertain. This paper aims to analyze the Spanish context, comparing sheltered employment with the ordinary labor market, and exploring how SECs might influence the labor conditions of PWD in the hotel sector over time. Additionally, the study investigates the potential role of Corporate Social Marketing in addressing these challenges. Methods: A bibliographic content analysis was conducted using the ProKnow-C methodology, reviewing the latest research on the subject. Results: The literature reveals two main groups of studies: those focused on the supply side (HR practices and managers' perceptions of PWD inclusion) and those on the demand side. The supply side is more aligned with this research's objectives. Few articles address SECs and Corporate Social Marketing, underlining the novelty of this research approach. Conclusions: The analysis suggests that labor discrimination is more prevalent in the regular market. In the long term, two contrasting outcomes may emerge: (a) SECs might reinforce social stigma, worsening the employment situation for PWD; (b) SECs could positively shift societal attitudes. Further research is needed, incorporating Corporate Social Marketing, to enhance sustainable employment for PWD

Secure communication for FSO links in the presence of eavesdropper with generic location and orientation

When the beam waist at the receiver is significantly larger than the receiver size, free-space optical (FSO) links may be vulnerable to some optical tapping risks at the physical layer. In this paper, we conduct a new framework for the analysis of the secrecy performance in terms of the secrecy outage probability (SOP) of FSO systems affected by gamma-gamma (GG) turbulence induced fading channels with pointing errors. As a key feature, we evaluate the SOP in the presence of an external eavesdropper with generic location and orientation. For that reason, a new misalignment error model is proposed to consider a non-orthogonal optical beam with respect to the photodetector plane at the eavesdropper’s receiver, where the effective area is determined by a rotated ellipse. New approximate and asymptotic solutions at high signal-to-noise-ratio (SNR) for the secrecy performance are obtained in closed-form, which are verified by exact Monte Carlo simulations. By using the developed expressions, we analyze in greater detail some effects such as the SNR of the eavesdropper’s channel, the normalized beamwidth at the receiver-side, and the location and orientation of the eavesdropper on the secrecy performance for different turbulence conditions.Qatar National Library (QNL); Ooredoo Research Sponsorship 2015; Texas A&M University at Qatar (TAMUQ) RRSG 2019

Impact of nonzero boresight pointing error on ergodic capacity of MIMO FSO communication systems

A thorough investigation of the impact of nonzero boresight pointing errors on the ergodic capacity of multiple-input/multiple-output (MIMO) free-space optical (FSO) systems with equal gain combining (EGC) reception under different turbulence models, which are modeled as statistically independent, but not necessarily identically distributed (i.n.i.d.) is addressed in this paper. Novel closed-form asymptotic expressions at high signal-to-noise ratio (SNR) for the ergodic capacity of MIMO FSO systems are derived when different geometric arrangements of the receive apertures at the receiver are considered in order to reduce the effect of nonzero inherent boresight displacement, which is inevitably present when more than one receive aperture is considered. As a result, the asymptotic ergodic capacity of MIMO FSO systems is evaluated over log-normal (LN), gamma-gamma (GG) and exponentiated Weibull (EW) atmospheric turbulence in order to study different turbulence conditions, different sizes of receive apertures as well as different aperture averaging conditions. It is concluded that the use of single-input/multiple-output (SIMO) and MIMO techniques can significantly increase the ergodic capacity respect to the direct path link when the inherent boresight displacement takes small values, i.e. when the spacing among receive apertures is not too big. The effect of nonzero additional boresight errors, which is due to the thermal expansion of the building, is evaluated in multiple-input/single-output (MISO) and single-input/single-output (SISO) FSO systems. Simulation results are further included to confirm the analytical results.The authors are grateful for financial support from the Junta de Andalucía (research group Communications Engineering (TIC-0102))

Novel approximation of misalignment fading modeled by Beckmann distribution on free-space optical links

A novel accurate and useful approximation of the well-known Beckmann distribution is presented here, which is used to model generalized pointing errors in the context of free- space optical (FSO) communication systems. We derive an approximate closed form probability density function (PDF) for the composite gamma-gamma (GG) atmospheric turbulence with the pointing error model using the proposed approximation of the Beckmann distribution, which is valid for most practical terrestrial FSO links. This approximation takes into account the effect of the beam width, different jitters for the elevation and the horizontal displacement and the simultaneous effect of nonzero boresight errors for each axis at the receiver plane. Additionally, the proposed approximation allows us to delimit two different FSO scenarios. The first of them is when atmospheric turbulence is the dominant effect in relation to generalized pointing errors, and the second one when generalized pointing error is the dominant effect in relation to atmospheric turbulence. The second FSO scenario has not been studied in-depth by the research community. Moreover, the accuracy of the method is measured both visually and quantitatively using curve-fitting metrics. Simulation results are further included to confirm the analytical results.Junta de Andalucía (research group "Communications Engineering (TIC-0102)") and Universidad de Málaga

Adaptive selective relaying in cooperative free-space optical systems over atmospheric turbulence and misalignment fading channels

In this paper, a novel adaptive cooperative protocol with multiple relays using detect-and-forward (DF) over atmospheric turbulence channels with pointing errors is proposed. The adaptive DF cooperative protocol here analyzed is based on the selection of the optical path, source-destination or different source-relay links, with a greater value of fading gain or irradiance, maintaining a high diversity order. Closed-form asymptotic bit error-rate (BER) expressions are obtained for a cooperative free space optical (FSO) communication system with Nr relays, when the irradiance of the transmitted optical beam is susceptible to either a wide range of turbulence conditions, following a gamma-gamma distribution of parameters α and β , or pointing errors, following a misalignment fading model where the effect of beam width, detector size and jitter variance is considered. A greater robustness for different link distances and pointing errors is corroborated by the obtained results if compared with similar cooperative schemes or equivalent multiple-input multiple-output (MIMO) systems. Simulation results are further demonstrated to confirm the accuracy and usefulness of the derived results.The authors wish to acknowledge the financial support given by Spanish MINECO Project TEC2012-32606