DTSC - GC - Artículos de Revistas

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On-Chip Terahertz antenna array based on amalgamation of metasurface-inspired and artificial magnetic conductor technologies for next generation of wireless electronic devices
(Published by Elsevier GmbH., 2023-07-01) Alibakhshikenari, Mohammad; Virdee, Bal Singh; Salekzamankhani, Shahram; Babaeian, Fatemeh; Ali, Syed Mansoor; Iqbal, Amjad; Al-Hasan, Muath; European Commission
The paper presents a feasibility study on an innovative terahertz (THz) on-chip antenna array designed to reliably meet the high-performance connectivity requirements for next generation of wireless devices to enable bandwidth intensive applications, superfast fast streaming, bulk data exchange between internet of things (IoT) devices/smartphones and the development of holographic video conferencing. The significantly smaller wavelength of the THz-band and metasurface-inspired and artificial magnetic conductor (AMC) technologies are exploited here to realize an on-chip antenna. Several experimental on-chip antenna arrays of various matrix sizes were investigated for application at millimeter-wave/Terahertz RF front-end transceivers. The technique proposed here is shown to enhance the antennas impedance bandwidth, gain and radiation efficiency. Purely for experimental purposes a 2 × 24 radiation element array was fabricated. It exhibits an average measured gain of 20.36 dBi and radiation efficiency of 37.5% across 0.3-0.314 THz. For proof of the concept purposes a THz receiver incorporating the proposed on-chip antenna was modelled. The results show that with the proposed antenna array a THz receiver can provide a gain of 25 dB when the antenna is directly matched to low-noise amplifier stage.
High Performance Antenna System in MIMO Configuration for 5G Wireless Communications Over Sub-6 GHz Spectrum
(American Geophysical Union, 2023-10-01) Iftikhar ud Din,; Alibakhshikenari, Mohammad; Virdee, B. S; Ullah, S.; Ullah, S.; Akram, M. R; Ali, S. M.; Livreri, P; Limiti, E.
This paper presents a high-performance multiple input and multiple output (MIMO) antenna comprising 2 × 2 configuration of radiating elements that is designed for sub-6 GHz applications. The proposed MIMO antenna employs four identical radiating elements. High isolation between the radiating elements and therefore reduced mutual coupling is achieved by spatially arranging the radiating elements in an orthogonal configuration. Also, a novel frequency selective surface (FSS) was employed to increase the gain of the MIMO antenna over a wide bandwidth from 3 to 6 GHz. This was achieved by locating the FSS above the antenna at a certain height. The FSS essentially enhanced the antenna's directivity, reduced back lobe radiation and mutual coupling. The antenna was fabricated on a standard Rogers RT Duroid 5880 dielectric substrate with a 0.8 mm thickness. The overall dimension of the MIMO antenna is 50 × 50 × 12.5 mm3 and it operates from 3.8 to 6 GHz, which corresponds to a fractional bandwidth of 41%. The proposed MIMO antenna has a measured peak gain of 4.8 dBi and inter radiation element isolation >20 dB. Its envelope correlation coefficient is less than 0.1 and diversity gain >9.9 (dB). These characteristics make the proposed MIMO antenna system suitable for 5G communication systems.
A Miniaturized and Highly Sensitive Microwave Sensor Based on CSRR for Characterization of Liquid Materials
(MDPI, 2023-04-27) Abdullah Al-Gburi, Ahmed Jamal; Zakaria, Zahriladha; Abd Rahman, Norhanani; Althuwayb, Ayman A.; Ibrahim, Imran Mohd; Saeidi, Tale; Dayo, Zaheer Ahmed; Sarosh, Ahmad
In this work, a miniaturized and highly sensitive microwave sensor based on a complementary split-ring resonator (CSRR) is proposed for the detection of liquid materials. The modeled sensor was designed based on the CSRR structure with triple rings (TRs) and a curve feed for improved measurement sensitivity. The designed sensor oscillates at a single frequency of 2.5 GHz, which is simulated using an Ansys HFSS simulator. The electromagnetic simulation explains the basis of the mode resonance of all two-port resonators. Five variations of the liquid media under tests (MUTs) are simulated and measured. These liquid MUTs are as follows: without a sample (without a tube), air (empty tube), ethanol, methanol, and distilled water (DI). A detailed sensitivity calculation is performed for the resonance band at 2.5 GHz. The MUTs mechanism is performed with a polypropylene tube (PP). The samples of dielectric material are filled into PP tube channels and loaded into the CSRR center hole; the E-fields around the sensor affect the relationship with the liquid MUTs, resulting in a high Q-factor value. The final sensor has a Q-factor value and sensitivity of 520 and 7.032 (MHz)/Er) at 2.5 GHz, respectively. Due to the high sensitivity of the presented sensor for characterizing various liquid penetrations, the sensor is also of interest for accurate estimations of solute concentrations in liquid media. Finally, the relationship between the permittivity and Q-factor value at the resonant frequency is derived and investigated. These given results make the presented resonator ideal for the characterization of liquid materials.
University training on entrepreneurship in communication and journalism business projects
(Grupo Comunicar, 2018-10-01) Aceituno Aceituno, Pedro; Casero-Ripollés, Andreu; Escudero Garzas, José Joaquín; Bousoño Calzón, Carlos
The current scenario of crisis and change has prompted the idea of entrepreneurship as a way to develop new media business models that can be promoted by university training. In this study, we aim to assess the effects of such training. A qualitative study was conducted using in-depth interviews of Spanish journalism and communication entrepreneurs who have undergone university training in business creation and management. Our results show the positive effects of this training on entrepreneurship both in general and on specific aspects of entrepreneurial projects such as organization, business plan/model, marketing, in-novation, social aspects and quality of life. Different patterns between the effects of university training on new initiatives and advanced projects were also observed. In this respect, the training supported the creation of new businesses and the development of existing ones. Finally, the suggestions for improving training and the limitations to entrepreneurship have revealed the importance of providing this type of education with a more practical, up-to-date approach that is interconnected with the business and university world. Therefore, examples of this work can be of vital importance in opening up new opportunities for sector development to enable future generations of journalists to fulfill their important social function.
Design of a Planar Sensor Based on Split-Ring Resonators for Non-Invasive Permittivity Measurement
(MDPI, 2023-06-01) Alibakhshikenari, Mohammad; Virdee, Bal S.; Elwi, Taha A.; Lubangakene, Innocent D.; Jayanthi, Renu K. R.; Al-Behadili, Amer Abbood; Abdul Hassain, Zaid A.; Mansoor Ali, Syed; Pau, Giovanni; Livreri, Patrizia; Aissa, Sonia; European Commission; Universidad Carlos III de Madrid
The permittivity of a material is an important parameter to characterize the degree of polarization of a material and identify components and impurities. This paper presents a non-invasive measurement technique to characterize materials in terms of their permittivity based on a modified metamaterial unit-cell sensor. The sensor consists of a complementary split-ring resonator (C-SRR), but its fringe electric field is contained with a conductive shield to intensify the normal component of the electric field. It is shown that by tightly electromagnetically coupling opposite sides of the unit-cell sensor to the input/output microstrip feedlines, two distinct resonant modes are excited. Perturbation of the fundamental mode is exploited here for determining the permittivity of materials. The sensitivity of the modified metamaterial unit-cell sensor is enhanced four-fold by using it to construct a tri-composite split-ring resonator (TC-SRR). The measured results confirm that the proposed technique provides an accurate and inexpensive solution to determine the permittivity of materials.
Acoustic Wave Reflection in Water Affects Underwater Wireless Sensor Networks
(MDPI, 2023-06-01) Sathish, Kaveripakam; Hamdi, Monia; Venkata, Ravikumar Chinthaginjala; Alibakhshikenari, Mohammad; Ayadi, Manel; Pau, Giovanni; Abbas, Mohamed; Shukla, Neeraj Kumar
The phenomenon of acoustic wave reflection off fluid-solid surfaces is the focus of this research. This research aims to measure the effect of material physical qualities on oblique incidence acoustic attenuation across a large frequency range. To construct the extensive comparison shown in the supporting documentation, reflection coefficient curves were generated by carefully adjusting the porousness and permeability of the poroelastic solid. The next stage in determining its acoustic response is to determine the pseudo-Brewster angle shift and the reflection coefficient minimum dip for the previously indicated attenuation permutations. This circumstance is made possible by modeling and studying the reflection and absorption of acoustic plane waves encountering half-space and two-layer surfaces. For this purpose, both viscous and thermal losses are taken into account. According to the research findings, the propagation medium has a significant impact on the form of the curve that represents the reflection coefficient, whereas the effects of permeability, porosity, and driving frequency are relatively less significant to the pseudo-Brewster angle and curve minima, respectively. This research additionally found that as permeability and porosity increase, the pseudo-Brewster angle shifts to the left (proportionally to porosity increase) until it reaches a limiting value of 73.4 degrees, and that the reflection coefficient curves for each level of porosity exhibit a greater angular dependence, with an overall decrease in magnitude at all incident angles. These findings are given within the framework of the investigation (in proportion to the increase in porosity). The study concluded that when permeability declined, the angular dependence of frequency-dependent attenuation reduced, resulting in iso-porous curves. The study also discovered that the matrix porosity largely affected the angular dependency of the viscous losses in the range of 1.4 x 10(-14) m(2) permeability.
Miniature CRLH-based ultra wideband antenna with gain enhancement for wireless communication applications
(Elsevier B.V., 2016-06-01) Alibakhshikenari, Mohammad; Naser-Moghadasi, Mohammad; Sadeghzadeh, R. A.; Virdee, Bal S.; Limiti, Ernesto
A novel miniaturized ultra wideband (UWB) antenna based on composite right/left-handed (CRLH) metamaterial unit cells for modern wireless communication applications is presented. The physical size of the small and compact antenna is 15×7.87×1.6 mm3 or 0.15¿o×0.07¿o×0.01¿o in terms of the free-space wavelength at 3 GHz. The proposed antenna covers an impedance bandwidth of 3¿10.6 GHz, which is equivalent to a fractional bandwidth of 111%. The gain and efficiency of the antenna are greater than 2.89 dBi and 38.54%, respectively, with a peak gain of 9.41 dBi and a peak efficiency of 99.93%. The characteristics of the antenna were validated with measured results obtained from a fabricated prototype to establish the proof of concept. © 2016 The Korean Institute of Communications Information Sciences
Virtual antenna array for reduced energy per bit transmission at Sub-5 GHz mobile wireless communication systems
(Elsevier BV, 2023-05-15) Alibakhshikenari, Mohammad; Virdee, Bal; Mariyanayagam, Dion; Zuazola, Ignacio Garcia; Benetatos, Haralambos Harry; Althuwayb, Ayman A.; Alali, Bader; Xu, Kai-Da; Falcone, Francisco; European Commission; Agencia Estatal de Investigación (España)
This paper presents an innovative technique to synthesize a virtual antenna array (VAA) that consumes less energy than conventional antenna arrays that are used in mobile communica-tions systems. We have shown that for a specific spectral efficiency a wireless system using the pro-posed virtual antenna array consumes significantly less energy per bit (-3 dB) than a wireless system using a conventional multiple-input multiple-output (MIMO) array. This means the adop-tion of the proposed VAA technology in smartphones, iPad, Tablets and even base-stations should significantly reduce the carbon footprint of wireless systems. The proposed VAA is realized by employing a pair of linear antenna arrays that are placed in an orthogonal configuration relative to each other. This orthogonal arrangement ensures the radiation is circularly polarized. The size of the standard radiating elements constituting the VAA were miniaturized using the topology opti-mization method. The design of the VAA incorporates substrate integrated waveguide (SIW) and metasurface technologies. The function of SIW in the design was twofold, namely, to reduce energy loss in the substrate on which the VAA is implemented, and secondly to mitigate unwanted electro-magnetic interactions between the neighboring radiating elements and thereby enhancing isolation which otherwise would degrade the radiation characteristics of the array. Metasurface technology served to effectively increase the effective aperture of the array with no impact on the footprint of the array. The consequence of SIW and metasurface technologies was improvement in the gain and radiation efficiency of the array. The proposed four orthogonal 4-element VAA covers the entire sub-5 GHz frequency range, and it radiates bidirectional in the azimuth plane and omnidirectional in the elevation plane. Moreover, it is relatively easy to design and fabricate. The proposed VAA has dimensions of 0.96k0 x 0.96k0 x 0.0016k0 at mid-band frequency of 3 GHz. VAA has a measured gain of 25 dBi and radiates with 90% efficiency. The average isolation between the linear arrays constituting the virtual array is better than 27 dB.
Ultra-Wideband Compact Fractal Antenna for WiMAX, WLAN, C and X Band Applications
(MDPI, 2023-03-25) Marzouk, Mohamed; Rhazi, Youssef; Nejdi, Ibrahime Hassan; Zerrad, Fatima-Ezzahra; Saih, Mohamed; Sarosh, Ahmad; Ghaffar, Adnan; Hussein, Mousa
In this paper, a compact dual-wideband fractal antenna is created for Bluetooth, WiMAX, WLAN, C, and X band applications. The proposed antenna consists of a circularly shaped resonator that contains square slots and a ground plane where a gap line is incorporated to increase the gain and bandwidth with a small volume of 40 × 34 × 1.6 mm3. The patch was supported by the FR4 dielectric, which had a permittivity of 4.4 and tan δ = 0.02. A 50 Ω microstrip line fed this antenna. The antenna was designed by the HFSS program, and after that, the simulated results were validated using the measured results. The measurement results confirm that the suggested antenna achieves dual-band frequencies ranging from 2.30 to 4.10 GHz, and from 6.10 GHz to 10.0 GHz, resonating at 2.8, 3.51, 6.53, and 9.37 GHz, respectively, for various applications including commercial, scholarly, and medical applications. Moreover, the antenna’s ability to operate within the frequency range of 3.1–10.6 GHz is in accordance with the FCC guidelines for the use of UWB antennas in breast cancer detection. Over the operational bands, the gain varied between 2 and 9 dB, and an efficiency of 92% was attained. A good agreement between the simulation and the measured results was found.
UWB Circular Fractal Antenna with High Gain for Telecommunication Applications
(MDPI, 2023-04-02) Nejdi, Ibrahime Hassan; Bri, Seddik; Marzouk, Mohamed; Ahmad, Sarosh; Rhazi, Youssef; Lafkih, Mustapha Ait; Sheikh, Yawar Ali; Ghaffar, Adnan; Hussein, Mousa
The present study proposes a new, highly efficient fractal antenna with ultra-wideband (UWB) characteristics. The proposed patch offers a wide simulated operating band that reaches 8.3 GHz, a simulated gain that varies between 2.47 and 7.73 dB throughout the operating range, and a high simulated efficiency that comes to 98% due to the modifications made to the antenna geometry. The modifications carried out on the antenna are composed of several stages, a circular ring extracted from a circular antenna in which four rings are integrated and, in each ring, four other rings are integrated with a reduction factor of 3/8. To further improve the adaptation of the antenna, a modification of the shape of the ground plane is carried out. In order to test the simulation results, the prototype of the suggested patch was built and tested. The measurement results validate the suggested dual ultra-wideband antenna design approach, which demonstrates good compliance with the simulation. From the measured results, the suggested antenna with a compact volume of 40 × 24.5 × 1.6 mm3 asserts ultra-wideband operation with a measured impedance bandwidth of 7.33 GHz. A high measured efficiency of 92% and a measured gain of 6.52 dB is also achieved. The suggested UWB can effectively cover several wireless applications such as WLAN, WiMAX, and C and X bands.
Frequency Switchable Global RFID Tag Antennae with Metal Compatibility for Worldwide Vehicle Transportation
(MDPI, 2023-04-02) Mazumder, Krishna; Ghosh, Anumoy; Bhattacharya, Anagha; Ahmad, Sarosh; Ghaffar, Adnan; Hussein, Mousa
This paper presents an effective way to design an RFID tag antenna to operate at three different frequencies by incorporating a switching technique. PIN diode has been used to switch the RF frequency because of its good efficiency and simplicity. The conventional dipole-based RFID tag has been improvised with added co-planar ground and PIN diode. The layout of the antenna is designed with a size of 0.083 λ0 × 0.094 λ0 at UHF (80–960) MHz, where λ0 is the free-space wavelength corresponding to the mid-point of the targeted UHF range. The RFID microchip is connected to the modified ground and dipole structures. Bending and meandering techniques on the dipole length help to match the complex chip impedance with the dipole impedance. Additionally, it scales down the total structure of the antenna. Two PIN diodes are placed along the dipole length at appropriate distances with proper biasing. The ON-OFF switching states of the PIN diodes enable the RFID tag antenna to switch over the frequency ranges (840–845) MHz (India), 902–928 MHz (North America), and 950–955 MHz (Japan).
Ka band microstrip fed slot array antenna with PMC packaging
(Institution of Engineering and Technology (IET), 2020-11) Sánchez Cabello, Carlos; Herran, Luis Fernando; Uz Zaman, Ashraf; Rajo Iglesias, Eva; Agencia Estatal de Investigación (España)
A wideband slot array antenna fed by perfect magnetic conductor (PMC) packaged microstrip lines at 28 GHz frequency range is presented. The slot array is designed with conventional microstrip technology and a PMC layer is used as a packaging solution to stop surface waves, cavity modes or any unwanted field leakage, coupling or radiation from the feeding lines. The PMC is implemented with a periodic metal pin structure. The array is fed by a corporate feed system and a good agreement with experimental results is obtained.
Single-fed broadband CPW-fed circularly polarized implantable antenna for sensing medical applications
(PLOS, 2023-04-01) Butt, Arslan Dawood; Khan, Jalal; Ahmad, Sarosh; Ghaffar, Adnan; Al-Gburi, Ahmed Jamal Abdullah; Hussein, Mousa
Biomedical telemetry relies heavily on implantable antennas. Due to this, we have designed and tested a compact, a circularly polarized, a low-profile biomedical implantable antenna that operate in the 2.45 GHz ISM band. In order to keep the antenna compact, modified co-planar waveguide (CPW) technology is used. Slotted rectangular patch with one 45-degree angle slot and truncated little patch on the left end of the ground plane generate a frequency-range antenna with circular polarization. Using a 0.25-millimeter-thick Roger Duroid-RT5880 substrate with a thickness of εr = 2.2, tanδ = 0.0009 provides flexibility. The volume of the antenna is 21 mm x 13.5 mm x 0.254 mm (0.25λg × 0.16λg × 0.003λg). The antenna covers 2.35–2.55 GHz (200 MHz) in free space and 1.63–1.17 GHz (1.17 GHz) in epidermal tissue. With skin tissue that has more bandwidth, the (x and y)-axis bends of the antenna are also simulated via the simulation. Bended antenna simulations and measurements show excellent agreement. At 2.45 GHz, the skin-like gel had -10dB impedance and 3dB axial ratio (AR) bandwidths of 47.7 and 53.8%, respectively. The ultimate result is that the SAR values are 0.78 W/kg in skin over 1 g of bulk tissue, as determined by simulations. The suggested SAR values are lower than the FCC’s maximum allowable limit (FCC). This antenna is small enough to be implanted in the body, making it perfect for biomedical applications.
Efficient radio resource management for future 6G mobile networks: A Cell-Less Approach
(IEEE, 2023-06-01) Kooshki, Farinaz; Rahman, Arifur; Mowla, Md Munjure; García-Armada, Ana; Flizikowski, Adam; European Commission
Existing mobile communication systems are unable to support ultra high system capacity and high reliability for the edge users of future 6G systems, which are envisioned to guarantee the desired quality of experience. Recently, cell-less radio access networks (RAN) are exploited to boost the system capacity. Therefore, in this letter we propose a cell-less networking approach with an efficient radio resource optimization mechanism to improve the system capacity of the future 6G networks. The simulation results illustrate that the proposed cell-less NG-RAN design provides significant system capacity improvement over the legacy cellular solutions.
Energy-Efficient Sleep Mode Schemes for Cell-Less RAN in 5G and Beyond 5G Networks
(IEEE, 2022-12-30) Kooshki, Farinaz; García-Armada, Ana; Mowla, Md Munjure; Flizikowski, Adam; Pietrzyk, Slawomir; European Commission
In 5G and beyond 5G networks, the new cell-less radio access network architecture is adopted to overcome the extreme network capacity challenges generated by massive wireless devices used for diverse scenarios and various applications. At the same time, the evolution of mobile communications faces the important challenge of increased network power consumption. To fulfill user demands for various user densities and meanwhile reduce the power consumption, we present a novel energy-efficiency enhancement scheme, i.e., (3×E) to increase the transmission rate per energy unit, with stable performance within the cell-less radio access network (RAN) architecture. Our proposed (3×E) scheme activates two-step sleep modes (i.e., certain phase and conditional phase) through the intelligent interference management for temporarily switching access points (APs) to sleep, optimizing the network energy efficiency (EE) in highly loaded scenarios, as well as in scenarios with lower load. An intelligent control over underutilized/unused APs is considered, taking their interference contribution into account as the primary main criteria in addition to load-based conditional criteria. Therefore, our proposed scheme assures a stable performance enhancement and maintains an efficient power saving when the number of UEs increases, improving existing works not addressing this performance stability in peak-traffic hours. Simulation results show that the network EE is improved up to 30% compared to the reference algorithm and up to 60% with respect to the baseline algorithm in which all APs are active all the time.
Radio Resource Management Scheme for URLLC and EMBB coexistence in a Cell-Less Radio Access network
(IEEE, 2023-03-13) Kooshki, Farinaz; García-Armada, Ana; Mowla, Md Munjure; Flizikowski, Adam; European Commission
We address the latency challenges in a high-density and high-load scenario for an ultra-reliable and low-latency communication (URLLC) network which may coexist with enhanced mobile broadband (eMBB) services in the evolving wireless communication networks. We propose a new radio resource management (RRM) scheme consisting of a combination of time domain (TD) and frequency domain (FD) schedulers specific for URLLC and eMBB users. We also develop a user ranking algorithm from a radio unit (RU) perspective, which is employed by the TD scheduler to increase the efficiency of scheduling in terms of resource consumption in large-scale networks. Therefore, the optimized and novel resource scheduling scheme reduces latency for the URLLC users (requesting a URLLC service) in an efficient resource utilization manner to support scenarios with high user density. At the same time, this RRM scheme, while minimizing the latency, it also overcomes another important challenge of eMBB users (requesting an eMBB service), namely the throughput of those who coexist in such highly loaded scenario with URLLC users. The effectiveness of our proposed scheme including time and frequency domain (TD and FD) schedulers is analyzed. Simulation results show that the proposed scheme improves the latency of URLLC users and throughput of the eMBB users compared to the baseline scheme. The proposed scheme has a 29% latency improvement for URLLC and 90% signal-to-interference-plus-noise ratio (SINR) improvement for eMBB users as compared with conventional scheduling policies.
Entrepreneurship, intrapreneurship and scientific mobility: The Spanish case
(2018-09-05) Bousoño Calzón, Carlos; Aceituno Aceituno, Pedro; Danvila Del Valle, Joaquin; Gonzalez Garcia, Abel
Scientific mobility can stimulate entrepreneurship and intrapreneurship, acting as a catalyst for reducing imbalances between local and global science and the resulting socio-economic damage. This study evaluates both whether scientific mobility effectively promotes these concepts and the fundamental reasons to articulate effective policies for scientific mobility. Toward this end, a survey has been prepared following the methodology of Global Entrepreneurship Monitor (GEM) and current scientific literature. A total of 364 researchers involved in Spanish scientific mobility took part in the study: Spanish scientists abroad (135) and scientists returned to Spain (52), as mobile groups, and young researchers in Spain (177), as a group of scientists who could go abroad, but that have not yet begun to leave. The results demonstrate that scientific mobility does promote entrepreneurship and, especially intrapreneurship. Moreover, since permanent positions are scarce for these groups and their mobility decisions largely depend on job opportunities, the involved Spanish authorities and agents can improve scientific mobility by means suitable policies that make the most of this potential to the benefit of economic growth and job creation.
Cumulative advantages and social capabilities in scientific mobility in the Health Sciences: The Spanish case
(Public Library of Science (PLoS), 2017-03-15) Aceituno-Aceituno, Pedro; Melchor, Lorenzo; Danvila del Valle, Joaquín; Bousoño Calzón, Carlos; Ministerio de Empleo y Seguridad Social (España); Universidad Carlos III de Madrid
This study develops a survey to measure and analyze the following crucial variables: research career, training, funding, working with a world-class team, institutional prestige, wages, facilities/infrastructure, working conditions in the organization of the destination country, fringe benefits in the organization of the destination country and social responsibility in the organization of the departure country. A total of 811 researchers have participated in the survey, of which 293 were from the health sector: Spanish scientists abroad (114), scientists that have returned to Spain (32) and young researchers in Spain (147). The most crucial variables for Spanish scientists and young researchers in Spain in Health Sciences moving abroad are the cumulative advantages (research career, training, funding and institutional prestige) plus wages. On the other hand, the return of Spanish scientists in the Health Sciences is influenced by cumulative variables (working with a world-class team, research career and institutional prestige) and also by other variables related to social factors, such as working conditions and fringe benefits in the destination country. Permanent positions are rare for these groups and their decisions regarding mobility depend to a large extent on job opportunities.
An analysis of the network selection problem for heterogeneous environments with user-operator joint satisfaction and multi-RAT transmission
(Hindawi, 2017-01-18) Escudero Garzas, José Joaquín; Bousoño Calzón, Carlos; Ministerio de Economía y Competitividad (España)
The trend in wireless networks is that several wireless radio access technologies (RATs) coexist in the same area, forming heterogeneous networks in which the users may connect to any of the available RATs. The problem of associating a user to the most suitable RAT, known as network selection problem (NSP), is of capital importance for the satisfaction of the users in these emerging environments. However, also the satisfaction of the operator is important in this scenario. In this work, we propose that a connection may be served by more than one RAT by using multi-RAT terminals. We formulate the NSP with multiple RAT association based on utility functions that take into consideration both user's satisfaction and provider's satisfaction. As users are characterized according to their expected quality of service, our results exhaustively analyze the influence of the user's profile, along with the network topology and the type of applications served.
Parametric model and estimator classifier for optimal averaging in mobile OFDM systems with superimposed training
(IEEE, 2023) Piqué Muntané, Ignasi; Fernández-Getino García, María Julia; Ministerio de Ciencia e Innovación (España)
Superimposed training (ST) is an attractive technique for channel estimation in orthogonal frequency division multiplexing (OFDM) modulation. However, its main challenge is the intrinsic interference due to the joint transmission of pilot and data symbols, which can be mitigated by averaging the received signal. Previous works analyzed the mean square error (MSE) of the channel estimation, for both least squares (LS) and minimum MSE (MMSE) estimators, and showed that, under realistic channel models, the optimum number of averaged symbols could be computed by solving a transcendental equation. In this paper, as a practical implementation proposal, these optimum averaging values are parametrically approximated with a multilinear regression model. Also, it is proposed an accurate classifier that, under delay and performance tolerances, is able to select the most suitable estimator between LS and MMSE.

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