DTSC - GC - Comunicaciones en congresos y otros eventos

Permanent URI for this collection


Recent Submissions

Now showing 1 - 20 of 77
  • Publication
    TCP-Based distributed offloading architecture for the future of untethered immersive experiences in wireless networks
    (Association for Computing Machinery (ACM), 2022-06-22) Gonzalez-Morin, Diego; López Morales, Manuel José; Pérez, Pablo; Villegas, Alvaro; European Commission
    Task offloading has become a key term in the field of immersive media technologies: it can enable lighter and cheaper devices while providing them higher remote computational capabilities. In this paper we present our TCP-based offloading architecture. The architecture, has been specifically designed for immersive media offloading tasks with a particular care in reducing any processing overhead which can degrade the network performance. We tested the architecture for different offloading scenarios and conditions on two different wireless networks: WiFi and 5G millimeter wave technologies. Besides, to test the network on alternative millimeter wave configurations, currently not available on the actual 5G millimeter rollouts, we used a 5G Radio Access Network (RAN) real-time emulator. This emulator was also used to test the offloading architecture for an simulated immersive user sharing network resources with other users. We provide insights of the importance of user prioritization techniques for successful immersive media offloading. The results show a great performance for the tested immersive media scenarios, highlighting the relevance of millimeter wave technology for the future of immersive media applications.
  • Publication
    Visible Light Communications for IoT services based on high-power LEDs in Industry 4.0
    (IEEE, 2022-01) Morales Céspedes, Máximo; Al-Sakkaf, Ahmed Gaafar Ahmed; European Commission; Ministerio de Economía y Competitividad (España)
    In the framework of Industry 4.0, visible light communications (VLC) are proposed for providing connectivity in those environments where radio-frequency (RF) transmission achieves a poor performance or it is even banned [1] . Specifically, VLC are potentially useful for providing Internet of Things (IoT) services while consuming a small portion of the transmission resources, considering a user-centric approach and subject to a low-cost implementation [2] . Recently, the European Commission warned about the need for employing low-cost and energy-efficient LEDs for future VLC systems to maintain the reduction in the energy consumption [3] . As a consequence, the VLC-IoT hardware implementations must consider commercial LEDs, which are subject to non-linearities, reduced and unknown bandwidth and other impairments for data transmission, while maintaining the energy efficiency for illumination purposes. In this work, a low-cost VLC-IoT implementation is presented based on commercial high-power LEDs. The proposed configuration is focused on providing connectivity in those environments where RF transmission is not efficient so that an external access point (AP) distributes the connectivity through a backhaul link that feeds the set of optical access points (APs).
  • Publication
    Tangential Power Allocation NOMA scheme for Visible Light Communications
    (IEEE, 2022-11-28) Al-Sakkaf, Ahmed Gaafar Ahmed; Morales Céspedes, Máximo; European Commission
    Non-orthogonal multiple access (NOMA) has been proposed in both radio-frequency (RF) and visible light communications (VLC) to both improve the achievable rate and overcome the constrains in the number of users of orthogonal multiple access (OMA) schemes. Despite the advantages of NOMA, there still exist some issues that require more investigation such as power allocation schemes. This is issue is more remarkable in VLC due to the small and confined coverage footprint of each optical access point. In this poster, we propose a novel methodology denoted by tangential power allocation (TPA) for NOMA in VLC. Basically, the power allocation coefficients are calculated based on the tangential point on the NOMA rate region that is parallel to the OMA region. It is shown that TPA achieves greater performance in terms of achievable rate and fairness in comparison with conventional NOMA schemes.
  • Publication
    Hardware Evaluation of Interference Alignment Algorithms Using USRPs for Beyond 5G Networks
    (IEEE, 2023-07-06) Urquiza Villalonga, David Alejandro; Lopez Barrios, Alejandro; Fernández-Getino García, María Julia; European Commission; Agencia Estatal de Investigación (España)
    Network densification is a key technology to achieve the spectral efficiency (SE) expected in 5G wireless networks and beyond. However, the proximity between transmitters and receivers increases the interference levels, becoming a major drawback. To overcome this problem, several interference management techniques have been proposed to increase the signal-to-interference-plus-noise ratio (SINR). Interference alignment (IA) algorithms have been extensively studied due to their capability to achieve optimal degrees of freedom (DoFs) in interference channels (ICs). Nevertheless, most of the works are limited to a purely theoretical analysis based on non-realistic assumptions such as perfect channel state information (CSI) and the synchronization of all nodes in the network. To the best of our knowledge, only a few articles address the IA implementation using reconfigurable hardware. To cover this lack, this paper proposes a practical design of the IA algorithm based on the SINR maximization, known as MAX-SINR, considering a multi-user IC. Each transmitter and receiver is implemented on the National Instruments USRP-2942. A practical solution for the channel estimation and synchronization stages in an IC, that are usually omitted in theoretical works, is developed. The performance of the proposed implementation is shown in terms of the SINR gain, SE, and bit error rate (BER). Unlike previous works, all the results are based on real measurements providing valuable insights into the performance of IA algorithms.
  • Publication
    Parametric approximation to optimal averaging in superimposed training schemes under realistic time-variant channels
    (IEEE, 2022) Piqué Muntané, Ignasi; Fernández-Getino García, María Julia; Ministerio de Ciencia e Innovación (España); Agencia Estatal de Investigación (España)
    Superimposed Training (ST) with orthogonal frequency division multiplexing (OFDM) scheme has become an attractive solution to meet the goals of the fifth generation (5G) of mobile communications, by improving the channel estimation performance, which is one of the main challenge in multiple input multiple output (MIMO) systems. This technique does not hinder the throughput, however, it introduces an intrinsic interference since the data and the reference symbols are sent together. In order to mitigate it, several studies propose a time averaging over several OFDM received symbols, where the optimal length of this averaging can be analytically computed by solving a transcendental equation. In this paper, this optimal averaging is approximated by a low complexity parametric approach based on a multiple linear regression model that inputs two parameters, the signal-to-noise ratio (SNR) and the relative speed between the transmitter and receiver, which effectively represents the variability of the channel in time. Results show that the approximated solutions give an error of 0.05% on average and 7% at most in terms of the provided mean square error (MSE) of the channel estimation.
  • Publication
    Near-Optimal Detection of CE-OFDM Signals with High Power Efficiency via GAMP-based Receivers
    (IEEE, 2023-01-12) López Morales, Manuel José; Dinis, Rui; García-Armada, Ana; European Commission; Agencia Estatal de Investigación (España)
    A quasi-optimum receiver based on the generalized approximate message passing (GAMP) concept is proposed for constant envelope orthogonal frequency division multiplexing (CE-OFDM) signals. Large modulation index results in large power efficiency for CE-OFDM, but the phase modulator introduces nonlinear distortion effects, precluding good performance for a simple phase detector. Our simulation results show that the GAMP receiver can achieve quasi-optimum performance and it can outperform the linear OFDM and CE-OFDM with phase detectors, for both additive white Gaussian noise (AWGN) and frequency selective channels.
  • Publication
    Simultaneous RIS tuning and differential data transmission for MISO OFDM wireless systems
    (IEEE, 2022) Chen Hu, Kun; Alexandropoulos, George C.; García-Armada, Ana; European Commission; Agencia Estatal de Investigación (España)
    The Reconfigurable Intelligent Surfaces (RIS) constitute one of the prominent technologies for the next generation of wireless communications. They are mainly envisioned to efficiently enhance the signal coverage in cases where the direct communication link is weak or obstructed. Recently, beam training based on codebook selection has been proposed as a low-latency means for tuning the RIS phase profile according to a desired performance metric. However, it requires the transmission of reference signals to measure the performance with different RIS phase configurations available in the codebook, which reduces the spectral efficiency. In this paper, we consider the uplink of a Multiple-Input Signal-Output (MISO) communication system with Orthogonal Frequency-Division Multiplexing (OFDM) and present a novel scheme for simultaneous RIS phase configuration and data transmission. The proposed scheme is based on non-coherent differential modulation, which is deployed both in the beam training and the data transmission phases. In the former phase, it also enables energy measurement for the determination of the best RIS phase profile. Then, in the latter phase, a higher throughput can be established through the high gain reflective link. Our numerical results showcase that our proposal can double the system throughput with lower complexity, as compared to the generic state-of-the-art approach.
  • Publication
    Performance bounds with precoding matrices compliant with standardized 5G-NR for MIMO transmission
    (IEEE, 2023-02-27) Urquiza Villalonga, David Alejandro; OdetAlla, Hatem; Fernández-Getino García, María Julia; Flizikowski, Adam; European Commission; Ministerio de Ciencia e Innovación (España)
    Advanced multiple-input multiple-output (MIMO) beamforming techniques are crucial in 5G New Radio (NR) to achieve the expected data rate values. Therefore, the 3rd Generation Partnership Project (3GPP) has proposed a codebook-based MIMO precoding strategy to provide high diversity, array gain, and spatial multiplexing. The main goal is to obtain a tradeoff between performance, signal overhead, and complexity. The precoding matrix is selected from a set of predefined codebooks based on the knowledge that the 5G-NR base station (gNB) acquires about the channel status. In this work, a detailed study of the precoding matrix design is provided following the guidelines reported in the technical specifications 38-211 and 38-214 of the 3GPP. An analysis of the performance in terms of spectral efficiency (SE) achieved by the 5G-NR precoding matrices is illustrated for a single-user MIMO scenario. These results are contrasted against the optimal singular value decomposition (SVD) solution in order to explore the gap between the standardized precoding proposal and the optimal one. Several values of signal-to-noise ratio (SNR) and different antenna array configurations are considered. Moreover, the multiplexing gain for a different number of parallel data streams is evaluated. Numerical results show the SE bounds that can be obtained with the 5G-NR precoding matrices. These insights are of key importance for practical implementation of precoding strategies in 5G-NR systems and beyond.
  • Publication
    An innovative and simple impedance matching network using stacks of metasurface sheets to suppress the mismatch between antennas and RF front-end transceivers circuits
    (IEEE, 2021-03-22) Alibakhshikenari, Mohammad; Virdee, Bal S.; Althuwayb, Ayman A.; Falcone, Francisco; Limiti, Ernesto; Ministerio de Ciencia e Innovación (España)
    A innovative and simple impedance matching network is presented that is implemented by stacking together metasurface (MTS) sheets. The technique is shown to reduce the mismatch between free-space and RF front-end antenna of a receiver. The MTS based impedance matching network is modeled as a transmission-line loaded with shunt and series capacitances and inductances, respectively. The proposed MTS impedance matching network can be employed to effectively interface the free-space to the antenna of an RF receiver and thereby optimize power absorption. Each MTS impedance matching sheet comprises two-dimensional periodic array of subwavelength microstrip resonator unit-cells that are spaced at a wavelength that is smaller than the frequency of operation. The unit-cells are square shaped patches and embedded with cross-shaped slots that are grounded through a via-hole. The MTS impedance matching network was fabricated using FR-4 substrate. 3D full-wave EM tool by Ansys HFSS™ was used to verify its effectiveness. The proposed MTS impedance matching sheet is relatively easy to implement in practice.
  • Publication
    Analysis of the WiFi4EU initiative as a potential instrument to correct digital divide in rural areas in the EU
    (EconStor, 2019) Navío-Marco, Julio; Pérez Leal, Raquel; Ruiz-Gómez, Luis Manuel; Ministerio de Ciencia e Innovación (España)
    With the WiFi4EU initiative, the European Commission intends to reinforce local wireless Internet connectivity free of charge and without discriminatory conditions in the EU. This paper aims to analyse if this policy measure achieves its goals: to contribute towards digital inclusion and to improve coverage in disadvantaged areas. By analysing the results of the first call, we can conclude that WiFi4EU can be a good tool for promoting the necessary connectivity in local/rural environments of the European Union, but there is room for improvement to increase the positive impact of the initiative. The article proposes useful recommendations for municipalities and policymakers, and suggests improvements for the award procedure.
  • Publication
    Low-rank channel estimation for mm-Wave multiple antenna systems using joint spatio-temporal covariance matrix
    (IEEE, 2019-01-20) Chen Hu, Kun; Slock, Dirk T. M.; García-Armada, Ana; Ministerio de Ciencia e Innovación (España)
    Millimeter-Wave (mm-Wave) and very large multiple antenna systems (VLMAS) are two key technologies in the deployment of Fifth Generation (5G) mobile communication systems. In order to exploit all the benefits of VLMAS, spatial and temporal (ST) features must be estimated and exploited to compute the precoding/decoding matrices. In the literature, a practical channel estimation approach is proposed by assuming that the spatial features are completely unknown, leading to non-parametric estimation in which antenna array calibration is not required. Additionally, when the signal-to-noise ratio (SNR) is not so high, a low-rank (LR) version of the estimated channel is proposed that provides better performance than the full-rank (FR) one in terms of bias-variance trade-off in the mean squared error (MSE). However, previous work assumes that spatial and temporal characteristics of the channel can be estimated separately. Then, the performance is degraded in realistic channels. In this paper, we propose an alternative way to characterize the FR estimated channel using a joint ST covariance matrix, combined with a low-complexity semi-parametric spatial response and delay estimation technique. Moreover, we propose an automatic rank-selector (ARS) based on the MSE in order to provide the best LR channel estimation for each scenario. Numerical results show that the proposed technique outperforms existing approaches in the literature.
  • Publication
    New insights on channel hardening in cell-free massive MIMO networks
    (IEEE, 2020-06-07) Álvarez Polegre, Alberto; Riera-Palou, Felip; Femenias, Guillem; García-Armada, Ana
    The cell-free (CF) massive multiple-input multiple-output (M-MIMO) architecture has recently emerged as a key technology for future wireless networks that is shown to outperform alternative network deployments such as those based on small-cells. Despite the many characteristics CF-M-MIMO shares with conventional M-MIMO (i.e., centralized) systems, its distributed nature brings along new issues that need to be carefully accounted for. In particular, the so-called channel hardening effect that postulates that the variance of the compound wireless channel experienced by a given user from a large number of transmit antennas tends to vanish, effectively making the channel deterministic. This critical assumption, which permeates most theoretical results of M-MIMO, has been well investigated and validated in centralized architectures, however, it has received little attention in the context of CF-M-MIMO networks. Hardening in CF-M-MIMO is potentially compromised by the different large-scale gains each access point (AP) impinges to the transmitted signal to each user, a condition that is further stressed when not all APs transmit to all users as proposed in the user-centric (UC) variations of CF-M-MIMO. This paper aims at presenting a comprehensive study of the channel-hardening effect in CF-M-MIMO under realistic operational conditions (e.g, presence of pilot contamination, power control, different precoders). Closed-form expressions of the hardening coefficient for different precoding schemes are provided showing that the precoder's choice, the number of antennas at each AP and the geographical density of APs play a key role in achieving this property.
  • Publication
    Performance analysis of N-Fisher-Snedecor F fading and its application to N-Hop FSO communications
    (IEEE, 2021-09-06) Stefanovic, Caslav; Morales Céspedes, Máximo; Roka, Rastislav; García-Armada, Ana; European Commission; Ministerio de Ciencia e Innovación (España)
    The Fisher-Snedecor F distribution has been recently proposed as an experimentally verified and tractable turbulence induced fading model (TIFM) for free space optical (FSO) communications. This paper provides outage probability (OP) and higher-order (HO) performance analysis of the product of N independent but not identically distributed (i.n.i.d) Fisher-Snedecor F random variates (RVs). Accurate and closed-form (C-F) expressions for cumulative distribution function (CDF), level crossing rate (LCR) and average fade duration (AFD) of N-Fisher-Snedecor F distribution are successfully derived. The general property of a Laplace approximation approach for evaluation of N-folded complex integral-form (I-F) LCR expressions has been applied. The obtained statistical results are directly related to the performance evaluation of N-hop FSO communication links over weak, moderate and strong atmospheric turbulence conditions.
  • Publication
    Reference scenarios and key performance indicators for 5G ultra-dense networks
    (IEEE, 2020-07-20) Campos, Lués Miguel; Ribeiro, Luis; Karydis, Ioannis; Karagiannis, Stelios; Pedro, Dário; Martins, Jorge; Marques, Carlos; García-Armada, Ana; Pérez Leal, Raquel; López Morales, Manuel José; Velez, Fernando J.; Sebastiao, Pedro; Rocha Ramos, Anderson; European Commission
    The so-called 5G will revolutionize the way we live, and work. In order to demonstrate the profound changes, we can expect to experience within the next 5 to 10 years, we present use cases for the planned research within the TeamUp5G project. Some use cases are strongly linked to the network layer and aim at developing solutions capable of optimizing the main promising benefits of 5G: extremely low latency and extremely high bandwidth (e.g., handle video streams, traffic congestion, user profiles), in the most efficient way possible. Other use cases focus on commercial applications that make use of middleware applications to enhance their performance. The latter fall into two main areas: real-time virtual reality and live video streaming, which are extremely demanding in terms of latency and bandwidth to provide an acceptable QoE/QoS to multiple users. The use cases presented are built assuming that 5G is essential for their support with appropriate QoE/QoS. Key performance indicators and their range of variation are also identified.
  • Publication
    Performance analysis of the FBMC modulation format in optical fiber and wireless communications
    (IEEE, 2021-09-06) Roka, Rastislav; Stefanovic, Caslav; Morales Céspedes, Máximo; García-Armada, Ana; European Commission; Ministerio de Ciencia e Innovación (España)
    The FBMC is among the currently most researched techniques for signal processing and is explored here for passive optical access networks. This paper presents a performance analysis of the FBMC modulation format for applying in optical fiber and wireless communications. For analyzing, we realized simulation models that are based on well-known characteristics of the optical transmission medium and the free space environment that can describe mutual relations between optical signals and environmental influences. The FBMC model can be consequently applied for a purpose of advanced simulations performed in the complete optical transmission path. The results suggest that the FBMC format can be utilized for reliable optical fiber and wireless communication systems.
  • Publication
    Death/birth and SNR detection for vehicular Kalman channel trackers
    (IEEE, 2020-06-16) Méndez Romero, Diego; Fernández-Getino García, María Julia; Ministerio de Ciencia e Innovación (España)
    Wireless communication demand is increasing requirements due to expected smart mobility as well as modern vehicular technologies, such as Unmanned Air Vehicles (UAVs) or High-Speed Rail (HSR). In the latter scenario, high mobility through different physical environments, such as from viaducts to cuttings or tunnels, results in a fast variation of the multipath structure, giving rise to the phenomenon of birth-death of taps. To exploit the temporal correlation of each tap, however, a Kalman filter (KF) could be used; but KF's performance degrades catastrophically unless tap birth/death can be synchronically detected. To address this issue, several solutions based on particle filtering have been proposed, albeit with a prohibitive complexity. More recently, a Simplified Maximum A Posteriori (SMAP) algorithm for tap birth/death detection has been developed for the case where there is no signal-to-noise ratio (SNR) variation. With a similar purpose in mind, this paper develops a theoretical framework to understand death/birth detection when SNR is dynamical and may drift. This paper also analyzes how different quasi-ideal SNR detectors affect the SMAP algorithm's performance.
  • Publication
    Graph based interference analysis and resource allocation in mmWave IoT networks
    (IEEE, 2019-09-09) Vulchi, Hemalatha; Pérez Leal, Raquel; García-Armada, Ana; Ministerio de Ciencia e Innovación (España)
    IoT, Internet of Things is one of the most promising technologies of the fifth-generation (5G). The buzz is all about creating smart environments and getting every type of device connected to the internet. 5G will revolutionize the speed at which the data is transferred, and how much can be transferred at one time. Millimeterwave (mmWave) and massiveMIMO are the two key technologies which plays an essential role to address this problem and represents the next frontier of wireless technology, bringing 10 times higher frequencies and 10 times wider channel bandwidths than the most advanced Wi-Fi and cellular technologies. Millimeter-wave technology is going to become less expensive and easier to deploy, making it a candidate for many wireless connections, including backhaul, personal area networks and LANs. In the world of IoT, this translates into instant, reliable machine communication across every industry and application possible [1]. As the density of wireless devices increases and requirements of all their applications change drastically, it becomes more challenging to provide them connectivity within the stipulated amount of time to deliver the needs. As a result, several challenges such as improving the network capacity, coverage area, efficient data capturing, security, signal processing becomes a necessity to be handled. In line with these, a very recent area of research is to exploit mm-wave band for use in 5G IoT implementations unlike the traditional usage of Zigbee and Bluetooth technologies. One of the technical challenges in this broad area of research is coordinating communication among large number of devices ensuring highly reliable links and investigate on the potential of Resource allocation to envision a diverse set of usage scenarios and applications.
  • Publication
    Minimizing age of information on NOMA communication schemes for vehicular communication applications
    (IEEE, 2020-07-20) Torres Gómez, Jorge; Morales Céspedes, Máximo; García-Armada, Ana; Hirtz, Gangolf; Ministerio de Ciencia e Innovación (España)
    Real-time communication schemes supporting fresh information are of major importance for vehicular networks. In this direction, the Age of Information (AoI) concept is a power-full tool to operate with. Current publications bring equal importance to the AoI of packets in spite of the common case of unequal channel capacity and source entropy between them, this results in reduced user perception of fairness. This report analyses the use of power-domain NOMA to balance the assigned power between nodes to reduce the overall AoI. We verify an improved user perception of fairness in regard to the freshness of information at the destination.
  • Publication
    Drive tests-based evaluation of macroscopic pathloss models for mobile networks
    (IEEE, 2019-01-18) Álvarez Polegre, Alberto; Pérez Leal, Raquel; Garcia Garcia, Jose Antonio; García-Armada, Ana; Ministerio de Ciencia e Innovación (España)
    Mobile operators have already started their 5G network deployment and next generation user terminals commercial release is planned for the upcoming months. Knowing the future network system performance and capabilities seem to be key in order to have proper planning strategies. In this paper we present some field test trials for the latest release of 4G, which have lots of similarities with the forthcoming mobile broadband standard. Results for urban drive tests are presented too. We also bring pathloss simulation based on modern channel models that matches the results obtained in the real scenarios. Error is measured to have insights about the utility and accuracy of the pathloss models when comparison with specific scenarios is made. Some final brainstorming for future work with 5G network and concluding remarks are proposed.
  • Publication
    Characterization of the visible light communications during the construction of tunnels
    (IEEE, 2019-08-27) Morales Céspedes, Máximo; García-Armada, Ana; Ministerio de Ciencia e Innovación (España)
    Visible Light Communications (VLC) are proposed to provide connectivity within the framework of the Industry 4.0 because of their resilience in industrial environments in comparison with radio-frequency (RF) transmission systems. In this work, we focus on providing connectivity during the construction of tunnels. Notice that other aLTErnatives such as the radiant cable are restricted to implement them once the construction of the tunnel has been finished. First, we characterize the optical channel taking into consideration the reflections that occur in a confined structure. It is shown that the quality of the channel, and therefore, the symbol error rate, depends on the angle of incidence of the receiver. We propose the use of receivers composed of multiple photodiodes following an angle diversity arrangement with the aim of ensuring a minimum symbol error rate (SER). Simulation results show that this approach allow us to improve the robustness of the VLC systems during the construction of tunnels or other confined structure.