DTSC - GC - Capítulos de Monografías

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Now showing 1 - 20 of 32
  • 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
    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
    Pilot-less massive MIMO TDD system with blind channel estimation using non-coherent DMPSK
    (IEEE, 2023-01-11) López Morales, Manuel José; Chen Hu, Kun; García-Armada, Ana; European Commission; Ministerio de Economía y Competitividad (España)
    A novel time division duplex massive MIMO approach based on performing a blind channel estimation in the uplink using differentially encoded data and a precoding in the downlink, also with differentially encoded data, is proposed. In this system, the use of any type of explicit pilot symbol is completely avoided while maintaining spatial multiplexing capabilities in the downlink. We perform an analysis of the full system in terms or signal-to-interference-and-noise ratio (SINR) for the uplink and the downlink. The performance of the channel estimation using differentially encoded data is also analyzed, since it affects the performance of the downlink data transmission. A multi-user allocation strategy in an OFDM grid is proposed. The analysis is corroborated via numerical results and the proposed scheme is shown to outperform its coherent counterpart.
  • Publication
    Design of DMRS schemes for 5G vehicular communications
    (IEEE, 2021-06-15) Riol Martin, Juan; Pérez Leal, Raquel; García-Armada, Ana; Ministerio de Economía y Competitividad (España)
    The arrival of the fifth generation (5G) of mobile communications is boosting vehicular communications, an important use case addressed in the recent years. LTE introduced a sidelink radio interface through which user equipment would communicate directly with no necessary dependence on the network, named PC5. 5G has defined its own sidelink interface, NR-Sidelink, envisaged to improve PC5. This paper analyses the use of Demodulation Reference Signals (DMRS) to estimate the channel in sidelink communications. Improving several mappings proposed by the standards, the main contribution proposed in this paper is a new DMRS mapping with a better performance. The proposed Unequal Pilot Spacing (UPS) mapping can enhance the standard with a satisfactory trade-off between performance and overhead.
  • Publication
    Non-Coherent Massive MIMO-OFDM Down-Link Based on Differential Modulation
    (IEEE, 2020-10) Chen Hu, Kun; Liu, Yong; García-Armada, Ana; Ministerio de Economía y Competitividad (España)
    Orthogonal frequency division multiplexing (OFDM) and multiple-input multiple-output (MIMO) are wireless radio technologies adopted by the new Fifth Generation (5G) of mobile communications. A very large number of antennas (massive MIMO) is used to perform the beam-forming of the transmitted signal, either to reduce the multi-user interference (MUI), when spatially multiplexing several users, or to compensate the path-loss when higher frequencies than microwave are used, such as the millimeter-waves (mm-Waves). Usually, a coherent demodulation scheme (CDS) is used in order to exploit MIMO-OFDM, where the channel estimation and the pre/post-equalization processes are complex and time consuming operations, which require a considerable pilot overhead and also increase the latency of the system. As an alternative, non-coherent techniques based on a differential modulation scheme have been proposed for the up-link (UL). However, it is not straightforward to extend these proposals to the down-link (DL) due to the (usually) reduced number of antennas at the receiver side. In this paper we overcome this problem, and assuming that each user equipment (UE) is only equipped with one single antenna, we propose the combination of beam-forming with a differential modulation scheme for the DL, enhanced by the frequency diversity. The new transmission and reception schemes are described, and the signal-to-interference-plus-noise ratio (SINR) and the complexity are analysed. The numerical results verify the accuracy of the analysis and show that our proposal outperforms the existing CDS with a significant lower complexity.
  • Publication
    Cutting the cord: key performance indicators for the future of wireless virtual reality applications
    (IEEE, 2020-11-10) González Morín, Diego; García-Armada, Ana; Pérez, Pablo; European Commission
    The new generation of telecommunication networks (5G) are considered a key technology enabler for the future of Virtual Reality (VR) technologies. 5G improved throughput and low latency capabilities open the door for novel distributed VR architectures that will accelerate the development of wireless immersive VR. While the downlink requirements for wireless VR have been previously studied, the uplink transmissions have been completely neglegted. However, for the succesful consecution of a fully immersive wireless VR, the uplink stream becomes as important as the downlink. In this paper, we thoroughly analyze VR thecnologies state of art to extract an initial set of data flow and processing times requirements for a subgroup of identified key algorithms. Besides, we propose the peak throughput and latency requirements Key Performance Indicators (KPIs) estimation as a simple optimization problem, given the data gathered in the state of the art analysis. Finally, we propose a set of valid ranges of peak throughput and latency requirements for a selected group of three different offloading scenarios.
  • Publication
    MmWave massive MIMO small cells for 5G and beyond mobile networks: an overview
    (IEEE, 2020-11-10) Mchangama, Aboubacar; Ayadi, Jaouhar; Gil Jiménez, Víctor Pedro; European Commission; Ministerio de Economía y Competitividad (España)
    Promising technologies are being investigated to integrate them into the fifth generation (5G) and beyond mobile network systems. The main goal of these technologies is to evolve cellular network that will significantly stress forward the limit of legacy network systems through all dimensions performance metrics. One of the most potential key enabler technologies is millimeter wave (mmWave) massive multipleinput multiple-output (MIMO) small cells (SC) system. These set of technologies will dramatically increase the network throughput, enhance the spectral and energy efficiency, increase the network capacity and improve the network coverage by using the joint capabilities of the huge available bandwidth in mmWave frequencies while achieving high multiplexing gains through the extreme antenna arrays gains and achieving full coverage network by network densification through small cells. In this paper we present detailed overview of millimeter wave, massive MIMO, small cells, channel estimation, beamforming technology, signal processing techniques in mmWave, beyond 5G systems, and challenges and future research trends.
  • Publication
    TeamUp5G: a multidisciplinary approach to training and research on new RAN techniques for 5G ultra-dense mobile networks
    (IEEE, 2020-11-10) Pérez Leal, Raquel; Da Silva Vélez, Fernando José; Miguel Campos, Luis; García-Armada, Ana; European Commission
    This paper presents a summary of the main research directions being followed in TeamUp5G European Training Network, teaming up a new generation of researchers and entrepreneurs ready to address complex engineering problems and innovation to work both at university and industry in the 5G field. This project is focused on new radio access network (RAN) techniques for 5G, considering ultradense mobile networks as a key ingredient of the actual mobile networks and their evolution. Research covers a wide spread of topics from physical layer and medium access control to applications, looking at spectrum sharing and energy efficiency as important features.
  • Publication
    Performance comparison of interference alignment algorithms in an energy harvesting scenario
    (IEEE, 2020-11-10) Urquiza Villalonga, David Alejandro; Fernández-Getino García, María Julia; European Commission; Ministerio de Economía y Competitividad (España)
    Energy-efficient interference alignment (IA) algorithms that simultaneously satisfy continuous coverage and green communications requirements are an open problem in 5G cellular networks. IA is one of the most promising techniques to eliminate interference. However, a recent assumption in green communications is to utilize interference signals as an energy supply for electronic devices. In this scenario, simultaneous wireless information and power transfer (SWIPT) schemes are a common technique to harvest energy from wireless signals. This paper addresses a performance comparison of different IA algorithms to guarantee the best trade-off between sum-rate and the amount of harvested energy, with an in-depth analysis.
  • Publication
    A survey about deep learning for constellation design in communications
    (IEEE, 2020-11-10) López Morales, Manuel José; Chen Hu, Kun; García-Armada, Ana; European Commission; Ministerio de Economía y Competitividad (España)
    The performance of communication systems dependson the choice of constellations, designed in an end-to-endmanner. In case of a mathematical intractability, either becauseof complexity or even lack of channel model only sub-optimal solutionscan be provided with an analytical approach. We presentend-to-end learning, a recent technique in communications tolearn optimal transmitter and receiver architectures based ondeep neural networks (DNNs) architectures. We discuss cases inwhich this technique has been used to design constellations inwhich channel model intractability repressed from a mathematicalanalysis.
  • Publication
    Experimental Evaluation of Blind Interference Alignment
    (IEEE, 2015-05) Morales Céspedes, Máximo; Sánchez Fernández, Matilde Pilar; García-Armada, Ana
    An experimental evaluation of Blind Interference Alignment (BIA) over a hardware platform is presented in this work. In contrast to other transmission techniques such as Linear Zero Forcing Beamforming (LZFB) or Interference Alignment (IA), BIA achieves a growth in Degrees of Freedom (DoF) without channel state information at the transmitter (CSIT). A real implementation based on Orthogonal Frequency Division Multiplexing (OFDM) and LTE parameters is implement on a testbed made up of a transmitter equipped with two antennas and two users equipped with a reconfigurable antenna each. Furthermore, a full CSIT technique such as LZFB is also implemented for comparison purposes. First, the theoretic achievable rates are obtained for both techniques. After that, the bit error rate of both schemes is evaluated regarding the achieved sum-thorughput.
  • Publication
    Testbed for a LiFi system integrated in streetlights
    (IEEE Institute of Electrical and Electronics Engineers, 2015-06) Monzón Baeza, Victor; Sánchez Fernández, Matilde Pilar; García-Armada, Ana; Royo, A.
    In this paper, a functional LiFi real-time testbed implemented on FPGAs is presented. The setup evaluates the performance of our design in a downlink scenario where the transmitter is embedded on the streetlights and a mobile phone’s camera is used as receiver, therefore achieving the goal of lighting and communicating simultaneously. To validate the design, simulations of the whole system are performed. where simulations of the channel between streetlight and mobile device show the scope of the reflection in an outdoor environment. The measurements are carried out to characterize the modulator, in particular the FPGA resources and latency due to the encoder blocks. In addition the feasibility of the communication function in presence of the ambient light is verified.
  • Publication
    A non-coherent multi-user large scale SIMO system relaying on M-ary DPSK
    (IEEE Computer Society., 2015-06) García-Armada, Ana; Hanzo, Lajos
    A non-coherent detection assisted Differential Phase Shift Keying aided large-scale MIMO system is designed in a wireless uplink where multiple single-antenna users are transmitting to the base station's receiver equipped with a very large number of receive antennas. We show that the signal to interference plus noise ratio (SINR) scales with the number of receive antennas, which confirms the same scaling law found in coherent systems. We propose a range of constellation designs that allow us to separate the users' signals at the receiver by relying only on the knowledge of the average received power per user. We analyse the error probability and provide insights into the beneficial selection of the constellation parameters. Finally, we provide some numerical results showing that our proposals require a lower number of receive antennas to achieve a given error probability than other non-coherent benchmark schemes available in the literature, while they are not far from an equivalent coherent system relying on realistic channel estimation settings.
  • Publication
    Joint Strategy for LTE Resource Allocation: Multicast Subgrouping & Unicast Transmissions
    (Universitat de Les Illes Balears, 2015-10) Fuente Iglesias, Alejandro de la; Pérez Leal, Raquel; García-Armada, Ana
    Mobile broadband services are growing rapidly in the last few years due to the deployment of Long Term Evolution (LTE) cellular networks. Among them, multicast services can be provided using Evolved Multimedia Broadcast and Multicast Service (eMBMS), available with 3rd Generation Partnership Project (3GPP) release 9, which can deliver broadcast/multicast content using a single-frequency network mode. This means sending the same multimedia content to a mass audience within a specific area. The utilization of the Conventional Multicast Scheme (CMS) approach for multicast resource allocation presents intrinsic inefficiencies, because of the different channel conditions of the users which demand the service. This paper proposes a Joint Multicast Subgrouping and Unicast Transmissions (JMSUT) strategy for resource allocation, which consists of the use of the multicast and the unicast transmissions, by means of the subframes reserved by the LTE standard for each purpose, to deliver a multicast service. The goal of the JMSUT algorithm is to maximize the service throughput whereas it guarantees the fulfillment of the Quality of Service (QoS) requirements of every user. This paper solves the former maximization problem of the joint resource allocation; on the one hand, splitting the multicast resources into different subgroups that transmit the same content with different Modulation and Coding Scheme (MCS), and on the other hand, the users with worst channel conditions are served by means of the unicast transmissions.
  • Publication
    Señales DCO-OFDM eficientes para VLC utilizando Redes Neuronales adaptativas Difusas (ANFIS)
    (Universidad Politecnica de Valencia, 2014-09) Genovés Guzmán, Borja; Gil-Jiménez, Víctor P.
    In this paper, Adaptive Neural Fuzzy Inference Systems (ANFIS) are used for obtaining Direct Current biased Optical Orthogonal Frequency Division Multiplexing (DCOOFDM) signals with low power envelope. Signals with very low crest factor obtained from Active Constellation Expansion (ACE) method are used for training our fuzzy systems. After the off-line training, the ANFIS are able to generate from the original realvalued signal another real-valued one with more than 2 dB of power envelope reduction which impacts in the final performance after going through the LED.
  • Publication
    Sincronización y Estimación de canal eficiente y robusta en sistemas CoMP OFDM
    (Universidad Politecnica de Valencia, 2014-09) Lancho Serrano, Alejandro; Gil-Jiménez, Víctor P.
    In this paper, an efficient and robust simultaneous timing synchronization and channel estimation method for Cooperative MultiPoint Transmission and Reception (CoMP) is proposed. Efficiency is obtained by using the same two Orthogonal Frequency Division Multiplexing (OFDM) symbols for simultaneously transmitting preambles by all the base stations. Robustness is achieved by specially designed orthogonal sequences both in time and frequency domain. The proposed method is able to estimate the channels from several base stations without losing anything in performance with respect to the single transmission scenario. Furthermore, our proposed synchronization outperforms single transmitter methods and so, it could also be adapted for single base station OFDM systems.
  • Publication
    Radio-over-Fiber Aided Base Station Coordination for OFDM
    (IEEE - The Institute Of Electrical And Electronics Engineers, Inc, 2014-09-15) García-Armada, Ana; Thomas, Varghese Antony; El-Hajjar, M.; Hanzo, Lajos
    Radio over Fiber (RoF) distribution aided co-operation of Remote Access Points (RAPs) is proposed for jointly transmitting data to the users in the downlink (DL) of a Multiple Input Multiple Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) system. Joint transmission is performed with the aid of Block Diagonalization (BD), where the transmitted signal is pre-distorted in order to overcome the non-linearity imposed by the optical modulator. We demonstrate that with adequate design, the users can obtain high data rates with very small degradation introduced by the RoF transmission. Quantitatively, when M=7 RAPs, each equipped with t=2 transmit antennas (TAs) each, cooperate to serve N=7 simultaneous users, also equipped with r=2 receive antennas (RAs), the SNR degradation is kept below 0.1 dB compared to a system assuming a perfect RoF channel. On the other hand, the SNR performance degradation is around 1.2 dB, when the number of antennas at the transmitters and the receivers is increased to t=r=8.
  • Publication
    Asymptotic analysis of multiuser-MIMO networks with battery-constrained receivers
    (IEEE - The Institute of Electrical and Electronics Engineers, Inc, 2014-05) Rubio, Javier; Pascual Iserte, Antonio; García-Fernández, Juan José; García-Armada, Ana; Font Bach, Oriol; Font Bach, Nikolaos
    In this paper, we present an asymptotic analysis of the behavior of a network where the mobile terminals are considered to be battery-powered devices provided with energy harvesting capabilities. The asymptotic analysis is based on a multiuser MIMO resource allocation strategy where the battery status of the mobile terminals are considered explicitly in the proposed allocation policy. We provide some numerical results and analytic expressions of the expected value of the data rates and the battery levels for different decoding power consumption models when convergence is attained.
  • Publication
    A control theoretic approach to solve a constrained uplink power dynamic game
    (IEEE - The Institute of Electrical and Electronics Engineers, Inc, 2014-09) Zazo, Santiago; Zazo, Javier; Sánchez-Fernández, Matilde
    This paper addresses an uplink power control dynamic game where we assume that each user battery represents the system state that changes with time following a discrete-time version of a differential game. To overcome the complexity of the analysis of a dynamic game approach we focus on the concept of Dynamic Potential Games showing that the game can be solved as an equivalent Multivariate Optimum Control Problem. The solution of this problem is quite interesting because different users split the activity in time, avoiding higher interferences and providing a long term fairness.
  • Publication
    A unified framework for linear function approximation of value functions in stochastic control
    (IEEE - The Institute of Electrical and Electronics Engineers, Inc, 2013-09) Sánchez-Fernández, Matilde; Valcárcel, Sergio; Zazo, Santiago
    This paper contributes with a unified formulation that merges previous analysis on the prediction of the performance (value function) of certain sequence of actions (policy) when an agent operates a Markov decision process with large state-space. When the states are represented by features and the value function is linearly approximated, our analysis reveals a new relationship between two common cost functions used to obtain the optimal approximation. In addition, this analysis allows us to propose an efficient adaptive algorithm that provides an unbiased linear estimate. The performance of the proposed algorithm is illustrated by simulation, showing competitive results when compared with the state-of-the-art solutions.