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Adaptive OFDM has the potential of providing bandwidth-efficient communications in hostile propagation environments. Currently, bit loading algorithms use M-ary quadrature amplitude modulation of the OFDM sub-carriers, where the number of bits per symbol modulating each of them is obtained in order to maximize the performance. SNR gap approximation for M-QAM signaling makes the algorithms simpler to implement. However, in some circumstances it may be preferable to use. Mary phase shift keying. In this letter an approximation is derived for M-PSK similar to the SNR gap of M-QAM so that bit loading algorithms can be extended to this type of modulation. In addition, the performance obtained when using M-PSK is compared to that of M-QAM in a practical situation ; This work has been partly funded by Spanish Government with research project TIC2002-03498 ; Publicado

The proceeding at: 2015, IEEE International Conference on Communications (ICC) took place 8-12 June in London (UK) ; 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. ; This work was supported by projects CSD2008-00010, TEC2011-29006-C03-03 and by a mobility grant of Spanish Ministry of Education. The financial support of the UK Government's Engineering & Physical Sciences Research Council (EPSRC) as well as that of the Research Councils UK (RCUK) and of the European Research Council's Senior Research Fellow Grant is also gratefully acknowledged.

Frequently, Wireless Sensor Networks (WSN) are designed focusing on applications and omitting transmission problems in these wireless networks. In this paper, we present a measurement campaign that has been carried out using one of the most commonly used WSN platforms, the micaZ from Crossbow°c . Based on these measurements, some guidelines to deploy a robust and reliable WSN are provided. The results are focused on security and environmental applications but can also be extrapolated to other scenarios. A main conclusion that can be extracted is that, from the transmission point of view, a dense WSN is one of the best choices to overcome many of the transmission problems such as the existence of a transitional region, redundance, forwarding, obstructions or interference with other systems. ; The authors would like to acknowledge the work of Ramon Duato and Omar Ahmad for the set up of the testbed and measurements. This work has been partly funded by the Spanish government with project MULTIADAPTIVE (TEC2008-06327-C03-02) and COMONSENS (CSD2008-00010). ; Publicado

Augmented reality (AR) has been presented lately as one of the key technology fields in which 5G networks can become a disruptive tool, raising interest from both industry and academia. The main goal of this article is to extend the current state of the art of distributed AR studies and implementations by extracting the main AR algorithms' offloading requirements individually. This extension is further achieved by depicting the data flow between these algorithms and their hardware requirements. From the obtained results, we estimate a preliminary set of network key performance indicators (KPIs) for a subset of three examples of distributed AR implementations highlighting the necessity of 5G technologies and their ecosystem to unveil the full potential of AR. Finally, based on these KPls, we propose a set of 5G configuration parameters for a successful distributed AR implementation. As most of the described algorithms are also used in virtual reality (VR) applications, our contributions can facilitate future distributed implementations of both AR and VR applications. ; This work has received funding from the European Union (EU) Horizon 2020 research and innovation programme under the Marie Skodowska-Curie ETN TeamUp5G, grant agreement no. 813391.

Proceeding of: 12th IEEE/IET International Symposium on Communication Systems, Networks and Digital Signal Processing, (CSNDSP 2020), 20-22 July, Online ; 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. ; This work has received funding from the European Union (EU) Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie ETN TeamUp5G, grant agreement No. 813391.

In this letter the discrete rate maximization problem is investigated for FBMC/OQAM. The analysis reveals that if there is crosstalk certain bit allocations violate the power constraints. Aiming at ensuring the feasibility along with alleviating the complexity we have devised a novel iterative algorithm, which always converges. Simulation-based results show that the proposed algorithm performs close to the upper bound for high-coherence bandwidth channels. Under highly frequency selective channels the existing algorithms are not able to guarantee the target SER whereas our approach guarantees the QoS. ; This work was supported by the Spanish Ministry of Science and Innovation under Projects TEC2011-29006-C03-02 (GRE3N-LINK-MAC), TEC2011-29006-C03-03 (GRE3N-SYST), and TEC2008-06327-C03-01, and by the Catalan Government (2009SGR0891). ; Publicado

In this paper, a novel and practical transmission scheme for a Multiple Input Multiple Output–Orthogonal Frequency Division Multiple Access (MIMO-OFDMA) relay-based network is proposed and evaluated. We coin the term Virtual Maximum Ratio Transmission (VMRT) for the scheme which obtains diversity and array gain at both links in a two-hop transmission, while keeping the complexity low. Besides, the requirements of Channel State Information needed at the different network elements such as the Base Station, Relay Station or User Terminals are also limited, and so the feedback. The obtained global performance by using proposed VMRT outperforms other schemes. Diversity gains larger than 6 can be easily obtained with a reduced number of relays. For this reason, VMRT is a good candidate to achieve high speed transmission or increase coverage and reliability in slow varying channels for relay-based networks. ; This work has been partly funded by the Spanish government with projects MACAWI (TEC 2005-07477-C02-02), MULTIADAPTIVE (TEC 2008-06327-C03-02), COMONSENS (CDS2008-00010) and CODIV (ICT-2007-215477). ; Publicado

Proceeding of: IEEE 95th Vehicular Technology Conference (VTC2022-Spring), Helsinki, Finland, 19-22 June 2022 ; In this work, a spike-QAM, a regular QAM constellation where one to four of the elements with the largest amplitudes are placed further from the center, is proposed as the optimum constellation that minimizes the ratio of the symbolerror-rate (SER) to peak-to-average-power-ratio (PAPR) in simultaneous-wireless-information-and-power-transfer (SWIPT) applications. This constellation is capable of maximizing the SER performance for a given design PAPR, or maximize the PAPR given a SER performance. The relationship between these parameters is defined. An approximation to the SER performance is given for the spike-QAM in AWGN channels and it is demonstrated to be valid via numerical simulations. ; This work has received funding from the European Union Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie ETN TeamUp5G, grant agreement No. 813391, and the Spanish National Project IRENE-EARTH (PID2020-115323RB-C33) (MINECO/AEI/FEDER, UE).

Proceedings of: IEEE Global Communications Conference (GLOBECOM), 9-11 December 2021, Madrid. ; A rigorous analysis of the effect of spatial corre-lation for non-coherent (NC) massive multiple-input-multiple-output (MIMO) in Rician channels is important to determine its applicability in these scenarios. We conduct such analysis for a single base station (BS) and a more general case of several BSs, all of them showing correlation among their own antennas but with uncorrelated channels with respect to each other. We first perform an analysis of the distribution of the received symbols, then propose some approximations to give a closed form expression of the symbol error probability (SER) and the signal-to-interference-and-noise-ratio (SINR) as performance measures. Finally, we extract some conclusions from this analysis to show how the combined use of several BSs and larger Rician components can be beneficial in this scenario. Some numerical results are added to confirm the accuracy of the analysis. ; This work has received funding from the European Union Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie ETN TeamUp5G, grant agreement No. 813391, and the Spanish National Project TERESA-ADA (TEC2017-90093-C3-2-R) (MINECO/AEI/FEDER, UE).

Proceeding of: 12th IEEE/IET International Symposium on Communication Systems, Networks and Digital Signal Processing, (CSNDSP), 20-22, July 2020, (Online). ; 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. ; This work has received funding from the European Union (EU) Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie ETN TeamUp5G, grant agreement No. 813391, and from the Spanish National Project TERESA-ADA (TEC2017-90093-C3-2-R) (MINECO/AEI/FEDER, UE).

Pilot symbol assisted modulation (PSAM) is widely used to obtain the channel state information (CSI) needed for coherent demodulation. It allows the density of pilot symbols to be dynamically chosen depending on the channel conditions. However, the insertion of pilots reduces the spectral efficiency, more severely when the channel is highly time-variant and/or frequency-selective. In these cases a significant amount of pilots is required to properly track the channel variations in both time and frequency dimensions. Alternatively, non-coherent demodulation does not require any CSI for the demodulation independently of the channel conditions. For the particular case of up-link (UL) based on massive single input -multiple output (SIMO) combined with orthogonal frequency division multiplexing (OFDM), we propose to replace the traditional reference signals of PSAM by a new differentially-encoded data stream that can be non-coherently detected. The latter can be demodulated without the knowledge of the CSI and subsequently used for the channel estimation. We denote our proposal as hybrid demodulation scheme (HDS) because it exploits both the benefits of a coherent demodulation scheme (CDS) and a non-coherent demodulation scheme (NCDS) to increase the spectral efficiency. The mean squared error (MSE) of the channel estimation, bit error rate (BER), achieved throughput and complexity are analyzed to highlight the benefits of this differential data-aided channel estimation as compared to other approaches. We show that the channel estimation is almost as good as PSAM, while the BER performance and throughput are improved for different channel conditions with a very small complexity increase. ; This work has received funding from the European Union (EU) Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie ETN TeamUp5G, grant agreement No. 813391, and from the Spanish National Project TERESA-ADA (TEC2017-90093-C3-2-R) (MINECO/AEI/FEDER, UE).

Plug-in electric vehicles (PEVs) have recently attracted much attention due to their potential to reduce CO2 emissions and transportation costs and can be grouped into entities (aggregators) to provide ancillary services such as frequency regulation. In this paper, the application of aggregators to frequency regulation by making fair use of their energy storage capacity is addressed. When the power grid requires frequency regulation service to the aggregator to adjust the grid frequency, the PEVs participating in providing the service can either draw energy (as it is usually done to charge the vehicle) or deliver energy to the grid by means of the vehicle-to-grid (V2G) interface. Under the general framework of optimizing the aggregator profit, different methods, such as state-dependent allocation and the water-filling approach, are proposed to achieve a final state of charge (SOC) of the PEVs that satisfy the desired fairness criteria once the regulation service has been carried out. ; The work of J. J. Escudero-Garzás and G. Seco-Granados was supported by the Grant of Spanish Government TEC2011-28219. The work of A. García-Armada was supported by the GRE3N TEC2011-29006-C03-03 and COMONSENS CSD2008-00010 projects.

This paper considers short-term power constrained cell-free massive multiple-input multiple-output (MIMO) scenarios where a large set of multi-antenna access points (APs) provide service to a group of single-antenna mobile stations (MSs) on a spatially correlated multipath environment. Based on a probabilistic approach, the spatially correlated propagation links are modeled using either Ricean or Rayleigh fading channel models that combine a deterministic line-of-sight (LOS) propagation path with a small-scale fading caused by non-line-of-sight (NLOS) multipath propagation. Assuming the use of minimum mean square error (MMSE) channel estimates, closed-form expressions for the downlink (DL) achievable spectral efficiency of a cellfree massive MIMO network with short-term power constraints (i.e., a vector normalized conjugate beamformer (NCB)) are derived and benchmarked against that provided by the conventional cell-free massive MIMO network with long-term power constraints (i.e., the conventional conjugate beamforming (CB)). These expressions, encompassing the effects of spatial antenna correlation, Ricean/Rayleigh fading and pilot contamination, are then used to derive both pragmatic and optimal max-min peruser power allocation strategies and to gain theoretical insight on the performance advantage provided by the use of short-term power constraints instead of the conventional long-term power constrained approach. ; This work was supported in part by the Agencia Estatal de Investigacion (AEI) of Spain under Grants TEC2017-90093-C3-2-R and TEC2017-90093-C3-3-R, and in part by the European Regional Development Fund (ERDF) funds of the European Union (EU) (AEI/FEDER, UE).

This proceding at: IEEE 80th Vehicular Technology Conference (VTC)Fall. Took place 2014, September 15-19, in Vancouver (Canada). ; 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. ; This work was supported by projects CSD2008-00010, TEC2011-29006- C03-03 and by a mobility grant of Spanish Ministry of Education. The financial support of the UK Government's Engineering & Physical Sciences Research Council (EPSRC) as well as that of the Research Councils UK (RCUK) and of the European Research Council's Senior Research Fellow Grant is also gratefully acknowledged. ; Publicado

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 ultra-dense 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. ; This work has received funding from the European Union (EU) Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie ETN TeamUp5G, grant agreement No. 813391. ; info:eu-repo/semantics/acceptedVersion