arXiv subjects

Ana I. Pérez-Neira

Publications and source records attributed to Ana I. Pérez-Neira.

15 recordsLinked to original sources

arXiv2026

Satellite Swarms for Direct-to-Cell Networks: A Distribution-Performance Trade-off Analysis

This work investigates 2D distributed satellite swarm configurations for direct-to-cell (D2C) applications. Unlike previous studies, which primarily considered swarms as deployment alternatives to monolithic arrays, this paper focuses on exploiting the increased spatial resolution enabled by large distributed apertures. Simulation results show that, for the considered scenarios, increasing the level of antenna distribution across satellite platforms enlarges the effective aperture and improves the system sum rate under ideal operating conditions. While gains are moderate for uniformly distributed users, they become particularly pronounced in scenarios including hotspot with high user densities. The results further show that user scheduling strategies do not invalidate the superiority of highly distributed configurations, as these architectures provide a more balanced rate distribution across the coverage area, including hotspot regions. In addition, the paper analyzes several key implementation challenges associated with large distributed swarms, including errors in inter-satellite relative positioning, synchronization impairments, and limited beamforming and user-position update rates. Although within the range of swarm configurations and scenarios considered in this work, performance gains continue to increase with aperture size, these practical constraints may restrict swarm sizes in the medium term. Nevertheless, the observed performance gains strongly motivate further research into scalable synchronization, positioning and data distribution techniques for future large-scale satellite swarms.

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arXiv2023

From 5G to 6G: Revolutionizing Satellite Networks through TRANTOR Foundation

5G technology will drastically change the way satellite internet providers deliver services by offering higher data speeds, massive network capacity, reduced latency, improved reliability and increased availability. A standardised 5G ecosystem will enable adapting 5G to satellite needs. The EU-funded TRANTOR project will seek to develop novel and secure satellite network management solutions that allow scaling up heterogeneous satellite traffic demands and capacities in a cost-effective and highly dynamic way. Researchers also target the development of flexible 6G non-terrestrial access architectures. The focus will be on the design of a multi-orbit and multi-band antenna for satellite user equipment (UE), as well as the development of gNodeB (gNB) and UE 5G non-terrestrial network equipment to support multi-connectivity.

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arXiv2023

Adaptive function approximation based on the Discrete Cosine Transform (DCT)

This paper studies the cosine as basis function for the approximation of univariate and continuous functions without memory. This work studies a supervised learning to obtain the approximation coefficients, instead of using the Discrete Cosine Transform (DCT). Due to the finite dynamics and orthogonality of the cosine basis functions, simple gradient algorithms, such as the Normalized Least Mean Squares (NLMS), can benefit from it and present a controlled and predictable convergence time and error misadjustment. Due to its simplicity, the proposed technique ranks as the best in terms of learning quality versus complexity, and it is presented as an attractive technique to be used in more complex supervised learning systems. Simulations illustrate the performance of the approach. This paper celebrates the 50th anniversary of the publication of the DCT by Nasir Ahmed in 1973.

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arXiv2023

Polarization-Based Security: Safeguarding Wireless Communications at the Physical Layer

Physical layer security is a field of study that continues to gain importance over time. It encompasses a range of algorithms applicable to various aspects of communication systems. While research in the physical layer has predominantly focused on secrecy capacity, which involves logical and digital manipulations to achieve secure communication, there is limited exploration of directly manipulating electromagnetic fields to enhance security against eavesdroppers. In this paper, we propose a novel system that utilizes the Mueller calculation to establish a theoretical framework for manipulating electromagnetic fields in the context of physical layer security. We develop fundamental expressions and introduce new metrics to analyze the system's performance analytically. Additionally, we present three techniques that leverage polarization to enhance physical layer security.

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arXiv2020

On the Use of AI for Satellite Communications

This document presents an initial approach to the investigation and development of artificial intelligence (AI) mechanisms in satellite communication (SatCom) systems. We first introduce the nowadays SatCom operations which are strongly dependent on the human intervention. Along with those use cases, we present an initial way of automatizing some of those tasks and we show the key AI tools capable of dealing with those challenges. Finally, the long term AI developments in the SatCom sector is discussed.

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arXiv2020

3D Polarized Modulation: System Analysis and Performance

In this paper we present a novel modulation technique for dual polarization communication systems, which reduces the error rate compared with the existent schemes. This modulation places the symbols in a 3D constellation, rather than the classic approach of 2D. Adjusting the phase of these symbols depending on the information bits, we are able to increase the bit rate. Hence, the proposed scheme conveys information by selecting both polarization state and the phase of radiated electromagnetic wave. We also analyse the performance of 3D Polarized Modulation (PMod) for different constellation sizes and we obtain a curve of rate adaptation. Finally, we compare the proposed 3D PMod with other existing schemes such as single polarization Phase Shift Keying (PSK) and double polarization Vertical Bell Laboratories Layer Space-Time (V-BLAST), both carrying the same number of information bits. The results show that 3D PMod always outperforms all other schemes, except for low order modulation. Therefore, we can conclude that 3D PMod is an excellent candidate for medium and high modulation order transmissions.

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arXiv2018

A Low Complexity Space-Frequency Multiuser Scheduling Algorithm

This work presents a resource allocation algorithm in K-user, M-subcarrier and NT-antenna systems for on-line scheduling. To exploit temporal diversity and to reduce complexity, the ergodic sum rate is maximized instead of the instantaneous one. Dual optimization is applied to further diminish complexity together with a stochastic approximation, which is more suitable for online algorithms. Weighted sum rate is considered so that users can be either prioritized by higher layers or differentiated by proportional rate constraints. The performance and complexity of this algorithm is compared with well-known benchmarks and also evaluated under real system conditions for the MIMO Broadcast channel.

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arXiv2018

Link Adaptation Algorithms for Dual Polarization Mobile Satellite Systems

The use of dual polarization in mobile satellite systems is very promising as a means for increasing the transmission capacity. In this paper we study a system which uses simultaneously two orthogonal polarizations in order to communicate with the users. The application of MIMO signal processing techniques along with Adaptive Coding and Modulation in the forward link can provide remarkable throughput gains up to 100 % when compared with the single polarization system. The gateway is allowed to vary the MIMO and Modulation and Coding Schemes for each frame. The selection is done by means of a link adaptation algorithm which uses a tunable margin to achieve a prede ned target Frame Error Rate.

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arXiv2018

Dual Polarized Modulation and Receivers for Mobile Communications in Urban Areas

Achieving an increase in the spectral efficiency (SE) has always been a major driver in the design of communication systems. The use of MIMO techniques in mobile communications has achieved significant benefits in improving the system throughput. The basic underlying concept of MIMO is to exploit the signal and channel characteristics to eliminate interference between multiple transmissions. Departing from the work carried out under the industrial projects \cite{NGW,Henarejos}, we extend the results provided in their respective reports. The goal is to increase the SE without an increment of radiated energy without any Channel State Information at Transmitter (CSIT) and feedback at the transmitter and maintaining a very low computational complexity at the receiver. Although a priori additional power is required to increase the SE, we demonstrate that the proposed Polarized Modulation (PMod) scheme exploits the polarization diversity reducing the required EbN0 and adding an extra bit. We also introduce two receivers to demodulate this scheme of different computational complexities. We describe a Near Optimal Detector (NOD) which achieves almost the same performance as the optimal detector based on the Maximum Likelihood Detection (MLD), but with lower computational complexity. Finally, the results demonstrate that the PMod requires less EbN0 compared with the single polarization case, guarantees the robustness in the presence of the cross-polarization and validates that PMod can multiplex two streams of different Quality of Service (QoS).

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arXiv2018

Dual Polarized Modulation and Reception for Next Generation Mobile Satellite Communications

This paper presents the novel application of Polarized Modulation (PMod) for increasing the throughput in mobile satellite transmissions. One of the major drawbacks in mobile satellite communications is the fact that the power budget is often restrictive, making unaffordable to improve the spectral efficiency without an increment of transmitted power. By using dual polarized antennas in the transmitter and receiver, the PMod technique achieves an improvement in throughput of up to $100$\% with respect to existing deployments, with an increase of less than $1$ dB at low \ebn regime. Additionally, the proposed scheme implies minimum hardware modifications with respect to the existing dual polarized systems and does not require additional channel state information at the transmitter; thus it can be used in current deployments. Demodulation (i.e. detection and decoding) alternatives, with different processing complexity and performance, are studied. The results are validated in a typical mobile interactive scenario, the newest version of TS 102 744 standard (Broadband Global Area Network (BGAN)), which aims to provide interactive mobile satellite communications.

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arXiv2018

Capacity Analysis of Index Modulations over Spatial, Polarization and Frequency Dimensions

Determining the capacity of a modulation scheme is a fundamental topic of interest. Index Modulations (IM), such as Spatial Modulation (SMod), Polarized Modulation (PMod) or Frequency Index Modulation (FMod), are widely studied in the literature. However, finding a closed-form analytical expression for their capacity still remains an open topic. In this paper, we formulate closed-form expressions for the instantaneous capacity of IM, together with its $2$nd and $4$th order approximations. We show that, in average, the $2$nd approximation error tends to zero for low Signal to Noise Ratio (SNR) and is $o\left(\textrm{SNR}\right)$. Also, a detailed analysis of the ergodic capacity over Rayleigh, Rice and Nakagami-$m$ channel distributions is provided. As application of the capacity analysis, we leverage the proposed expressions to compute the ergodic capacities of SMod for different antenna configuration and correlations, PMod for different channel components and conditions, and FMod for different frequency separations.

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arXiv2018

Forward Link Interference Mitigation in Mobile Interactive Satellite Systems

We present the results of the performance evaluation of polarization-time coding and soft interference cancellation in multi-beam satellite systems affected by co-channel interference in realistic setups. The standard of Broadband Global Area Network service (BGAN) has been considered as reference for the physical layer and realistic interference and channel models have been adopted. The work has been carried out in the framework of the Next Generation Waveform for Increased Spectral Efficiency (NGWISE) project founded by the European Space Agency (ESA).

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arXiv2015

Generalized Multicast Multibeam Precoding for Satellite Communications

This paper deals with the problem of precoding in multibeam satellite systems. In contrast to general multiuser multiple-input-multiple-output (MIMO) cellular schemes, multibeam satellite architectures suffer from different challenges. First, satellite communications standards embed more than one user in each frame in order to increase the channel coding gain. This leads to the different so-called multigroup multicast model, whose optimization requires computationally complex operations. Second, when the data traffic is generated by several Earth stations (gateways), the precoding matrix must be distributively computed and attain additional payload restrictions. Third, since the feedback channel is adverse (large delay and quantization errors), the precoding must be able to deal with such uncertainties. In order to solve the aforementioned problems, we propose a two-stage precoding design in order to both limit the multibeam interference and to enhance the intra-beam minimum user signal power (i.e. the one that dictates the rate allocation per beam). A robust version of the proposed precoder based on a first perturbation model is presented. This mechanism behaves well when the channel state information is corrupted. Furthermore, we propose a per beam user grouping mechanism together with its robust version in order to increase the precoding gain. Finally, a method for dealing with the multiple gateway architecture is presented, which offers high throughputs with a low inter-gateway communication. The conceived designs are evaluated in a close-to-real beam pattern and the latest broadband communication standard for satellite communications.

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arXiv2015

Precoding in Multigateway Multibeam Satellite Systems

This paper considers a multigateway multibeam satellite system with multiple feeds per beam. In these systems, each gateway serves a set of beams (cluster) so that the overall data traffic is generated at different geographical areas. Full frequency reuse among beams is considered so that interference mitigation techniques are mandatory. Precisely, this paper aims at designing the precoding scheme which, in contrast to single gateway schemes, entails two main challenges. First, the precoding matrix shall be separated into feed groups assigned to each gateway. Second, complete channel state information (CSI) is required at each gateway, leading to a large communication overhead. In order to solve these problems, a design based on a regularized singular value block decomposition of the channel matrix is presented so that both inter-cluster (i.e. beams of different clusters) and intra-cluster (i.e. beams of the same cluster) interference is minimized. In addition, different gateway cooperative schemes are analysed in order to keep the inter-gateway communication low. Furthermore, the impact of the feeder link interference (i.e. interference between different feeder links) is analysed and it is shown both numerically and analytically that the system performance is reduced severally whenever this interference occurs even though precoding reverts this additional interference. Finally, numerical simulations are shown considering the latest fixed broadband communication standard DVB-S2X so that the quantized feedback effect is evaluated. The proposed precoding technique results to achieve a performance close to the single gateway operation even when the cooperation among gateways is low.

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arXiv2015

On-Board Beam Generation for Multibeam Satellite Systems

This paper aims at designing an on-board beam generation process for multibeam satellite systems with the goal of reducing the traffic at the feeder link. Full frequency reuse among beams is considered and the beamforming at the satellite is designed for supporting interference mitigation techniques. In addition, in order to reduce the payload cost and complexity, this on-board processing is assumed to be constant and the same for forward and return link transmissions. To meet all these requirements a novel robust minimum mean square error (MMSE) optimization is conceived. The benefits of the considered scheme are evaluated with respect to the current approaches both analytically and numerically. Indeed, we show that with the DVB-RCS and DVB-S2 standards, our proposal allows to increase the total throughput within a range between 6\% and 15\% with respect to other on-board processing techniques in the return and forward link, respectively. Furthermore, the proposed solution presents an implicit feeder link bandwidth reduction with respect to the on-ground beam generation process.

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