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The computation of statistical moments of the radar echo-signals with the objective of translating the decision to the moments space has shown potential in recent work. However, the moments space has not been considered for multiple targets classification, nor its combination with supervised classifiers has been studied. This paper proposes the use of moments as input features for several supervised classifiers and evaluates their performance. Among the considered methods are the Bayesian classifier, k-nearest neighbors, Support Vector Machines and artificial neural networks. The results show the usefulness of the moments space for classifying radar targets with high accuracy, precision and low complexity.

Los sistemas de radio cognitivo permiten un uso más eficiente del espectro a partir de la reutilización de las bandas asignadas a otros servicios como la televisión digital. En estos sistemas, el reconocimiento automático de la modulación es un tema crucial para la implementación de sus principales funcionalidades. Específicamente, las modulaciones QAM se encuentran entre las más empleadas por los sistemas de telecomunicaciones modernos. El presente artículo expone un nuevo método para reconocer automáticamente las modulaciones 16-QAM, 32-QAM y 64-QAM, basado en una variante del algoritmo k-means. Este se emplea con el fin de disminuir la dispersión de las muestras recibidas producto del ruido en el canal de comunicaciones. La salida del clasificador se basa en la comparación de los centros calculados mediante el método de k-means con las constelaciones esperadas. El método propuesto logra mayor eficiencia en la velocidad de cómputo mediante una reducción de los cálculos de distancias en k-means. Además, mejora el desempeño de algoritmos similares reportados en la literatura científica para niveles de SNR superiores a 8 dB.

Taking The present article deals with the topic of windowing techniques for sidelobe reduction inlinearly frequency modulated (LFM) pulses compressed by an adapted filter. Main characteristics ofwindow´s techniques are presented; focusing on those that improves the window´s performance. Designsare simulated in a Graphic User Interface in MatLab and Simulink to conform it on FPGA. Simulationof carried out softwares allows the selection of the best choice as the case of interest.

The increasing demand of mobile users imposes a better utilization of the available spectrum. In this regard, Cognitive Radio (CR) technology represents a novel solution for avoiding spectrum scarcity. The implementation of the CR system follows two different approaches: Mitola Radio, which takes control of all parameters, and Cognitive Radio with just Spectrum Sensing (SS) techniques. This paper will be concerned with SS techniques. From a theoretical point of view, CR is addressed through several solutions in regard to novel SS methods. However, system and hardware development is progressing at a lower pace. Today, field-programmable gate arrays (FPGAs) and regular desktop computers are fast enough to handle complete baseband processing chains. There are several platforms, both open source and commercial, providing such solutions for supporting the development of novel SS methods. The aims of this paper is to give an overview of some of the available platforms and testbeds and their characteristics, and compare the features and performance measures of the different systems.

Synchronizing the local oscillators in multibeam satellites with the objective of coherent communications is still an open challenge. It has to be addressed to implement full-frequency reuse approaches, such as precoding techniques using the already deployed multibeam satellites. This article addresses the required phase synchronization to enable precoding techniques in multibeam satellite systems. It contains the detailed design of a frequency and phase compensation loop based on the proportional-integral controller, which deals with the phase drift introduced by the hardware components. Specifically, the phase noise of the local oscillators used for up and down conversion at each system element (gateway, satellite, and user terminals). The implementation of the two-state phase noise model used to emulate this phase drift is included in the article. Besides, a comparative analysis of several methods to combine the frequency and phase measurements obtained from the user terminals is also included. Finally, the performance of the proposed closed-loop synchronization method is validated through simulations using our in-house developed MIMO end-to-end satellite emulator based on SDR platforms.

In this paper we demonstrate end-to-end precoded multi-user multiple-input single-output communications over a live GEO satellite link. Precoded communications enable full frequency reuse schemes in satellite communications to achieve broader service availability and higher spectrum efficiency than with the conventional four-color and two-color reuse approaches. In this scope, we develop a novel over-the-air test-bed for end-to-end precoding validations. We were able to demonstrate precoded communications over an actual geostationary orbit multi-beam satellite using the DVB-S2X standard-compliant state-of-the-art gateway and user terminals. The developed system is capable of fully end-to-end real-time communications over a satellite link and demonstrates novel channel measurements and channel compensation techniques for differential frequency and phase tracking. It is shown, that by successfully canceling inter-user interference in the actual satellite link, the precoding improves the received SINR and increases the total system goodput in aggressive full frequency reuse scenarios.

Linear and symbol-level precoding in satellite communications have received increasing research attention thanks to their ability to tackle inter-beam interference, allowing the use of spectral resources more efficiently. However, there are still challenges and open questions regarding the implementation of practical precoding systems taking the phase uncertainties in estimating the channel state information into account. This work assesses the impact of phase variations and uncertainties inherent to the satellite communication system operating a precoded forward link. Specifically, we address the inability to measure at the user terminal, the absolute phase rotation introduced by the channel, and the transponder local oscillator phase noise effects on the precoding operations considering the use of frequency division multiplexing in the forward-uplink transmission. We formally demonstrate that the system performance for linear and non-linear precoding operations is not affected by the uncertainty in the phase measurements at the user terminal. Additionally, we show that using a single frequency reference for all the local oscillators at the transponder does not avoid the phase variations related to the frequency division multiplexing in the forward-uplink. This work demonstrates that these phase variations would not affect the system performance for an ideal zero-delay precoding loop. However, this is not feasible in practical scenarios, where the phase noise of the frequency reference at the transponder and the loop delay determine the impact on the system performance. We validate our results by simulations considering three frequency references with different stability levels in a typical geosynchronous orbit (GEO) satellite system. Our results suggest that practical implementations of multiuser-MISO precoding systems must include a differential phase synchronization loop to compensate for this performance degradation.

Cohesive Distributed Satellite Systems (CDSSs) is a key enabling technology for the future of remote sensing and communication missions. However, they have to meet strict synchronization requirements before their use is generalized. When clock or local oscillator signals are generated locally at each of the distributed nodes, achieving exact synchronization in absolute phase, frequency, and time is a complex problem. In addition, satellite systems have significant resource constraints, especially for small satellites, which are envisioned to be part of the future CDSSs. Thus, the development of precise, robust, and resource-efficient synchronization techniques is essential for the advancement of future CDSSs. In this context, this survey aims to summarize and categorize the most relevant results on synchronization techniques for Distributed Satellite Systems (DSSs). First, some important architecture and system concepts are defined. Then, the synchronization methods reported in the literature are reviewed and categorized. This article also provides an extensive list of applications and examples of synchronization techniques for DSSs in addition to the most significant advances in other operations closely related to synchronization, such as inter-satellite ranging and relative position. The survey also provides a discussion on emerging data-driven synchronization techniques based on Machine Learning (ML). Finally, a compilation of current research activities and potential research topics is proposed, identifying problems and open challenges that can be useful for researchers in the field.