Selection of CSI-based precoding techniques in the HF channel

Multi-carrier modulations are widely employed in ionospheric communications to mitigate the adverse effects of the HF channel. In this paper we show how performance achieved by these modulations can be further increased by means of CSIbased precoding techniques in the context of our research on interactive digital voice communications. Depending on communication constraints and channel parameters, we will show which of the studied modulations and precoding techniques to select so that to maximise performance

Optimization of Arq Parameters of Stanag 5066 for the HFDVL Modem

The reliability of bidirectional communication link can be guaranteed with Automatic Repeat Request Procedures (ARQ). The standard STANAG 5066 describes the ARQ procedure for HF communications that can either be applied to existing HF physical layers modems or adapted to future physical layer designs. In this contribution the physical layer parameters of an HF modem (HFDVL), developed by the authors over the last decade, are chosen to optimize the performance of the ARQ procedure described in STANAG 5066. Besides the interleaving length, constellation size and coding type, the OFDM-based HFDVL modem permits the selection of the number of receiver antennas. It will be shown that this parameter gives additional degrees of freedom and permits reliable communication over low SNR HF communication links

Efficiency improvement of HF communications using cognitive radio principles

Cognitive Radio principles can be applied to HF communications to make a more efficient use of the extremely scarce spectrum. In this contribution we focus on analyzing the usage of the available channels done by the legacy users, which are regarded as primary users since they are allowed to transmit without resorting any smart procedure, and consider the possibilities for our stations -over the HFDVL (HF Data+Voice Link) architecture- to participate as secondary users. Our goal is to enhance an efficient use of the HF band by detecting the presence of uncoordinated primary users and avoiding collisions with them while transmitting in different HF channels using our broad-band HF transceiver. A model of the primary user activity dynamics in the HF band is developed in this work. It is based on Hidden Markov Models (HMM) which are a powerful tool for modelling stochastic random processes, and is trained with real measurements from the 14 MHz band

Hybrid UCB-HMM: A Machine Learning Strategy for Cognitive Radio in HF Band

International audienceMultiple users transmit in the HF band with worldwide coverage but collide with other HF users. New techniques based on cognitive radio principles are discussed to reduce the inefficient use of this band. In this paper, we show the feasibility of the Upper Confidence Bound (UCB) algorithm, based on reinforcement learning, for an opportunistic access to the HF band. The exploration vs. exploitation dilemma is evaluated in single-channel and multi-channel UCB algorithms in order to obtain their best performance in the HF environment. Furthermore, we propose a new hybrid system which combines two types of machine learning techniques based on reinforcement learning and learning with Hidden Markov Models. This system can be understood as a metacognitive engine that automatically adapts its data transmission strategy according to HF environment's behaviour to efficiently use spectrum holes. The proposed hybrid UCB-HMM system increases the duration of data transmission's slots when conditions are favourable, and is also able to reduce the required signalling transmissions between transmitter and receiver to inform which channels have been selected for data transmission. This reduction can be as high as 61% with respect to the signalling required by multi-channel UCB

Analog mitigation of out of band strong interferers in wide band acquisition for multiband HF transmissions

It is clear that in the near future much broader transmissions in the HF band will replace part of the current narrow band links. Our personal view is that a real wide band signal is infeasible in this environment because the usage is typically very intensive and may suffer interferences from all over the world. Therefore, we envision that dynamic multiband transmissions may provide better satisfactory performance. From the very beginning, we observed that real links with our broadband transceiver suffered interferences out of our multiband but within the acquisition bandwidth that degrade the expected performance. Therefore, we concluded that a mitigation structure is required that operates on severely saturated signals as the interference may be of much higher power. In this paper we address a procedure based on Higher Order Crossings (HOC) statistics that are able to extract most of the signal structure in the case where the amplitude is severely distorted and allows the estimation of the interference carrier frequency to command a variable notch filter that mitigates its effect in the analog domain

Bernát Munkácsi's letter to Ignaz Goldziher

We envision that dynamic multiband transmissions taking advantage of the receiver diversity (even for collocated antennas with different polarization or radiation pattern) will create a new paradigm for these links guaranteeing high quality and reliability. However, there are many challenges to face regarding the use of broadband reception where several out of band (with respect to multiband transmission) strong interferers, but still within the acquisition band, may limit dramatically the expected performance. In this paper we address this problem introducing a specific capability of the communication system that is able to mitigate these interferences using analog beamforming principles. Indeed, Higher Order Crossing (HOCs) joint statistics of the Single Input ? Multiple Output (SIMO) system are shown to effectively determine the angle on arrival of the wavefront even operating over highly distorted signals

Mujeres y escritoras no canónicas de la literatura española e hispanoamericana: Fuentes bibliográficas para su didáctica e investigación en formato digital

Repositorio abierto de editoras y escritoras de la literatura española e hispanoamericana no canónicas, con fuentes de información bibliográficas necesarias para su investigación y su didáctica en las aulas.Depto. de Literaturas Hispánicas y BibliografíaFac. de FilologíaFALSEsubmitte