Cognitive Radio in HF Communications: Selective Transmission and Broadband Acquisition
L. Melián-Gutiérrez · accedaCRIS (University of Las Palmas de Gran Canaria) · 2016
The HF band (3-30 MHz) promotes the establishment of trans-horizon radio links by using the ionosphere as a passive reflector.Although HF radio links have this transhorizon behaviour, most HF stations are allocated by national regulators.This allocation results in multiple collisions between HF users even if they are legacy users in their respective countries.Furthermore, HF communications make use of the Automatic Link Establishment (ALE) protocol, which has been referred to as an example of a primitive form of cognitive radio.It is based on a listen-before-transmit strategy to avoid interfering with on-going communications.However, the ALE protocol has several limitations: it does not manage the spectrum in a wide-band sense and it does not monitor the evolution of the users' activity in the channels.Due to these limitations, more dynamic techniques than the ALE protocol must be implemented in HF stations to reduce the amount of collisions between users.New capabilities such as adaptability and cognition have to be introduced in HF stations to reduce the inefficient use of this band in terms of successful access to the spectrum resources.In this Thesis, the application of cognitive radio principles is proposed to reduce the amount of collisions between HF users and to reduce the inefficient use of this band.The cycle of tasks that a cognitive radio should face can be divided into three main tasks: Observe, Learn, and Decide & Act.They represent the cycle from the spectrum acquisition to the selection of the best channel to transmit, according to the observed and learned activity of other users.A database of real measurements of the activity in the HF band is created in order to evaluate and validate the proposed cognitive techniques in this Thesis.This database contains wideband measurements of the power spectrum of the HF band.By using an energy detector to perform the spectrum sensing task, the acquired power spectrum is converted into users' activity information.The energy detector is the most appropriate technique in such a heterogeneous environment as the HF band.When I look back on the long process of this work, I think of the people who have contributed in some way to its development.First of all, I would like to thank my supervisor Prof. Iván Pérez for giving me the opportunity to join his research team quite a few years ago, and for sharing his knowledge and experience during all these years.I would also like to thank my supervisor Prof. Santiago Zazo for advising me throughout this time.I am extremely grateful for their good advice.I would like to thank Prof. Carlos Bader, Prof. Christophe Moy, and Navik from CentraleSupélec -Rennes, for their willingness to face new challenges.I would also like to thank the rest of members of the SCEE group