On Wednesday, May 10, 2023, at 11 a.m., the reading of Josep-Maria Masó Llinàs's doctoral thesis will be carried out, entitled "Study, design and implementation of low power polarisation diversity multicarrier NVIS uplink communications" (Estudio, diseño e implementación del enlace ascendente de comunicaciones NVIS multiportadora de baja potencia y diversidad de polarización), which it is directed by Dr. Joan Lluís Pijoan Vidal. The doctoral student is part of Smart Society.
The doctoral thesis talks about the number of IoT (Internet of Things) devices is increasing every day, and consequently new protocols and radio technologies are appearing focused on the communication of these types of devices according to their needs. In the case of RIoT (Remote Internet of Things) devices that are located in areas far away from telecommunications infrastructures or where the orography does not allow direct vision between transmitter and receiver, satellite and HF (High Frequency) communications are options that can guarantee the link. In the case of HF communications, they are a low-cost alternative due to the propagation characteristics of their waves, which are capable of being reflected by the ionosphere, covering thousands of kilometres. Although the band of use (3-30 MHz) is well below than the satellite, they are a valid option for the bandwidth required in RIoT devices. Regarding HF communications standards, we can highlight MIL-STD-188-110D and STANAG 4539, which vary the modulation and bandwidth according to the required bitrate. These standards are generic for HF link subtypes: DX (Distance X) for links above 250 km and NVIS (Near Vertical Incidence Skywave) for links below 250 km. Due to the differences in channel parameters between the two link subtypes, current standards can be more robust if they are based on a single link subtype.
Therefore, through this PhD thesis, the NVIS ionospheric channel in the antarctic polar region has been characterised in order to define a physical layer transmission protocol as close as possible to the channel characteristics. For this purpose, due to the fact that narrowband modulations are mainly susceptible to the channel delay spread, the use of OFDM (Orthogonal Frequency Division Multiplexing) multicarrier modulation is proposed due to its design to avoid the delay spread. In order to verify the results, the designed OFDM has been tested in a real scenario, maintaining the bitrate and bandwidth of the standards in order to compare the robustness of the communication. Furthermore, since the standards are not focused on very low power transmissions, in RIoT devices energy management is of great importance because they are off-grid and require high energy autonomy. Therefore, the research has also focused on the analysis of narrowband modulations and OFDM modulation at very low powers (less than 6 W). Finally, to further increase the robustness of the modulation, the behaviour of narrowband modulations and OFDM modulation has been analysed using polarisation diversity techniques such as SC (Selection Combining) and EGC (Equal-Gain Combining) in a SIMO (Single Input Multiple Output) link to receive ordinary and extraordinary waves.
The tribunal is made up of the President, Dr. Gabriel Montoro López; the Secretary, Dr. Rosa Maria Alsina Pagès; and the vocal, Dr. José Antonio Morán Moreno.