Although situated within the highly active research field of WiFi sensing, this paper introduces a novel method based on digital receive beamforming using samples of the Channel State Information (CSI) that is able to advance the state-of-the-art. Key contributions include: a) the definition of a new set of features based on the digital receive beamforming technique, and, b) the test of the proposed method over two different environments exploiting a unique training set for both environments. The excellent results achieved in two different environments using the same trained system push the boundaries of the capabilities of current systems.

This paper characterizes the angular dispersion and Second-Order Fading Statistics (SOFS) for sub- THz communication channels in several representative indoor and outdoor environments for different sub- THz frequencies ranging from 125 to 300GHz. In particular, Level Crossing Rate (LCR) and Average Fade Duration (AFD) are studied by extracting Angle-of-Arrival (AoA) measurements available in the existing open literature considering Rician fading conditions. Key findings include the characterization of angular spread, angular constriction, the direction of maximum fading, and Rice K-factor for the considered angular measurements. Furthermore, the impact of various channel and physical parameters, such as velocity and direction of receiver motion, on the SOFS is thoroughly investigated. It has been observed that the environments that represent a widespread angular profile leads to an elevated LCR. Moreover, specific to sub- THz bands that include a dominant Line-of-Sight (LoS) path and a limited number of diffused scattered Multipath Components (MPCs), the Rice K-factor directly influences the SOFS. The provided analysis is of high significance in the design of various aspects at the physical layer of the communication protocol stack, such as antenna design (elements spacing), modulation, coding, and error correction schemes, especially when adaptive schemes are considered. A notable state-of-the-art application of such SOFS is in the design of Ultra Reliable Low Latency Communication (URLLC) services in Beyond 5G/6G communications.

This study focuses on the innovative field of quantum synchronization for satellite-based navigation systems including Global Navigation Satellite Systems (GNSSs) and the Non-Terrestrial Network (NTN) component of future 6G networks integrating both communication and navigation services. By combining a four-qubit system with the theoretical approach of the Lindblad master equation, we transcend the inherent limits of standard synchronization techniques. This achievement represents a quantum leap in satellite-based positioning, highlighting the scalability and cost-effectiveness of our technique for smaller satellites. The study demonstrates the possibility of reducing synchronization errors to less than one meter, significantly improving the reliability and precision of satellite-based navigation systems. The results of this study may contribute to the future development of both user-centric localization systems (typically GNSS systems) and network-centric localization systems (typically through the NTN component of 6G networks), leading to better positioning performance, more flexible multi-functional systems with the potential to limit both cost and size of satellites.

This paper addresses the crucial challenge of geo-localization of ultra-low power Internet-of-Remote-Things (IoRT) devices placed in remote areas communicating directly with a Low Earth Orbit (LEO) satellite constellation. Accurate localization of IoRT devices is critical in various applications such as asset tracking, logistics, and environmental monitoring. Moreover, location information can also vastly support the employment of 3GPP-based standards for communication over satellite links. Location estimation of such ultra-low power and low-cost devices is only feasible on the satellite side. Use of Global Navigation Satellite System (GNSS) receivers at the IoRT terminals is not advised as they consume high power and add substantial computational complexity and cost. This paper proposes a novel geometric framework that enables the localization of static IoRT nodes on the satellite side using a single-antenna-equipped single LEO satellite. The proposed solution is based on the computation of the Round Trip Time (RTT) which can be used together with the prior available geometric parameters to compute the direct satellite-to-node distance and Angle-of-Arrival (AoA) parameters. Imprecision in RTT measurement translates into an error in the node localization. The error can be reduced by taking RTT measurements at multiple instances along the satellite's orbit, while minimum 2 measurements are required. A numerical analysis is conducted to prove the validity and usefulness of the proposed framework. The impact of the error in RTT measurements on the performance of the proposed localization scheme is also thoroughly investigated.

Combining the use of Extremely High Frequencies (EHF) and Free Space Optics (FSO) for the feeder links of future High Throughput Satellites (HTS) is recognized as a key element to optimize system efficiency in terms of costs, power consumption and to increase the data rate to unprecedented levels (Terabit/s). This paper provides an overview of the main challenges to be faced to make the exploitation of hybrid EHF/FSO links feasible and cost-effective. In this framework, propagation and HW impairments mitigation techniques will play a key role. Therefore, the paper also presents a vision on how the use of SDN/SDR and NFV, extended down to lower layers of the protocol stack, could provide novel, so far unexplored, opportunities for optimizing the performance of such mitigation techniques.

Constant-Envelope (CE) multicarrier techniques have been recently proposed in order to enable the use of multicarrier waveforms in channels characterized by severe nonlinear distortions. They are based on a phase modulation applied to the multicarrier signal, generated in the time domain by means of a real-valued DFT. Such techniques, known as CE-OFDM and CE-SC-FDMA, demonstrated their superior performance with respect to conventional OFDMA and SC-FDMA, when applied to nonlinear satellite channels, at the price of reduced spectral efficiency. An open issue still to be evaluated is related to the impact of phase noise on the performance of CE multicarrier systems. This is especially important in view of the use of EHF bands for broadband satellite communications. This paper aims at analyzing the effects of phase noise on CE-OFDM and CE-SC-FDMA, highlighting the different behavior of conventional and CE multicarrier signals in the presence of such impairment. Then, simulation results will be discussed considering two different phase noise masks. The performed analysis demonstrates that CE multicarrier signals have globally better performance when both phase noise and nonlinear distortions are considered. Moreover, the sensitivity to the phase noise is strongly dependent from the modulation order and the angular modulation index.

The exploitation of extremely high-frequency (EHF) bands (30-300 GHz) for broadband transmission over satellite links is currently a hot research topic. In particular, the Q-V band (30-50 GHz) and W-band (75-110 GHz) seem to offer very promising perspectives. This paper aims at presenting an overview of the current status of research and technology in EHF satellite communications and taking a look at future perspectives in terms of applications and services. Challenges and open issues are adequately considered together with some viable solutions and future developments. The proposed analysis highlighted the need for a reliable propagation model based on experimental data acquired in orbit. Other critical aspects should be faced at the PHY-layer level in order to manage the tradeoff between power efficiency, spectral efficiency, and robustness against link distortions. As far as networking aspects are concerned, the large bandwidth availability should be converted into increased throughput by means of suitable radio resource management and transport protocols, able to support very high data rates in long-range aerospace scenarios.

In this paper an analysis on the use of Adaptive Coding and Modulation (ACM) techniques for EHF satellite communications is presented. In particular, our analysis is focused on W-band channels and includes the main channel impairments in this frequency band, i.e. rain fading and HPA non-linearity. The aim of the analysis is to identify modifications to the ACM mode switching algorithm to optimize their use at those high frequency bands.

The recently allocated 71-76 GHz and 81-86 GHz bands provide an opportunity for Line Of Sight (LOS) links for directional point-to-point “last mile” links. An efficient use of this spectrum may allow wireless to finally “catch up” with wires, leading to systems such as “multi-Gigabit wireless Ethernet,” and “wireless fiber.” However, the transmission at such a frequency range is characterized by several additional challenges compared to lower frequency bands, from the technological and propagation point of view, which makes difficult to use them efficiently. In this scenario, IR-UWB technology might offer some more degrees of freedom for the design of a highly integrated, low cost transceiver. This work has at its core the design and BER (Bit Error Rate) performance evaluation of an IR-UWB architecture based on an 85 GHz (this frequency belongs to W band/75-110 GHz) up-conversion stage of train of Gaussian pulses having a duration lower than 1 ns. Finally, we compare performance of this architecture with the ones of a more traditional continuous wave communications system with FSK (Frequency Shift Keying) modulation. Simulation results show that BER performance, in presence of RF non-linearities, for an IR-UWB transceiver architecture operating at W band (with same data rate and bandwidth) are better than a coherent BFSK scheme working in a similar scenario.

In this paper, the design of a minisatellite FLOwer constellation (FC), deploying millimeter-wave (MMW) scanning RADiometers, namely, FLORAD, and devoted to tropospheric observations, is analyzed and discussed. The FLORAD mission is aimed at the retrieval of thermal and hydrological properties of the troposphere, specifically temperature profile, water-vapor profile, cloud liquid content, and rainfall and snowfall rate. The goal of frequent revisit time at regional scale, coupled with quasi-global coverage and relatively high spatial resolution, is here called pseudogeostationary scale and implemented through a FC of three minisatellites in elliptical orbits. FCs are built on compatible (resonant) orbits and can offer several degrees of freedom in their design. The payload MMW channels for tropospheric retrieval were selected following the ranking based on a reduced-entropy method between 90 and 230 GHz. Various configurations of the MMW radiometer multiband channels are investigated, pointing out the tradeoff between performances and complexity within the constraint of minisatellite platform. Statistical inversion schemes are employed to quantify the overall accuracy of the selected MMW radiometer configurations.

WAVE (W band Analysis and VErification) is a project funded by the Italian Space Agency (ASI) with the aim to design and deploy different missions for scientific experimental use of the W band channel in satellite data communications. The second phase (A2) of the Project is currently in progress. This paper summarises the main scientific results early achieved in the WAVE A2 Project on the analysis assessment of W band GEO and LEO satellite missions.