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 describes the integration of Terrestrial and Non-Terrestrial Networks, wherein space-based network entities collaborate with traditional and emerging terrestrial communication frameworks to furnish pervasive, resilient, and three-dimensional wireless connectivity worldwide toward the 6th Generation of communication networks. This integration supports heterogeneous services, such as enhancing coverage, user experience, system capacity, service reliability, and availability, while also providing high-speed connectivity in remote or disaster-affected areas, improving existing 5th Generation technologies. Various Use Cases are detailed, highlighting the pivotal roles that Non-Terrestrial Networks play in distinguishing between urban/suburban and rural environments, with particular emphasis on transportation ecosystems. Through this analysis, Key Performance Indicators and requirements are delineated to characterize the requisite service quality for these diverse Use Cases. The paper further presents an overview of potential and standards-compliant integrated Terrestrial/Non-Terrestrial architectures, delineating their roles both in backhauling and access across different layers of Non-Terrestrial systems and elements. These insights are derived from studies conducted within the Integrated Terrestrial And Non-Terrestrial Networks (ITA-NTN) project, part of the European Union initiative defined as the Italian National Recovery and Resilience Plan (NRRP) RESTART Research Program.

Delay/disruption-tolerant networking (DTN) is a networking technology conceived to manage opportunistic connections with no consistent end-to-end link connectivity which is common in both terrestrial and space communication environments. DTN is recognized as a baseline technology for implementing deep-space networks. Considered as the primary transport protocol of DTN in space, Licklider transmission protocol (LTP) is expected to provide reliable data delivery service in a challenging networking environment regardless of presence of random link disruptions and/or extremely long propagation delays. The National Aeronautics and Space Administration (NASA) has implemented the use of DTN protocols on the International Space Station (ISS) for data delivery to the earth ground station. However, little work has been done in studying the performance of LTP for reliable data/file delivery in such a communication environment, especially in presence of link disruption. There is a lack of a solid performance evaluation of LTP for its use in the space station communications. In this paper, an analytical framework is presented to evaluate the performance of LTP for reliable file delivery between the space station and the ground stations with a focus on the effect of link disruption, which may occur either over the downlink or over the uplink. The effect of data loss due to channel error is also integrated. Realistic data block transmission experiments using a PC-based experimental infrastructure are conducted to validate the analytical models.

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.

This paper is motivated by the observation that M2M/IoT traffic is rather heterogeneous. By using traffic data collected in a real scenario, we prove that some M2M devices might generate a signaling traffic more similar to the traffic of a smartphone than to the traffic of a traditional M2M device used for metering applications. This makes difficult the task of a mobile operator to understand the impact of the introduction of M2M/IoT devices into the network. The paper presents a classification of the M2M/IoT heterogeneous world in three classes. The classification has been performed using the C-plane attributes and its effectiveness has been assessed by performing a clustering analysis over the U-plane data, which represent the ground truth. We found a good matching between the results of the classification task carried out by using the C-plane data and the results of the clustering task carried out by exploiting the U-plane data. This means that, by using the C-plane data (simpler with respect to using U-plane data) the network operator can understand with a good accuracy which type of M2M devices are active on the network, and what are the applications that they run and the data traffic that they generate. Therefore, the results may be useful for a proper dimensioning and management of the evolution of an EPC network.

Mobile satellite services are extremely important when continuity of service is requested while the user is moving over a wide area. A notable example is represented by live TV services, or more in general by the Multimedia Broadcast/Multicast Services (MBMSs) and its evolved version enhanced MBMS. In this paper, we present the combined use of multicast resource allocation schemes based on subgrouping and application layer joint coding to enhance the performance of live video streaming in mobile satellite systems. The reference architecture foresees a satellite-based long term evolution transmission using orthogonal frequency division multiple access in the forward link. The results show that the combined use of multicast subgrouping resource allocation and application layer joint coding allows high-throughput transmissions with satisfactory user quality of experience of the received video over different satellite channel propagation environments.

In the last few years, there has been a growing interest in developing sensing systems using RF signals of opportunity, especially exploiting radar-based techniques. Long Term Evolution (LTE) signals are excellent candidates as signals of opportunity thanks to their wide availability and penetration in indoor environments. This is the first work investigating the possibility to use LTE signals for crowd density estimation. The proposed approach is not radar-like but it exploits the correlation between the variations of the received LTE signals (in particular, of the Reference Signal Received Power) and the number of people. An experimental evaluation of the performance is carried out in a indoor environment testing three different positions of the LTE receiver. Achieved results in terms of classification accuracy are very promising.

In the last few years, there has been a growing interest on the usage of passive WiFi signals for detecting and classifying human behavior activities. In most generality, the idea underlying most state of the art approaches is to monitor changes in the Channel State Information (CSI) or equivalent spectral metrics, caused by the different multi- path conditions (and their temporal variations) induced by human activity. The (implicit) underlying intuitive assumption is that, in a static environment, i.e. with no moving humans, the multi-path conditions do not vary, and hence the CSI gathered at the passive receiver side should remain substantially stable in time. Goal of this paper is to document, with an extensive set of experimental measurements, a perhaps surprising result: with modern multi-antenna 802.11n/ac access points, such an intuitive assumption does not seem to hold anymore. Rather, the measured CSI time pattern, which differs for different access point brands, appears to be affected by access points' implementation artifacts. Indeed, our measurements unveil frequent fluctuations of the CSI pattern among multiple ``modes". Albeit still preliminary and, at least in part, still requiring a more thorough understanding (that only the reverse engineering of the access points' implementation may ultimately provide), our measurements unveil a phenomenon which may play havoc with several CSI-based human behavior detection approaches proposed in past works, and especially with those based on CSI measured on data frames, opposed to those based on relatively more stable (but still to be reconsidered in sight of our results) Beacon frames.

This paper investigates the possibility to use Channel State Information (CSI) extracted from Long Term Evolution (LTE) signals for signal fingerprinting localization. Being the first work in this direction, several types of signal fingerprinting-based approaches have been compared (e.g., CSI-based vs RSSI-based, statistic vs deterministic matching rule). In particular, the paper proposes a novel CSI-based signal fingerprinting that uses as fingerprint not directly the vector of channel gains per subcarrier, but rather some features extracted from these vectors. This method would greatly reduce the memory requirement of the database as well as the computational complexity of the matching phase. Experimental results, shown for both indoor and outdoor environments, confirm the effectiveness of the proposed method and also provide interesting insights on the use of LTE signal fingerprinting based on CSI.

Radio receivers, besides acting as wireless network nodes participating to the Internet of Things (IoT) communication task, may act as opportunistic sensors participating to the IoT sensing task. In particular, a radio receiver is intrinsically an electronic sensor which may be used for device-free human activity recognition. In this paper, we analyze recent results on how the identification of the human body presence and movement can be carried out analyzing the RF signals transmitted by sources of opportunity. The impact of channel bandwidth, transmission mode, carrier frequency, and signal descriptors on the recognition performance is discussed. Moreover, we present a novel crowd counting system and assess the performance considering two different types of signal descriptors. Results prove the effectiveness of the presented crowd counting system and allow to get more insights into the relation among the specific sensed environment, chosen signal descriptors, and classification accuracy.

This paper presents a WiFi-based device-free crowd counting and occupancy estimation system that can be used in rooms/environments different from the ones in which the training process has been performed. Therefore, crowd counting is achieved without requiring another training phase in each new environment. The proposed approach analyzes the shape of the Doppler spectrum of the received signal which is correlated to the number of people moving in the monitored environment. Unlike a radar-like approach, the use of a reference signal is not required. Experimental results are presented for two different rooms/environments without any constraint on the movements of the volunteers.

This paper focuses on the use of satellite communication systems for the support of Internet of Things (IoT). We refer to the IoT paradigm as the means to collect data from sensors or RFID and to send control messages to actuators. In many application scenarios, sensors and actuators are distributed over a very wide area; in some cases, they are located in remote areas where they are not served by terrestrial access networks and, as a consequence, the use of satellite communication systems becomes of paramount importance for the Internet of Remote Things (IoRT). The enabling factors of IoRT through satellite are: 1) the interoperability between satellite systems and sensors/actuators and 2) the support of IPv6 over satellite. Furthermore, radio resource management algorithms are required to enhance the efficiency of IoT over satellite. In this work, we provide an integrated view of satellite-based IoT, handling this topic as a jigsaw puzzle where the pieces to be assembled are represented by the following topics: MAC protocols for satellite routed sensor networks, efficient IPv6 support, heterogeneous networks interoperability, quality of service (QoS) management, and group-based communications.

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.

Satellite constellation designers take into consideration the entire telecommunication network and their design choices are influenced by many factors including: number of satellites, orbital characteristics, coverage area, network interconnections, system cost, and complexity. When the satellite constellation design method does not include a large number of possible configurations, then the final result of the design process is a suboptimal solution. Flower Constellation (FC) design provides a relatively new design approach which can overcome this problem. The time evolution of the FC theory is here summarized and the fundamental mathematics allowing the constellation design is provided. In particular, the theory is applied to the design and optimization of constellations maximizing the global coverage and the network connectivity via intersatellite links. Performance results are compared to the classical type of satellite constellations, i.e., the Walker Constellations. The performance improvement provided by FC design with respect to Walker Constellation design is shown. Finally, considerations regarding the cost for deployment and orbital control are also provided.

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.

Future space exploration missions will need a robust, efficient and flexible communication infrastructure. This implies new communications and networking challenges, which are the ones of the so called InterPlaNetary (IPN) Internet. In that framework, the paper provides a description of the challenging scenario, surveys its technical problems and envisages possible advanced communications and networking solutions starting from the analysis of a specific IPN architecture, which represents the main contribution of the work.

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.

Wireless Personal Area Networks (WPANs) are short-range ad-hoc networks centered around a person that make use of unlicensed bands for data transmission. Two complementary types of standards have been proposed by IEEE working groups for both High Data Rate (HDR) and Low Data Rate (LDR) WPANs. However, because of the unlicensed nature of WPANs, interference issues exist between uncoordinated WPANs. These interference issues are particularly severe when two or more nodes are closely located (e.g. in a multimode LDR/HDR device). This paper proposes a novel collaborative coexistence mechanism named Alternating Wireless Activity (AWA, patent pending) between a HDR WPAN based on the standard IEEE 802.15.3 and a LDR WPAN based on the standard IEEE 802.15.4. The AWA coexistence mechanism does not require any modification to the mentioned standards because it exploits their already available features.

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.

This paper proposes a novel slow transmit power control (TPC) algorithm which exploits a cross layer approach in order to optimize the energy efficiency of a single link. This optimization process has been applied to a short range wireless link (i.e. IEEE 802.15.3-based transmission) and it takes into account the signal fluctuations due to the multipath fading of typical indoor environments. Analytical results have shown that the proposed TPC can improve the battery life duration of 25% with respect to a non optimized strategy, without losing transmission quality

The issue of the performance degradation of transmission control protocol/Internet Protocol (TCP/IP) over wireless links due to the presence of noncongestion-related packet losses has been addressed with a physical layer approach. The effectiveness of automatic repeat request techniques in enhancing TCP/IP performance depends on the tradeoff between frame transmission delay and residual errors after retransmissions. The paper shows how a truncated power control can be effectively applied to improve that tradeoff so that a higher transmission reliability is provided without increasing the frame transmission delay through the radio link layer and without increasing the energy consumption. An analytical framework has been developed to show the feasibility and effectiveness of the proposed power control. The analytical results, which are carried out assuming a constant multiuser interference level, show that the proposed algorithm turns out to be very effective when the time variability of the channel is high, which-in case of constant interference level-means that the Doppler frequency is high. Simulations carried out in a variable interference scenario show that the proposed strategy is very effective in improving the end-to-end throughput of a TCP connection. Moreover, these improvements are higher when the traffic is more bursty, like in typical Internet data applications such as e-mail and web surfing.