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This paper deals with IoT devices deployed in remote areas without terrestrial Internet connectivity. We consider connecting IoT devices on the ground to the Internet through an aerial system based on an Unmanned Aerial Vehicle (UAV) for smart agriculture and environmental monitoring. The UAV flying over the remote area receives data from distributed IoT devices. The transmissions between the ground sensors and the UAV are carried out via LoRa. We have proposed a synchronization protocol for the opportunistic communication of LoRa IoT devices with a gateway onboard the UAV to save node battery life. Class A LoRa nodes on the ground transmit only when the UAV is expected to pass close to them; otherwise, they stay in the sleeping state most of the time. This paper provides a detailed description of the formulation of the synchronization protocol. The UAV's flying dynamics have been considered for characterizing its speed and the time of visibility of each IoT sensor. Our model has allowed an analytical approach that can help to determine the best settings for LoRa transmissions. Finally, experiments have been carried out to assess the path loss attenuation, and a laboratory setup of the synchronization protocol has been implemented for the preliminary validation of our scheme. [ABSTRACT FROM AUTHOR]

Mega-constellation networks (MCNs) based on low earth orbit (LEO) satellites have become increasingly important with many projects in the design or implementation phase. For those MCN systems with inter-satellite links (ISLs), the large number of satellites increases the routing complexity and the required hop-count of ISL paths. This paper aims to provide insights into the topology and routing design in MCNs through the analysis of ISL paths. We propose a theoretical model to explicitly estimate the ISL hop-count between ground users in MCNs with inclined orbits. The spatial distribution properties of hop-count are derived based on the proposed method. Based on an exemplary constellation, that is Starlink, the global distribution patterns of hop-count and the path difference caused by different access satellites are illustrated for the first time. In Starlink, the difference of the paths from different starting satellites can be up to 45 hops. The numerical results show that optimizing the constellation phasing factor can effectively reduce the average hop-count, for both the whole network and specific regional users. [ABSTRACT FROM AUTHOR]

The high data-rate of terminals together with the demand for anywhere-anytime user connectivity makes the simultaneous use of terrestrial and satellite infrastructures a necessity in mobile scenarios. To achieve a reliable and timely distribution of contents, there are important technical challenges concerning the implementation of multipath communication protocols and robust recovery mechanisms to cope with the signal degradation because of the effects of the mobile fading channel. In this respect, this paper proposes a new technique called path-based network coding to jointly exploit the availability of multiple paths and network coding to maximize the system transmission control protocol (TCP) goodput. An analytical approach allowing a formal optimization based on approximate derivations is proposed, which proves to be in good agreement with simulation results and a more accurate optimization method based on a genetic algorithm. [ABSTRACT FROM AUTHOR]

Future 5G mobile communication systems are expected to integrate different radio access technologies, including the satellite component. Within the 5G framework, the terrestrial services can be augmented with the development of HTS systems and new mega-constellations meeting 5G requirements, such as high bandwidth, low latency, and increased coverage including rural areas, air, and seas. This article provides an overview of the current 5G initiatives and projects followed by a proposed architecture for 5G satellite networks where the SDN/NFV approach facilitates the integration with the 5G terrestrial system. In addition, a novel technique based on network coding is analyzed for the joint exploitation of multiple paths in such an integrated satellite-terrestrial system. For TCP-based applications, an analytical model is presented to achieve an optimal traffic split between terrestrial and satellite paths and optimal redundancy levels. [ABSTRACT FROM AUTHOR]

Forests play a fundamental role in preserving the environment and fighting global warming. Unfortunately, they are continuously reduced by human interventions such as deforestation, fires, etc. This paper proposes and evaluates a framework for automatically detecting illegal tree-cutting activity in forests through audio event classification. We envisage ultra-low-power tiny devices, embedding edge-computing microcontrollers and long-range wireless communication to cover vast areas in the forest. To reduce the energy footprint and resource consumption for effective and pervasive detection of illegal tree cutting, an efficient and accurate audio classification solution based on convolutional neural networks is proposed, designed specifically for resource-constrained wireless edge devices. With respect to previous works, the proposed system allows for recognizing a wider range of threats related to deforestation through a distributed and pervasive edge-computing technique. Different pre-processing techniques have been evaluated, focusing on a trade-off between classification accuracy with respect to computational resources, memory, and energy footprint. Furthermore, experimental long-range communication tests have been conducted in real environments. Data obtained from the experimental results show that the proposed solution can detect and notify tree-cutting events for efficient and cost-effective forest monitoring through smart IoT, with an accuracy of 85%. [ABSTRACT FROM AUTHOR]

This paper presents a performance analysis of Worldwide Interoperability for Microwave Access (WiMAX) contention-based access under nonsaturated conditions, taking different protocol parameters into account. We model the system by considering both the queuing of packets at subscriber stations and the queuing of bandwidth requests at the base station, which are serviced according to a round-robin cycle. Delay analysis is carried out through an M/G/1 queuing model with rest periods. Simulation results allow us to prove the accuracy of this analysis. A method for the optimization of the access phase is presented and compared with other results in the literature to prove the originality of the approach proposed. [ABSTRACT FROM PUBLISHER]

Satellite systems are a valid alternative to cover wide areas on the earth and to provide broadband communications to mobile and fixed users. Satellite systems should be able to provide to mobile users the same access characteristics of the terrestrial counterparts. This paper investigates packet scheduling aspects for Satellite Universal Mobile Telecommunication System (S-UMTS) transmissions based on Satellite – High Speed Downlink Packet Access (S-HSDPA). A geostationary bent-pipe satellite has been considered. The performance of different scheduling schemes has been compared in the envisaged S-HSDPA scenario, considering video streaming and Web traffic flows. We have obtained that the Proportional Fairness scheduler with Exponential Rule (PF-ER) permits to achieve the best performance for video traffic. Moreover, video traffic traces have been used to evaluate the objective video quality achieved at the application layer, considering the physical medium behavior and different S-HSDPA scheduling schemes. [ABSTRACT FROM AUTHOR]

Presents a study which dealt with the capacity analysis of a direct-sequence code-division multiple-access cellular system in the presence of heterogeneous traffics. Information on environmental description and external interference statistics evaluation; Performance analysis for a two traffic-classes scenario; Numerical results.

Presents information on a study which proposed a log-linear model to study the closed-loop power control (CLPC) performance in code-division multiple access cellular systems. Description of the system model; Analytical approach for the derivation of the optimum quantization step size; Simulation results; Conclusions.

Envisages a modified packet reservation multiple access (PRMA) for supporting voice and data transmission in low earth orbit (LEO) mobile satellite systems. Description on PRMA; Implications for the use of PRMA in LEO-global mobile personal communications via satellite; Information on the proposed PRMA-like protocol.

New Internet of Things (IoT) based applications with stricter key performance indicators (KPI) such as round-trip delay, network availability, energy efficiency, spectral efficiency, security, age of information, throughput, and jitter present unprecedented challenges in achieving next-generation ultra-reliable and low-latency communications (xURLLC) for sixth-generation (6 G) communication systems and beyond. In this paper, we aim to collaboratively utilize technologies such as deep reinforcement learning (DRL), unmanned aerial vehicle (UAV), and multi-access edge computing (MEC) to meet the aforementioned KPIs and support the xURLLC services. We present a DRL-empowered UAV-assisted IoT-based MEC system in which a UAV carries a MEC server and provides computation services to IoT devices. Specifically, we have employed twin delay deep deterministic policy gradient (TD3), a DRL algorithm, to find optimal computation offloading policies while simultaneously minimizing both the processing delay and the energy consumption of IoT devices, which inherently influence the KPI requirements. Numerical results illustrate the effectiveness of the proposed approach that can significantly reduce the processing delay and energy consumption, and converge quickly, outperforming the other state-of-the-art DRL-based computation offloading algorithms including Double Deep Q-Network(DDQN) and Deep Deterministic Policy Gradient (DDPG). [ABSTRACT FROM AUTHOR]

Provisioning of Internet of Things/machine-to-machine (M2M) services over satellite has been experiencing a continuous growth in the last few years, which is expected to further increase in the near future so as to meet the demands of users and enterprises. The design of a suitable network architecture is, hence, of paramount importance to properly take into account the requirements imposed by the technology available nowadays and to properly consider the interaction of the so-defined physical layer with transport and application layers. In this light, this paper analyzes the use case of TCP-based M2M services operating over DVB-RCS2 satellite links, where a contention resolution diversity slotted ALOHA access scheme is applied. The main goal of this paper is to provide a thorough understanding of the interactions of TCP and random access schemes, recognized as key elements to enable efficient M2M services over satellite. In this regard, this paper also develops a novel TCP throughput model, which has been validated through extensive simulation campaigns, proving the value of the proposed theoretical framework and its applicability to study the performance of M2M services in more general satellite scenarios. [ABSTRACT FROM AUTHOR]

Presents a study which dealt with low earth orbit mobile satellite systems belonging to third-generation mobile networks and proposed a novel packet-access scheme suitable for hybrid time-code wide-band air interface. System analysis; Performance analysis; Results and conclusion.

Focuses on the Wireless Application Protocol for providing mobile information services as envisaged by the Personalized Access to Local Information and Services for Tourists project within the fifth research framework of the European Commission. System description; Traffic model; Performance analysis; Results and conclusion.

The article discusses various reports on the topic of cooperative and relay communications published within the issue, including by Q. Zhang and colleagues on the interplay of cooperation and cognitive radio technologies and another by R. Mudumba and colleagues on beamforming.

UTRA-TDD is one of the adopted air interfaces for third-generation mobile communication systems (UMTS). In UTRA-TDD, information packets are transmitted organized into radio frames. A radio frame is divided into a fixed number of time slots and different packets can be sent on the same time slot by means of the Code Division Multiple Access technique. Packets belong to different traffic classes and have different formats and Quality of Service (QoS) requirements in terms of delay, transmission error probability and priority level. In this paper, we address the problem of scheduling packets for downlink transmissions in the time slots of a frame, in such a way that QoS requirements are fulfilled. In particular, exact pseudo-polynomial and heuristic scheduling algorithms are compared in terms of typical performance parameters. Computational results for three traffic classes show that the proposed algorithms are suitable for UTRA-TDD implementation, both for solution quality and computational time. [ABSTRACT FROM AUTHOR]

Satellite communication is a promising transmission technique to implement 5G and beyond networks. Attenuation due to rain begins at a frequency of 10 GHz in temperate regions. However, some research indicates that such attenuation effects start from 5–7 GHz, especially in tropical regions. Therefore, modeling rain attenuation is significant for propagating electromagnetic waves to achieve the required quality of service. In this survey, different slant link rain attenuation prediction models have been examined, classified, and analyzed, and various features like improvements, drawbacks, and particular aspects of these models have been tabulated. This survey provides various techniques for obtaining input data sets, including rain height, efficient trajectory length measurement techniques, and rainfall rate conversion procedures. No survey of the Earth–space link models for rain attenuation is available to the best of our knowledge. In this study, 23 rain attenuation models have been investigated. For easy readability and conciseness, the details of each model have not been included. The comparative analysis will assist in propagation modeling and planning the link budget of slant links. [ABSTRACT FROM AUTHOR]