The healthcare sector is experiencing a profound transformation, fueled by the rapid evolution of sixth-generation (6G) cellular networks and Internet of Things (IoT) technologies. At the heart of this shift lies the concept of medical digital twins (MDTs), which serve as dynamic virtual representations of physical systems or biological processes. MDTs offer a secure environment to simulate and evaluate therapeutic strategies, leading to reduced costs and more informed clinical decision-making. They also enable real-time support and in-depth data analysis, setting new standards for patient care. Nonetheless, realizing the full capabilities of MDTs remains challenging due to the inherent complexity of human life cycles. Crucial aspects include selecting appropriate data sources and defining robust communication protocols between the physical and digital realms. In particular, integrating wearable technologies with edge computing and WiFi-based Channel State Information (CSI) can significantly enhance health monitoring and activity recognition for elderly individuals within indoor settings. The synergy of IoT advancements and 6G networks paves the way for improved data exchange and continuous synchronization between digital and physical counterparts. This paper, part of the HIPPOCRATES project, presents an IoT-driven architecture for MDTs that incorporates wearable sensors and CSI data to strengthen health monitoring and early intervention strategies, with a focus on elderly care.

The next generation of high-accuracy positioning services is required to satisfy the sub-meter accuracy level for more than 95% of the network area, including indoor, outdoor, and urban deployments. In this vein, inter-agent measurements appear to provide additional position information and, hence, have the capacity to boost localization accuracy . This paper researches cooperative positioning techniques by means of device-to-device (D2D) and reconfigurable intelligent surfaces (RIS) technologies leveraging received signal strength (RSS) based ranging. We estimate the maximum capacities of the positioning systems in terms of accuracy through the Gaussian noise model, proposed universal theoretical distance-dependent noise model, and empirical noise model. We also evaluate the positioning error achieved by combining two or more technologies. Numerical results reveal the use cases advantageous for RIS- and D2D-aided localization. Then, based on the results, valuable guidelines are derived on the optimal sensor fusion metric – median – that minimizes the mean error of the cooperative localization.

Mobile network traffic has seen a significant surge, doubling in the past two years, due to increased adoption of fifth-generation ($\mathbf{5 G)}$ subscriptions. This emphasizes the need for efficient solutions like multicasting to manage escalating data demands. Multicast communications, however, encounter challenges in highly directional transmission scenarios, typical for 5G and sixth-generation (6G) systems. In such scenarios, characterized by the presence of obstacles or signal attenuation affecting one user, the performance degradation propagates across the entire multicast group. While Reconfigurable Intelligent Surfaces (RISs) have shown promise in mitigating blockage issues and optimizing wireless propagation environments, limited research has been done on their application to multicast communication. To address this gap, this study introduces a novel multicast group formation framework designed for highly directional RIS-enhanced multicast communications. The framework utilizes Self-Organizing Map (SOM) to organize close-range users into multicast groups based on the similarity of their azimuth angles relative to the RIS, while either microwave multicasting or mmWave unicasting are considered for users at greater distances. Furthermore, the study provides closed-form expressions for the transition threshold from SOM to either microwave multicasting or mmWave unicasting. Our results (in terms of data rate) demonstrate that the proposed approach with microwave technology outperforms all benchmark schemes and remains stable as the number of users increases, while the mmWave unicast approach exhibits performance similar to pure unicasting.

Digital Twins (DTs), which are paired to Internet of Things (IoT) devices to represent them and augment their capabilities, are gaining ground as a promising technology to enable a wide variety of applications in the sixth-generation (6G) ecosystem, ranging from autonomous driving to extended reality and metaverse. In particular, “social” IoT (SIoT) devices, which are devices capable to establish social relationships with other devices, can be coupled with their virtual counterparts, i.e., social DTS (SDTs), to improve service discovery enabled by browsing the social network of friend devices. However, the mobility of SIoT devices (e.g., smartphones, wearables, vehicular on board units, etc.) may require frequent changes in the corresponding SDT placement in the edge domain to maintain a low latency between the physical device and its digital replica. Triggering SDT relocation at the right time is a critical task, because an incorrect choice could lead to either increased delays or a waste of network resources. This work proposes a learning-powered social-aware orchestration that predicts the mobility of SIoT devices to make more judicious migration decisions and efficiently move the paired SDTs accordingly, while ensuring the minimization of both intra-twin and inter-twin communication latencies. Different machine learning (ML) and deep learning (DL) algorithms are used for SIoT device mobility prediction and compared in terms of a wide set of meaningful metrics in order to identify the model that achieves the best trade-off between prediction accuracy and inference times under different scenarios. Simulation results showcase the improvements of the proposal in terms of reduced network overhead (by up to a factor of 3) and intra-twin and inter-twin communication latency (by up to 10%) compared to a more traditional solution, which activates the relocation of the DTs at fixed time intervals following periodic optimizations.

The outbreak of the Covid-19 pandemic has caused a severe overload of intensive care units with a consequent drastic reduction of ordinary hospitalization, diagnostic tests, and interventions that has led to a significant increase in the number of deaths due to diseases other than the new coronavirus. Information and Communication Technologies (ICT) and the forthcoming Sixth-Generation (6G) system may revolutionize the doctor-patient relationship and healthcare modalities owing to the introduction of eHealth (or digital health). In this context, Non-Terrestrial Networks (NTNs) have vital importance in providing global connectivity thus improving the availability of eHealth services, especially in rural and remote areas. In this paper, we propose a Reliable Satellite Routing Algorithm (RSRA) for a 3D NTN based on Low-Earth Orbit (LEO) satellites. RSRA enables health data detected by sensors worn by the patients to be transmitted to health professionals by selecting a chain of reliable LEO satellites in order to protect such sensitive data. The system-level performance of proposed RSRA algorithm is assessed through simulation campaigns and compared against a routing approach that neglects LEO satellite reliability.

The support of multicast communications in the fifth-generation (5G) New Radio (NR) system poses unique challenges to system designers. Particularly, the highly directional antennas do not allow to serve all the user equipment devices (UEs) that belong to the same multicast session in a single transmission. The capability of modern antenna arrays to utilize multiple beams simultaneously, with potentially varying half-power beamwidth, adds a new degree of freedom to the UE scheduling. This work addresses the challenge of optimal multicasting in 5G millimeter wave (mmWave) systems by presenting a globally optimal solution for multi-beam antenna operation. The optimization problem is formulated as a special case of multi-period variable cost and size bin packing problem that allows to not impose any constraints on the number of the beams and their configurations. We also propose heuristic solutions having polynomial time complexity. Our results show that for small cell radii of up to 100 meters, a single beam is always utilized. For higher cell coverage and practical ranges of the number of users (5-50), the optimal number of beams is upper bounded by 3.

According to the 6G vision, the evolution of wireless communication systems will soon lead to the possibility of supporting Tbps communications, as well as satisfying, individually or jointly, a plethora of other very stringent quality requirements related to latency, bitrate, and reliability. The achievement of these goals will naturally raise many research issues within radio communications. In this context, a promising 6G wireless communications enabler is the reconfigurable intelligent surface (RIS) hardware architecture, which has already been recognized as a game-changing way to turn any naturally passive wireless communication setting into an active one. This paper investigates RIS-aided multicast 6G communications by first modeling the system delay as a first-come-first-served (FCFS) M/D/1 queue and analyzing the behavior under different blockage conditions. Then the study of multi-beam operation scenarios, covering multicast and RIS-aided multicast communications, is conducted by leveraging an M/D/c queue model. Achieved results show that large-size RISs outperform even slightly obstructed direct BS-to-user paths. In contrast, RISs of smaller sizes require the design of sophisticated power control and sharing mechanisms to achieve better performance.

The reconfigurable intelligent surface (RIS) adoption has drawn significant attention for the upcoming generation of cellular networks, i.e., 5G New Radio (NR)/6G, as a technology for forming virtual line-of-sight (LoS) links during human blockage or non-line-of-sight (NLoS) transmissions. However, the exploration of RIS placement under realistic conditions of multiple user operations has been limited by 1-2 user scenarios, but still is crucial since RIS deployment affects system performance. This paper addresses the challenge of optimal RIS deployment in 5G NR/6G cellular networks with directional antennas. Specifically, we formulate the RIS deployment problem as a facility location problem that maximizes the total data rate. We then evaluate and analyze the impact of various parameters on RIS-aided communications, such as RIS height, blockers density, number of users, and user distribution. The results confirm that the optimal RIS placement is near the BS for the case of uniform and cluster user distributions with RIS height of more than 5 m and close to the hotspots in the case of the cluster user distribution with RIS height of less than 5 m.

Internet of Space Things (IoST) is a challenging paradigm, which is currently attracting great interest from the scientific and industrial communities. IoST is based on the integration of the space segment into the global Internet-of-Things (IoT) infrastructure. In the relevant literature, reference is generally made to multiple constellations of nanosatellite platforms, used to enable IoT services on a global scale, including also disadvantaged and poorly infrastructured areas. In this article, we focus on multitenant IoT scenarios, wherein multiple CubeSats constellations are enabled to offer services by exploiting a dynamic federation model. The objective is to efficiently provide services in an IoST scenario by leveraging an effective cooperation strategy originally designed for terrestrial IoT networks, the Mobile-IoT-Federation-as-a-Service (MIFaaS) paradigm. We extend this vision to IoT satellite networks in order to allow a constellation of satellites to effectively execute tasks through a tight cooperative behavior with other CubeSats constellations. The reported performance evaluation studies show that better performance, in terms of percentage of tasks successfully completed, can be achieved through the implementation of the proposed cooperation paradigm.

As the fifth-generation (5G) and beyond (5G+/6G) networks move forward, and a wide variety of new advanced Internet of Things (IoT) applications are offered, effective methodologies for discovering time-relevant information, services, and resources are being demanded. To this end, computing-, storage-, and battery-constrained IoT devices are progressively augmented via digital twins (DTs) hosted on edge servers. According to recent research results, a further feature these devices may acquire is social behavior; this latter offers enormous possibilities for fast and trustworthy service discovery, although it requires new orchestration policies of DTs at the network edge. This work addresses the dynamic placement of DTs with social capabilities [social digital twins (SDTs)] at the edge, by providing an optimal solution under IoT device mobility and by accounting for edge network deployment specifics, types of devices, and their social peculiarities. The optimization problem is formulated as a particular case of the quadratic assignment problem (QAP); also, an approximation algorithm is proposed and two relaxation techniques are applied to reduce computation complexity. Results show that the proposed placement policy ensures a latency among SDTs up to 1.4 times lower than the one obtainable with a traditional proximity-based only placement while still guaranteeing appropriate proximity between physical devices and their virtual counterparts. Moreover, the proposed heuristic closely approximates the optimal solution while guaranteeing the lowest computational time.

The COVID-19 pandemic has changed the world. Today, the use of information and communications technology (ICT) in support of education, medicine, business, and administration has become a reality practically everywhere. In particular, the eHealth (digital Health) sector is on the cusp of a revolution, fueled by the worldwide health emergency due to the spread of the new coronavirus. With a view to developing new sixth-generation (6G)-oriented architectures, advanced eHealth services like telemonitoring would benefit from the support of technologies that guarantee secure data access, ultralow latency and very-high reliability targets, which are hardly achievable by the fifth generation (5G). This is the reason why this work proposes an eHealth system architecture, in which low-latency enabling technologies like Device-to-Device (D2D) communications and multiaccess edge computing (MEC) are integrated and supported by security mechanisms for an optimal management of sensitive health data collected by Internet of Medical Things (IoMT) devices. A preliminary evaluation of the proposed framework is provided that shows promising results in terms of data security and latency reduction.

The adoption of abundant millimeter-wave (mmWave) spectrum offers higher capacity for short-range connectivity in various Unmanned Aerial Vehicle (UAV)-centric communications scenarios. In contrast to the conventional cellular paradigm, where the coordination of connected nodes is highly centralized, the distributed deployments, such as those operating over unlicensed frequency bands, maintain robust interactions in the absence of central control. These agile decentralized systems are being naturally created by dynamic UAV swarms that form a temporary 3D structure without reliance on remote management or pre-established network infrastructures. While much effort has been invested in the performance assessment of distributed, directional, and 3D systems individually, a combination of these three angles allows capturing more realistic UAV swarm scenarios and produces a novel research perspective. This work addresses one of the fundamental challenges in mmWave-based 3D networks– directional deafness– which is known to adversely affect the overall system performance. Particularly, we develop a mathematical framework by taking into account the peculiarities of 3D directional and distributed deployments. We provide a holistic analytical assessment of directional deafness and propose several powerful approximations that capture realistic antenna patterns.

Massive multiple-input-multiple-output (MaMIMO) multicasting has received significant attention over the last years. MaMIMO is a key enabler of 5G systems to achieve the extremely demanding data rates of upcoming services. Multicast in the physical layer is an efficient way of serving multiple users, simultaneously demanding the same service and sharing radio resources. This work proposes a subgrouping strategy of multicast users based on their spatial channel characteristics to improve the channel estimation and precoding processes. We employ max-min fairness (MMF) power allocation strategy to maximize the minimum spectral efficiency (SE) of the multicast service. Additionally, we explore the combination of spatial multiplexing with orthogonal (time/frequency) multiple access. By varying the number of antennas at the base station (BS) and users’ spatial distribution, we also provide the optimal subgroup configuration that maximizes the spectral efficiency per subgroup. Finally, we show that serving the multicast users into two orthogonal time/frequency intervals offers better performance than only relying on spatial multiplexing.

Technology is continually undergoing a constituent development caused by the appearance of billions new interconnected “things” and their entrenchment in our daily lives. One of the underlying versatile technologies, namely wearables, is able to capture rich contextual information produced by such devices and use it to deliver a legitimately personalized experience. The main aim of this paper is to shed light on the history of wearable devices and provide a state-of-the-art review on the wearable market. Moreover, the paper provides an extensive and diverse classification of wearables, based on various factors, a discussion on wireless communication technologies, architectures, data processing aspects, and market status, as well as a variety of other actual information on wearable technology. Finally, the survey highlights the critical challenges and existing/future solutions.

Cooperation to access wireless networks is a key approach towards optimizing the use of finite radio spectrum resources in overcrowded unlicensed bands and to help satisfy the expectations of wireless users in terms of high data rates and low latency. Although solutions that advocate this approach have been widely proposed in the literature, they still do not consider a number of aspects that can improve the performance of the users’ connections, such as the inclusion of (1) cooperation among network operators and (2) users’ quality requirements based on their applications. To fill this gap, in this paper we propose a centralized framework that is aimed at providing a “win‐win” cooperation among Wi‐Fi and cellular networks, which takes into account 5G technologies and users’ requirements in terms of Quality of Service (QoS). Moreover, the framework is supported by smart Radio Access Technology (RAT) selection mechanisms that orchestrate the connection of the clients to the networks. In particular, we discuss details on the design of the proposed framework, the motivation behind its implementation, the main novelties, its feasibility, and the main components. In order to demonstrate the benefits of our solution, we illustrate efficiency results achieved through the simulation of a smart RAT selection algorithm in a realistic scenario, which mimics the proposed “win‐win” cooperation between Wi‐Fi and cellular 5G networks, and we also discuss potential benefits for wireless and mobile network operators.

Non-Terrestrial Networks (NTNs) based on the emerging 5G New Radio (NR) technology stand as an effective solution to complement terrestrial networks in service provisioning, owing to their ability to satisfy requests of anywhere and anytime connection, and to increase network scalability by delivering multicast/broadcast services to groups of NTN terminals through Point-to-Multipoint transmissions. However, current satellite systems operating at different orbits remain isolated islands and fail to express their true potential if not properly made interoperable with ground networks. In the light of effectively integrating existing 5G networks into a unified system, we propose a cooperative radio resource management scheme that enhances the performance of an integrated terrestrial-NTN system based on the emerging 5G NR technology. It leverages the principles of multicast subgrouping techniques to determine which users will get connected to either terrestrial base station (i.e., gNB) or NTN cell (i.e., NTN-gNB) and properly allocate resources in order to improve the overall network throughput. Simulation results show the effectiveness of the proposed solution.

Age of Information is a new metric used in real-time status update tracking applications. It measures at the destination the time elapsed since the generation of the last received packet. In this paper, we consider the co-existence of critical and noncritical status updates in a two-hop system, for which the network assigns different scheduling priorities. Specifically, the high priority is reserved to the packets that traverse the two nodes, as they experience worse latency performance. We obtain the distribution of the age and its natural upper bound termed peak age. We provide tight upper and lower bounds for priority updates and the exact expressions for the non-critical flow of packets with a general service distribution. The results give fundamental insights for the design of age-sensitive multi-hop systems.

The ever-increasing demand for high-quality video contents over mobile networks is pushing Telco operators towards the design of new delivery solutions. 3GPP has defined Multimedia Broadcast/Multicast Service Single Frequency Network (MBSFN) to enable the simultaneous transmission of the same content within multiple cells over the same radio resources, with improved network scalability and spectral efficiency. This paper proposes a Dynamic MBSFN Area Formation (DMAF) algorithm that suitably selects the adjacent synchronized cells to include in any MBSFN Area of a 5G New Radio (NR) system to the purpose of increasing the system Aggregate Data Rate while avoiding user outage. The proposed algorithm dynamically creates MBSFN Areas by leveraging the multicast “subgrouping” paradigm for Scalable Video Coding (SVC) traffic delivery. Cells are grouped into different MBSFN Areas and any cell can be part of Disjoint MBSFN Area or Overlapping MBSFN Area. Each Overlapping MBSFN Area broadcasts a Base video flow at a given quality level to all users, whereas Enhancement Layers are only delivered to users with better channel conditions. Simulation results testify to the better performance achieved by the proposed algorithm w.r.t. other schemes available from the literature.

A new class of miniaturized satellites, named CubeSats, have recently drawn the attention of the academic community first, and later of industry too, because they appear as a high attractive solution to provide a true widespread connectivity that allows also objects in remote areas to be part of the global Internet of Things (IoT). In this paper, we study the integration of this kind of satellites into multi-tenant scenarios, wherein multiple CubeSats constellations may be able to offer services even in an integrated manner. In particular, an IoT platform running within SDN/NFV-ready infrastructures which also includes CubeSat segments is designed. In the proposed architecture, CubeSats are considered as IoT sensing and actuation devices in the sky always available and able to provide enhanced services through their virtual counterpart (i.e., the virtual object). Useful scenarios are described and studied in which different constellations of CubeSats can be orchestrated via the proposed virtualisation platform to cooperate in providing IoT services.

The ever-increasing demand for ubiquitous high- data rate services pushes the Telco operators to face high challenging requirements for supporting bandwidth-hungry applications and for ensuring service continuity when a user is moving over a wide area. To guarantee this, Mobile Satellite Services (MSSs), especially Multimedia Broadcast Multicast Services (MBMSs), have gained great importance. Therefore, in this paper we propose a novel Radio Resource Management scheme for the efficient allocation of radio resources when delivering multicast video flows in 5G Satellite systems. The proposed Satellite - Multicast Subgrouping Multiple Layers (S-MSML) scheme jointly exploits both the Multicast Subgrouping and the Scalable Video Coding (SVC) technique to provide a minimum required quality to all multicast users and enhanced video quality to users in good channel condition. Finally, the results show that the proposed algorithm achieves better performance than the Legacy approach when considering multiple multicast groups in all considered environments.

Device-to-Device (D2D) communication will be one of the key enabling technologies for the future fifth generation (5G) cellular systems. A D2D communication allows nearby devices to transmit data directly, without passing through the network. Thanks to the proximity between devices, it allows to boost network performance by improving data rate, energy saving, and delay. Objective of the proposal in this paper is to securing future D2D communications. To this purpose, a new mechanism is designed which leverages (i) social trustworthiness, achieved through the Social Internet of Things (SIoT) paradigm, and (ii) encryption based on the Diffie-Hellman Key Exchange (DHKE) protocol for public key distribution. Results of a simulation campaign carried out by using MATLAB demonstrate that the proposed protocol can effectively enhance the protection of transmitted data by excluding users considered to be unreliable on the basis of both their reputation and their past behavior.

The coexistence of human type communications (HTC) with an ever-increasing number of machine type communications (MTC) is a challenge that the forthcoming Fifth Generation (5G) network is claimed to tackle. Ultra-Reliable and Low Latency Communications (URLLC) are among the most demanding services that 5G network will support. Also referred to as mission-critical services, URLLC often requires group communications. The evolved Multimedia Broadcast and Multicast Services (eMBMS) architecture, currently specified by 3GPP to support group-based services in cellular networks, needs a revision to deliver future mission-critical services. In this paper, we analyze the performance of different machine-type multicast service (MtMS) scenarios and we compare three subgroup based approaches for multicast data delivery to MTC devices with limited channel bandwidth. Achieved simulation results provide useful guidelines for the design of multicasting schemes able to support delay-sensitive applications in 5G networks.

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 this paper the MIFaaS (Mobile-IoT-Federation-as-a-Service) paradigm is proposed to support delay sensitive applications in the Internet of Things (IoT). This objective is reached by leveraging on the federation of distributed services and things at the infrastructure Edge and exploiting the real-world awareness and capabilities of IoT devices at the ground. MIFaaS enables value-added services by implementing the dynamic cooperation among private/public clouds of IoT objects with the purpose to enhance the efficiency in the provisioning of delay-constrained IoT services and increase the number of successfully delivered IoT services. The proposed paradigm is studied in a cellular environment based on standard Long Term Evolution (LTE). The simulative results we present demonstrate how the proposed federation solution of private/public IoT clouds outperforms alternative solutions with no federations and support of resources offered by the Cloud. Moreover, an analysis of the limitations and of the possible enhancements for cellular systems to support the proposed paradigm is drawn.

In emerging fifth generation (5G) systems, mobile social networks are expected to play an important role to enable proximity-based content distribution among devices. In this paper, we address social-awareness aspects and device-to-device (D2D) communications for information diffusion solutions in emergency scenarios. Context-aware information is collected from a set of devices deployed in the environment and received data are integrated and elaborated at the cellular base station before being delivered. In such a framework, we model the expected information diffusion time by taking into account both networking- and sociality-related metrics. In particular, we introduce the so-called social intercontact time which is able to model the interaction frequency between the user and a generic social platform. The proposed approach is compared with alternative solutions where the dissemination process is either managed through direct links from the central base station, as a conventional multicast scheme, or with the support from proximity communications, as a D2D-enhanced multicast scheme. The results of a performance assessment study show that the proposed framework achieves considerable gains, up to 50%, in terms of overall information diffusion time and data rate per user equipment.

Fifth generation (5G) systems are expected to introduce a revolution in the ICT domain with innovative networking features, such as device-to-device (D2D) communications. Accordingly, in-proximity devices directly communicate with each other, thus avoiding routing the data across the network infrastructure. This innovative technology is deemed to be also of high relevance to support effective heterogeneous objects interconnection within future IoT ecosystems. However, several open challenges shall be solved to achieve a seamless and reliable deployment of proximity-based communications. In this paper, we give a contribution to trust and security enhancements for opportunistic hop-by-hop forwarding schemes that rely on cellular D2D communications. To tackle the presence of malicious nodes in the network, reliability and reputation notions are introduced to model the level of trust among involved devices. To this aim, social-awareness of devices is accounted for, to better support D2D-based multihop content uploading. Our simulative results in small-scale IoT environments, demonstrate that data loss due to malicious nodes can be drastically reduced and gains in uploading time be reached with the proposed solution.

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.

This paper investigates relay-based schemes in cellular systems, where multihop device-to-device (D2D) communications are exploited for content uploading toward the eNodeB. All user equipments (UEs) are sources of their own content and form a multihop D2D chain, with the head of the chain being in charge of uploading all the generated content to the eNodeB. By pooling the cellular radio resources assigned to the D2D chain and by using high-quality short-range radio links, the proposed cooperative content uploading scheme guarantees lower upload delays than in the traditional cellular mode operation. To model the D2D chain formation in a cell and to best characterize self-interested users concerned about their own payoff, a constrained coalition formation game is defined, where each UE is a player whose cost is identified as the content upload time. The solution of the game determines the stable feasible partition for the UEs in the cell. We demonstrate through simulations that with this solution the content uploading time is reduced by 52% with respect to the traditional cellular mode.

Recently, mobile multimedia services have represented an increasingly large source of revenue for the telecommunication industry. Subscribers are often interested in simultaneously receiving the same data flow and, hence, they fuel the growing demand for multicast multimedia services. Therefore, the design of efficient radio resource management strategies to jointly handle multicast and more traditional unicast traffic and to increase user satisfaction is of primary importance for the successful deployment of future mobile networks. This paper proposes an efficient radio resource management framework to handle unicast and multicast multi-layer video services. The proposed virtual unified group (VUG) approach makes use of a channel-aware subgrouping principle to provide fair throughput to both unicast and multicast users. The idea is to assign unicast subscribers to a virtual group, thus allowing them to compete for network resources on an equal footing with multicast users. Simulations highlight the benefits that VUG provides in a long term evolution network scenario, under different traffic load conditions, in terms of throughput and fairness in the distribution of resources to unicast and multicast users.

This paper addresses the radio resource management of multicast transmissions of video streaming services in the emerging 5G-Satellite systems. A subgroup-based approach is used to split any multicast group into subgroups. This allows an effective exploitation of multi-user diversity according to the experienced channel conditions and the achievement of a high throughput level. The main drawback is the high computational cost usually related to the selection of the optimal subgroup configuration. In this paper, we propose a low-complexity subgroup-based algorithm that achieves performance close to optimum. Our solution is suitable for implementation in practical systems, such as Satellite-Long Term Evolution (S-LTE), since the computational cost does not depend on the multicast group size and the number of available resources. Through simulations conducted in different radio propagation and multicast group environments, the effectiveness of our proposed scheme is assessed.

Current and future releases of 3GPP standards will include enhancements in LTE-Advanced for machine-type communications (MTC). The main reason for this new trend is the fact that 5G wireless systems will need to enable the coexistence between MTC and human-type communications (HTC). Therefore, novel solutions are needed to efficiently exploit the radio resources for MTC, considering, among others, the need to optimize transmissions for small data packets. With this aim, this paper addresses the use of short-range device-to-device (D2D) communications as enabling technology to efficiently manage the radio spectrum and to reduce the energy consumption of MTC devices. We consider a scenario where MTC devices are grouped in a cluster; among the cluster members, one terminal acts as aggregator in charge for (i) receiving data from neighboring terminals via D2D links and (ii) relaying the aggregated data to the base station via macro-cellular link. The main contribution of this paper is to compare the performances of the two most popular D2D technologies, i.e., WiFi-Direct and LTE-Direct, used to transmit data toward the aggregator. The performance evaluation in terms of latency and energy efficiency has been conducted in a wide set of scenarios by varying the number of clustered devices and the data to upload per single MTC device.

This paper investigates on novel effective schemes based on Device-to-Device (D2D) communications for data relaying, to upload content from a set of cooperating User Equipments (UEs) acting as sources of the data towards a cellular base station (eNodeB). Enabling factors of the resulting cooperative data uploading able to improve the system performance are: (i) the differentiated channel quality experienced by UEs and (ii) the introduced possibility to pool together the allocated radio resources. A constrained coalition formation game is used for multi-hop D2D overlapping coalition formation, where the time needed to upload the content is the utility for the players. The proposed model directly considers the coverage constraints for the D2D links among the players. The proposed solution allows to determine the final cooperating network topology as a tree of overlapping coalitions. We demonstrate that the solution guarantees an average gain in the uploading time for the UEs up to a 23% with respect to non-cooperative content uploading methods.

Dense Networks (DenseNet) and Multi-Radio Access Technologies (Multi-RATs) are considered as key features of the emerging fifth generation (5G) wireless systems. A Multi- RAT DenseNet is characterized by a very dense deployment of low- power base stations (BSs) and by a multi-tier architecture consisting of heterogeneous radio access technologies. In this work, we propose an effective RAT selection algorithm that efficiently manages the RAT handover procedure by (i) choosing the most suitable RAT that guarantees high system and user performance, and (ii) reducing unnecessary handover events. In particular, the decision to trigger a handover is based on a new system parameter named Reference Base Station Efficiency (RBSE). This parameter takes into account metrics related to both the system and the user: the BS transmitted power, the BS traffic load and the users' spectral efficiency. We compare, by simulation, the proposed scheme with the standardized 3GPP policies. Results show that the proposed RAT selection scheme significantly reduces the number of handovers and the end-to- end delay while maintaining high system throughput and user spectral efficiency.

The rapid demand growth for group-oriented services mandates telco operators to efficiently manage the contemporary presence of the unicast services and the emerging multicast applications. We propose a novel radio resource management approach for providing fair throughput to unicast and multicast users in a broadband wireless network. The idea is to assign unicast subscribers to a virtual group in order to compete on an equal footing with multicast users for network resource distribution. We also revisit the traditional fairness indexes in order to capture the fairness in the degree of user satisfaction for unicast and multicast users. Simulations highlight the effectiveness of the virtual group strategy in terms of achieved fairness in several scenarios and under different traffic loads.

This paper deals with the management of multicast transmissions in Satellite-Long Term Evolution (S-LTE) networks. With the purpose of offering high session quality by exploiting the multi-user diversity, we propose a framework for multicast subgroup formation in satellite networks. In particular, the idea at the basis of the proposed solution is to split the multicast satellite users in subgroups, according to the experienced channel conditions. Such an approach allows to convey multicast content without requiring additional data coding and guarantees high throughput and user fairness. The comparison among the results achieved through the designed framework and those present in literature demonstrates the effectiveness of the proposed approach for providing efficient multicast transmissions via satellite.

Multicast services over Long Term Evolution (LTE) have recently attracted the interest of the research community. Particular attention has been put on handling fairness requirements of multicast users and experienced channel quality. Conventional Multicast Scheme (CMS), Opportunistic Multicast Scheme (OMS), and multicast subgroup formation are the principal policies adopted to address this research issue. Little attention has been given so far to multicarrier systems like LTE-Advanced although the need for solutions appropriate to this system is strongly felt. In this paper we design radio resource management policies for the efficient delivery of multicast services in multicarrier LTE-Advanced systems and show how the relation between fairness and system efficiency can be controlled. Concerning the system resource management, game theoretic bargaining solutions are considered to best model fairness and efficiency (expressed in terms of throughput).

Long Term Evolution (LTE) is considered the most promising cellular system able to support the growing demand of multicast services (e.g., IPTV, video streaming) over mobile terminals. The design of effective strategies for the management of these applications is still an open issue, especially in scenarios where several multicast streams are simultaneously transmitted in a cell. In this paper we propose different resource allocation policies for the delivery of multicast scalable video flows. Such policies efficiently exploit the multi-user diversity and the frequency selectivity in order to match the requirements of both users and providers. The performance of the proposed strategies is analyzed through simulations by evaluating different cell deployment and user load environments and by focusing on spectral efficiency, throughput, fairness, and amount of resources needed for multicast service delivery. The last parameter is important in practical scenarios where multicast services share the available resources with other flows, e.g., unicast services.

Long Term Evolution (LTE) is the emerging 4G wireless technology developed to provide high quality services in mobile environments. It is foreseen that multimedia services and mobile TV will assume an important role for the LTE proliferation in mobile market. However, several issues are still open and meaningful improvements have to be introduced for managing physical resources when group-oriented services should be supplied. To this end, we propose a Frequency Domain Packet Scheduling (FDPS) algorithm for efficient radio resource management of Multimedia Broadcast/Multicast Services (MBMS) in LTE networks. The proposed scheduler exploits an optimization process to organize multicast subscribers in subgroups according to channel quality feedbacks provided by users. Optimization is driven by the aim of minimizing the “user dissatisfaction” with a consequent improvement in the network capacity. The effectiveness of the proposed scheduling algorithm is evaluated through simulation; obtained results demonstrate significant improvement in the multicast traffic performance.

This paper focuses on the design of radio resource management policies for multicast service delivery in WiMAX networks. With the purpose of finding an alternative solution to the conventional multicast scheme that is conservative towards resource utilization, we propose to use a subgroup-based link adaptation technique that dynamically chooses the modulation and coding schemes based on the perceived channel conditions in each subgroup of multicast receivers. The main idea is to split the multicast destinations into different subgroups depending on the perceived channel quality, and to apply subgroup-based adaptive modulation and coding for a more efficient spectrum exploitation. The performance of different solutions for the subgroups formation will be analyzed and their effectiveness evaluated through simulations to show how the network can take advantage from the proposed subgrouping approach.

This paper focuses on the design of radio resource management policies for efficient delivery of multicast services in Long Term Evolution (LTE) systems. In order to find alternative solutions to the Conventional Multicast Scheme (CMS), an effective framework is proposed that splits multicast destinations into different subgroups, depending on the User Equipments (UEs) channel quality, and applies a subgroup based Adaptive Modulation and Coding (AMC) scheme. This approach allows a more efficient spectrum exploitation. Game theoretic notions are used for the multicast subgroups formation and the resource allocation problems. The effectiveness of the proposed framework is evaluated and four different bargaining solutions are compared in terms of data rate, fairness, and subgroup configurations.

In this paper, a delay tolerant approach for traffic management in LTE over satellite link is presented. Due to the long propagation delays and frequent disruptions, mobile satellite communications pose many challenges, especially to the transport layer when the TCP protocol is used. We design and evaluate the performance of a transport protocol solution based on the DTN architecture in the satellite-LTE system. Our proposal, named Tiny Bundle Layer, acts as an overlay on top of different versions of TCP in order to overcome the satellite link impairments.

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.

Abstract Multicast service delivery can be easily guaranteed to users in disadvantaged areas by effectively integrating HAPs (High Altitude Platforms) into the terrestrial cellular system. HAPs are meant to be as unmanned aerial vehicles, airships or aircrafts, which remain relatively stationary in the stratosphere at short distance from Earth compared to satellites. In the scientific literature, there is evidence of the effectiveness of a UMTS (Universal Mobile Telecommunications Systems) system augmented by the presence of HAPs, which are equipped with UMTS payloads and play the role of additional base stations. This integrated terrestrial‐space platform intrinsically fits the exigencies of rural and emergency scenarios, which are characterized by network resource scarcity, due to either geographical reasons (such as in rural areas) or to temporary resource over‐utilization/reduction (due to emergency status). In this paper, the focus is on the delivery of Multimedia Broadcast/Multicast Services (MBMS) in the reference integrated architecture. Main objectives are designing resource allocation policies to manage multicast groups between space and terrestrial coverages, and analysing their feasibility and performances in terms of offered grade of service. Copyright © 2008 John Wiley & Sons, Ltd.

Multimedia broadcast multicast services (MBMS), introduced by Third Generation Partnership Project (3GPP) in universal mobile telecommunications system (UMTS) release 6 specification, have the aim to support downlink streaming and game services to groups of users. MBMS can supply users with resources in two different modalities: point-to-point (PtP) and point-to-multipoint (PtM). The power consumed by the network is an important topic to discuss when considering the presence of MBMS services. The UMTS system is, in fact, interference- limited; thus, the power available to Node B is limited and it must be enough to serve any user under its coverage. Therefore, the choice of the most efficient transport channel in terms of power consumption is a key aspect for the MBMS, since a wrong transport channel selection for the transmission of the MBMS data could adversely affect the overall capacity of the system. In this paper we search for the most efficient transport channel to convey MBMS data, by comparing the performance of the high speed downlink shared channel (HS-DSCH), the dedicated channel (DCH), and the forward access channel (FACH), for given transmission power levels and cell coverage size.

Focus of the present paper is the integration between high altitude platforms (HAPs) and terrestrial UMTS system to support multimedia broadcast/multicast services. HAPs are characterised by a wide coverage area, which makes them a very attractive solution to support broadcast and multicast applications, while increasing both resource capacity and grade of services. In the depicted scenario, we propose to enhance the system efficiency by envisaging a novel radio resource management (RRM) protocol based on the evaluation of the power consumption relevant to users belonging to each multicast group. We demonstrate that the use of the proposed RRM policy, coupled to a wise selection of transport channels, leads to the effective management of multiple multicast groups.

This paper introduces a novel seamless handoff approach for DVB-H networks aimed at reducing the user terminal power consumption and at making the handoff algorithm be driven by the quality of the user received signal. This implies the substitution of standard RSSI-based procedures with a method based on the Modulation Error Rate (MER) monitoring. The additional use of an underlying cellular network, for DVB-H related data delivering, allows to achieve additional advantages: a superior power saving and a faster handoff execution. Obtained results suggest that the DVB-H handoff protocol design is an issue, which definitely deserves further investigation in the view of making DVB-H an effective solution for delivering broadcast content to mobile users.

The strong user need for receiving multimedia content while on the move opens up new challenges in future hybrid wireless communication scenarios. Delivering broadcast and multicast multimedia services through existing cellular networks is surely one of the toughest issues to investigate. The wide coverage area of High Altitude Platforms (HAPs) makes them a very attractive solution to deliver multicast/broadcast applications to a large number of sparse users. The authors examine the implications arising from the integration of UMTS and HAP systems to provide Multimedia Broadcast and Multicast Services (MBMS). In this reference scenario, two radio resource management policies are compared in terms of overall offered Grade of Service (GoS). By a thorough simulation investigation, the performance trade-off between a "User Number oriented" vs. a "User Distribution oriented" solution is evaluated. The different conditions under which one approach outperforms the other are investigated, and the degree of achieved performance augmentation is highlighted.

Key issues in the design of soft handoff policies for DVB-H systems are energy saving and constant monitoring of the received signal quality. With this idea in mind, a novel algorithm is proposed in this paper with the aim of reducing the frequency of handoff-related measurements in DVB-H systems, thus enabling manifest power saving in portable terminals than in the case of standard RSSI-based procedure. The objective is accomplished by making handoff algorithm be driven by the quality of the signal received by the user, constantly monitored through techniques of MER (Modulation Error Rate) measurement and estimation. The performing behavior of the proposed mechanism, assessed through a comprehensive evaluation campaign, allows us being confident that this is a direction to consider for future research activities in the field of effective DVB-H handoff protocols design.

The focus of this paper is on the integration of High Altitude Platforms (HAPS) into a terrestrial UMTS system to effectively support MBMS applications. Its main objective is the efficient allocation of transmission resources to multicast traffic streams (by suitably selecting terrestrial and/or HAP channels) while still preserving the desired Grade of Service of background unicast traffic. Specifically, we compare two different approaches to the Radio Resource Management (RRM) in the depicted scenario: the first one takes into account the Number of users in each multicast group to drive the RRM policies; while the second one bases the RRM behavior on the Distribution of users belonging to each multicast group. By conducting a thorough investigation, the performance trade-off between "User Number oriented" vs. "User Distribution oriented" solutions is evaluated. The different conditions under which one approach outperforms the other are investigated and the degree of performance augmentation is always highlighted.

In this paper the authors' attention is on the specification of a middleware functionality for dynamic QoS control in multimedia cellular environments, such as UMTS. The functionality implements a soft QoS paradigm, at the same time optimising the perceptual QoS provided to the end user according to his/her needs. It will be shown that by exploiting suitable performance indexes and resource redistribution algorithms both an acceptable grade of service and a good degree of user satisfaction can be achieved, without an excessive increase in the network-signalling load.

A large amount of research is currently focusing on the issue of the adaptive control of the quality-of-service (QoS) provided to multimedia applications in heterogeneous wireless systems. In this paper, the authors aim at contributing to this issue by proposing a mechanism that exploits user profiling techniques and suitable QoS mapping functions to introduce the soft QoS idea into a wireless multimedia scenario. The research objective is a QoS control architecture, which enables the continuous convergence between the actual user preferences and expectations and the resource constraints of the underlying wireless system. The proposed architecture operates between the system and the application layer. This allows it to achieve the intended results, by means of an effective dynamic reconfiguration of the applications and the contemporary renegotiation of the wireless resources.

This paper presents the analysis of some MAC protocols for multimedia applications in wireless ATM networks. The novelty of the approach is the delivery of multimedia applications over separate bearers over the radio interface while maintaining the original synchronisation degree. The presented techniques are able to guarantee low jitter, high degree of synchronization among different streams of the same user application, as well as to effectively exploit the limited radio spectrum of a wireless air interface.