Artificial intelligence (AI)-native edge networks are promising solutions to seamlessly integrate AI into modern network architectures, promoting intelligent and hyper-flexible behavior in self-adaptation and reconfiguration of hybrid networks. AI-native edge nodes have to promptly react to any change in network conditions and to be linked to Internet of Everything (IoE) deployed in etherogeneous communication domains. This paper deals with a next-generation programmable edge node capable of being employed in different domains in a unified and flexible manner. With the aim to achieve a low re-configuration overhead in such herogeneous contexts, this paper proposes the integration of a generative-AI module within an edge node exploiting foundation models for efficient general-purpose time-series prediction, without involving overhead and costs due to models trained from scratch and overcoming data scarcity. This permits to manage IoE networks deployed in both homogeneous and heterogeneous domains, i.e., aqua, ground and air, autonomously, without the need for adjustments from the outside. As foundation models, we focused on Chronos and TimesFM, in both the zero-shot and fine-tuning learning paradigms. Finally, performance results in terms of prediction accuracy, training, and inference time are provided and compared with those achieved by the state-of-the-art recurrent neural networks trained from scratch and baseline alternatives. The obtained results corroborate the potential of foundation models as key enablers of native AI networks, achieving good accuracy despite the absence of a training phase (i.e., in zero-shot mode) or with limited training (fine-tuning), w.r.t. alternatives.

Nowadays, an ambitious target of the next generation networks is to develop intelligent overarching space-air-ground-aqua computing systems, in order to provide a smart ecosystem able to efficiently operate computation in heterogeneous domains. In particular, in such a context, the underwater environment requires a special attention, since it is recognized as the most challenging domain, due to channel impairments and adverse propagation conditions. This paper proposes a self-intelligent system able to efficiently perform underwater environment monitoring or underwater survey of critical infrastructure, by resorting to the use of the semantic communication paradigm to lower the impairments due to the underwater channel propagation conditions. In particular, in our case, images sent by underwater devices are collected by shore small base stations (SSBSs) to form their training dataset to take part in a federated learning process with a ground base station. In particular, the paper considers a semantic communication scheme based on a deep-convolution neural networks encoder-decoder architecture for an efficient exploitation of the data transmission from underwater devices to the linked SSBSs. Performance analysis is provided to show the better behavior of the proposed system in comparison with the conventional alternative that does not involve the use of the semantic communications approach. Finally, a specific performance evaluation analysis is devoted to the investigation of the convergence behavior of the proposed federated learning procedure in reference to the cross ground-aqua system considered in order to highlight its advantages with respect to a classical implementation.

Nowadays, the functional integration of Unmanned Aerial Vehicles (UAVs) as flying computing nodes with terrestrial networks is rapidly emerging as a promising and viable solution to enhance performance or lower drawbacks arising from unpredictable traffic load congestion occurrences. In particular, this paper considers a UAV-Aided Multiple Access Edge Computing system, in which heterogeneous traffic flows with different quality of service constraints, have to be offloaded on processing nodes consisting of terrestrial and flying edge computing nodes. Towards this goal, the paper proposes a matching algorithm to perform an efficient offloading strategy. In particular, the proposed matching algorithm provides decisions on the basis of per-flow end-to-end delay bounds formulated by resorting to the combined application of stochastic network calculus and martingale envelopes theory. Furthermore, matching stability has been theoretically discussed. Numerical results highlight the validity of the proposed stochastic framework in terms of both reliability, i.e., the probability with which the per-flow end-to-end delay is lower than the corresponding deadline, and its ability to fit the actual network behavior. For comparison purposes, the Boole bound is formulated, and a greedy algorithm is developed to compare the matching strategy designed.

This article deals with an artificial intelligence (AI) framework to support Internet-of-everything (IoE) applications over sixth-generation wireless (6G) networks. An integrated IoE-Edge Intelligence ecosystem is designed to effectively face the problems of Virtual Machines (VMs) placement based on their popularity, computation offloading optimization, and system reliability improvement predicting compute nodes faults. The main objective of the article is to increase performance in terms of minimization of worst end-to-end (e2e) delay, percentage of requests in outage, and the enhancement of reliability. The article focuses on the following main issues: (i) proposal of a channel-aware federated learning (FL) approach to forecast the popularity of the VMs required by IoE devices; (ii) use of an AI-based channel conditions forecasting module at the benefits of the FL process; (iii) development of a suitable VMs placement on the basis of their popularity and of an efficient tasks allocation technique based on a modified version of the auction theory (AT) and a proper matching game; (iv) enhancement of the system reliability by an echo-state-network (ESN), located on each computation node and running in the background to predict failures and anticipate tasks migration. Numerical results validate the effectiveness of the proposed strategy for IoE applications over 6G networks.

Although combining Full Duplex (FD) and Cognitive Radio (CR) technologies can provide several benefits, the presence of the residual self-interference (RSI) at the FD transceiver may influence the spectrum sensing capabilities. In particular, focusing on the blind eigenvalue-based detectors (EVDs), this paper shows that operating at mmWave widebands, the RSI is a colored noise strongly affecting the detection performance even when it is characterized by low power. Consequently, we propose here a whitened detector whose novelty consists in the real-time computation of the whitening matrix, differently from previous works which employ an offline computation. The proposed whitening matrix computation uses a sample covariance matrix (SCM) regularization tailored for the FD scenario, instead of the conventional SCM estimator. Particularly, we prove that the proposed whitened detector is robust against RSI power uncertainty, attaining a constant false alarm rate under typical FD operating conditions. Finally, we show that our method provides computational load reduction and faster convergence to the theoretical false alarm probability characteristic of the white noise case. Numerical simulations validate the theoretical analysis confirming the better performance of the proposed whitening approach, particularly when applied to the sphericity test, in comparison to the offline-based approach.

Recently, with the advances in self-interference cancellation, full-duplex (FD) techniques have become a feasible approach to improve the spectrum usage in new generation wireless systems. In particular, in cognitive radio networks, FD allows a secondary user to simultaneously sense the spectrum and transmit, improving the network efficiency. However, the residual self interference (RSI) arising from an imperfect cancellation, represents a bottleneck for the spectrum sensing performance. This paper analytically demonstrates that RSI represents a colored noise which leads to the SNR Wall phenomenon making the typical OFDM signal detectors no longer robust. To overcome this drawback, we propose a generalized likelihood ratio test detector exploiting the multipath correlation due to the primary user’s (PU) channel. It is proven that the proposed method is not affected by the SNR Wall, hence it is robust w.r.t an imperfect self-interference cancellation. Specifically, best detection performance is achieved when an approximated knowledge of the maximum delay spread of the PU channel is available, otherwise it is shown that a limited performance degradation occurs. Moreover, provided results highlight that our approach outperforms the classical alternatives in different scenarios, including when PU employs a mixed numerology OFDM signal, which characterizes the 5G New Radio waveform.

In the recent year, quantum computing and communications (QCC) represented two revolutionary technologies that are rapidly developing and integrating to interconnect heterogeneous quantum devices within the so-called Quantum Internet (QI). Despite several investigations and developments have been performed on terrestrial quantum communications over typical optical fiber links, there are some limitations in terms of extremely high losses that can be faced by deploying several repeaters, which in turns involves impractical costs for network management, especially in terms of forwarding procedures. Quantum Satellite Networks (QSNs) is capable to overcome the constraints of terrestrial optical networks, i.e., the remarkable attenuations over long distances which makes the intercontinental communications unaffordable. The recent technological developments in terms of quantum satellite communications motivated our investigation on an ad hoc quantum satellite backbone interconnecting quantum on Earth Servers in order to achieve an unprecedented computational capacity. Our aim is to investigate existing constellations, spanning from Low Earth Orbit (LEO) up to micro-satellites, to properly derive some guidelines for designing an efficient backbone. Specifically, the focus is on evaluating the impact of forwarding approaches on the end-to-end capacity (i.e., the entanglement generation rate) to achieve a trade-off between performance and cost.

The forthcoming sixth-generation (6G) network technology will trigger tremendous changes across several application scenarios and even in the way we work, communicate, and, more in general, organize our everyday life. In particular, in such a new digital era, virtual reality (VR) technology will play a fundamental role, carrying with it numerous challenges as regards the increasing demand of high rate, highly reliable, and low-latency communications, especially in reference to Internet-of-Things environments. In this sense, an effective end-to-end (e2e) delay analysis becomes imperative to pursue an efficient design of the foreseen VR services. Toward this goal, this article proposes the e2e delay investigation through the martingale theoretical bound and considering the stochastic network calculus principles for its formulation. The performance discussion focuses on the achieved communications reliability, comparing the analytical predictions obtained via the martingale bound with the simulation results, and the Markov queuing theory-based alternative. The presented results confirm the validity of the proposed approach, exhibiting noticeable closeness between the theoretical bound and the simulation outcomes.

This paper analyzes the end-to-end delay performance in an edge-computing scenario where a set of Internet of Things devices (IoTDs) access the computation facilities of an Edge Node by means of a 5G based network. In particular, the paper deals with a two power levels slotted Aloha non-orthogonal-multiple-access (NOMA) scheme and formulates a stochastic end-to-end delay bound, in terms of complementary cumulative probability distribution, by resorting to the application of the martingale theory. In order to validate the proposed analysis, the paper proposes comparisons between the achieved analytical predictions and actual values derived by resorting to extensive computer simulations. Furthermore, the well known Boole bound has been formulated and compared with the proposed Martingale approach to highlight the better behavior of the proposed solution.

The increasing diffusion of smart devices has triggered new Internet of Things (IoT) applications, where communications patterns are often in an autonomous mode. Key enabling technologies, such as relaying communications, cell size reduction and multicast communications have been identified to bring the next‐generation IoT to a complete fruition. In particular, the use of relay nodes is expected to be useful for coverage and capacity improvements, as well as to support point‐to‐multipoint services for data disseminating to subscribers communities. To this end, this study proposes a dynamic quorum links selection (DQ m ) procedure to optimise the throughput for the case of buffer‐aided relaying multicast communications. A theoretical analysis based on the Markov chain framework is provided and validated through simulation results in terms of multicast throughput and relay buffer occupancy for different sizes of the multicast group. The advantages of the proposed DQ m procedure have been highlighted by comparing the achieved performance with respect to classical conventional relay scheme. Finally, a protocol for channel state estimation is presented and the impact of the requested overhead on the performance of DQ m procedure is shown.

Spectrum sensing plays a key role in cognitive radio technology to acquire information on the occupancy status of the channel. Cyclostationary spectrum sensing is considered one of the most promising approaches. However, its performance is severely degraded by a mismatch between the actual and the nominal cyclic frequency [i.e. cyclic frequency offset (CFO)]. This is particularly true for vehicular networks, due to the high mobility and particularly to the presence of a non‐zero radial acceleration between the transmitter and the receiver that makes the signal filtered out by the Doppler channel chirped, thus introducing the CFO. Consequently, the signal to be detected has to be properly modelled as a generalised almost‐cyclostationary process. The proposed approach performs a maximum‐likelihood estimation of the CFO jointly to the detection exploiting multiple cycles, through a maximisation of the generalised likelihood ratio test. The closed‐form of false alarm probability is derived highlighting that this approach represents a constant false alarm rate detector. Numerical evaluations are provided to show the correctness of the theoretical analysis and that the performance is approximatively constant for a large range of CFO values. Moreover, comparisons with existing algorithms are provided.

Vehicular communication networks have emerged to enable numerous vehicular data services and applications. Conventional vehicularad hocnetworks (VANETs) are often operated in thead hocmode and mainly focus on road safety applications based on the connection between vehicles and roadside units (RSUs). To support vehicular communications, dedicated shortrange communication (DSRC) and car-to-car communication consortium (C2C-CC) have been initiated in the United States and Europe, respectively. With the new era of the Internet of Things (IoT), the conventional VANETs have evolved to the Internet of Vehicles (IoV). In IoV, each vehicle is envisioned as an intelligent object, equipped with sensing platforms, computing facilities, control units, and storages and is connected to any entity (other vehicles, RSUs, charging/gas stations, cloud, and so on) via vehicle-to-everything (V2X) communications. Intelligent vehicles can take different roles, i.e., being both a client and a server, taking and providing big data services, leading to numerous new IoV applications, from assisted/autonomous driving and platooning, secure information sharing and learning to traffic control and optimization.

Nowadays, industrial Internet of Things (IIoTs) has gained attention as an emerging application area of the Internet of Things paradigm to improve efficiency and reliability in a wide class of manufacture processes. This article focuses on a combined edge-cloud computing architecture for IIoT systems, and addresses the minimization of both the mean system response time and the number of requests dropping due to a response time greater than their time deadline. The problem is formulated as a matching game with externalities between the edge computing servers, and the applications themselves. The proposed strategy adopts a discard policy with the aim at favoring the IIoT-devices requests with a not-expired deadline. Moreover, a suitable discussion of the matching stability is proposed. Finally, the strategy's validity has been confirmed by the system performance expressed in terms of mean and worst system response time and outage probability, in comparison to methods recently proposed in the literature.

Recently, Edge Computing systems have emerged as a suitable solution to provide fast data processing with low latency to mobile users. In particular, in the case of real time computation demands, the users mobility often plays a very central role, requiring highly responsive information processing and interpretation of the data, retrieved by environment, in order to apply proper strategies for decision making. This paper proposes an approach based on the queuing theory in order to derive the performance of an Edge Computing systems in the case of real time applications demands and user mobility. In particular, on the basis of some simplifying assumptions, the proposed analytical method allows to identify the minimum (i.e., optimal) number of central process units to be allocated to an edge computing node in order to meet specific application constraints. The validity of our approach is then validated by providing performance comparisons between the obtained analytical predictions and simulation results derived by assuming actual application conditions.

Chaos theory constitutes a promising and powerful tool to address forecasting problems of nonlinear time series, since it catches the dynamical and geometrical structure of very complex systems, ensuring a superior accuracy on the predicted results in comparison to classical approaches, and lowering the complexity typical of the deep learning ones. This paper applies the nonlinear chaos theory principles to the passenger demand forecasting problem. The proposed scheme processes and analyzes the big data of passengers requests collected during one month in the city of Chengdu, China. In order to predict passenger demand behavior, the chaotic trend of the time series has been identified through the largest Lyapunov exponent research. Then, the phase space reconstruction has been pursued, through the detection of the suitable embedding dimension and time delay, to improve forecasting accuracy and avoid information redundancy. A combined local and global predictive method has been proposed, and the validity of the approach is confirmed by comparison with two state-of-art forecasting methods, the auto-regressive and the auto-regressive moving-average with exogenous input. System performance is evaluated in terms of mean squared error and mean percent forecasting error.

The explosive growth of mobile traffic needs that the fifth generation of wireless systems supports a thousand-fold increase of network capacity, thanks to new paradigms such as network densification. However, in dense networks interference can be a limiting factor, and must be suitably managed. In this paper multiple cells coordinate to mitigate the mutual interference: cross-tier interference is limited by means of the traditional enhanced Inter Cell Interference Coordination approach, while a new co-tier interference management strategy based on Matching Theory is proposed. The objective is to provide a stable matching between the set of small cells and the set of available subframes left almost blank by the macrocell and used by the small cells to communicate with their most vulnerable users. The proposed solution aims at improving the throughput of most critical users with an affordable computational complexity. The effectiveness of the proposed scheme has been verified in comparison with benchmark methods.

One of the main challenges of supporting massive machine-type-communications (MTCs) by future mobile networks, is the radio access network (RAN) congestion. A viable solution is a hierarchical architecture where cluster-grouped machines are indirectly connected to the mobile network through a cluster gateway. This paper considers such an architecture and focuses on radio resource allocation to machine-clusters where resources can be spatially reused for concurrent transmissions. In particular, resources can be accessed simultaneously by machines of different clusters and by different communication phases, thus resulting in an interference-limited system. Three different resource partitioning schemes are proposed and evaluated, mainly differing on how interference is taken into account. The aim is to minimize the packet loss probability, and thus maximizing the spectral efficiency. Numerical results show the effectiveness of the proposed schemes in comparison to benchmark methods. In particular, by joining resource reuse and interference-mitigation, the efficiency improves significantly.

Securing Internet of Things (IoT) devices and protecting their applications from privacy leaks is a challenge, due to their weak (computational and storage) capabilities, and their proximity with sensitive data. Considering the resource-constrains of such devices, their long lifetime, and the intermittent connections, classical security approaches are often too difficult or impractical to apply. Moving target defense is an established technique whose goal is to lower the attack surface to malicious users by constantly modifying device footprint. Changing the address to an IoT device without privacy leaks is, however, a nontrivial task. In this paper, we propose a novel method to perform a network-wide (Internet protocol and medium access control) address shuffling procedure, called address shuffling algorithm with HMAC (AShA), which is simple to implement, and whose network overhead is minimal. To demonstrate its effectiveness, we analyze our approach via theoretical analysis and simulations. Our analysis shows how AShA parameters can be adapted to various network sizes while our simulations results show how AShA can be used to successfully perform a global collision-free address renewal on networks of more than 2000 nodes using 16-bit addresses.

This paper proposes two virtual functions (VFs) placement approaches in a Fog domain. The considered solutions formulate a matching game with externalities, aiming at minimizing both the worst application completion time and the number of applications in outage, i.e., the number of applications with an overall completion time greater than a given deadline. The first proposed matching game is established between the VFs set and the fog nodes (FNs) set by taking into account the ordered sequence of services (i.e., chain) requested by each application. Conversely, the second proposed method overlooks the applications service chain structure in formulating the VF placement problem, with the aim at lowering the computation complexity without loosing the performance. Furthermore, in order to complete our analysis, the stability of the reached matchings has been theoretically proved for both the proposed solutions. Finally, performance comparisons of the proposed matching theory approaches with different alternatives are provided to highlight the superior performance of the proposed methods.

The use of satellite communications to support the Internet of Things paradigm is of paramount importance for application scenarios where machines are spread in remote and wide areas. In such context, this paper proposes an efficient hierarchical radio access scheme. Ground machines randomly access the radio channel to communicate with their cluster heads, which in turn relay the cluster's aggregated traffic toward the satellite. The aim is optimizing the resource allocation to different communication stages, allowing resource reuse among clusters, in order to minimize the packet drop probability, and hence, to maximize the system throughput. First, the optimal solution is derived for the single cluster, then it is extended to the multi-cluster scenario. Numerical results show the effectiveness of the proposed method, also in comparison with benchmark approaches.

Ultra Dense Networks (UDNs) are considered a key element to address the expected growing of communication capacity demand in an affordable and sustainable way, improving both spectral and energy efficiency. This paper focuses on the energy efficiency of a coordinated multicell multicast transmission in UDNs. In particular, a new iterative algorithm is proposed, whose goal is to maximize the energy efficiency of a single-group multicast service. Toward this goal, the cells are activated opportunistically, only when needed, using suitable transmission power. Moreover, small cells use adaptive beamforming weights in order to increase the efficiency of the radiated power. The effectiveness of the proposed method is proven in terms of energy efficiency and in comparison with different benchmark solutions. Benefits and limits of network densification are evaluated.

Energy efficiency (EE) is one of the main requirements for future fifth generation wireless networks to allow a sustainable network development. Toward this goal, this study proposes a novel iterative algorithm to maximise the EE of multicast services in ultra dense networks. Macrocells and small cells cooperate using a multicast beamforming strategy to efficiently radiate the power in the considered area. Moreover, small cells are activated opportunistically, and their power levels are adjusted suitably. Due to the high complexity of the optimisation problem, the proposed algorithm works calculating iteratively beamforming weights and power adjustments, thus reducing the set of possible solutions. Then, an exhaustive search is performed among the elements of this restricted set. This solution has reduced computational complexity, and the achieved EE is higher than benchmark alternatives. Performance in terms of EE and complexity is provided together with a solution feasibility evaluation.

Fog Computing (FC) is an emerging paradigm that extends cloud computing toward the edge of the network. In particular, FC refers to a distributed computing infrastructure confined on a limited geographical area within which some Internet of Things applications/services run directly at the network edge on smart devices having computing, storage, and network connectivity, named fog nodes (FNs), with the goal of improving efficiency and reducing the amount of data that needs to be sent to the Cloud for massive data processing, analysis, and storage. This paper proposes an efficient strategy to offload computationally intensive tasks from end-user devices to FNs. The computation offload problem is formulated here as a matching game withexternalities, with the aim of minimizing the worst case service time by taking into account both computational and communications costs. In particular, this paper proposes a strategy based on the deferred acceptance algorithm to achieve the efficient allocation in a distributed mode and ensuring stability over the matching outcome. The performance of the proposed method is evaluated by resorting to computer simulations in terms of worst total completion time, mean waiting, and mean total completion time per task. Moreover, with the aim of highlighting the advantages of the proposed method, performance comparisons with different alternatives are also presented and critically discussed. Finally, a fairness analysis of the proposed allocation strategy is also provided on the basis of the evaluation of the Jain’s index.

This paper proposes a channel allocation scheme for Wide-Area Low-Rate Wireless Personal Area Networks (LR-WPAN) based on a cooperative centralized spectrum sensing approach. We refer here to a three-tiers LR-WPAN architecture, where we can distinguish the sensor devices level, the Child-coordinators level and, finally, the super LR-WPAN coordinator level. In the proposed scheme, channels allocation is performed by the LR-WPAN coordinator upon receiving the spectrum sensing reports from the Child-coordinators. The performance of the proposed scheme is evaluated in terms of resulting detection probability and throughput, in a scenario where Industrial, Scientific and Medical (ISM) bands are saturated and different LR-WPANs compete to the channel access. Performance comparisons with a classical scheme where the channel allocation is accomplished without performing spectrum sensing, are also presented in order to highlight the advantages of the proposed scheme.

This paper analyzes the resource allocation problem in the LTE-Unlicensed spectrum to increase performance of the unlicensed systems. The problem is modeled with a matching game approach and the proposed resource allocation algorithm consists of a heuristic based on the usage of preference lists, one for each user equipment (UE) and on unlicensed bands, to determine a many-to-many matching between UEs and component carriers (CCs), aiming at maximizing the unlicensed overall network sum rate. Hence the proposed algorithm realizes a mapping between user equipments and unlicensed channels, also considering the carrier aggregation (CA) mechanism, which is typical of LTE-U. In the simulation evaluation, we compare the proposed algorithm with the Hungarian algorithm w.r.t. the system throughput and the robustness to perturbed input data. Both algorithms have almost equivalent performances, but the Hungarian algorithm presents a higher computational complexity than the proposed one.

Packet collision is a well-known severe impairment in ALOHA-based networks and, more generally, in any random access network. As a consequence, several methodologies have been considered with the aim of lowering the resulting performance degradation. A novel multiuser detection scheme exploiting channel diversity to separate collided signals is proposed here to enable multiple packet reception capability in random access schemes. The performance of this approach is analytically derived and optimized in terms of network throughput, and compared with that of different alternatives. The overall performance in terms of throughput shows the effectiveness of the proposed scheme in different operating conditions.

With the increasing use of Wireless Sensor Networks, the privacy of the user is of main concern. The sensors maintain a layer 2 address that lasts for the node lifetime. As a consequence, an eavesdropper can easy trace the user and his activities, even in case the nodes send ciphered traffic.We propose a 6LoWPAN-ND extension to improve privacy and overcome the traceability of the user. With our method all the nodes change periodically all their addresses, both at layer 2 and 3. The method requires a small overhead and leverages on existing 6LoWPAN messages. The security is analyzed to show the effectiveness of our work and its energy requirements.

Simple connectivity and data requirements together with high lifetime of battery are the main issues for the machine-to-machine (M2M) communications. 3GPP focuses on three main licensed standardizations based on Long Term Evolution (LTE), GSM and clean-slate technologies. The paper considers the last one and proposes a modified slotted-Aloha method to increase the capability of supporting a massive number of low-throughput devices. The proposed method increases the access rate of users belonging to each class considered in the clean-slate standard and consequently the total throughput offered by the system. To derive the mean access rate per class, we use the Markov chain approach and simulation results are provided for scenarios with different data rate and also in terms of cell average delay.

Device-to-device (D2D) communications enable the proximity communications among users with or without the use of the network infrastructure. D2D communications can increase the overall spectrum efficiency and reduce the power consumption thus a massive utilization of D2D is expected in the future 5G networks. The paper proposes a D2D resource allocation method based on the reuse of primary uplink resources. The method guarantees both a fixed quality of service (QoS) for D2D communication as well as the assigned QoS for cellular communications. It relies on the estimation of distances of all the actors related to D2D position: D2D pairs, base station and the primary devices. These distances are used to evaluate the minimum D2D transmission power which guarantees the D2D reception and jointly produces a controlled and acceptable level of interference on the primary system. The performance of primary system achieved by the proposed method is compared with the one of an unaware interference approach. The results obtained for the scenario with a D2D pair show how the method can limit the interference on primary system. For the scenario with different D2D pairs, the results highlight a better scalability with respect to the other method.

This paper proposes and compares different policies to perform the optimal link selection in the presence of buffer-aided relay for multicast communications. These policies are based on the knowledge of the instantaneous link quality indicators as well as the status of the relay buffer, and dynamically select the more suited link according to a deterministic or random criterion, whose parameters are optimized via a Markov chain theoretical framework. The performance for all the proposed methods are analytically derived and validated through intensive computer simulations for different multicast scenarios. The advantages of the proposed schemes are pointed out in terms of multicast throughput, buffer occupancy for different buffer size and multicast group size.

Power line communication technology receives today a renewed attention for a wide class of advanced applications and services, thanks to the advantage of using the existing electrical infrastructure, which requires only limited deployment costs. However, wires have been originally designed for power and not for data, and signal propagation is affected by several impairments such as impulsive noise and frequency selectivity. On the other end, new emerging application perspectives-mainly related to the smart grid or Internet of Things paradigms-need reliable unicast and/or multicast information delivery methodologies. This paper deals with an efficient multicast power line communication system based on the use of a decision direct impulsive noise mitigation scheme and of multiple transmissions of symbols in the frequency domain, allowing an efficient exploitation of the communication channel frequency diversity. The performance of the reliable multicast power line communication system is derived by resorting to the application of the absorbing Markov chain theory in terms of mean overall delivery delay and throughput, in relation to different application scenarios. Moreover, a suitable optimization procedure is also proposed here in order to achieve the best performance. The advantages of the proposed optimized reliable multicast power line communication system are finally validated by comparisons with a classical system.

A simple diamond half-duplex relay network composed of a source, two decode-and-forward half-duplex relays, and a destination is considered, where a direct link between the source and the destination does not exist. For this network, we study the case of buffer-aided relays, where the relays are equipped with buffers. Each relay can receive data from the source, store it in the buffer, and forward it to the destination, when the channel conditions are advantageous. Thereby, buffering enables adaptive scheduling of the transmissions and receptions over time, which allows the network to exploit the diversity offered by the fading channels. For the considered half-duplex network, four transmission modes are defined based on whether the relay nodes receive or transmit. In this paper, we derive the locally optimal scheduling of the transmission modes over time and investigate the achievable average rate, when the relays are affected by inter-relay interference. Since the proposed buffer-aided transmission policies introduce unbounded delay, we provide a sub-optimal buffer-aided transmission policy with limited delay. Moreover, for inter-relay interference cancellation, we consider two coding schemes with different complexities. In the first scheme, we employ dirty paper coding, which entails a high complexity, whereas in the second scheme, we adopt a low-complexity technique based on successive interference cancellation at the receiving relay nodes and optimal power allocation at the transmitting nodes. Our numerical results show that the proposed protocols, with and without delay constraints, outperform existing protocols for the considered network from the literature.

Abstract The impressive increase of innovative wireless communication technologies and applications represents nowadays a key approach to enable pervasive communications environments. In particular, the emerging paradigms of the Internet of Things and capillary networks offer effective ways to make devices connected. This has triggered the development of effective methodologies and procedures to allow an unlimited number of devices to exchange information mainly in an autonomous mode. However, it is a well‐known concept that wireless networks capacity usually decreases with the number of nodes. In particular, in order to improve the throughput scalability, a promising approach is that of resorting to the use of multiple radio interfaces at each node, in order to exploit spatial reuse of frequencies. Towards this end, game theory methodologies offer efficient approaches to solve the complex radio interfaces selection and allocation problems. This paper proposes a game theory‐inspired approach to efficiently select the number of radio interfaces to be used at each node site in order to lower the energy consumption and maximise the end‐to‐end throughput of any communication on which the node is involved in. The good behaviour of the proposed approach is validated by provided theoretical framework and numerical results derived by considering different data packets wireless forwarding schemes. Copyright © 2015 John Wiley & Sons, Ltd.

Long Term Evolution-Advanced (LTE-A) and the evolved Multimedia Broadcast Multicast System (eMBMS) are the most promising technologies for the delivery of highly bandwidth demanding applications. In this paper we propose a green resource allocation strategy for the delivery of layered video streams to users with different propagation conditions. The goal of the proposed model is to minimize the user energy consumption. That goal is achieved by minimizing the time required by each user to receive the broadcast data via an efficient power transmission allocation model. A key point in our system model is that the reliability of layered video communications is ensured by means of the Random Linear Network Coding (RLNC) approach. Analytical results show that the proposed resource allocation model ensures the desired quality of service constraints, while the user energy footprint is significantly reduced.

This paper focuses on a particular application of coalitional game theory to Vehicular Ad Hoc Networks (VANET), involving only vehicular-to-vehicular communications. Moreover, networking is performed in an ad hoc basis to pursue full context awareness of vehicles. The proposed approach relies upon the setting up of cluster as soon as convoys temporarily arise in traffic dynamics. First, we define a utility function for each node under the hypothesis of being an ordinary node, cluster head or free node. We further prove that a selfish approach is suboptimal when compared to a game of coalition. Then, the communication between clusters (inter clusters communications) has been implicitly modelled according to this approach. Finally, from the simulation results, it is shown that a coalitional game outperforms a selfish approach for different nodes spatial deployment and mobility patterns.

Machine-to-Machine (M2M) communications is one of the key enablers of the Internet of Things (IoT). Billions of devices are expected to be deployed in the near future for novel M2M applications demanding ubiquitous access and global connectivity. In order to cope with the massive number of machines, there is a need for new techniques to coordinate the access and allocate the resources. Although the majority of the proposed solutions are focused on the adaptation of the traditional cellular networks to the M2M traffic patterns, novel approaches based on the direct communication among nearby devices may represent an effective way to avoid access congestion and cell overload. In this paper, we propose a new strategy inspired by the classical Trunked Radio Systems (TRS), exploiting the Device-to-Device (D2D) connectivity between cellular users and Machine-Type Devices (MTDs). The aggregation of the locally generated packets is performed by a user device, which aggregates the machine-type data, supplements it with its own data and transmits all of them to the Base Station. We observe a fundamental trade-off between latency and the transmit power needed to deliver the aggregate traffic, in a sense that lower latency requires increase in the transmit power.

A simple diamond half-duplex relay network composed of a source, two half-duplex relays, and a destination is considered, where no direct link between the source and the destination is exists. For this network, we investigate the achievable rate when the relays are equipped with buffers. Buffer-aided relays can receive data from the source, store it in their buffers, and forward it to the destination when the channel conditions are more advantageous. Thereby, buffering enables adaptive scheduling of the transmissions and receptions over time, which allows the network to better exploit the diversity offered by the fading channel. For the considered network, because of the half-duplex relays, four transmission modes are employed based on whether the relay nodes receive or transmit. Considering these four transmission modes, in this paper, we derive the optimal transmission mode selection policy such that the received data rate at the destination is maximized. Furthermore, based on numerical examples, we show that the proposed protocol outperforms the existing protocols for the considered network in the literature.

The most recent trend in the Information and Communication Technology world is toward an ever growing demand of mobile heterogeneous services that imply the management of different quality of service requirements and priorities among different type of users. The long-term evolution (LTE)/LTE-advanced standards have been introduced aiming to cope with this challenge. In particular, the resource allocation problem in downlink needs to be carefully considered. Herein, a solution is proposed by resorting to a modified multidimensional multiple-choice knapsack problem modeling, leading to an efficient solution. The proposed algorithm is able to manage different traffic flows taking into account users priority, queues delay, and channel conditions achieving quasi-optimal performance results with a lower complexity. The numerical results show the effectiveness of the proposed solution with respect to other alternatives.

This paper deals with the performance evaluation and optimization of an efficient Hybrid Automatic Repeat Request (HARQ) scheme suitable for applications delivered over lossy multicast communication channels. In particular, differently from previously investigated strategies, this paper proposes a Modified HARQ scheme based on the Symbol Combining principle (MHARQ-SC) where multiple copies of a same packet are consecutively transmitted at each transmission opportunity. By considering as performance metrics the mean packet delivery delay and energy consumption per information packet, this paper presents suitable performance evaluation and optimization strategies tailored for multicast communications. For the sake of comparisons, it has been also analysed, under the same operational conditions, the performance of different HARQ schemes optimized for multicast communications. Numerical results have been provided in order to validate the proposed performance evaluation and optimization approaches in the case of the MHARQ-SC scheme. An important result devised here is that the reported analytical results clearly highlights the performance gain of the proposed strategy in comparison with all the other considered alternatives.

The Internet of Things and the Web of Things have focused on context awareness as a central issue in defining complex autonomic systems that rely on various layers, including devices, communications and applications. The spread usage of mobile devices that allow users to generate and to access distributed data makes it extremely important to organize the forwarding and gathering of such data in a user centered way, which may support a targeted process of data analytics. Data science should strongly take into account the individual and her/his needs to look at data from a personal perspective. In this contribution an integrated view of context awareness is presented, with the several technological and scientific issues that it raises.

Heterogeneous network deployment represents one of the main enhancements of future LTE-A networks to increase spectrum efficiency. However, the achievable improvements are limited by the interference that arises from a co-channel allocation of the cells. This paper proposes two cognitive resource allocation methods that work using the angle of arrival of the signals instead of the channel state information. Both methods reduce the interference towards the macro-cell User Equipments (MUEs) using Zero Forcing Beamforming to avoid transmission in the MUEs direction. At the same time they maximize the capacity of the femto-cell with a suitable allocation of the time-frequency resources to the femto-cell UEs (FUEs). The performance of the proposed methods is compared with that of a conventional maximum gain beamforming and conventional zero forcing beamforming. The results show that the proposed methods achieve a good trade off between maximization of the femto-cell capacity and reduction of the interference level at the MUEs side.

In this paper we propose couple power allocation strategies for layered video services delivery over evolved Multimedia Multicast/Broadcast Service (eMBMS) networks. The proposed allocations aim at reducing the power consumption of the eNodeB (eNB) and improving the user quality of experience characterizing the delivered eMBMS flows. We consider multiple challenging scenarios which differ by: (i) the number of eNBs transmitting the same service set, and (ii) how services are delivered. In particular, we consider scenarios where services can be delivered by resorting to the Random Network Coding principle or not. We compare the proposed resource allocation models to a strategy which equally shares the transmission power budget among layers of the delivered service. Analytical results show that the proposed resource allocation strategies are characterized by a transmission power which is on average 13% smaller than the considered alternative. In addition, the optimized resource allocation can deliver each layered video service over a geographical area which is up to 25% greater than that associated to the considered alternative.

This paper deals with a clustering approach for VANETs operating in highway scenarios, where a certain degree of correlation among vehicles emerges such that a group mobility pattern is expected. The proposed protocol is inherently mobility driven as the reference metric to select a Cluster Head (CH) takes into account the node connectivity within an estimated coherence time interval. Our clustering protocol handles both cluster set up and maintaining and communications among different clusters. In particular, the inter cluster communications are accomplished by means of relay node selection. The protocol design and validation have been focused on a practical scenario adopting IEEE 802.11p communication standard, highlighting good performance in terms of connection probability, overhead and complexity.

We consider a heterogeneous Long Term Evolution Advanced (LTE-A) network where a cognitive femtocell operates in the coverage area of a traditional macrocell sharing the same frequency band. A new method is proposed here to avoid the interference generated by the femtocell on the macrocell downlink communications. In particular, the estimation of the direction of arrival of the primary user signals is used to place nulls in the femtocell transmission paths by means of a suitable beamforming algorithm. The novelty of the proposed approach is that it works on a physical resource basis, taking into account the specific LTE-A access scheme. In this way it is able to manage the interference towards several macrocell users characterized by a high angle dispersion of the multipath components. The obtained numerical results show that the system is able to significantly reduce the interference in different operational conditions, especially when the physical resource blocks belonging to the same macrocell user can be clustered, thus increasing the dimension of the snapshot used for the direction of arrival estimation.

Heterogeneous network deployment is one of the key issues of future Long Term Evolution Advanced systems. However, the coexistence of high power macro-cells and low power femto-cells leads to co-channel interference problems that must be suitably counteracted. Enhanced Inter-Cell Interference Coordination allows a joint management of the resources among the cells so as to reduce the interference. The behaviour of this approach depends on the choice of some parameters, and in particular on the Almost Blank Subframes muting ratio. This paper proposes a simple approach to determine adaptively the most suitable value of the muting ratio as a function of the network traffic load, based on suitable threshold values. The performance is given in terms of network throughput percentage gain.

Machine-to-Machine (M2M) communications are gaining momentum due to the rapid deployment of smart devices with self-organizing capabilities, able to interact each other without the human operator support. Ultimately, M2M paradigm allows Machine-Type Communication Devices (MTCD) to exchange data in Peer-to-Peer (P2P) mode, avoiding the need of a core network handling end-to-end communication establishment between two machines. To this end, the recent Device-to-Device (D2D) feature, introduced by the Third Generation Partnership Project (3GPP) Release 12, fosters new types of service based on the device proximity concept and helps to offload cellular networks by enabling direct-mode communications among cellular users. Furthermore, D2D is also considered a suitable technology to fully support M2M communications thanks to the reduced power consumption and the hop gain. In this paper we first review crucial aspects of M2M communications and examine major issues involving terminals operating in D2D mode in LTE-A networks. Then, a multi-hop D2D communication scheme is proposed in order to enhance end-to-end connectivity among devices in a proximity area within an LTE-A cell. We also describe a promising resource allocation approach aware of the multi-hop D2D network configuration, able to fulfil bandwidth requests of all the cooperating devices, according to the related role in the network set-up.

Resource reuse among heterogeneous cells in LTE-A networks permits to increase the spectral efficiency but requires suitable interference mitigation techniques. Among these Coordinated scheduling and beamforming (CS/CB) is a promising solution. This paper proposes a new CS/CB scheme aiming to maximizing the mean system throughput taking into account the fairness among the cells. First the most suitable CB technique selection is analysed and a sub-optimum criterion based on the reciprocal angular distance between two concurrent users is proposed. Then a smart CS algorithm that allows to pair users with sufficient angular distance is introduced. The results show that the proposed scheme achieves performance close to the optimum CB scheme selection and the smart allocation permits to increase significantly the system throughput.

ABSTRACT This paper proposes a new method of data authentication and encryption for distributed networks supporting mobile software agents. Software agents are a valuable instrument in wireless distributed monitoring networks, because they can be used to concentrate monitoring efforts in certain areas where an event is taking place. In this way, events can be tracked in a dynamic and efficient way. Mobile agents have to send messages to each other in order to coordinate their actions, and those messages need to be secured by crypto credentials. However, when agents are moved over wireless networks, how can credentials be protected from sniffing by an attacker, besides layer II encryption? Moreover, if a rogue agent is injected in the network, is it possible to limit the damages it can produce? The proposed approach bridges mediated RSA with the trusted platform modules, in order to provide an efficient and secure communication between agents. The communication is secured using indeed Identity based cryptography, while maintaing the compatibility with standard RSA and eliminating the mediator introduced by mediated RSA. We will show that this approach is convenient in terms of traffic overhead, perfectly applicable to existing trusted platform modules specifications and able to limit damages that both external and internal attackers can produce to the network. Copyright © 2013 John Wiley & Sons, Ltd.

This paper deals with the issue of reliably transmission of short messages through satellite. The problem is of paramount importance for emergency and alerting scenarios. In particular, we propose a novel efficient Network Coding (NC) communication scheme aiming to improve the delivery probability of the transmitted information messages. A suitable analytical approach has been developed in order to highlight the performance of the proposed NC scheme and to allow its optimization. The accuracy of the proposed approach has been validated by resorting to computer simulations. Performance comparisons with the classical NC scheme are also presented here to highlight the advantages of the proposed NC scheme in the case of AWGN and Rician communication channels.

This paper deals with a cognitive approach used to reduce the co-channel interference arising from the coexistence of an LTE macrocell and an LTE femtocell sharing the same frequency band. Multiple-antennas technology is considered to exploit the angle dimension as a new spectrum opportunity: femtocell acts as a secondary system and inserts nulls in the directions of the UE connected to the macrocell thus protecting the downlink transmission of the primary base station. MuSiC algorithm is used to detect the DOA of the UE signal replicas in an indoor environment assuming a variable number of multipath components characterized by a very large angle spread. The proposed scheme permits to increase the signal to interference ratio at the UE side thus reducing the achieved error rate on the downlink connection even when the number of resolvable paths is higher than the number of antennas. Finally the UE mobility is considered to take into account the effect of variable DOAs.

In this paper, we propose a novel advanced multirate design for evolved Multimedia Multicast/Broadcast Service (eMBMS) in fourth generation (4G) Long-Term Evolution (LTE)/LTE-Advanced (LTE-A) networks. The proposed design provides: i) reliability, based on random network coded (RNC) transmission, and ii) efficiency, obtained by optimized rate allocation across multi-rate RNC streams. The paper provides an in-depth description of the system realization and demonstrates the feasibility of the proposed eMBMS design using both analytical and simulation results. The system performance is compared with popular multi-rate multicast approaches in a realistic simulated LTE/LTE-A environment.

This paper deals with the application of the so called Internet of Things paradigm to the setting up of intelligent and cooperative environments. In particular, it focuses on the management of wide area Wireless Sensor Networks comprised of objects belonging to the logistic domain with the aim of transparent managing them. The IPv6 global addressing is applied allowing the dynamic tracking, information upload and retrieval and nodes management, while coping with inherent mobility. The proposed solution has been adopted in a real world case study, pointing out flexibility and responsiveness.

The radio resource shortage is one of the most important issues to be taken into account when deploying modern wireless communication systems. A novel communication paradigm named cognitive radio, has been introduced in the last years for a more efficient exploitation of the limited available spectrum and cope with the inefficiency in the spectrum usage. Its main aim is to allow the co-existence of different wireless systems on the same spectral resources by limiting the mutual interference. The aim of this paper is to design a cognitive networking environment where the primary network is based on the OFDMA principle. The proposed Medium Access Control (MAC) technique for the secondary network, named Data Aided Cognitive Technique (DACT), aims to exploit the framing information broadcast by the primary network in order to setup transparently an independent network with a particular focus on Machine to Machine (M2M) communications.

The radio resource shortage is one of the most important problems to be considered when deploying modern wireless telecommunication systems. A novel communication paradigm named cognitive radio, has been introduced in the last years for a more efficient exploitation of the limited available spectrum. Its main aim is to allow the co-existence of different wireless systems on the same spectral resources by limiting the mutual interference. In this paper we consider a cognitive approach environment where the primary system is an OFDMA network. In this paper a MAC protocol based on the Wireless Token Ring approach is proposed for a secondary network aiming to exploit the OFDMA framing structure of the primary network.

This paper deals with the performance evaluation of Decode and Forward Physical Layer Network Coding schemes under multipath fading channel propagation conditions. Physical Layer Network Coding in Two Way Relay Networks ideally allows to drastically increase the network throughput. However, under the assumption of actual channel propagation conditions, the performance quickly degrades due to high decoding error probability. With the aim of counteracting this drawback, the paper proposes a suitable approach for Orthogonal Frequency Division Multiplexing systems based on a signal pre-equalization technique. Furthermore, in order to lower the decoding error probability, three subcarriers suppression methods are introduced. These methods differ from each other for the performance achieved and the required amount of signaling that nodes have to exchange. An important result obtained here is that the combined use of channel inversion and subcarriers suppression allows to enhance the system reliability with a slight decrease of the throughput.

ABSTRACT The last years have been characterized by an increasing interest in the grid and cloud computing that allow the implementation of high performance computing structures in a distributed way by exploiting multiple processing resources. The presence of mobile terminals has extended the paradigm to the so called pervasive grid networks, where multiple heterogeneous devices are interconnected to form a distributed computing resource. In such a scenario, there is the need of efficient techniques for providing reliable wireless connections among network nodes. This paper deals with the proposal of a suitable resource management scheme relying on a routing algorithm able to perform jointly the resource discovery and task scheduling for implementing an efficient pervasive grid infrastructure in a wireless ad hoc scenario. The proposed solutions have been considered within two different parallelization processing schemes, and their effectiveness has been verified by resorting to computer simulations. Copyright © 2011 John Wiley & Sons, Ltd.

This paper deals with a clustering approach for VANETs operating in sparse highway scenarios. The proposed protocol is able to keep high and stable the network connectivity level to allow data exchange among nodes and, thus, achieving context awareness. The criterion adopted in forming a cluster involves the periodic distributed evaluation of connectivity indicators combining the number of neighbors and their distances, without excessive signaling overhead. In this way, data propagation leverages on vehicles physical movements instead of setting up a communications backbone, which can not properly face a high mobility level. The performance has been analyzed in a practical scenario adopting IEEE 802.11p communications standard. In particular, the election period has been optimized for different coverage ranges, pointing out the suitability of the proposed metrics.

This work focuses on providing effective end-to-end (E2E) communications for critical monitoring applications through Wireless Sensor Networks. In particular, the case of frequent disconnection and reconnection has been analyzed, deriving effective routing strategies to cope with this problem. Basing on a recent IETF draft scheme, namely RPL, capable of accommodating several practical situations, a novel approach, called eN Route (NR), has been proposed. In particular, it relies on a two tier network architecture with a hybrid tree-mesh topology, which can be locally rearranged depending on link failures, mainly due to mobility. This is done in a completely distributed way by maintaining a specific neighbor table built only by sniffing data messages to not increase the signaling overhead. The proposed solutions functionalities have been described and compared in terms of connectivity efficiency, E2E path length distribution and E2E latency statistic, giving also some figures on overhead. The analyses have shown NR to achieve better results in in terms of network connectivity latency and overhead, despite some drawbacks, even though RPL is able to achieve comparable performance at the expenses of higher signaling overhead. As a consequence, it has been pointed out the way RPL future releases can profit from NR approach to improve performance.

This paper proposes an energy efficient antennas allocation method for network-coded MIMO multicast communications. By means of the definition of a suitable objective function it is shown that it is possible to select the optimal number of antennas in transmission/reception and the most convenient modulation scheme in order to minimize both the overall mean energy consumption and delivery delay. Simulation results are provided in the paper in order to validate the proposed optimization method and to highlight its advantages in comparison with similar rate-based approaches already proposed in literature, where symbol error rate is evaluated as a comparing metric for MIMO performance.

3GPP's Long Term Evolution (LTE) represents the one of the most valuable alternatives to offer a wireless broadband access in fully mobile network context. In particular LTE is able to manage several communication flows characterized by different QoS constrains. This paper deals with a network topology where the mobile users are clustered in Multicast Groups and the base station broadcasts a different traffic flow to each cluster. In order to improve the network throughput on a per-user basis, all communications rely on a Random Linear Network Coding (RLNC) scheme. A key aspect in the QoS management is represented by the power adaptation strategy in use. This paper proposes a novel convex formulation to the power adaptation problem for the downlink phase taking into account the specific RLNC scheme adopted by each communication flow. By the proposed convex formalization, an optimal solution of the problem can be early found in real time. Moreover, the proposed power adaptation strategy shows good performance for what concern throughput and fairness among the users when compared with other alternatives.

This paper analyzes the performance of the Physical Layer Network Coding (PLNC) approach based on Decode-and-Forward (DF) and operating in multipath fading channel. In actual channel affected by multipath fading the DF method has poor performance since the relay node cannot properly perform data decoding. In addition the decoding at the relay requires the knowledge of the channels involved in the communication with a consequent signaling overhead. In order to overcome these problems this paper proposes an Orthogonal Frequency Division Multiplex (OFDM) system where the pre-emphasis approach is considered jointly with an efficient method of sub-carrier suppression named Blind Subcarrier Suppression (BSS). Simulations results show that BSS achieves high throughput with a Bit Error Probability (BER) near to that of a classical OFDM system in multipath channel.

Long Term Evolution (LTE) is considered one of the main candidate to provide wireless broadband access to mobile users. Among main LTE characteristics, flexibility and efficiency can be guaranteed by resorting to suitable resource allocation schemes, in particular by adopting adaptive OFDM schemes. This paper proposes a novel solution to the sub-carrier allocation problem for the LTE downlink that takes into account the queues length, the QoS constraints and the channel conditions. Each user has different queues, one for each QoS class, and can transmit with a different data rate depending on the propagation conditions. The proposed algorithm defines a value of each possible sub-carrier assignment as a linear combination of all the inputs following a cross-layer approach. The problem is formulated as a Multidimensional Multiple-choice Knapsack Problem (MMKP) whose optimal solution is not feasible for our purposes due to the too long computing time required to find it. Hence, a novel efficient heuristic has been proposed to solve the problem. Results shows good performance of the proposed resource allocation scheme both in terms of throughput and delay while guarantees fairness among the users. Performance has been compared also with fixed allocation scheme and round robin.

In this paper we propose an end-to-end solution for urban infrastructure-to-vehicle traffic data delivery based on a class of unequal error protection (UEP) rateless codes called expanding window fountain (EWF) codes. The proposed solution relies on attractive features that rateless codes introduce to networks with unpredictable dynamics: the universal capacity approaching property which is well-matched to time-varying behavior of wireless links, and the innovative nature of each encoded packet which makes both time-consuming retransmission and content-reconciliation mechanisms unnecessary. Furthermore, usage of EWF codes allows separation of delivered data in importance classes with different error protection and recovery time guarantees, enabling mobile users to retrieve more important information more reliably and in shorter time span, thus making the proposed solution suitable for time-critical services. The addressed urban communication scenario consists of large number of sensors that sample and relay traffic flow information to network of Access Points (APs). APs use the existing underlying communication infrastructure, such as metropolitan area networks (MANs), to exchange traffic flow data, encode it using EWF coding principles, and finally disseminate it to roaming vehicles that join the network service in an ad-hoc manner in order to retrieve information regarding the surrounding environment. The proposed approach is suitable for real-time applications, such as frequent periodic reporting of urban traffic conditions, that could be used by on-board computers to provide improved navigation for end-users.

In this paper, an enhanced access protocol minimizing message delivering latency is proposed. It is basically based on modified version of Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol in which one sensor at a time is allowed to deviate from standard rules behaving like a cheater and keeping the Contention Window (CW) fixed and equal to the minimum value. The proposed scheme efficiency is proved resorting to game theoretic framework, while its performance is analytically derived through a Markov model for a worst case conditions. Focusing on Wireless Body Area Networks (WBANs) application scenario, main system figures, in terms of delivering delay and dropping probability, are further pointed out by means of numerical simulations, highlighting optimal agreement with theoretical results as well as the protocol suitability for critical situation management.

The interest towards real-time computing has lead an even more interest in grid computing. While in the past the implementation of grid computing has been done on high performance computers, in the recent years there is an increasing interest in the pervasive grid scenarios, where multiple devices can be used for a distributed computing. The most challenging idea is to use mobile devices connected among them with wireless connections for setting up pervasive grid environments. In this context, it is a crucial problem the optimization of the routing algorithms among the processing nodes, in order to satisfy the performance requirements of a distributed computing. Aim of this paper is the design of specific routing algorithms for different pervasive grid applications with a particular attention to time sensitive scenarios.

Wireless mesh networks suffer of scalability problems when the number of nodes grows. To solve this issue, wireless mesh networks with multi-interface nodes were introduced. In such networks it is possible to use multiple channels to implement spatial reuse of frequencies. These solutions offer a huge throughput performance improvement but they increase the complexity due to the need of implementing a selection interface policy. One of the most simple interface selection policy is random choice. In this paper we provide an analytical analysis of the Uniform Random Interface Selection strategy applied in a 802.11 DCF multi-radio network. Then we also present a set of performance results for the throughput and discard probability in function of the number of nodes and the number of interfaces.

In this paper, an approach minimizing delivery latency, while keeping transmitted power below a certain threshold, is proposed to provide reliable real time wireless communications when applying network coding principle in order to point out additional advantage in terms of capacity. An analytical tool is proposed to derive the performance of optimal power adaptation scheme NC scheme aiming at minimizing the number of coded packets transmitted on a link-by-link basis, thereby lowering the end-to-end delay and overall power consumption.

During last years modern telecommunication systems have achieved important results in terms of reliability, coverage and data rate, allowing a high variety of applications services. Among others, TETRA (Terrestrial Trunked Radio) is one of the most important in the professional market; in particular, the DMO (Direct Mode Operation) mode allows half-duplex direct communications among users without the need of an infrastructure. However, TETRA-DMO cannot perform multi-hop communications, limiting both the coverage and the scalability of the whole network. The idea behind our proposal is an integration between TETRA-DMO and another more flexible wireless system (e.g., IEEE 802.11), where the TETRA-DMO is the access technology, thus allowing the use of standard TETRA-DMO terminals, while the IEEE 802.11 technology can be used as a flexible multi-hop meshed backbone technology for interconnecting remote TETRA-DMO areas.

In the last years an even more attention has been focused on emergency and crisis management systems. Both communication and computing aspects are of primary importance for a fast and reliable response in these particular scenarios. Differently from other approaches, in this paper we consider an integrated communication and computing solution, by proposing a joint approach, where a distributed computing platform and a heterogeneous meshed communication system interoperate in order to enhance the system reliability and readiness.

This paper presents a data gathering scheme designed for an emergency monitoring Wireless Sensor Network (WSN), which employs distributed rateless encoding and dispersion of the encoded data toward the perimeter of the monitored area, where it is collected by a mobile collector (MC). Rate-less codes are low encoding/decoding complexity codes, suitable for resource constrained devices, such as sensor nodes, while the proposed distributed encoding and dispersion, performed using only local knowledge, are adapted to WSNs where the frequent changes in underlying topology and connectivity are expected. The proposed scheme allows for data persistence and efficient data gathering in the scenarios where decentralized WSNs are deployed in inaccessible locations with no infrastructure support, where nodes are prone to failures due to harsh operating conditions and where the access of the MC to the monitoring area is severely limited.

HSDPA (High Speed Downlink Packet Access) is drawing great attention as the 3.5G technology capable of providing higher data rate packet switch services over Universal Mobile Telecommunication System (UMTS) to support broadband services like multimedia conferencing, VoIP, or high-speed internet access. The paper proposes the use of a Learning Vector Quantization (LVQ) Neural Network able to estimate the quality of service (QoS) across analysis of Key Performance Indicators (KPIs) and to provide automatically a possible classification of warnings related to the load status of HSDPA radio resources or to the bad radio channel quality condition.

In this paper, we propose a novel approach for data gathering in wireless sensor networks (WSN) based on distributed rateless codes. Rateless codes are an efficient, lowcomplexity solution for coded data transmission over channels with packet erasures, which motivates their application in distributed network scenarios such as WSN. Recently proposed distributed rateless coding techniques for WSN are node-centric, i.e., collecting sufficient number of different sensor data packets and performing rateless encoding is the task of sensor nodes. In the proposed packet-centric approach, this task is assigned to encoded packets called rateless packets. While randomly moving through the network, rateless packets collect and encode into their content required number of uniformly sampled sensor data packets, completing their paths in randomly selected network nodes. Using this approach, any degree distribution of rateless codes can be exactly obtained. The problem of uniform combining of sensor data into rateless packets, and uniform dispersion throughout the network is addressed. The efficiency of the proposed scheme and comparison with the performance of centralized rateless codes are demonstrated by simulation results.

Abstract Wireless communications have achieved a great attention during the last decades due to the easy implementation, possibility of delivering multimedia services to rural communities, suitability for public safety and emergency communications. In particular, a wireless network designed for an emergency scenario seems to be the best solution to manage all the phases of an emergency situation, from the prevention to the post‐emergency management. This paper discusses the main features of a such wireless network aiming to interconnect several heterogeneous systems and providing multimedia access to groups of people involved in emergency operations as foreseen by the In.Sy.Eme. (Integrated System for Emergency) project. In particular, the focus here will be on a communication infrastructure able to efficiently support a pervasive high performance distributed elaboration structure based on the Next Generation Grid principle. Main scope of the proposed system is that of allowing functional integration of new technologies with actual or off‐the‐shelf technologies to provide fast responses to any emergency situations and efficient use of all available resources. Copyright © 2009 John Wiley & Sons, Ltd.

Abstract In the last few years the wireless metropolitan area networks (WMANs) have increased their popularity and attracted the interest of important research groups all over the world; as a consequence, several standards have been proposed. Among them, the IEEE 802.16 (WiMAX) is one of the most promising standard to carry out a full‐service broadband wireless network in an urban and suburban area. This standard provides high data rate within a wide coverage area with low implementation costs, possibility of multi‐traffic communications, and different network topologies. This paper deals with the analysis and performance comparison of different scheduling techniques for WiMAX networks for allowing quality of service (QoS) differentiation when different types of applications have to be supported and achieving a fair distribution of resource among users. In particular, the focus here is on the resource allocation problem for the case of mobile stations (MSs) active in an urban environment. The proposed scheduling algorithms exploit the orthogonal frequency division multiple access (OFDMA) scheme with adaptive modulation techniques in order to achieve a better network behavior. The performance of the proposed approaches will be derived here by means of theoretical analysis and computer simulations. Copyright © 2009 John Wiley & Sons, Ltd.

This paper deals with the allocation of resources and the creation of distribution trees for P2P video streaming. Assuming that the video distribution is based on a multiple description codec (MDC), the proposed approach performs jointly the two tasks, in a completely distributed client-based fashion, by means of an evolutionary (socially inspired) game played by all peers. The key idea of the evolutionary game is that each peer continuously measures its own utility (i.e., video quality) and, by periodical comparison with other randomly chosen peers, tries to mimic the behavior (i.e., resource allocation and video distributors) of peers with higher utility. Extensive simulation experiments by Peersim have been carried out in order to assess the performance of the proposed technique. The obtained results have highlighted remarkable benefits in terms of scalability, fast adaptation to churning, high degree of cooperation among peers and self-organization of the distribution multi-tree network.

This paper deals with the evaluation of the end-to-end packet delay for a lossy network where network coding is adopted to achieve better performance. Differently from previous published papers on this subject, connection oriented services are assumed, this means that packets have to be in-order received and wait at the receiver buffer till all the previous ones have been correctly delivered. The focus is on a network model where two source nodes broadcast packets to a group of two sink nodes over lossy wireless channels. Three different alternatives have been considered in order to assure a reliable data multicasting, namely: a classical random linear network coding scheme, a linear network coding combined with a basic ARQ or, alternatively, with a soft combined ARQ scheme. Performance comparisons provided by means of analytical and numerical results clearly highlight that the better solution is to adopt the latter alternative.

The lack of free frequency spectrum is becoming one of the most important problems in implementing novel wireless systems. The limited available spectrum and the inefficiency in the spectrum usage requires for a new communication paradigm to exploit the existing wireless spectrum. The key idea is based on the cognitive radio paradigm. Cognitive radio allows to different, independent networks to share a certain spectrum interval with low mutual interference. In the last years, one of the most important wireless system is the WiMAX, which is based on the OFDMA technique. The aim of this paper is to propose a cognitive networking environment where the primary network is constituted by an IEEE 802.16 network. Two approaches will be discussed for the secondary networks, by considering an ordinated technique and a collision resolution technique for both the network set-up and access control.

Wireless mesh networks suffer of scalability problems when the number of nodes grows. To solve this issue, multi-interface wireless mesh networks were introduced. In such networks it is possible to use multiple channels to implement spatial reuse of frequencies. However, channel assignment schemes make this kind of networks complex to manage and limit their applicability in presence of mobile nodes. In this paper a novel technique is introduced for the optimization of resources allocation in a multi-interface wireless mesh network where channel assignment is fixed. With this technique the scalability of the network is improved and the support for mobility is easily granted.

This paper deals with the application of Kalman filtering (KF) techniques to the localization of a swarm of mobile agents in a wireless sensor network (WSN). In particular, both extended (EKF) and unscented (UKF) Kalman filters have been investigated referring to a typical urban scenario with energetic and resource constraints. A cooperation strategy among sensor nodes, based on a virtual diversity scheme, has been introduced allowing the swarm tracking under severe propagation conditions. The effectiveness of the proposed solution has been assessed by means of simulations concerning a squad of robots moving in realistic scenarios. It has been shown that UKF achieves a higher accuracy and reliability than EKF in localizing the barycenter of the robot squad. Further, the proposed solution provides advantages in terms of measurement update frequency and, hence, of energy saving.

Kademlia is a Distributed hash table widely used in P2P networks that has been applied to commercial and non commercial distribution of files. In this paper the authors review some security issues connected with Kademlia and a technique to leverage its security using an external certification service.

This paper deals with a communication infrastructure needed to allow a swarm of robots performing dust cleaning and garbage collection task in an urban area. It outlines the required communication links, analyses them regarding security, describes in details the implementation and figure out some performance test results.

Wireless communications have achieved a great attention during the last decades due to the easy implementation, possibility of delivering multimedia services to rural communities, suitability for public safety and emergency communications. In particular, a wireless network designed for an emergency scenario has to be capable of managing all the phases of an emergency situation, from the prevention to the post-emergency management. This paper discusses the main features of a wireless network aiming to interconnect several heterogeneous systems and providing multimedia access to groups of people by introducing the main outcome of the In.Sy.Eme. (Integrated System for Emergency) project. Particular attention will be devoted to the approach of the project, aiming to consider a communication infrastructure strictly connected with an information processing side.

In this paper, we propose a novel approach for data gathering in wireless sensor networks (WSN) based on distributed rateless codes. Rateless codes are an efficient, low-complexity solution for coded data transmission over erasure channels, which motivates their application in distributed network scenarios such as WSN. Recently proposed distributed rateless coding techniques for WSN are node-centric, i.e., the task of collecting sufficient number of different sensor data packets and performing rateless encoding is responsibility of sensor nodes. In the proposed packet- centric approach, this task is assigned to encoded data packets called rateless packets. While randomly moving through the network, rateless packets collect required number of uniformly sampled sensor data packets, finishing their paths in randomly selected network nodes. Using this approach, any degree distribution of rateless codes can be exactly obtained. The problem of uniform combining of sensor data into rateless packets, and uniform dispersion throughout the network is addressed. The efficiency of the proposed scheme and its comparison with the performance of centralized rateless codes are demonstrated by simulation results.

Cooperative relaying systems represent a promising solution for future wireless communications. In this paper simple cooperative relaying strategies are proposed in order to improve the performance of a WiMAX network, overcoming the drawbacks of a non-line-of-sight (NLOS) propagation. The cooperative schemes proposed combine the amplify and forward (AAF) and the decode and forward (DAF) algorithm with delay diversity (DD) and cyclic delay diversity (CDD) techniques, in order to exploit the features of the wireless communication channel. We investigated the pros and cons of each scheme, comparing the assumptions which are required and the simulation results with respect to two cooperative implementations of the Alamouti scheme.

WiMax is one of the most important technologies for providing a broadband wireless access (BWA) in a metropolitan area. The use of OFDM transmissions has been proposed to reduce the effect of multipath fading in wireless communications. Moreover, multiple access is achieved by resorting to the OFDMA scheme. Adaptive subcarrier allocation techniques have been selected to exploit the multiuser diversity, leading to an improvement of performance by assigning subchannels to the users accordingly with their channel conditions. A method to allocate subcarriers is to assign almost an equal bandwidth to all users (fair allocation). However, it is well known that this method limits the bandwidth efficiency of the system. In order to lower this drawback, in this paper, two different adaptive subcarrier allocation algorithms are proposed and analyzed. Their aim is to share the network bandwidth among users on the basis of specific channel conditions without loosing bandwidth efficiency and fairness. Performance comparisons with the static and the fair allocation approaches are presented in terms of bit error rate and throughput to highlight the better behavior of the proposed schemes in particular when users have different distances from the BS.

This paper deals with a wireless pervasive communication system to support advanced healthcare applications. The proposed system is based on an ad hoc interaction of mobile body sensor networks with independent wireless sensor networks already deployed within the environments in order to allow a continuous and context aware health monitoring for patients along their daily life scenarios with an unprecedented precision and flexibility of sensing. After an accurate protocol characterization, simulation results are provided, underlining remarkable performance with respect to existing solutions, for different mobility models and node density values.

The six articles in this special issue focus on the technology and applications of body area networking.

Abstract This paper deals with an efficient secure communication system based on a speech watermarking approach. The main goal of the system is to efficiently support air traffic control (ATC) communications by improving safety and security of the existing ATC equipment embedding digital side information into speech signals in order to allow anautomatic identification of the talker. An implementation based on the use of the well known LPC (linear predictive coding) principle is discussed. The LPC residual is split up into voiced and unvoiced segments; while the voiced segments cross the system unmodified, the watermarking data are embedded into the unvoiced segments, spectrally similar to a white noise. The watermark signal is decoded by a very similar scheme. We provide also a statistical analysis on the unvoiced parts of the ATC communications that demonstrates the system feasibility. In addition to this, an optimization of the entire system has been also performed to increase performance. The obtained results highlight that the watermark data are nearly imperceptible and providea data channel with rate from 2000 to 5000 kbits/s, withhigh robustness to channel noise; the system requires only modular, low‐cost and easy‐to‐install encoders and decoders, maintaining compatibility with legacy RF DSB‐AM transceivers. Moreover, it is well suited both for the actual 25 kHz RF channels and for the new 8.33 kHz European RF channels. Copyright © 2008 John Wiley & Sons, Ltd.

The demand for high-speed services and multimedia applications anywhere and anytime has led to the rise of wireless communications. In particular, WiMAX technology is nowadays considered one of the most prominent solutions capable to provide a Broadband Wireless Access (BWA) in metropolitan areas with a simpler installation and lower cost than traditional wired alternatives. This paper deals with the proposal of efficient adaptive modulation and coding techniques to be used in WiMAX based wireless networks, that allow to improve network performance in the case of Non Line-of-Sight communications, which are typical in urban environments. Through these techniques it is possible to switch the modulation order and coding rate in order to better match the channel conditions, and, hence, obtaining better performance both in terms of error probability and data throughput.

Abstract In the last few years, the metropolitan area networks (MAN) have increased their popularity and attracted the interest of the most important research groups all over the world. Among several standards, IEEE 802.16 has taken a relevant role providing high data rate in a big covering range with low implementation costs and multi‐traffic communications. The IEEE 802.16 networks can have a pre‐defined structure, with a central base station (BS) covering a cell in which a variable number of subscriber stations (SSs) can work. This paper deals with the proposal of a quality of service (QoS) driven scheduling algorithm to be used in an IEEE 802.16 network where different traffic types coexist. In particular, the paper mainly focuses on best effort data and VoIP communications, by proposing a scheduling technique that allows an efficient resource management of both traffic types by considering their specific QoS flavor. The performance evaluation has been carried out by considering both the phases of contention and packet scheduling, by means of a theoretical approach and computer simulations. Numerical results show the performance of the proposed algorithm by focusing on a scenario where the BS schedules the best effort and VoIP traffics of several SSs. Copyright © 2008 John Wiley & Sons, Ltd.

Abstract One of the most promising trends for next generation networks is to consider an integrated approach to the communication infrastructure and the processing layer. In particular, the introduction of broadband and reliable wireless networks allows the interaction of a huge number of devices all creating a single network. On the other hand, the grid paradigm is considered as one of the most promising approach for pervasive and dynamic applications. Aim of this paper is to present a novel integrated approach between grid paradigm and wireless networks by highlighting the main advantages of their cooperation. In particular, it will be shown here how a wireless heterogeneous network can be exploited for implementing a pervasive and dynamic grid (mobile grid) and, on the other hand, a mobile grid allows the optimization of the communication infrastructure. The integrated approach can be an effective method for solving applications, such as emergency management, where a huge amount of data derived from a wireless infrastructure needs to be processed efficiently and adaptively, and the traffic flow in the wide area wireless networks needs to be coordinated and optimized. Copyright © 2008 John Wiley & Sons, Ltd.

This paper deals with the problem of finding an optimal subcarrier allocation strategy for uplink and downlink communications in an OFDMA metropolitan wireless system. In particular a two steps approach is considered; at the first step the scheduler establishes the amount of resources to assign to users on the basis of their quality of service (QoS) constraints, while, at the second step, channel conditions are used to allocate subcarriers to users. A simple strategy for choosing the appropriate modulation and coding scheme according to the channel conditions of the assigned subcarriers is also proposed.

Wireless sensor networking (WSNing) is drawing the attention of both scientific and industrial communities as it represents a low cost and effective approach to develop intelligent environments. As a result, a remarkable effort is nowadays spent to standardize a reference communication platform, as far as the PHY and MAC layers are concerned. Recently, indicated as IEEE 802.15.4a standard, IR-UWB technology is an efficient candidate for PHY layer, due to its high transmission rate and the additional benefit of localization capability. This paper deals with a localization scheme that makes use of an innovative time of arrival protocol based on dirty templates correlation, with the aim of improving their performance in noisy channels. Achieved results point out the suitability of the proposed approach for several realistic scenarios, despite the fact that the ranging accuracy is reduced by the influence of long term fading effects.

The paper studies the performance of the bandwidth request procedure for a proactive digital video broadcasting - return channel satellite (DVB- RCS) terminal in comparison with a reactive one. The proactive terminal uses an adaptive predictor to forecast the future input traffic flow along with a predictive bandwidth controller to generate bandwidth requests according to a receding horizon policy. On the other hand, the reactive terminal generates requests, at the end of each frame, depending on the current queue lengths [1] [2]. The simulated scenario involves adaptive coding and modulation (ACM) techniques and Quality of Service (QoS) management. Simulation experiments highlight the effectiveness of the proactive bandwidth control under different traffic load and channel conditions.

Wireless sensor networks (WSN) are large scale networks of unattended devices, aimed at monitoring environmental parameters. Their extremely scarce hardware resources constitute a huge limitation to the use of standard security protocols to secure communications, so that custom ones must be designed. In this article we describe the development of a novel access control system for WSN based on a distributed threshold scheme. Our model gives support for mobility and limits the needed communication and consequent energy drain, which is a fundamental parameter for the lifetime of WSN.

The demand for high-speed services and multimedia applications in wider wireless environments leads to the growth of wireless communications, due to the simplicity of installation and the reduction of costs with respect to traditional cabled links. In particular, WiMAX technology is considered one of the most prominent solutions capable to provide a Broadband Wireless Access in metropolitan areas. In this paper two schemes of adaptive modulation and coding are proposed with the aim of improving performances in Non Line-of-Sight communications, typical of urban environments. Through these techniques it is possible to switch the order of the modulation and the coding rate to better match the channel conditions, obtaining comforting results in terms of probability of error and throughput. The system has been modeled with a finite state structure in which every state consists in a possible scheme of transmission (i.e. a specific modulation and coding rate), and the switch among different states happens when multiple thresholds on channel attenuation are reached. The adaptation is realized at the physical level of the transmission for a WiMAX OFDMA structure. The two proposed techniques are suitable for different kind of traffic and, therefore, can be used for respecting different QoS requirements.

WiMAX is one of the most important technologies for providing a Broadband Wireless Access (BWA) in a metropolitan area. The use of OFDM transmission has been proposed to reduce the effect of multipath fading in wireless communications; moreover, multiple access is achieved by resorting to the use of OFDMA. Adaptive subcarrier allocation techniques have been selected to exploit the multiuser diversity, leading to an improvement of performances by assigning subchannels to the users accordingly with their channel responses. In this paper, three adaptive subcarrier allocation algorithms have been proposed; they are based on channel capacity and aim to assign an equal amount of capacity to all the users or to distribute the capacity proportionally to the users' channel conditions. The algorithms performances have been valued and compared in terms of bit error rate and throughput. The proposed strategies show a substantial improvement with respect to a static allocation, turning the multiuser diversity into a significant increase of data rate.

In the last years the wireless metropolitan area networks have increased their popularity and attracted the interest of the most important research groups all over the world. Several standards have been defined, in particular IEEE 802.16 has taken a relevant role in achieving a full-service broadband wireless network all over a urban and suburban area. This paper deals with the resource allocation problem by considering the resource request and data scheduling of the active stations. The considered scenario is foreseen in an urban environment where multiple stations can move around the Base Station. The proposed scheduling algorithms exploit the orthogonal frequency division multiple access scheme with adaptive modulation techniques for maximizing the network performance. The performance results have been obtained by resorting to theoretical analysis and computer simulations.

Abstract In this paper, we present the comparison between a distributed and a centralized authentication protocol for wireless sensor networks (WSN). We outline the difference between authentication and key‐agreement schemes and we propose a novel approach based on the use of polynomial functions to produce a distributed bi‐directional authentication. The advantages of this approach are: speed of operation that can allow multiple subsequent authentications, thus support to mobility; balanced energy consumption if compared with the imbalanced centralized approach and the prevention of partition attacks. Copyright © 2008 John Wiley & Sons, Ltd.

In modern wireless communication systems, power control plays a fundamental role for efficient resource utilization, in particular in the systems where the users share the same bandwidth at the same time. In such systems, in fact, many users transmit over the same radio channel using the same frequency band and time slots so that the signal of an individual user becomes interference for the other users. Hence the transmission power levels need to be smartly manipulated so as to achieve an adequate quality of service for as many users as possible and, thus, an efficient network utilization. Conventional power control algorithms adopt the Signal-to-Interference-plus-Noise Ratio (SINR) as controlled variable and neglect the important effects of the manipulated control variables (transmission powers) and of the retransmission mechanism on the queueing dynamics. In this paper, we pursue a different queue-based approach which takes into account the queueing dynamics and adopts the queue size as controlled variable. In particular, a novel queue-based power control algorithm with low on-line computational burden is proposed and its performance is evaluated both theoretically and via simulation experiments.

This paper deals with a class of localization protocols conceived for applications to wireless sensor networks (WSN), in the presence of typical energetic and resource constraints. It has been supposed that only one mobile anchor node is always localized by resorting to global navigation satellite system (GNSS) support system. The first scheme proposed (GNSS Alone, GA) assumes that sensor nodes may interact only with this anchor node to evaluate their own positions. In addition to this, a smart cooperation strategy among sensor nodes, i.e., GNSS in ranging (GIR) scheme, has been introduced to face possible anchor node outage, due to hostile operation scenario. The proposed solutions have been in-depth characterized and evaluated within a practical scenario. The obtained results point out the protocol localization accuracy, latency and overhead, with respect to the nodes density. According to this, the most suited applications for both GA and GIR approaches are indicated.

WiMAX is considered one of the most prominent technologies for providing a broadband wireless access (BWA) in a metropolitan area. Among several strategies, the adaptive modulation techniques has been selected for providing an efficient non line of sight (NLOS) coverage. Adaptive modulation allows the system to adapt the modulation scheme according to the channel conditions in order to enhance the system performance. This paper deals with the proposal of a state model to be used for the performance comparison of two different adaptation algorithms based on the maximization of different functional costs suitable for use in WiMAX system with an OFDMA physical structure. The algorithms' performance has been derived and compared in terms of error rate and throughput. The algorithms show a significant improvement of the system performance compared with the static case, i.e., no adaptive modulation; in particular each algorithm is suited for satisfying different QoS requirements.

This paper deals with the problem of supporting sink mobility in a wireless sensor network. It focuses on a specific scenario, where mobile nodes act themselves as both end-users, when querying the WSN for specific information, and as sinks, when gathering the queried data. Due to the mobility of users and to the topology of the network, sinks experience frequent disconnections from the WSN. A system architecture, and the related protocols, capable of supporting the envisioned application domain has been proposed. The performance of the proposed system architecture has been evaluated by means of simulative studies, together with addressing the impact of mobility, deployment geometry and routing parameters.

The nodes of a multi-hop wireless mesh network often share a single physical media for terminal traffic and for the backhaul network, so that the available resources are extremely scarce. Under these conditions it is important to avoid that unwanted traffic may traverse the network subtracting resources to authorized terminals. Packet filtering in wireless mesh networks is an extremely challenging task, since the number of possible connections is quadratic with respect to the number of the terminals of the network; for each connection a rule is needed and the time needed for filtering grows linearly with the number of rules. Moreover nodes can be in possession of end users and the administrator might want to keep the explicit ruleset as much secret as possible while giving the nodes enough data to behave as a firewall. In this article we present a solution for distributed firewalling in multi-hop mesh networks based on the use of Bloom Filters, a powerful but compact data structure allowing probabilistic membership queries.

This paper analyzes some critical security issues in the family of IEEE 802.16 standard that has not been addressed so far. In particular two of the key features of the standard, the dynamic resources allocation and the mesh mode revealed to be vulnerable to attacks that represent serious threats to the robustness and privacy of the communications. In the first case the attacker is able to reduce bandwidth assigned to its neighbors, with the aim of obtaining more resources for himself; in the second case, we observed that there might be no real privacy in communications between two nodes of the mesh network. These vulnerabilities are still present even after the latest amendment to the standard, IEEE 802.16e that solved some previously addressed security flaws.

In this paper an original detection strategy for satellite digital broadcasting communications is defined; particularly, we consider the DVB-S2 system, which is proposed as a development of the DVB systems and exploits iterative decoding and higher order modulation. The proposed approach relies on the use of the information which can be obtained by proper soft demapping schemes. Moreover, we introduce an original receiver which is based on iterative demapping and decoding. The adoption of these strategies permits a remarkable performance gain and an improvement of the system throughput.

In modern wireless networks the functions included into layer II have to deal with complex problems, such as security and access control, that were previously demanded to upper layers. This growing complexity led some vendors to implement layer II primitives directly in software, e.g. IEEE 802.111 has been largely distributed as a software patch to be used with legacy 802.11b/g hardware. In any extremely complex software the likelihood of committing errors during the implementation raises, and it is well known that software bugs can lead to instability of the system and possibly to security vulnerability. Software bugs are the most common cause of successful attacks against any kind of network and represent a real plague for system administrators. Stress test is a widely used methodology to find and eliminate software bugs. In this paper we present a platform to perform a stress test of generic network protocols implementations but especially optimized for Layer II stress tests, that present specific problems. With our approach a generic network protocol described with ABNF language can be tested transmitting arbitrary frame sequences and interpreting the responses to verify consistence with the communication standard used. Our platform can interact dynamically with the tested machine (an access point, a router etc.) to verify its robustness and its compliance with the standard. Experiments confirmed the validity of our approach both as a stress test technique for system under development and as a reverse engineering technique for interaction with closed source system.

This paper deals with a system level design solution to support information gathering in the presence of a mobile querying node that experiences frequent disconnections from a Wireless Sensor Network (WSN), an application scenario that embraces the area of Intelligent Transportation Systems (ITS). The proposed scheme basically relies on the network capability of autonomously adapting to sink mobility in order to properly deliver the requested data. The system is defined as far as its functional elements and related communications protocols, together with validating its effectiveness by means of a simulative study. In particular, the performance in terms of delivering latency and packet delivery ratio has been investigated for several network topologies, architecture and mobility pattern, always highlighting a remarkable quality of provided services together with robustness with regard to operative conditions.

The adoption of wireless sensor networks (WSN) for wide area environmental monitoring is currently considered one of the most challenging application scenario for this emerging technology. The promise of an unmanaged, self-configuring and self-powered wireless infrastructure, with a continuously decreasing cost per unit, attracts the attention of both final users and system integrators, replacing previously deployed wired solutions and opening new business opportunities. This challenge might be afforded by resorting to a complete system level design to jointly address and optimize all the involved aspects. Besides, the design guide lines need to be inspired by the application requirements rather than technology driven. Following this approach, this paper presents an overall solution focusing both on node, network and remote user interface issues. The proposed platform in finally applied to a realistic user defined scenario oriented to agro-food production phase monitoring within GoodFood Integrated Project. The results of the validation phase presented highlight remarkable advantages both in terms of cost and complexity reduction and experienced QoS enhancement as well and, consequently, validating the WSN technology adoption.

WiMAX is considered one of the most prominent technologies for providing a Broadband Wireless Access (BWA) in a metropolitan area. Among several strategies, the adaptive modulation techniques has been selected for providing an efficient non line of sight (NLOS) coverage. Adaptive modulation allows the system to adapt the modulation scheme according to the channel conditions in order to enhance the system performance. This paper deals with the proposal of a state model to be used for the performance comparison of two different adaptation algorithms based on the maximization of different functional costs suitable for use in WiMAX system with an OFDMA physical structure. The performance of the algorithms has been derived and compared in terms of error rate and throughput. The algorithms show a significant improvement in the system performance compared with the static case, i.e., no adaptive modulation; in particular each algorithm is suitable for satisfying different QoS requirements.

This paper deals with the performance evaluation of an efficient medium access control (MAC) technique based on the use of an adaptive modulation and coding (AMC) scheme that significantly improves the downstream data rate and guarantees specific quality of service (QoS) requirements in wireless communication systems. Basically, the access scheme considered in this paper relies on physical channel monitoring and state mapping into a variable rate packet format. In particular, a suitable analytical model is proposed herein in order to predict the system performance, i.e., the average packet queuing delay in the case of a non-stationary transmission channel. Comparisons between analytical predictions and simulation results are provided to validate our model and highlight the improvement of the AMC technique with respect to a static rate allocation scheme, especially in the case of heavy tailed traffic conditions.

This paper proposes an approach to analyze pulse waveform dependent bit error rate (BER) performance of a DS-CDMA ultra wideband (UWB) radio, which operates in a frequency selective fading channel. The analysis takes into account almost all real operational conditions, such as asynchronous transmissions, RAKE receiver, multiple access interference (MAI), multipath interference (MI), log-normal shadowing, and noise. The main objective of the paper is to reveal the relationship between time domain characteristics of pulse waveforms and BER of a UWB radio. It is shown through analysis (also validated by simulation) that the normalized mean squared auto-correlation function (ACF) of the pulse waveforms can be used as an effective merit figure to judge the suitability for their applications in a DS-CDMA UWB radio. In fact, the normalized mean squared auto-correlation function (ACF) governs the average inter-chip interference caused by imperfect auto-correlation function of the pulse waveforms. The paper concludes that, as long as the power spectral density (PSD) functions of the pulse waveforms fit the FCC spectral mask, the pulse waveforms' normalized mean squared ACF should be minimized to ensure an acceptable BER.

This paper deals with a turbo multiuser detector suitable for applications in overloaded coded DS-CDMA systems. The turbo-MUD receiver is based on the use of a linear MMSE detector in the first iteration and a parallel interference cancellation scheme in the successive ones. The inputs of the interference cancellator are both the detector outputs and the soft information from a bank of turbo decoders. The performance of the proposed receiver has been derived by means of computer simulations and applications of the density evolution theory: in particular, this technique permits to properly evaluate the number of MMSE iterations, simplifying the overall receiver design.

The adoption of wireless sensor networks (WSNs) in several key applications has recently became affordable thanks to technological advancements, leading to the definition of IEEE 802.15.4 standard. However to realize reliable end-to-end application by means of unreliable elements (since nodes usually cope with several limitations in terms of power supply, maintenance, hardware and software resources), a great deal of work needs to be done to design and optimize proper communications protocols. In particular, the medium access control (MAC) layer issues seems to be the most challenging in realizing such a system. In this paper, a novel class of MAC layer protocols, optimizing IEEE 802.15.4 basic scheme, is proposed. In particular, to enhance the overall performance, we resort to an adaptive approach able to dynamically vary the duty cycle at each node basing on the traffic load estimation. To this purpose, we first analyze an ideal algorithm, according to which, the traffic load is exactly known at the coordinator side. Moreover, we propose a real version of the MAC protocol in which the traffic amount is estimated by means of the channel occupation. Simulations performed on a realistic scenario point out remarkable gain both in term of communications efficiency, link throughput, node lifetime and adaptability in comparison with the static scheme.

In modern wireless communication systems, power control plays a fundamental role for efficient resource utilization, in particular in the systems where the users share the same bandwidth at the same time. In such systems, in fact, many users transmit over the same radio channel using the same frequency band and time slots so that the signal of an individual user becomes interference for the other users. Hence the transmission power levels need to be smartly manipulated so as to achieve an adequate quality of service for as many users as possible and, thus, an efficient network utilization. Conventional power control algorithms adopt the Signal-to-Interference-plus-Noise Ratio (SINR) as controlled variable and neglect the important effects of the manipulated control variables (transmission powers) and of the retransmission mechanism on the queueing dynamics. In this paper, we pursue a different queue-based approach which takes into account the queuing dynamics and adopts the queue size as controlled variable. In particular, a novel queue-based power control algorithm with low on-line computational burden is proposed and its performance is evaluated both theoretically and via simulation experiments.

The adoption of Wireless Sensor Networks (WSN) for wide area environmental monitoring is currently considered one of the most challenging application scenario for this emerging technology. The promise of an unmanaged, self-configuring and self-powered wireless infrastructure attracts the attention of both final users and system integrators, replacing previously deployed wired solutions and opening new business opportunities. Even if many habitat monitoring applications usually do not provide for strictly real-time performances, however, smart power saving procedures have to be adopted, especially to increase the network lifetime. A common approach is to introduce a low power sleep mode, in which the node's radio section is switched off. In adhoc networking scenarios, this definitely requires the adoption of synchronization procedures, properly scheduling the packet transmission time and avoiding both overhearing effects and collisions. In this paper, a novel class of MAC layer protocols, named STAR MAC, that aims at efficiently managing the node's low power mode, is presented, and properly integrated within a routing scheme, according to the cross-layer design for minimizing the signaling overhead. The proposed solution is applied to a realistic user defined scenario oriented to agro-food production phase monitoring, highlighting remarkable advantages both in terms of cost and complexity reduction and QoS enhancement as well and, consequently, validating the WSN technology adoption.

In this paper, an analytical framework aiming at evaluating the performance, in terms of both buffer occupation and packet delay, for an ARQ-SR protocol application in wireless communications has been proposed. The present analysis involves a general communication channel model including both shadowing and fading effects. In particular, following a hierarchical approach, it has been modeled as a time discrete nested Markov chain. Moreover the traffic source model has been assumed as Markovian. The accurateness of the proposed solution has been validated by means of numerical simulation under several practical scenarios, as far as the physical channel and the traffic model are concerned. In particular, three different traffic models have been taken into account, always highlighting a remarkable accordance between the analytical predictions and numerical results.

In this paper, a middleware architecture that enables transparent inter-operability between two different wireless networks is presented. In particular, access to the communication channel is maintained by adaptively switching between GPRS (General Packet Radio Service) and Bluetooth interfaces, both established automatically with the assistance of an RFID tag. The access channels are continuously monitored, allowing the device to switch to the Bluetooth interface, whenever this lower-cost alternative is available. A preliminary field trial has been set up, which has demonstrated the effectiveness of the approach in supporting seamless handover procedures within a heterogeneous network as envisioned for future wireless communications systems.

Wireless networks that support client mobility have to face the challenge of providing a secure, performant handoff between different access points. IEEE 802.1X [1] model provides a secure mechanism used by many standard protocols to securely generate keying material between two peer hosts when one of the two is accessing the network for first time, but that is hardly usable for reauthentication during handoff procedures without loss of performance. This paper deals with the proposal of a novel scheme to transport authentication credentials during handoff that uses a two-way only exchange with the backend authentication server maintaining the security of the system. As a high-level method it can be applied to different types of network, such as IEEE 802.11i [2] infrastructure or ad-hoc mode networks in a mesh environment.

In the last years the Metropolitan Area Networks (MAN) have increased their popularity and kept the interest of the most important research groups all over the world. Several standards have been published which represent the first step for developing metropolitan networks: IEEE 802.16 (WiMAX) has taken a relevant role in reaching the goal of realizing a full-service network all over a urban and suburban area. This standard provide high data rate in a big covering range with low implementation costs, multi-traffic communication and the possibility of creating broadcast, multicast and mesh networks. The WiMAX networks can have a pre-defined structure, with a central Base Station (BS) covering a cell in which a variable number of Subscriber Stations (SS) could work, or a mesh distribution with SSs communicating together without BS participation. In this paper a QoS management model is proposed for a centralized structure in which the BS schedules the Best-Effort and VoIP traffics of several SSs.

Among several wireless network scenarios, the in-home environment is one of the most challenging research areas in recent years. In particular, the Wireless Personal Area Networks (WPANs) seem to be one of the most interesting application scenarios, as it works in small area for delivering multimedia traffic. The IEEE 802.15.3 is the emerging standard for WPAN. This standard is designed to provide low complexity, low cost and low power-consumption for personal area networks that manage multimedia traffic, video and audio between different devices in a small area environment. This paper deals with an adaptive management technique at the Medium Access Control (MAC) layer technique for high data-rate WPANs. The proposed system aims to maximize the performance of the WPAN in terms of throughput, considering multimedia traffic, constituted by data and video traffic.

Ultra-wideband (UWB) systems have been envisaged as optimal candidates to provide high data rate communications within short range. In this paper, a novel cross-layer approach suitable for TH-UWB systems is proposed, named punctured hopping (PH). PH scheme permits to limit the throughput reduction of the basic full rate turbo coding scheme, while maintaining the same code free distance. The proposed coding scheme performs parity bits puncturing. However, different from the rate compatible punctured turbo codes (RCPTC) scheme, it works on the idea that the less significant bits in a coded frame are not completely discarded as only half of their impulses are punctured. Thus preserving the error correcting capabilities jointly with a better spectral efficiency. The performance of the proposed PH coding scheme has been examined using theoretical analysis in additive white Gaussian noise channel and simulations in a realistic multipath fading channel. It has been compared with the uncoded, the basic full rate, and the RCPTC systems in order to underline its effectiveness. The results show a significant performance gain in comparison with the RCPTC and, hence, a significant reduction of the performance loss in comparison with the basic full rate turbo coding scheme, while maintaining the same throughput of the RCPTC.

This letter deals with an advanced minimum mean-squared error receiver for applications to uplink transmissions in a multiuser code-division multiple-access system. The receiver is implemented by means of a suitable neural network in order to enhance the receiver convergence speed in the case of fast fading. Performance comparisons with classical approaches highlights a better behavior for the proposed scheme.

In this paper, an efficient adaptive link control (ALC) technique is presented with the aim of improving the throughput, and preserving quality of service (QoS) requirements in wireless data communication systems. Basically, the proposed access scheme relies on selecting different modulation and coding schemes (MCS) in relation to the channel propagation conditions estimated by means of acknowledgment messages. Further, two different strategies for selecting the most suitable MCS are proposed and optimized. Comparisons with the static rate allocation scheme highlight a remarkable gain even in the presence of heavy tailed traffic conditions and significant user mobility

In orthogonal frequency division multiple access systems clusters of subcarriers are assigned to different users for parallel data transmissions. The subcarriers are overlapped, but orthogonal to each other such that there is no intercarrier interference (ICI). However, synchronization errors among users cause the loss of the orthogonality and introduce ICI resulting in multiple-access interference. Synchronization between users is particularly difficult in the uplink channel where the user signals are potentially asynchronous and affected by different frequency offsets due to misalignment in carrier frequencies and Doppler shifts. This paper proposes a method to lower the effects of different frequency offsets among user signals in an OFDMA uplink system. The multiple access interference due to the user frequency misalignments is reduced by reconstructing and removing the interfering signals in the frequency domain. An approach based on the selective cancellation method, is proposed and its performance is analyzed by means of theoretical analysis and computer simulations. The effectiveness of the proposed system has been evaluated in the case of ideal and no-ideal frequency offset estimation and has been compared with that of the classical successive and parallel cancellation schemes. Simulation results show that the proposed approach allows performance close to the ideal case, i.e., with ideal frequency synchronization among users, with a low increase of the implementation complexity. Moreover, it is also highlighted here, that the successive cancellation method slightly outperforms the selective scheme, at the expense of a higher computational complexity and processing delay

This paper deals with a novel cross-layer approach, involving both physical and data link layers, suitable for TH-UWB systems, named punctured hopping (PH). PH scheme permits to limit the throughput reduction of the basic full rate turbo coding scheme, while maintaining the same code free distance. The proposed coding scheme performs a puncturing of the parity bits, but, differently from the rate compatible punctured turbo codes (RCPTC) scheme, the less significant bits within a coded frame are not completely discarded as only half of their impulses are punctured, thus preserving the error correcting capabilities jointly with achieving a better spectral efficiency. The performance of the proposed PH coding scheme has been derived in an indoor multipath fading channel and compared with the uncoded, the basic full rate and the RCPTC systems. The results show a significant performance gain in comparison with the RCPTC and, hence, a significant reduction of the performance loss in comparison with the basic full rate turbo coding scheme, while maintaining the same throughput of the RCPTC

Recently, ad-hoc networks have obtained a growing interest due to their advantages in many practical applications. One of the most critical points is the definition of an efficient medium access control (MAC) protocol that allows the transmission of packets generated by a node and routing of packets arriving from other nodes. Moreover the growth of several applications with different requirements in terms of QoS has raised the problem to manage their priority also at the MAC layer. This paper deals with a traffic priority management technique at the MAC layer based on the code division multiple access (CDMA) scheme, where an adaptation of the used spreading factor to the network congestion is foreseen in order to minimize the energy consumption and maximize the network throughput

This paper deals with a variable rate discrete multi-tone modulation (DMT) system for broadband power-line communications (PLCs), based on the bit-loading algorithm proposed by Leke and Cioffi. In the proposed system a suitable LMS channel estimator is considered, which is based on the insertion of a training sequence (TS). The proposed approach will be compared with the ideal channel estimates, showing its effectiveness. Moreover, different TS lengths will be compared. The performance of the system, expressed in terms of bit-rate and bit error rate (BER), with and without an estimation error is derived by simulation under the assumption of frequency-selective multipath fading channel and additive colored Gaussian noise, according to the in-building networks model.

Precision agriculture (PA) represents a novel paradigm for managing agro-food production, by monitoring the physical parameters of different farming zones. This might be pursued by means of different communication infrastructures, but the most promising technology seems to be the wireless sensor network (WSN). However, merely applying this approach to the PA context, while resulting in a more flexible communication platform, still exhibits a rigid information management architecture. This limitation can be overcome by applying the ambient intelligent (AmI) paradigm to create an environment highly interactive with all the users involved in the process. Our proposal deals with the porting of the AmI concepts on a highly-integrated WSN platform with a special focus on the routing strategies. In particular, we investigate a class of dynamic flooding algorithm which is aware of the status of neighbor nodes in terms of geographical position and residual battery charge. By comparing this approach with the gossiping and the static flooding schemes, we are able to highlight a remarkable improvement in the network life-time with a particular regard to the most solicited nodes, without increasing complexity.

This paper deals with an efficient dynamic bandwidth allocation technique is presented based on traffic prediction. In particular, the self-similar traffic modeling is herein considered and the accuracy of several prediction techniques is taken into account. With the aim of improving the overall system performance a corrective factor is introduced applying it to predicted traffic level. This approach is then applied to a satellite IP network based on the DVB-RCS standard highlighting the noticeable advantages of the proposed allocation policy in terms of link delay both in the case of a single traffic class and in a multiclass environment based on the DiffServ model.

This paper presents the design, the analysis and the optimization of some efficient channel coding schemes for the enhanced data services provisioning within next generation wireless systems, specifically the TETRA Release 2 system. Three different turbo codes schemes are compared: the parallel and serial concatenation of convolutional codes, respectively, PCCC and SCCC, and block turbo coding (BTC). Basing on the specific-services, some practical rules are drawn to lead to an efficient codes design, while respecting the physical and MAC layers features. By means of numerical simulations, SCCC are proved to outperform not only BTC but also PCCC, though the latter is the scheme widely accepted within the majority of communications standards. Besides, the advantages obtained both in terms of performance and complexity, afford the high-speed, interactive and QoS-oriented multimedia services supply.

The paper proposes an adaptive admission control (AC) policy, that reduces call dropping probability, resorting to rate adaptation in accordance with the instantaneous connection configurations. We describe the philosophy of the proposed adaptive scheme and analyze the effective call dropping probability when considering a single cell UMTS scenario with an additive white Gaussian noise (AWGN) channel. Our simulations demonstrate that, by employing the proposed scheme, the network performance can be extremely increased while the quality of service (QoS) requested is respected.

Future wireless systems need higher support in terms of QoS support. In particular, when several connections with different QoS attributes are allowed, a prioritization system has to be foreseen. In UMTS and other systems that exploit the WCDMA approach, the problem of mitigating multiple access interference arises, too. Admission control algorithms have been introduced in the literature in order to prevent any congestion status in the network. An admission control algorithm that works by exploiting the current interference level is presented; moreover, each type of traffic is managed in order to respect its QoS in terms of priority.

In this paper, a middleware architecture allowing the transparent mobility among two different wireless networks is presented. The proposed scheme is basically based on adaptively maintaining the access to the communication channel for a mobile client enabled with GPRS (General Packet Radio Service) and Bluetooth interfaces. In particular, both the GPRS and the Bluetooth connections are automatically established by means of an RFID tag. To validate this architecture, a preliminary field trial have been set up pointing out the effectiveness of the proposed approach in supporting seamless handover procedures within a heterogeneous network.

Wireless local area networks represent one of the most interesting technological improvements in the last period. Many people are using WLAN commonly just to connect to the Internet or for e-mail downloading. WLAN do not offer at the moment a satisfactory QoS support for multimedia traffic. The aims of the IEEE 802.11e standard is to develop some schemes for supporting multimedia traffic in an in-home environment. On the other hand, in the last few years link adaptation has gained a lot of attention due to its improvement to the channel occupancy and capacity optimization. In this paper a link adaptation algorithm suitable for using in a WLAN, based on the IEEE 802.11e draft, with QoS support is proposed.

Recently, ad-hoc networks have obtained a growing interest due to their advantages in many practical applications. One of the most critical points is the definition of an efficient medium access control (MAC) protocol that allows the transmission of packets generated by a node and routing of packets arriving from other nodes. This paper deals with a MAC technique based on code division multiple access (CDMA) scheme that adapts the used spreading factor to the network congestion in order to minimize the energy consumption and maximize the network throughput.

An original turbo multiuser detector for overloaded coded DS-CDMA systems is presented and studied; the performance of the proposed system is tested by Monte Carlo simulations and by means of the density evolution theory. The turbo-MUD receiver is based on the use a combination of a linear MMSE detector in the first stage and an interference cancellation scheme in the successive ones. The inputs of both receivers are the soft information from a bank of turbo decoders. The performance of the proposed receiver can be effectively predicted in overloaded communication systems by means of the density evolution technique; the use of this technique also permits the proper number of MMSE iterations to be evaluated, making the design of the receiver easier.

Abstract This paper investigates the use of bi‐orthogonal modulations in multiuser communication systems based on ultra wide band impulse radio (UWB‐IR) technology: the communication systems considered herein use Gaussian waveforms in AWGN channel and rely on the utilization of a time‐hopping spreading technique. A hybrid pulse modulation is defined, which is obtained by combining pulse amplitude modulation (PAM) and pulse position modulation (PPM) techniques. Particularly, we have compared the bi‐orthogonal system performance to the classical orthogonal one, also in the condition of lack of a general synchronism, possibly caused by the presence of interfering users that belong to a separate network. Moreover, we have taken into account the use of an M‐ary alphabet, in the case of orthogonal and bi‐orthogonal modulation schemes. Copyright © 2005 John Wiley & Sons, Ltd.

In multiple access OFDM systems (OFDMA) the separation of different users is achieved by exploiting the orthogonality of the subcarriers. However, a well-known problem in OFDM-based systems is the vulnerability to synchronization errors which leads to a loss of orthogonality. In this paper, a method is proposed to counteract the effect of different frequency offsets among users in an OFDMA uplink system with a frequency selective Rayleigh fading channel. The multiple access interference due to the user frequency misalignments is reduced by reconstructing and removing the interfering signals in the frequency domain. This is performed by means of a successive or selective cancellation method. In particular, the performance of these cancellation schemes is analyzed by assuming either an ideal or estimated frequency offset. Simulation results show that it is possible to achieve, with the interference cancellation, a performance close to the ideal case, i.e., without frequency offset among users.

In this paper, a medium access control (MAC) technique for wireless systems that efficiently manages adaptive modulation and coding (AMC) schemes is presented with the aim of improving the downstream data rate, together with preserving quality of service (QoS) requirements. Basically, the proposed access scheme relies on physical channel monitoring and state mapping into a variable rate packet format. A suitable analytical model is proposed herein in order to predict the system performance, i.e., the average packet queuing delay or, equivalently, the average queue length. In particular, the non-stationary transmission channel is modeled as a Markov chain and each state is associated with a particular modulation and coding scheme (MCS) for a specified data rate. Comparisons between analytical predictions and simulation results are provided to validate our model and to highlight the improvement of the proposed technique with respect to a static rate allocation scheme, especially in the presence of heavy tailed traffic conditions, like those arising in remote file transfer typical of a Web connection.

The paper presents a novel approach for dynamic bandwidth allocation (DBA) in GEO satellite networks based on adaptive predictive control. In the proposed DBA scheme each satellite gateway (SG) uses an adaptive predictor to forecast the future input traffic flow along with a predictive bandwidth controller to generate a bandwidth request to the network control center (NCC) according to a receding-horizon policy, via solution of an optimal control problem. A multi-service traffic scenario is considered with a careful eye to guarantee differentiated quality of service requirements. Simulation experiments demonstrate that the DBA technique proposed in this work outperforms fixed allocation as well as existing DBA methods.

In modern satellite communication systems, the quality of service (QoS) management has became a crucial topic due to the increasing interest in multimedia traffic. The actual trends consider the satellite networks as an integrated part of the terrestrial data networks. In IP networks, the differentiated service (DiffServ) approach seems to be the best that satisfies the QoS constraints, due to its end-to-end philosophy. Actual trend considers the satellite on-board switching capabilities for managing multibeam inputs and outputs. In particular this paper deals with the proposal of a new cellular neural network (CNN) for the on-board switching problem to reduce the computational complexity; several traffic classes, according to the DiffServ approach, have been considered and the switch takes into account their priority, queue length and time spent inside queues. Numerical results have shown that the performance is similar to the optimal switching solution of the flexible cellular neural network. Simulation results have been driven with a memoryless distribution and heavy-tailed distribution for several input buffer size and switch dimension.

This paper presents a turbo multiuser detector for turbo-coded DS-CDMA systems, based on the utilization of a PIC and a bank of turbo decoders in which the PIC performs interference cancellation after each constituent decoder of the turbo decoding scheme. Moreover, the soft output of the turbo decoders are used iteratively to improve the updating step of the channel parameter estimation which is formally equivalent to one step of the expectation-maximization algorithm. By means of computer simulations, we have shown that the proposed receiver achieves performance comparable with systems which suppose perfect channel parameters knowledge for medium to high system loads in AWGN channel. The proposed receiver is also tested in a satellite channel.

This paper deals with a modified version of the packet reservation multiple-access (PRMA) protocol suitable for integration of real-time (voice) and best effort (data) traffic in low Earth orbit (LEO) satellite communication systems. The proposed scheme differs from previous alternatives on the method adopted to handle access requests for voice and data terminals, and to transmit data messages. An analytical approach is proposed and validated in the case of voice and classical (i.e., geometric distributed) data traffic in order to derive system performance in terms of mean data message delay and voice packet dropping probability. However, in order to better highlight the advantages of the proposed approach typical interactive and background traffics types have been also considered. Performance comparisons with previous proposed PRMA protocols for voice and data transmission in LEO satellite communication systems are also shown in order to highlight the better behavior of the proposed scheme. Finally, a brief discussion concerning the extension of the proposed S-PRMA protocol to the case of different satellite communication systems is also provided.

This paper deals with an efficient receiver for applications in direct sequence-code-division multiple access wireless communication systems. This receiver combines a modified scheme of a parallel interference cancellation detector with antenna arrays with optimum beamforming and is used at the base station for the detection of asynchronous user signals. Each user's transmission channel is assumed to be a multipath frequency-selective independent Rayleigh fading channel. The receiver operates by dividing the signals into reliable and unreliable sets following space-time combining. The reliable signals are detected and canceled from the whole signal received at each sensor. Unreliable signals are then detected to improve the decision reliability. The receiver performance in terms of bit-error probability is analytically derived and optimized. According to the analytical and simulation results, this receiver outperforms previously proposed schemes and, thanks to its low implementation complexity, real-time operation is achieved.

This paper deals with a modified version of a blind adaptive multiuser detector for direct sequence code-division multiple-access (DS-CDMA) wireless communication systems which is named precombining blind adaptive multiuser detector (PBA-MUD). The main properties of this receiver are low complexity, multiple-access interference mitigation and remarkable near-far resistance in time-varying multipath fading scenarios. In particular, the PBA-MUD is based on a blind adaptive algorithm that allows the detector to avoid deep fading impairments and the cancellation of the desired signal due to signature sequence mismatch. Nevertheless, such a receiver experiences a performance degradation in fast fading channels. In order to overcome this problem, a window reprocessing technique (Del Re et al., 2001) was introduced which yielded a new blind detection algorithm. It will be shown that this receiver, together with this new algorithm [precombining reprocessing window blind adaptive multiuser detector (PWBA-MUD)] allows a high performance without requiring training sequences or the knowledge of the interfering signature waveforms in multipath fast fading channels.

Recent research addresses towards multitransmit, multireceive antenna scheme to improve the performance in high data rate wireless communications. In this paper, we examine the combination of Bell-Labs layered space time (BLAST) wireless architecture and the iterative demapping and decoding, the turbo decoding principle. This structure, known as T-BLAST, was evaluated according to the IEEE 802.11b standard requirements for wireless LAN. The paper considers the design of the modified 'soft' Complementary Code Keying (CCK) modulation/demodulation scheme more suitable for the iterative interference cancellation receiver and shows the performance evaluation of this T-BLAST and SOFT CCK MODEM in the specific environment of the IEEE 802.11b standard. The paper also presents the throughput versus distance to receiver varying the number of transmit antennas in the indoor environment.

In the last decade, code division multiple access (CDMA) has gained even more importance due to its capabilities of wider band occupancy without any time constraints. A lot of the recent implemented systems for wireless communications, as Universal Mobile Telecommunication System (UMTS) or IEEE 802.11b wireless local area network (WLAN), use the CDMA approach to allow the simultaneous access of multiple users. One of the main drawbacks of CDMA systems is the so called multiple access interference (MAI). In the literature, several multiuser receivers were developed. Among them, receivers that perform mean square error minimization are very attractive for their very simple implementation. On the other hand, neural networks have gained recently an increasing importance due to their capabilities in solving many engineering problems, involving minimization of errors or some other cost functionals. In this paper, an advanced MMSE receiver based on the use of neural networks is proposed, where at every bit time neural network achieves the optimum values for the coefficient set of receiving filter, thus minimizing the error rate.

In this paper, the performance of a multiuser detection (MUD) receiver is investigated for a multi-carrier-code division multiple access (MC-CDMA) system in an indoor environment. Furthermore, low complexity pilot-aided methods are introduced for estimating channel parameters in an effort to study the resistance of the proposed solution to imperfect channel estimates. Simulation results show that benefits of MC-CDMA schemes, in terms of capacity and probability of error (P/sub e/), are enhanced by means of a selective parallel interference cancellation (S-PIC) receiver (at the expense of moderate increases in overall system complexity). The proposed channel estimation methods, based on a classical mean and a newly adaptive mean square error (AMSE) algorithm, introduce low performance loss, in terms of P/sub e/ and throughput, with respect to the ideal channel estimate situation. Moreover, the AMSE shows better accuracy and faster convergence than the mean algorithm.

This paper deals with the implementation and the assessment of a wideband directional channel model (WDCM) based on the COST 259 recommendations. Cluster of replicas are introduced by means of tapped delay line (TDL). A good compromise between accuracy of the model and complexity required by the simulator is guaranteed by a suitable statistical approach based on deterministic considerations. In the paper a WDCM implementation for a micro cell case is presented, with particular attention to the cluster position and the mobility model concept. Finally, channel model assessment is performed by comparing simulation results in the general street los radio environment with a recent measurement campaign. Proposed channel model can be used in a link level simulator (LLS).

This paper deals with the comparison among two schemes of space-time MMSE reception implemented for the forward link of a WCDMA multisatellite UMTS environment The so called space-time transmit diversity technique (STTD) has been coupled with the minimum mean square error (MMSE) interference suppression technique. The idea has come from the realization that the diversity gain is limited by a medium-high level of multiple access interference (L. Mucchi et al., 2002). The proposed schemes can be distinguished by the order in which the space-time processing and the MMSE interference suppression are performed. We named ST-MMSE Pre STTD Combining if the MMSE filtering is performed before the space-time combining and ST-MMSE Post STTD Combining if the interference suppression and the space-time combining are jointly processed. A realistic multisatellite UMTS environment has been simulated in order to compare the proposed detectors. Bit error rates have been calculated by mean of Monte Carlo simulations assuming a time-varying satellite channel model. Simulations show that the Post-combining scheme gives the best results, but it implies more complexity to the mobile terminal. Anyway, both the proposed ST-MMSE schemes yield significantly better performance than the standard STTD receiver or the conventional RAKE receiver.

Next generation wireless systems, as Universal Mobile Telecommunications System (UMTS), aim at revolutionizing the actual wireless communication paradigm offering real time multimedia services now available on fixed terminals whose quality of service (QoS) requirements could be satisfied by network resources adaptation to traffic conditions. Since radio interface is based on CDMA technology, this system suffers form mutual interference among active connections. Approximately, the communication quality decreases at the increasing of active users number. As a consequence, there exists an active user threshold below which an intolerable QoS degradation is produces, especially for those applications named in 3GPP standard as interactive or background. Therefore, proper admission control (AC) algorithm that mitigates mutual interference by keeping active users under a dynamic threshold, is a crucial topic in UMTS system optimization. This paper deals with an advanced AC scheme proposal that estimates the requesting connections signal to noise plus interference ratio (SINR) by means of accurate multiple access interference (MAI) analysis results. Basically, this algorithm verifies the possibility of a new call admission by valuating if an overall power configuration there exists, whose predicted SINR values satisfy each QoS constraints. Whenever a new connection is accepted, a further optimization is performed in order to allow a QoS higher than the requested value under a maximum radiated power constraint. This value is delivered to power control (PC) algorithm jointly with the associated SINR value. Numerical simulations, closely related to an UMTS system, underline a remarkable number of active users increase up to four times traditional AC policies, together with the maximization of QoS requirements.

This paper deals with the application of hybrid automatic repeat request (H-ARQ) techniques to reliable data communications in wireless 3G networks, whose typical applications have to match accurate quality of service (QoS) requirements. A common approach to guarantee such services enhances the H-ARQ features by exploiting turbo codes error correction capabilities. This paper, following the previous approach, investigates the further benefits achievable by developing a strategy that establishes a connection between packet retransmissions and decoding results. Two kinds of these techniques, belonging to soft recombining schemes, are proposed and applied, respectively, to consecutive received packet replicas, or to decoding algorithm outputs, in both cases, without remarkable hardware complexity increase. By means of analytical derivations and simulations, focused on a typical universal mobile telecommunication system (UMTS) environment, a noticeable bit error rate (BER) and, then, frame error rate (FER) improvements have been shown. For the proposed schemes, whenever communications suffer from low signal to noise ratio (SNR) values, significant link throughput increase is also pointed out. As a consequence, these techniques can assure a lower packet delivery delay, besides avoiding transmitted power wasting, if compared with protocols commonly used in wired networks.

This paper deals with the proposal and performance evaluation of a fixed microwave communication (FMC) system that shares the same bandwidth as that of an existing UMTS network. The main application of the FMC system is for wireless connections between remote base stations and a core network access point for an UMTS network implementation in a dense urban environment, where a wired connection could be very expensive for service providers. Besides, sharing of the same frequency band could be attractive for the actual cost and lack of frequency spectrum. The mutual interference effects between the FMC and the existing UMTS systems are investigated by focusing on typical application scenarios. The performance for the two systems under consideration has been evaluated in terms of bit error rate by means of computer simulations for proposed receiving scheme where mutual interference are, firstly, detected and then canceled from the other system. The obtained results between the proposed FMC system and an existing UMTS network and the improvement of performance in terms of bit error rate with proposed receiving system.

This paper deals with an advanced admission control (AC) scheme that estimates the requesting connections signal-to-noise plus interference ratio (SINR) by means of accurate multiple access interference (MAI) analysis results. This algorithm verifies the possibility of a new call admission by valuating if a power configuration exists, whose predicted SINR values satisfy each QoS constraints. Numerical simulations, closely related to the UMTS system, underline a remarkable number of active users increase up to four times traditional AC policies, together with the maximisation of QoS requirements.

This paper deals with the application of hybrid automatic repeat request (H-ARQ) techniques to reliable data communications in wireless 3G networks. Basically, retransmission of coded data is endowed with soft combining schemes applied, respectively, to packet replicas, or to decoding algorithm outputs. By means of analytical derivations and simulations on UMTS environment, a noticeable bit error rate (BER) and, then, frame error rate (FER) improvements have been shown. A significant link throughput increase is also pointed out with a consequent reduced packet delivery delay and power wasting.

This paper presents a turbo multiuser detector for turbo-coded DS-CDMA systems, based on the utilization of a PIC and a bank of turbo decoders, in which the PIC performs interference cancellation after each constituent decoder of the turbo decoding scheme. Moreover, we propose a new enhanced estimator of the signal-to-noise-plus-interference-ratio used in the decision device and in the MAP decoding algorithm. By means of computer simulations, we show that the proposed receiver outperforms other similar schemes for medium to very high system loads, in AWGN and multipath fading channel.

In order to enhance the bandwidth utilization, new advanced receivers for next generation mobile communications are developed. Adaptive blind multiuser detection has been widely proposed for applications in CDMA (code division multiple access) wireless communication systems for its principal advantage of eliminating training sequence to set-up receiver filter coefficients. Main drawback of this technique is that it reaches the optimum behavior after a certain number of bit times, which precludes its use in typical time-varying environments. A new neural network approach is proposed in order to solve this drawback. In particular, this paper considers the use of a modified Kennedy-Chua (1988) neural network, based on the Hopfield (1984) model. Numerical results are given to demonstrate the effectiveness of the proposed approach in different time-varying application scenarios.

A multiuser detection scheme is presented, which is based on the interference cancellation principle for noncoherent optical direct-sequence code division multiple access (CDMA) systems. The performance of the proposed receiver, in terms of bit error probability, is derived by means of an analytical approach. Simulation results are also reported in order to validate the analytical predictions. Performance comparisons with the classical matched filter receiver and other non-coherent optical CDMA (OCDMA) receivers already proposed in the literature are discussed in order to highlight the good behavior of the receiver scheme under consideration.

Mobile satellite systems (MSSs) are expected to play a significant role in providing users with communication services worldwide. In such a context, low Earth orbit (LEO) satellite constellations seem to be a good solution to attain a global coverage and to allow the use of low-power lightweight mobile terminals. This paper analyzes the performance of a novel medium access control (MAC) scheme suitable for applications in LEO-MSSs, named packet reservation multiple access with hindering states (PRMA-HS), that has been derived by proper modifications of the well-known PRMA protocol. We envisage a mixed traffic with voice sources and data sources with different quality of service (QoS) requirements. The good behavior of the proposed PRMA-HS scheme is validated by extensive comparisons with the classical PRMA protocol. Finally, it is shown that PRMA-HS efficiently supports integrated voice and data traffic in LEO-MSSs.

A novel medium access control (MAC) protocol, named dynamic resource assignment multiple access enhanced version (DRAMA+), is proposed for low Earth orbit-mobile satellite systems (LEO-MSSs). It is based on a time division multiple access air interface and utilizes access slots distinct from information slots. The DRAMA+ scheme realizes an efficient access phase and manages transmission requests with an on board scheduler. On the basis of suitable models for both isochronous voice sources with activity detection and data bursty sources, we have shown that DRAMA+ outperforms other protocols in the literature.

This paper deals with a multiuser cancellation detection scheme combined with antenna arrays, for wideband code division multiple access (WCDMA) communication systems where different traffic load and different data rate are considered. The proposed receiver, defined as space time-selective parallel interference cancellation detector, is designed to be used at the base station of a WCDMA communication system. Asynchronous users and multipath fading phenomena are considered in our analysis. The proposed receiver basic assumption is to divide signals into two different groups according to the received power level. The reliable ones are directly detected and cancelled from the whole received signal, by each sensor, before making the decision on not reliable signals, without any further processing delay. Performance evaluation has been carried out in terms of P/sub e/ (bit error probability) by means of computer simulations. In particular, it is shown here that the proposed receiver exhibits a good behaviour and lowers the computational complexity in comparison with previously proposed alternatives.

The UMTS terrestrial radio access (UTRA), based on a wideband DS-CDMA technique, fully supports the UMTS requirements and has flexible support for real-time, variable-bit-rate services, as well as an efficient packet mode. This paper presents a description and a performance evaluation of a medium access protocol which may be used in the UTRA system to provide constant-bit-rate (voice), variable bit-rate (video), and low priority data services. The performance evaluation of voice and data services has been carried out by a suitable analytical approach. Simulation results are also shown in order to validate analytical predictions.

This paper deals with a random reservation TDMA protocol able to support constant bit-rate services as well as variable bit-rate services. In particular, we consider here the case of voice communications and data transmissions in a fading channel environment with nonindependent errors. Voice terminals are assumed to have higher priority than data terminals, in accessing the shared channel. A suitable analytical approach is proposed in order to evaluate the data and voice subsystem performance. Computer simulations are also shown in order to validate the obtained analytical predictions. The results shown here highlight that the proposed protocol permits an efficient integration of voice and data transmissions in the same wireless network even in the presence of a nonideal transmission channel.

This paper deals with a random reservation TDMA protocol able to support constant bit rate services as well as variable bit rate services. In particular, voice communications and data transmissions are considered. Voice terminals have a higher priority assigned than data terminals in accessing the shared channel. A suitable analytical approach is proposed in order to evaluate the data and voice subsystem performance. Comparisons to the well known PRMA scheme are also given in order to highlight the superior performance of the proposed approach in terms of maximum data load and overall throughput.

This paper deals with a RAKE receiver architecture which makes use of a pilot signal broadcast by the base station to obtain channel parameter estimates in a direct-sequence code division multiple access (DS-CDMA) indoor wireless network. A suitable cancellation algorithm, which is different from previous approaches, is used to reduce multipath interference due to the pilot signal. Numerical results are used to demonstrate the performance of the proposed RAKE receiver in terms of the bit error probability under typical multipath fading propagation conditions. Performance comparisons with the ideal case of perfect channel parameter estimation are given in order to highlight the good behavior of the proposed approach.

In this paper, a modified version of the packet reservation multiple-access (PRMA) protocol is proposed to provide spatially dispersed voice and data user terminals wireless access to a base station over a common short-range radio channel. An analytical approach is presented in order to derive system performance in terms of mean data message delay and voice packet dropping probability. A suitable permission probability design is also proposed to enhance system performance. Performance comparisons with an extension of the PRMA protocol to voice data systems previously reported in literature are shown to highlight the better behavior of this approach.

This paper deals with the performance evaluation of various resource management strategies that are suitable for low Earth orbit mobile satellite systems (LEO-MSSs). A user mobility model has been proposed and its statistical parameters have been derived. Both fixed channel allocation (FCA) and dynamic channel allocation (DCA) techniques have been considered. Moreover, in order to reduce the handover failure probability, we have assumed that interbeam handover requests which do not immediately obtain service can be queued. In particular, two different queuing disciplines have been compared: (a) the first input first output (FIFO) scheme and (b) a new technique called last useful instant (LUI) which is based on the knowledge of the maximum time within which the handover procedure must be accomplished. Implementation aspects for the LUI technique in a LEO-MSS have been discussed also in comparison with the measurement-based priority scheme (MBPS), previously proposed in the literature on this subject. The efficiency of the LUI queuing scheme as regards the FIFO technique has been investigated by simulations for both DCA and FCA techniques. An analytical approach has been also presented in order to allow the performance evaluation of the FCA scheme with different handover queuing disciplines.

This paper deals with a multiuser detector based on a new decorrelating approach for asynchronous up-link DS/CDMA communications in which the QPSK modulation scheme is used in transmission. It is shown that the receiver proposed is near-far resistant and exhibits a low complexity which allows real-time operation. The performance is expressed in terms of the bit error rate (BER) which has been derived by simulations under the assumption of a slow frequency-selective Rayleigh fading channel.

This article presents a new generalized selective repeat automatic repeat request (ARQ) scheme for error control in broadcast and point-to-point satellite communication systems. In the proposed scheme, each bit in a packet is repeated m times consecutively to increase the transmission reliability. Finite capacity buffers have been assumed at the earth stations. The throughput, theoretically derived for the proposed scheme, is optimized with respect to the number of copies transmitted per bit. A suitable algorithm to adaptively choose this number in relation to the transmission channel propagation conditions can also be used. In comparison with classical and modified versions of the selective repeat ARQ scheme as described in the literature, the proposed scheme provides enhanced throughput, especially with poor channel conditions and a high number of receiving earth stations.

This letter investigates the possibility of integrating voice and data communications in a CDMA wireless packet network to provide access to a base station over a common short-range radio uplink channel for many spatially dispersed voice and data user terminals. Speech activity detection is assumed for voice communications to temporarily devote codes unused by voice user terminals during silence periods to data transmissions. The network proposed exhibits a good performance both in terms of quality of voice communications which is independent of data transmissions and maximum data traffic load supported with bounded delay.

We propose an implementation in terms of a cellular neural network (CNN) of the packet selection discipline in an input queueing fast packet switching (FPS) fabric. A neural network is designed which is devoid of spurious (suboptimal) responses and is guaranteed to take optimal decisions for switching packets. Such a neural network permits to lower the buffer memory requirements and to achieve throughput-mean switching delay performance close to the optimum (output) queueing alternative.

This paper discusses the design of a neural network for solving some classes of combinatorial optimization problems in real time. By means of a suitable design procedure which is not based on energy arguments, it is guaranteed that the network is devoid of spurious responses. An important application is considered to a typical optimization problem arising in the telecommunications field. More specifically, we show how the neural network can be used to take decisions for switching packets and improve switching performance in a fast packet switching fabric with input buffers.

Efficient dynamic channel allocation techniques with handover queuing suitable for applications in mobile satellite cellular networks, are discussed. The channel assignment on demand is performed on the basis of the evaluation of a suitable cost function. Geostationary and low Earth orbit (LEO) satellites have been considered. In order to highlight the better performance of the dynamic techniques proposed, a performance comparison with a classical fixed channel allocation (FCA) has been carried out, as regards the probability that a newly arriving call is not completely served. It has also been shown that a higher traffic density, with respect to GEO systems, is manageable by means of LEO satellites.>

This paper presents some generalized error control techniques that allows one to fulfill the delay and reliability demands of applications over integrated service packet networks (ISPNs). Binary frequency shift keying (FSK) modulation, which is suitable for lightwave packet networks and which, in addition, allows noncoherent detection in place of the classical coherent detection, has been considered. Performance is derived in terms of region-by-region and end-to-end error control. The proposed protocols performed better than previously described techniques, especially under poor channel conditions. In addition, the use of noncoherent detection produced a considerable reduction in receiver implementation complexity.>

Modeling alternatives for a fast packet switching system are analyzed. A nonblocking switch fabric that runs at the same speed as the input/output links is considered. The performance of the considered approaches are derived by theoretical analysis and computer simulations. Performance comparison between input queueing approaches with different selection policies are presented. Novel input and output queueing techniques are also proposed. In particular it is shown that, depending on the implementation, the input queueing approach studied in this paper achieves the same performance as the optimum (output) queueing alternative, without resorting to a faster packet switch fabric.>

Frequency-division multiple access (FDMA) and single channel per carrier (SCPC) in the uplink and time-division multiplexing (TDM) in the downlink are employed in the system described. To interface FDMA in the uplink and TDM in the downlink, multicarrier demodulation (MCD) is required onboard the satellite. The operation of the onboard MCD is the separation of each individual channel and subsequent demodulation. The results, which concern onboard frequency demultiplexing and demodulation for low-bit-rate carriers, are constrained by the requirement that new-generation payloads could serve the stations already active in the INTELSAT Business System. A digital hardware design that implements an MCD that can process three channels at 4.4 Mb/s or 12 channels at 1.1. Mb/s is described. The test results confirm the MCD feasibility, and further improvements are expected from a semicustom implementation.>

The author presents an efficient stop-and-wait ARQ (automatic repeat request) technique for error control in data communication systems. Performance of the proposed stop-and-wait ARQ scheme is derived in terms of throughput efficiency, mean waiting time and buffer occupancy. It is shown that the scheme provides better performance with the respect to previously proposed schemes. In particular it is attractive for error control in data communication systems under high error rate conditions.>

A multibeam fast packet switching satellite communication network serving multiple zones is studied. The synchronous time division multiple access protocol (TDMA) is used in transmitting messages in the uplink channels while the asynchronous time division multiple access protocol (ATDMA) is used in the downlink channels. Moreover, fast packet switching capabilities are assumed on-board the satellite. Alternatives for the architecture of the on-board fast packet switching fabric are considered. The performance of the considered approaches has been derived by theoretical analysis and computer simulations. A novel input queuing technique is also proposed and analyzed to show that it achieves better performance with respect to the classical input queuing approach. Therefore, by means of the novel input queuing approach it is possible to lower the end-to-end delay without increasing the complexity of the on-board equipment.>

The performance of generalized automatic repeat request (ARQ) schemes with continuous-phase frequency-shift-keying (CPFSK) modulation schemes and noncoherent detection is analyzed. In the proposed schemes, each bit of a block is transmitted m times consecutively to increase the transmission reliability. Efficient CPFSK schemes are considered because they represent a class of joint power- and bandwidth-efficient digital modulation schemes with constant amplitude, which can be coherently or noncoherently demodulated. The theoretically derived throughput is optimized for each bit's transmitted copies. In comparison with the classical ARQ schemes, the proposed schemes provide enhanced throughput, especially under high error rate conditions. The use of the noncoherent detection greatly reduces the receiver implementation complexity. The schemes can also be used when coherent detection is required.>

Generalized continuous automatic-repeat-request schemes with compound error detection (compound go-back-N, or CGBN) and increased bit interval (IGBN) are presented. In the proposed CGBN scheme, sets of identical copies of each block are continuously transmitted through the forward channel to the receiver where soft error detection is performed in conjunction with the standard hard demodulation algorithm on each received block. In this way, errors can often be corrected without the implementation of an explicit correction procedure. Throughput efficiency is increased by optimization of the soft demodulation algorithm and by derivation of the optimum value of the number of identical copies to be transmitted for each data block. The IGBN scheme achieves performance close to that of the optimized CGBN with no additional implementation complexity over a hard-decision decoder by increasing suitably the bit interval. In comparison to classical and and modified versions of continuous ARQ schemes described in the literature, the CGBN and IGBN schemes also achieve better performance in terms of mean buffer occupancy and waiting times.>

A two-dimensional signal-scrambling method implemented by digital signal-processing techniques that eliminate the need for frame synchronization without impairing security is presented. Such techniques include short time Fourier analysis and the filter bank concept. The use of special digital finite-impulse-response filters, which make it possible to implement the system algorithm completely via commercial processor software, is discussed. As a result, the system can be configured with very little hardware. Methods for determining available keyspace and selecting keys are also presented.>

The integration of channel coding and modulation in a communication system to increase the Euclidean distance between modulated signals is analyzed. Systems using binary continuous-phase frequency-shift keying modulation and some block codes, such as Hamming codes and shortened Hamming codes, are considered. It is shown that the minimum Euclidean distance depends on the configuration of the parity-check matrixHof the code. For the examined codes the optimum configurations ofH, which give the maximum values of the minimum Euclidean distance, are determined.

In this work, a combined amplitude-phase modulation communication system is considered. Amplitude modulation is used to transmit a voice signal, and phase modulation is used for data transmission. Such a scheme was studied as a possible realization of a data channel between aircraft and ground station, which can be introduced without great modifications of the actual on-board equipment. The performance of the combined modulation system is evaluated through a computer simulation.