This paper investigates a co-design framework for wireless networked control systems (WNCSs) that integrates multi-hop IEEE 802.15.4-based links under Wi-Fi interference, addressing the challenges of signal-to-interference-plus-noise ratio (SINR) degradation in adverse industrial environments. Multihop configurations are essential for extending the operational range and improving SINR in harsh propagation conditions, but they introduce trade-offs in control stability, latency, and computational complexity. We investigate the impact of multi-hop communication on system performance, comparing Bernoulli and Markovian control strategies. Our results demonstrate that multihop links effectively extend the operational range and mitigate SINR degradation, but at the cost of increased latency and computational cost. We analyze the spectral radius of the system stability verification matrix and control costs for Bernoulli and Markovian control strategies, illustrating that network latency and hop counts can be balanced while maintaining the stability of the multi-hop WNCS. Markovian strategy, although more computationally intensive, outperforms Bernoulli strategy under high interference, offering a robust solution for industrial WNCSs. The proposed framework provides a practical approach for deploying reliable WNCSs in interference-prone environments.

Time-domain macromodeling represents an effective technique for generating compact models of the linear time-invariant portion of complex electromagnetic systems. Among the various techniques, a well-known one involves the computation of the port impulse response at the system’s ports, which is then used for calculating convolution integrals. Such computation is typically slow. Recently, a method has been proposed to accelerate such computation by exploiting a piecewise constant approximation of the impulse responses, leading to the so-called segment fast convolution approach. The contribution of the present work is twofold: i) to extend the aforementioned method to the case of piecewise linear approximation of the port impulse responses in the case of linear time-invariant circuits; ii) to define a highly efficient quasi-recursive convolution computation algorithm for both constant and linear piecewise approximations. Moreover, vectorization is exploited to further improve computational efficiency. The proposed convolution schemes are validated in the case of a simple two-port network and then applied to relevant case studies of large-scale electromagnetic systems. Specifically, Reconfigurable Intelligent Surfaces (RISs) and neuromorphic circuits are modeled and validated. The numerical evaluation shows that the proposed schemes are able to guarantee high accuracy together with significant computational speed-ups.

Early Exiting (EE) is an emerging computing paradigm where Deep Neural Networks (DNNs) are equipped with earlier classifiers, enabling trading-off accuracy with inference latency. EE can be effectively combined with edge computing, a paradigm that allows mobile nodes to offload complex tasks, such as the execution of DNNs, to servers at the edge of the network, thus reducing computing times and energy consumption at the mobile devices. The integration of such technologies is particularly attractive for the support of applications for connected and automated driving. In this paper, we consider a system that jointly leverages the benefits of EE and edge computing, and we model their complex interactions by means of a Markov Decision Process (MDP). We then formulate an optimization problem to select the inference strategy that maximizes the average task accuracy. Importantly, such an optimization problem has low complexity, as the optimal policy can be derived by mapping the MDP into a linear program. Our numerical results focus on a use case centered on automated vehicles connected with an edge server under varying channel and network conditions, and show that our solution achieves up to 11% higher accuracy compared to the optimal policy with no EE.

Intelligent Reflective Surfaces (IRSs) enable controlling the radio propagation environment to enhance wireless communications and are particularly relevant for vehicle-to-everything (V2X) applications. This paper explores the integration of IRSs for virtual line-of-sight (VLOS) propagation in urban vehicle platoons that operate with New Radio (NR)-V2X mode 2 sidelink communications and proposes a semi-analytical framework to assess the performance of such systems. The framework considers the availability of resources, the number of interference vehicles, and their relative positions. A Nakagami-Lognormal composite channel model is assumed to describe the propagation environment. This approach provides a cost-effective and accurate estimate of packet success rates, facilitating optimal configuration and parameter adjustments for vehicle platoons. We demonstrate that under typical inter-vehicle distances and with large numbers of vehicles, VLOS communication via IRS can even surpass the performance of conventional Line-of-Sight (LOS) scenarios.

While data quality and quantity directly affect the estimation accuracy of deep learning-based localization techniques, obtaining empirical position data is often costly due to time-consuming experiments, especially for large-scale indoor environments. This paper proposes a novel data collection method to build deep learning-based localization models for indoor vehicle navigation services using multi-directional beacons. By defining the directed graph of the model applicability, we show that high-resolution position labeling data of a limited number of beacons is sufficient to train the localization model for the whole indoor scenario. However, obtaining the ideal directed graph of the model applicability still requires costly high-resolution empirical data from all beacons. We thus propose an autoencoder-based predicted graph method using only cost-effective low-resolution proximity data. We derive the minimum set of beacons needed to collect high-resolution empirical data to train the localization model. We evaluate the proposed beacon selection method in terms of the estimation accuracy and the data collection cost to the beacon-specific model and the ideal directed graph-based method through the extensive set of experimental measurements. The evaluation results show that the proposed localization model using the autoencoder-based predicted graph provides good estimation accuracy while considerably reducing the required training beacons.

While indoor vehicle navigation is an essential component in large-scale parking garages of major cities, technical limitations and challenging propagation environments considerably affect the accuracy of existing localization techniques. We propose practical and robust proximity and direction detection schemes of vehicles for indoor navigation services using low-cost beacons. Specifically, the proposed solution allows a handheld mobile device within a moving vehicle to autonomously detect its approximate position and moving direction by only observing received signal strength (RSS) values of beacon signals. The proposed approach essentially exploits the differential RSS technique over perpendicularly oriented directional beams to reduce the impact of uncontrolled factors, including the vehicle and the mobile device. A low-cost multidirectional beacon prototype is developed using Bluetooth technology. The localization performance is evaluated using 96 beacons in an underground parking garage within an area of$394.8 \mathrm {m} \times 304.3 \mathrm {m}$. Experimental results show that the 90th percentiles of the average proximity and direction detection errors are 0.8 and 1.64 m, respectively. Furthermore, our proposed scheme provides robust proximity and direction detection performance with various vehicles and mobile devices’ orientations.

In this paper, we propose a framework for cross-layer analysis of multi-static passive RFID systems. The model takes into account details of the shared wireless channel, including fading and capture effect, whereas, at the medium access control (MAC) layer, the anti-collision mechanism proposed in the EPC Generation 2 standard is taken as a reference. To address the complexity of the system model, we rely on a semi-analytical approach, that combines a moment matching approximation method to abstract the physical layer and Monte-Carlo simulations to describe the MAC dynamics. Furthermore, based on the space diversity feature offered by the multi-static settings, we introduce the concept ofcapture diversityand propose a modification to the standard to fully support this form of diversity. Numerical results show the impact of deployment conditions and the relative positions of interrogator, tags, and detection points on the performance of tags’ identification. We show how the number of detection points impacts the system performance under various channel conditions and MAC parameters’ settings. Finally, we validate the proposed update of the MAC protocol, showing substantial performance improvement with respect to the standard collision resolution policy.

This paper deals with the design and implementation of security mechanisms in Wireless Sensor Networks(WSN) based applications, without the support of external “resource unconstrained” facilities. In particular, this paper provides a global overview of a long lasting research project and then reports on recent design upgrades denoted as the “Secure Platform”. This has been the target of the SEAMLESS Project, that was oriented to design and validate monitoring architectures for Internet of Things services such as services ranging from featuring temperature, humidity, pressure, light, accelerometer, GPS to non-conventional operational scenarios for military surveillance. This paper then reports security and performance test results of the main components in the “Secure Platform”: the Topology Authenticated Key Scheme (TAKS) and the WPM-based Intrusion Detection System (WIDS). The measurement campaign involved the typical parameters (e.g., encryption / decryption time, key generation time) and a conventional statistical analysis on the results has been also performed.

The challenges in analysis and co-design of wireless networked control systems are well highlighted by considering wireless industrial control protocols. In this perspective, this paper addresses the modeling and design challenge by focusing on WirelessHART, which is a networking protocol stack widely adopted for wireless industrial automation. Specifically, we first develop and validate a Markov channel model that abstracts the WirelessHART radio link subject to channel impairments and interference. The link quality metrics introduced in the theoretical framework are validated in order to enable the accurate representation of the average and extreme behavior of the radio link. By adopting these metrics, it is straightforward to handle a consistent finite-state abstraction. On the basis of such a model, we then derive a stationary Markov jump linear system model that captures the dynamics of a control loop closed over the radio link. Subsequently, we show that our modeling framework is able to discover and manage the challenging subtleties arising from bursty behavior. A relevant theoretical outcome consists in designing a controller that guarantees stability and improves control performance of the closed-loop system, where other approaches based on a simplified channel model fail.

In this paper, we propose a model for the analysis of distributed passive backscattering systems for Radio Frequency Identification with physically separated illuminator and reader. The model takes into account the physical channel characteristics including shadow fading components and thresholds for powering and detection. The dynamic framed ALOHA medium access mechanism defined by the EPC Global Generation 2 standard is considered to evaluate the performance. To address the complexity of the system model, our framework is based on a semi-analytical approach that combines moment matching approximation method at channel level and Monte-Carlo approach for the medium access control dynamics. Results show the impact of deployment conditions and the relative positions among illuminator, tags, and reader on the identification performance. Interestingly, the detection of the back-scattered signal at a remote reader can improve the performance with a higher probability of capture. However, as the distance increases, the impact of shadow fading counterpoises the capture effect. The resulting trade-off is accurately described by our model.

This paper considers channel modeling and evaluation of second-order outage statistics of mixed radio frequency/free space optical (RF/FSO) relay systems over mixed turbulence induced fading (TIF) and non-turbulence induced fading (non-TIF) channels. The derived statistics are directly related to the performance measures. In particular, we derive fast computing closed form expressions for relevant statistics such as cumulative-distribution-function (CDF), level-crossing-rate (LCR), and average-fade-duration (AFD). Approximation through Laplace integration of the products of random processes modeled as Gamma-Gamma (G-G) and Nakagami-m (N-m) are exploited. The proposed framework is then applied to two different scenarios for vehicular networks: i) I2I (infrastructure-to-infrastructure) direct communications enabled by FSO link, ii) V2V (vehicle-to-vehicle) communications enabled by RF/FSO/RF AaF (amplify-and-forward) relay link. Moreover, we provide numerical results for various settings of RF/FSO system model parameters.

In this paper, we propose an equivalent channel model for the analysis of passive backscattering systems (e.g., Radio Frequency Identification systems). The proposed framework accurately models radiation efficiencies at the backscattering nodes whose communication channels are affected by spatially correlated shadowing. First, we derive the distribution of interference in the system and the probability that a node will activate as a function of a specific geographical distribution of the nodes. Then, we approximate the capture probability using a multivariate moment matching approach. The rationale is to provide an underlying structure for the cross-layer analysis of current MAC protocols with the perspective of performance enhancement. Numerical results illustrate the performance of a standard MAC protocol for passive RFID systems, including an accurate evaluation of the impact of the channel characterization.

Latest developments in satellite communications encompass semitransparent transponder architectures. Such architectures have potentials: 1) to operate with enhanced frequency planning flexibility and physical layer specifications of evolving communications standards and 2) to support dynamic reconfiguration of connectivity plans. In this frame, significant on-board digital processing is involved, which calls for careful system modeling and accurate digital hardware design to achieve feasible tradeoffs between hardware efficiency and overall link-budget performance. In our recent works, we have proposed and validated a quantitative framework for performance analysis and design of digital transparent processors (DTPs): the model relies on an extended notion of noise figure that allows a radio link-budget to natively incorporate the nonideal behavior (e.g., quantization and rounding errors and linear distortions) of the various DTP segments. This paper complements the previous works by providing: 1) an explicit computation of implementation complexity of a DTP and 2) a methodology to carry out a complete design flow that moves from system requirements and brings to a detailed definition of digital hardware (HW) components in the DTP. Through numerical examples, we demonstrate that, given a requirement on the overall link budget performance in contexts of practical interest, significant differences in HW complexity are obtained for different design choices.

Energy harvesting is a key technology for future energy neutral ubiquitous wireless communication systems. Among the many available sources of energy, RF harvesting is a natural choice for wireless communications since the devices can be efficiently designed for RF harvesting operations. To achieve energy autonomy a rechargeable energy storage is needed. However, the bursty nature of energy arrival associated with wireless power transfer and the energy usage pattern induced by devices' activity may cause considerable stress to the battery and reduce its life span. In fact, deep charging and discharging cycles degrade the battery state of health, that is, the maximum amount of energy that can be stored. In this paper, a framework for the optimization of wireless nodes' transmission and charging strategy is presented, where the battery aging rate is made explicit as a performance metric. The proposed framework is based on MDP theory, where the embedded stochastic model captures the energy arrival and data generation processes, and the control variable takes the form of a transmission power selection and energy acceptance/rejection. The tradeoff between the achievable throughput and the aging rate is explored for different parameters setting.

Latest developments in satellite communications encompass semi-transparent transponder architectures. Such architectures have potentials i) to operate with enhanced frequency planning flexibility and physical layer specifications of evolving communications standards, and ii) to support dynamic reconfiguration of connectivity plans, especially desirable in packet switching transport modes. In this frame, significant on-board digital processing is involved, which calls for careful system modelling and accurate digital hardware design to achieve feasible trade-offs between hardware efficiency and overall link-budget performance. In a companion paper [1] we have proposed and validated a quantitative framework for performance analysis and design of Digital Transparent Processors (DTP): the model relies on an extended notion of noise figure that allows a radio link-budget to natively incorporate the non-ideal behaviour (e.g. quantization and rounding errors, linear distortions) of the various DTP segments. The present paper complements the work presented in [1] by providing i) an explicit computation of implementation complexity of a DTP, and ii) a methodology to carry out a complete design flow that moves from system requirements and brings to a detailed definition of digital HW components in the DTP. Examples are provided in contexts of practical interest.

Current perspectives for satellite communications are massively envisaging the introduction of a new generation of satellites based on semi-transparent transponder architectures. In this frame, technological constraints related to the development and implementation of novel payloads, that include significant on-board digital processing, call for careful system modeling and accurate digital hardware design in order to enable feasible trade-offs between hardware efficiency and overall link-budget performance. In this perspective, the present paper proposes a system model and a theoretical framework that include the following steps: i) fine characterization of the causes of non ideal behavior in all stages of a digital on-board processor, with definition of equivalent noise sources for the various blocks and derivation of their parameters, namely the noise figure and the noise temperature; ii) extension of the typical link-budget approach to incorporate contributions of the on-board digital segments. Numerical results are provided to validate the accuracy of approximations introduced in analytical modeling of the various blocks; a comparison with results obtained through C based Monte Carlo simulation is provided. Then a set of results are reported to illustrate - in a real satellite link design example - how the model can support advanced trade-offs that are of primary interest in the design of next generation satellite transponders, e,g. those based on translucent processors (digital transparent).

Passive tags based on backscattered signals yield low energy consumption and enable a rich set of applications. In this paper, the performance of the dynamic framed ALOHA of the ISO/IEC 18000-6C standard is investigated. A Markov chain model of the protocol is developed by including the effects of the channel under different propagation scenarios. Depending on the air interface parameters and the fading components, it is shown that multiple access interference determines complex and unexpected effects on the system performance. An explicit analysis of the successful interrogation probability is obtained with respect to the number of tags, number of interrogation rounds and fading severity. It is shown that channel statistics may induce significant degradation, although a moderate spread of the fading can be beneficial especially for those contexts that include time-varying conditions.

The analysis of a network path between a source and a destination using traditional networking tools like ping and traceroute, does not provide informations about the return path. In the absence of those informations, malfunctions and faults can not be managed with adequate effectiveness. In this paper we propose two techniques to perform network path discovery in production networks, without the necessity of a centralized network monitoring system. The first solution is suitable for IPv6 networks, while the second one is suitable in both IPv4 and IPv6 contexts. In order to pursue troubleshooting efficiency and because of possible restrictive policies, the path discovery is triggered by acting only on a single device (from now on called the Discovery Router), without the need of retrieving informations on multiple network equipments. The IPv6-only approach relies on the use of the Hop-by-Hop Option Extension Header without the definition of new options; the second proposed approach aims at the activation on the target device of a traceroute back through the discovery router, then combining the capabilities of SNMP and TFTP. Therefore, it is possible to identify the path between any two routers, for both directions, in a traceroute-like format.

Efficient handover algorithms are essential for highly performing mobile wireless communications. These algorithms depend on numerous parameters, whose settings must be appropriately optimized to offer a seamless connectivity. Nevertheless, such an optimization is difficult in a time varying context, unless adaptive strategies are used. In this paper, a new approach for the handover optimization is proposed. First, a new modeling of the handover process by a hybrid system that takes as input the handover parameters is established. Then, this hybrid system is used to pose some dynamical optimization approaches where the probability of outage and the probability of handover are considered. Since it is shown that these probabilities are difficult to compute, simple approximations of adequate accuracy are developed. Based on these approximations, a new approach to the solution of the handover optimizations is proposed. A distributed optimization algorithm is then developed to maximize handover performance. From an extensive set of results obtained by numerical computations and simulations, it is shown that the proposed algorithm improves performance of the handover considerably when compared to more traditional approaches.

Although the performance of the medium access control (MAC) of the IEEE 802.15.4 has been investigated under the assumption of ideal wireless channel, the understanding of the cross-layer dynamics between MAC and physical layer is an open problem when the wireless channel exhibits path loss, multi-path fading, and shadowing. The analysis of MAC and wireless channel interaction is essential for consistent performance prediction, correct design and optimization of the protocols. In this paper, a novel approach to analytical modeling of these interactions is proposed. The analysis considers simultaneously a composite channel fading, interference generated by multiple terminals, the effects induced by hidden terminals, and the MAC reduced carrier sensing capabilities. Depending on the MAC parameters and physical layer thresholds, it is shown that the MAC performance indicators over fading channels can be far from those derived under ideal channel assumptions. As novel results, we show to what extent the presence of fading may be beneficial for the overall network performance by reducing the multiple access interference, and how this information can be used for joint selection of MAC and physical layer parameters.

The IEEE 802.15.4 communication protocol is a de-facto standard for wireless applications in industrial and home automation. Although the performance of the medium access control (MAC) of the IEEE 802.15.4 has been thoroughly investigated under the assumption of ideal wireless channel, there is still a lack of understanding of the cross-layer interactions between MAC and physical layer in the presence of realistic wireless channel models that include path loss, multi-path fading and shadowing. In this paper, an analytical model of these dynamics is proposed. The analysis considers simultaneously a composite Rayleigh-lognormal channel fading, interference generated by multiple terminals, the effects induced by hidden terminals, and the MAC reduced carrier sensing capabilities. It is shown that the reliability of the contention-based MAC over fading channels is often far from that derived under ideal channel assumptions. Moreover, it is established to what extent fading may be beneficial for the overall network performance.

This paper deals with the design and implementation of security mechanisms in networked embedded systems (e.g. Wireless Sensor Networks (WSN)), without the support of external “resource unconstrained” facilities. While most literature contributions propose to put intelligence (that is usually more consuming both in computational resources and in memory as well) outside the WSN, we have already reported in some previous works that, under certain limitations, a WSN can operate as a functionally “autonomous entity” not only for sensing operations. This paper provides a global overview of the related research project and then reports on recent design upgrades to what we denote as the “Secure Platform”, i.e. the SW platform over WSN that is able to support a wide range of applications in non-standard environment such as monitoring of critical infrastructures, data acquisition in hazardous environments under standard security conditions. The work presented here is a partial achievement of the internal project WINSOME (WIreless sensor Network-based Secure system fOr structural integrity Monitoring and AlErting) at our Centre DEWS, whose target is to develop a cross-layer secure framework for advanced monitoring and alerting applications.

In this paper, we introduce a new framework to compute the Outage Probability (Pout) and the Average Symbol Error Probability (ASEP) of dual-hop Amplify-and-Forward (AF) relaying in the presence of noise, fading, and network interference. The interfering nodes are randomly distributed in the 2D Euclidean plane according to a homogeneous Poisson point process. Our framework provides closed-form expressions of Poutand ASEP over Rayleigh fading channels, additive noise at the relay and at the destination, and network interference at the destination. The accuracy of our analytical derivation is substantiated through extensive Monte Carlo simulations.

In this paper, we introduce an analytical framework for performance analysis and design of Single-Input-Multiple-Output (SIMO) wireless systems in the presence of noise, fading, and radio frequency interference produced by randomly distributed active interferers surrounding an intended probe receiver. The framework leverages recent application of stochastic geometry and Poisson Point Processes (PPPs) theory to network interference modeling. To assess the impact of spatial dependence across multiple receive-antennas, three models of network interference are studied: i) the isotropic model, where all receive-antennas see interferers belonging to the same PPP; ii) the independent model, where each receive—antenna sees interferers belonging to an independent PPP; and iii) the mixture model, which is a superposition of isotropic and independent interferences. Depending on the fading distribution of the interferers, the Nakagami-m fading parameter of the probe link, and the number of receive-antennas, either exact or upper-bound formulas of the error probability averaged over noise, fading, and spatial interference are given. Our analysis shows that, depending on the interference model, performance can either improve or get worse with multiple antennas at the receiver. The proposed analytical methodology is applicable to single- and multi-PPPs interference environments.

Accurate modeling of network interference, deep understanding of its impact on the achievable performance, and development of efficient techniques to mitigate or exploit it are three important and fundamental research assets in current and next-generation cellular networks. In this context, Andrews, Baccelli, and Ganti [1] have recently introduced a new analytical approach to estimate coverage and rate of cellular networks subject to other-cell interference. In this paper, we move from the approach developed in [1], and propose an alternative analytical derivation to compute the rate of cellular networks. More specifically, by using stochastic geometry and Poisson point processes theory, we derive a simple and easy-to-compute expression of the rate, which can be used for arbitrary network and channel parameters, e.g., path-loss exponent, receiver noise, density of Base Stations (BSs), etc. Compared to [1], our framework has two main distinguishable features: i) the rate can be computed via a single numerical integral, rather than via a three-fold numerical integral; and ii) the formula is applicable to arbitrary fading distributions on the intended link, rather than being useful for Rayleigh fading only. Our analytical derivation is substantiated through extensive Monte Carlo simulations.

In this paper, we introduce a new framework to compute the Average Symbol Error Probability (ASEP) of an intended wireless communication system subject to network interference and noise. The interfering nodes are assumed to be randomly distributed in the 2D Euclidean plane according to a homogeneous Poisson point process. Our framework is applicable to performance prediction and optimization of, e.g., emerging heterogeneous cellular and cognitive radio networks. More specifically, we move from and generalize the semi-analytical framework recently introduced by Pinto and Win [1], and develop a new mathematical model which offers a simple single-integral expression of the ASEP under very general channel and interference conditions. The framework is exact, avoids Monte Carlo methods for its computation, and is applicable to asynchronous and synchronous scenarios. Our numerical examples show that both setups have almost the same performance, and that the ASEP in the presence of synchronous interference is a very tight upper-bound of the ASEP in the presence of asynchronous interference. This is a relevant result, as we show in this paper that in the former case all parameters of interest can be computed in closed-form. Our analytical derivation is substantiated through extensive Monte Carlo simulations.

Knowing exactly where a mobile entity is and monitoring its trajectory in real-time has recently attracted a lot of interests from both academia and industrial communities, due to the large number of applications it enables, nevertheless, it is nowadays one of the most challenging problems from scientific and technological standpoints. In this work we propose a tracking system based on the fusion of position estimations provided by different sources, that are combined together to get a final estimation that aims at providing improved accuracy with respect to those generated by each system individually. In particular, exploiting the availability of a Wireless Sensor Network as an infrastructure, a mobile entity equipped with an inertial system first gets the position estimation using both a Kalman Filter and a fully distributed positioning algorithm (the Enhanced Steepest Descent, we recently proposed), then combines the results using the Simple Convex Combination algorithm. Simulation results clearly show good performance in terms of the final accuracy achieved. Finally, the proposed technique is validated against real data taken from an inertial sensor provided by THALES ITALIA.

The demonstration proposal moves from the capabilities of a wireless biometric badge [4], which integrates a localization and tracking service along with an automatic personal identification mechanism, to show how a full system architecture is devised to enable the control of physical accesses to restricted areas. The system leverages on the availability of a novel IEEE 802.15.4/Zigbee Cluster Tree network model, on enhanced security levels and on the respect of all the users' privacy issues.

In this paper, we propose a comprehensive framework for performance analysis of multi-hop multi-branch wireless communication systems over log-normal fading channels. The framework allows to estimate the performance of amplify and forward (AF) relay methods for both channel state information (CSI-) assisted relays, and fixed-gain relays. In particular, the contribution of this paper is twofold: i) first of all, by relying on the Gauss quadrature rule (GQR) representation of the moment generation function (MGF) for a log-normal distribution, we develop accurate formulas for important performance indexes whose accuracy can be estimated a priori and just depends on GQR numerical integration errors; ii) then, in order to simplify the computational burden of the former framework for some system setups, we propose various approximations, which are based on the Improved Schwartz-Yeh (I-SY) method. We show with numerical and simulation results that the proposed approximations provide a good trade-off between accuracy and complexity for both Selection Combining (SC) and Maximal Ratio Combining (MRC) cooperative diversity methods.

In this paper, we investigate the performance of a general multi-layer decentralized system setup for cooperative spectrum sensing, which includes realistic sensing/reporting channels and correlated log-normal shadow-fading in all wireless links of the cooperative network. Our investigations will show that, even though often overlooked in typical cooperative spectrum sensing analysis, shadowing correlation on the reporting channel can yield similar performance degradations as shadowing correlation on the sensing channel. All findings will be substantiated via theoretical arguments and Monte Carlo simulations, and, in particular, novel approximation methods to account for correlated Log-Normal shadowing in cooperative spectrum sensing problems will be introduced.

We propose a comprehensive theoretical framework to evaluate reliability and energy consumption of distributed source coding (DSC) in wireless sensor networks (WSNs) applications. Energy efficiency and the amount of measurements that can be successfully decoded in tree-based WSNs employing DSC in the presence of different coding topologies and packet aggregation schemes (PA) are accurately characterized. The system model includes a realistic network architecture with multi-hop communication, automatic repeat request protocol (ARQ), packet losses due to channel impairments and collisions, and correlation properties of the sensed phenomena. Four DSC topologies and three alternatives of PA are considered. The analysis is carried out by evaluating the expressions of reliability of DSC in terms of probability of measurements that cannot be decoded (loss factor), and the efficiency in terms of average energy consumption of the network. Numerical results show that the best choice of DSC topology and packet aggregation depends highly on the network parameters and source characteristics. Therefore, the analysis developed in this paper can be used as an effective mean to optimize network operations.

In this paper, a general framework for performance evaluation of cooperative spectrum sensing methods over realistic propagation environments is proposed. In particular, the framework accounts for correlated Log-Normal shadowing in both sensing and reporting channels, and yields simple and easy-to-use formulas for computing the Detection Probability of a distributed network of secondary users using Amplify and Forward (AF) relying for data reporting to the fusion center. Numerical results are also shown to substantiate the accuracy of the proposed framework.

The demonstration proposal focuses on presenting the capabilities of a wireless biometric badge, which integrates a localization and tracking service along with an automatic personal identification mechanism, to control the access to restricted areas with a high level of security. The wireless biometric badge is the result of R&D activities conducted by several professors, researchers, and students in the Center of Excellence in Research DEWS at the University of L' Aquila in Italy, as well as its R&D Spin-Off WEST Aquila S.r.l.

A fundamental component to enable Dynamic Spectrum Access (DSA) capabilities in the future generation of wireless communication systems is the design of robust and efficient spectrum sensing methods to detect licensee users transmitting in a given frequency band. In this context, collaborative methods have been proposed to improve spectrum sensing capabilities over wireless channels, by counteracting shadow-fading phenomena via distributed diversity. However, recent results have shown that the expected benefits of cooperation, which are obtained at the expenses of increased traffic overhead and the need for a control channel, may be significantly hampered when the signals sensed by the cooperative users experience correlated shadow- fading. Moreover, it has been argued that spatial correlation of shadow-fading yields fundamental limits to the performance of cooperative spectrum sensing methods, and practical implications in terms of protocol design and network deployment. Motivated by the above considerations, in this paper we propose an analytical framework for the analysis and design of cooperative spectrum sensing methods over correlated shadow- fading environments, when each cooperative user is equipped with a simple energy-based detector. We will show that the framework requires efficient and accurate methods for modeling the power-sum of correlated Log-Normal Random Variables (RVs), which well describe shadowing phenomena. In particular, three main technical contributions can be found in the present paper: i) we generalize some recently proposed methods to approximate the power-sum of independent Log-Normal RVs to correlated scenarios, ii) we analyze the accuracy of several approximation techniques to compute detection probability over correlated Log-Normal shadowing, which is an unexplored field so far, and iii) we rely on the proposed framework to study the detrimental effect of correlation on the performance of cooperative spectrum sensing methods. Furthermore, numerical results will be shown to validate the proposed framework.

In this manuscript, we propose an accurate framework for the analysis of cooperative dual-hop wireless systems over fading channels, which use an Amplify and Forward (AF) relaying mechanism with fixed-gain relays. In particular, the proposed framework provides either exact results or very accurate bounds for computing the Moment Generating Function (MGF) of the end-to-end Signal-to-Noise Ratio (SNR) over Nakagami- m and Weibull fading. Furthermore, with the help of the MGF-based approach for performance analysis of wireless systems over fading channels, we will show that important performance indexes can be easily derived from the MGF. Numerical results will be shown to substantiate the proposed analytical framework.

Approximating the sum of log-normal random variables (RVs) is a long-standing open issue and many studies in the old and recent literature resort to assume that the "power sum" can be well modeled via another log-normal RV. Such a log-normal approximation can be effectively used for accurate outage probability (Pout) analysis and modeling of signal-to-(noise+interference) ratio (SNIR) behaviors in the context of radio resource management in wireless systems; nevertheless, it is recognized that i) an adequate accuracy can only be obtained for a sub-range of values taken by the distribution; ii) the achievable accuracy depends on the parameters of the set of RVs; iii) log-normal approximation may not provide a satisfactory accuracy for estimating bit error probabilities. Moreover, all contributions in the open technical literature are referred to model the "power sum" distribution, i.e., the weighted linear combination of log-normal RVs with weights that may take only positive values. While this setup is consistent with typical scenarios where summands add incoherently, it has recently been shown that in some high frequency-selective multipath channels with log-normal distributed shadow- and fast-fading, e.g., in impulse radio ultra wide band (IR-UWB) systems, the signal- to-noise ratio (SNR) is more accurately modeled by the weighted linear combination of log-normal RVs with weights that may assume both positive and negative values. Motivated by the above considerations, and moving from recent results, which show that approximating the "power sum" of log-normal RVs can boil down to a model selection problem within the pearson system of distributions, the specific contribution of this paper can be summarized as follows, i) We show that the pearson type IV distribution can not only be used to accurately approximate the probability density function (PDF) of the "power sum" of log-normal RVs with positive weights, but it can also accurately model the scenario with both positive and negative weights, as well as the scenario with generically correlated RVs. ii) For the scenario with independent RVs, we propose a numerical technique, which is based on the moment generating function (MGF) matching principle and uses a least- squares criterion, to accurately estimate the four parameters of the pearson type IV distribution, iii) A byproduct of this analysis.

In, we have recently proposed a general approach for approximating the power sum of Log-Normal Random Variables (RVs) by using the Pearson system of distributions. Therein, we have also highlighted the main advantages of using Pearson approximation instead of the usual Log-Normal one, and compared the proposed method with other approaches available in the open technical literature. However, despite being very accurate, the proposed method may be, in some circumstances, computational demanding since a non-linear least-squares problem needs to be solved numerically to get an accurate approximation. Motivated by the above consideration, the aim of this Letter is to provide an alternative approach for computing the parameters of the approximating Pearson distribution. The proposed solution is based on the Method of Moments (MoMs) in the logarithmic domain. In particular, by using some known properties of the Laplace transform, we will show that the MGF of the Log-Normal power sum in the logarithmic domain (denoted as log-MGF) can be obtained from the Mellin transform of the MGF of the Log-Normal power sum in the linear domain. From the estimated log-MGF, we will then compute the desired log-moments required for Pearson approximation. Numerical results will be also shown in order to substantiate the accuracy of the proposed method.

In this paper, we develop a general and unified framework for estimating the Cumulative Distribution Function (CDF) of "quadratic-form" receivers. The expression of the CDF that we finally achieve takes on the form of a single integral with finite limits and integrand composed of elementary functions, which can be readily integrated using standard techniques. In particular, the specific contribution of this manuscript is twofold: i) we present a comprehensive framework for the analysis of multi-channel reception systems using either non-coherent or differentially-coherent detectors, diversity systems with practical (i.e., noisy) channel estimators, and Transmitted-Reference (TR) receiver architectures working in frequency-selective fading channels, and ii) we show that the framework can be efficiently used for performance assessment of wireless systems over generalized fading channels and, under mild assumptions, over generalized fading channels further impaired by in-band multi-tone interference.

In this Letter, we propose a comprehensive framework for performance analysis of cooperative wireless systems using Amplify and Forward (AF) relay methods. The framework relies on the Moment Generating Function (MGF-) based approach for performance analysis of communication systems over fading channels, and on some properties of the Laplace Transform, which allow to develop a single-integral relation between the MGF of a random variable and the MGF of its inverse. Moreover, a simple lower bound for Outage Probability (Pout) and Outage Capacity (OC) computation is also introduced. Numerical and simulation results are provided to substantiate the accuracy of the proposed framework.

In the present contribution, we propose a comprehensive framework for the analysis of cooperative dual-hop wireless systems over generalized fading channels, which use an amplify and forward (AF) relaying mechanism with blind and semi-blind relays. In particular, the proposed framework provides either exact results or very accurate bounds for computing the moment generating function (MGF) of the end-to-end signal-to-noise ratio (SNR) for various fading channel models typically encountered in real propagation environments. Furthermore, with the help of the MGF-based approach for performance analysis of wireless systems over fading channels, we will show that important performance indexes can be easily derived from the MGF. With respect to previous published articles on the matter, the main contribution of the paper is twofold: i) by relying on the properties of the Meijer-G function, either exact expressions or accurate bounds for the MGF of the end-to-end SNR are provided, and ii) the analysis encompasses the vast majority of fading channel models. Numerical and simulation results will be compared to substantiate the analytical derivation.

In this Letter, we propose an advanced framework for performance analysis and design of decentralized data fusion problems. In particular, the performance of a multilayer system setup for data detection, which includes realistic sensing/reporting channels and correlated log-normal shadow-fading in all wireless links of the cooperative network, will be studied. The system setup will be used to analyze the performance of cooperative spectrum sensing problems adopting an amplify-and-forward (AF) relay protocol.We will show that, even though often overlooked in typical cooperative spectrum sensing analysis, shadowing correlation on the reporting channel can yield similar performance degradations as shadowing correlation on the sensing channel. All findings will be substantiated via theoretical arguments and Monte Carlo simulations, and, in particular, novel approximation methods to account for correlated log-normal shadowing in cooperative spectrum sensing problems will be introduced in this paper.

In two recent contributions, we have provided a comparative analysis of various optimization algorithms, which can be used for atomic location estimation, and suggested an enhanced version of the Steepest Descent (ESD) algorithm, which we have shown to be competitive with other distributed localization algorithms in terms of estimation accuracy and numerical complexity. Moreover, therein we have conducted a preliminary statistical characterization of the positioning error distribution, by showing that it can be well approximated by the family of Pearson distributions, as well as pointed out that its knowledge may be efficiently used to speed-up the analysis of iterative-based positioning algorithms by avoiding the need of simulating the whole location discovery algorithm, and allowing simulation at the atomic level only. In this contribution, based on the preliminary results shown in, we propose a comprehensive statistical analysis of the positioning error distribution for the ESD algorithm, by providing the parameters of the Pearson fitting distribution with respect to two important design factors for wireless sensor networks (WSNs): i) the ranging error standard deviation, which represents the input parameter for every localization algorithm, and ii) the geometric dilution of precision factor, which provides a simple parameter to account for different network topologies. In particular, we report an extensive number of simulation results that may provide important insights to the system designer: i) allow a parametric analysis to figure out the joint effect of ranging errors and network topology on the performance of the localization algorithms, and ii) give a general framework for modeling the statistics of the positioning error, which may be used for network planning, as well as for the analysis and design of the upper layers of the protocol stack.

In recent years, there has been a growing interest in antenna sharing systems, and many analytical frameworks have been developed to analyze the performance of various relying protocols in a variety of propagation environments. However, among the different propagation scenarios, the less investigated are those characterized by log-normal fading. Motivated by this consideration, we propose a comprehensive framework for performance analysis of multi-hop multi-branch wireless systems over log-normal fading channels. More specifically, the developed framework allows to estimate the performance of amplify and forward (AF) relay methods for both channel state information (CSI-) assisted analog relays, and semi-blind and blind analog relays. In particular, the contribution of the paper is twofold: i) first of all, by relying on the Gauss quadrature rule (GQR) representation of the moment generation function (MGF) for a log-normal distribution, we develop very accurate formulas for important performance indexes; ii) then, in order to simplify the computational burden of the former framework for some system setups, we also propose an approximation, which is based on the improved Schwartz-Yeh (I-SY) method. We show with numerical and simulation results that the proposed approximation provides a good trade-off between accuracy and complexity.

Virtual antenna array (VAA) systems (also known as cooperative communications, cooperative diversity, cooperative relaying or antenna sharing systems) are a new and recently proposed kind of (cooperative) spatial diversity, which have been receiving a significant interest in various communities as a means for improving the performance of both infrastructure-based and ad-hoc-based transmission systems operating over multipath fading channels. In particular, in antenna sharing systems the mobile radios share their single-antennas to create a distributed virtual antenna array through distributed transmissions and distributed signal processing operations. Although cooperative wireless communications exhibit various design challenges and research opportunities at different protocol layers, in this contribution we mainly focus on physical layer issues. In particular, we propose a comprehensive and unified framework for performance analysis of multi-hop multi-branch wireless systems with channel state information (CSI-) assisted analog relays over generalized fading channels. The framework relies on the moment generating function (MGF-) approach for performance analysis of digital communication systems over fading channels and on some properties of the Laplace transform, which allow to develop a simple single-integral relation between the MGF of a random variable and the MGF of its inverse. Numerical and simulation results are also provided to substantiate the accuracy of the proposed framework.

This paper proposes a novel hybrid cryptographic scheme for the generation of pair-wise network topology authenticated (TAK) keys in a Wireless Sensor Network (WSN) using vector algebra in GF(q). The proposed scheme is deterministic, pair-wise keys are not pre-distributed but generated starting from partial key components, keys management exploits benefits from both symmetric and asymmetric schemes (hybrid cryptography) and each key in a pair node can be generated only if nodes have been authenticated (key authentication). Network topology authentication, and hybrid key cryptography are the building blocks for this proposal: the former means that a cryptographic key can be generated if and only if the current network topology is compliant to the ldquoplanned network topologyrdquo, which acts as the authenticated reference; the latter means that the proposed scheme is a combination of features from symmetric (for the ciphering and authentication model) and asymmetric cryptography (for the key generation model). The proposal fits the security requirement of a cryptographic scheme for WSN in a limited computing resource. A deep quantitative security analysis has been carried out. Moreover the cost analysis of the scheme in terms of computational time and memory usage for each node has been carried on and reported for the case of a 128-bit key.

We have recently proposed a general approach for approximating the power sum of log-normal random variables (RVs) by using the Pearson system of distributions, and then used it for performance analysis of Ultra Wide Band (UWB) wireless systems. Therein, we have also highlighted the main advantages of using the Pearson approximation instead of the usual Log-Normal one, and compared the proposed method with other approaches available in the open technical literature. However, despite being very accurate, the proposed method may be, in some circumstances, computational demanding since a non-linear least-squares problem needs to be solved numerically. Motivated by the above considerations, the aim of this paper is to provide an alternative approach for computing the parameters of the approximating Pearson Type IV distribution. The proposed solution is based on the method of moments (MoMs) in the logarithmic domain. In particular, the specific contribution of this paper is to provide closed-form expressions for the log- moments of the log-normal power sum. By using some known properties of the Laplace transform, we will show that the MGF of the log-normal power sum in the logarithmic domain (i.e., the log-MGF) can be obtained from the Mellin transform of the MGF of the Log-Normal power sum in the linear domain. From the estimated log-MGF, we will then compute the desired log-moments required for Pearson Type IV approximation. Numerical results will be also shown in order to substantiate the accuracy of the proposed method.

In the emerging context of wireless (mobile) ad-hoc networks, cross-layer design has been proposed in recent years to pursue joint optimization at various layers. Modifications to the OSI reference model have been envisaged in order to allow description of cross-layer solutions. Nevertheless, it can be also observed that a sound and reference methodology does not yet exist to support optimization, and this might severely restrict effective adoption and deployment of cross-layer solutions [1]. In this work we propose some conjectures about exploitation of OSI-like layered approach to model and design cross-layer solutions. Specifically, we apply our method to the modelling and analysis of a particular class of cross-layer solutions, namely energy-aware routing protocols. We analyze two proposals available in the literature according to a layered structure. The applied method drives the definition of a novel energy-aware solution that, compared to the previous ones, shows better performance and provides interesting and clear insights on the role that each layer does play in the overall optimization process.

Recent advances in the technology of wireless electronic devices have made possible to build ad-hoc wireless sensor networks (WSNs) using inexpensive nodes consisting of low power processors, a modest amount of memory, and simple wireless transceivers. Over the last years, many novel applications have been envisaged for distributed WSNs in the area of monitoring, communication, and control. One of the key enabling and indispensable services in WSNs is localization (i.e., positioning), given that the availability of nodes' location may represent the fundamental support for various protocols (e.g., routing) and applications (e.g., habitat monitoring). In the depicted context, the present contribution reports our recent research advances along two main directions: i) first of all, we provide a comparative analysis of various optimization algorithms that can be used for atomic location estimation, which include: triangulation, steepest descent, non-linear least squares, conjugate gradient, and an enhanced version of the Steepest Descent (ESD) that is introduced in this paper, and ii) then, we provide a statistical characterization of location errors, by showing that the distribution of error positions can be well approximated by the family of Pearson distributions. In particular, we will show that i) the ESD algorithm may be competitive with the other algorithms in terms of estimation accuracy and numerical complexity, and ii) the knowledge of location error distribution may be efficiently used to speed-up the analysis of iterative-based positioning algorithms by avoiding the need of simulating the whole location discovery algorithm and allowing simulation at the atomic level only.

In this letter, we propose a framework for analyzing the performance of ultra wide band (UWB) receiver architectures in sparse multipath channels with overlapped multipath components (MPCs). The proposed methodology is based on approximating the moment generating function (MGF) of the received signal-to-noise ratio (SNR) via Pade expansion. The method can be applied to any fading scenarios and to any UWB receiver architectures, provided that the MGF of the SNR can be characterized in terms of a convergent Pade expansion. By comparing the results obtained from the analysis with those obtained from simulations in selected reference scenarios, it can be observed that the proposed approximation is very accurate.

This paper deals with the analysis of the timing acquisition (synchronization) process in Impulse Radio (IR-) Ultra Wide Band (UWB) systems based on Differential Transmitted Reference (DTR) receiver architectures. The fundamental contribution includes a theoretical framework for timing acquisition analysis, which is not only able to describe the first moment (Mean Acquisition Time, MAT), and the second moment (standard deviation of the acquisition time) of the acquisition process, but which also provides a consistent and comprehensive analysis of the probability mass function of the acquisition time, i.e., Acquisition Time Mass Probability. In particular, the specific novelty insights of this paper are as follows: (i) the proposal of a new synchronization algorithm, which is based on a two-step approach and relies on the specific characteristics and peculiarities of DTR receivers, as well as the analysis of its performance via a framework based on the theory of Markov processes; (ii) the exploitation of the LATTICE- POISSON algorithm to accurately estimate the Acquisition Time Mass Probability and Overall Acquisition Probability PD(ov), i.e., the probability to get synchronized before a given time; (iii) the performance analysis and comparison of one-step and two-step solutions with respect to the acquisition threshold; and (iv) the analysis of two approaches to estimate MAT and PD(ov)in multipath fading channels, i.e., "Tacq Average" and "Pd Average', which are shown to lead to different results in different scenarios. We observe that restricting the analysis to the MAT may lead to hasty conclusions about the effect of the acquisition threshold on the design of DTR receivers, thus substantiating the need for a more general analysis using PD(ov), as well as the necessity of specifying the characteristics of the wireless channel (e.g., quasi-static, slowly- or fast-fading) for an accurate performance analysis.

Approximating the sum of Log-Normal random variables (RVs) is a long-standing open issue, in the old and recent literature, and many approaches have been proposed to deal with that problem. However, all previous contributions are referred to model the "power sum" distribution, i.e. the weighted linear combination of Log-Normal RVs with weights that may take only positive values. In this paper, we extend that analysis by assuming that the weights may also take negative values. We also point out the importance that this scenario may have for the accurate analysis of ultra wide band (UWB) systems when intra-pulse interference due to multipath propagation cannot be neglected. In this perspective, (i) we show that the weighted linear combination of Log-Normal RVs can be well approximated by the Pearson Type IV distribution in the logarithmic domain, (ii) we use the obtained results for the accurate estimation of the average bit error probability (ABEP) of UWB receiver architectures.

In this paper, we propose an analytical framework for the accurate analysis of Rake and transmitted reference (TR) ultra wide band (UWB) receivers in multipath channels with log-normal fading. The framework relies on approximating the logarithm of the signal-to-noise ratio (SNR) at the detector input by the Pearson type IV distribution, which turns out to provide a simple but surprisingly effective and accurate approximation for the whole SNR probability density function (pdf). The framework includes the analytical derivation of i) the average bit error probability (ABEP) via Gauss-Legendre Gaussian quadrature rules (GQR), ii) the SNR cumulative distribution function (CDF) via the hypergeometric function2F1(middot, middot; middot; middot), which is useful for outage probability (Pout) analysis and iii) the SNR moment generating function (MGF) via Gauss-Legendre GQR. The validity and accuracy of the theoretical approach are also substantiated via Monte Carlo simulations.

An adaptive handover algorithm for wireless communication systems is addressed in this paper. Moving from the Generalized Extended Least Square handover algorithm proposed in N. Benvenuto et al. (2002), we model the handover mechanism as a hybrid system, and we include it in a dynamic optimization problem which is solved through the use of a trellis diagram. The objective function takes into account the parameters that influence the handover mechanism. The optimal solution of the program allows to evaluate performance of the handover in terms of the probability of handover and probability of outage.

Presents abstracts of forthcoming articles.

In this paper, a lognormal approximation is proposed for the sum of lognormal processes weighted by binary processes. The analytical approach moves from the method early proposed by Wilkinson for approximating first-order statistics of a sum of lognormal components, and extends to incorporate second-order statistics and the presence of both time-correlated random binary weights and cross-correlated lognormal components in moments' matching. Since the sum of weighted lognormal processes models the signal-to-interference-plus-noise ratio (SINR) of wireless systems, the method can be applied to evaluate in an effective and accurate way the outage occurrence rate and outage duration for different wireless systems of practical interest. In a frequency-reuse-based cellular system, the method is applied for various propagation scenarios, characterized by different shadowing correlation decay distances and correlations among shadowing components. A further case of relevant interest is related to power-controlled wideband wireless systems, where the random weights are binary random variables denoting the activity status of each interfering source. Finally, simulation results are used to confirm the validity of the analysis.

Abstract — Spatio-Temporal processing is a control technique to increase the quality of the received signals in wireless networks. Outage events have a strong influence not only on the performance of the physical layer, but also on routing, MAC, and application layer. In this paper, we propose an outage based performance analysis of collaborative STP for WSNs. After an accurate characterization of the wireless channel, we derive the outage statistics as function of the STP coefficients, and investigate the effects of STP on the probability, average duration and rate of the outage events. Furthermore, we show that a proper control policy of the STP coefficients can be derived according to the requirements from the applications and WSNs communication layers.

In this paper, we propose a theoretical setup for evaluation of energy efficiency of wireless sensor networks (WSNs) with distributed source coding (DSC) algorithms and packet aggregation (PA). We consider four topologies for DSC and three alternatives for PA, and the system model includes a realistic network architecture with multi-hop communication, automatic repeat request protocol (ARQ), and packet losses. The analysis is carried out in two steps. Firstly we derive the packet loss probability, and then evaluate the average number of packets transmitted throughout the network. This second performance index can then be mapped onto an energy efficiency indicator. The proposed model is specifically adopted for performance comparison of the different coding strategies and aggregation schemes in terms of energy efficiency. Numerical results show that packet overheads have a relevant influence on performance, while the ARQ protocol introduces negligible effects on the energy consumption. Furthermore, DSC topologies with master- slave approach and fragmentation of packets exhibit better performance.

This paper deals with timing acquisition (synchronization) for ultra wide band (UWB) systems based on differential transmitted reference (DTR) receiver architectures. In particular, the paper represents an extension to multipath scenarios of our previous work [1] and aims at comparing the performance of two different search schemes (i.e. one- and two- step), by considering two verification mechanisms (i) returning false alarm and (ii) absorbing false alarm. The analysis of mean acquisition time (MAT) and overall detection (acquisition) probability (PDov) shows that the proposed two-step scheme allows to improve synchronization capabilities (i.e. faster acquisition) while guaranteeing the same bit error probability (BEP).

In this paper we propose a framework for analyzing synchronization performance of UWB systems based on differential receiver architectures. We introduce an extended signal flow graph representation based on the Markov chain theory, which is able to easily and efficiently include realistic Verification/False Alarm Recovery Systems and whose analysis has been typically simplified so far. The proposed model, which turns out to fall within the Markov chain theory with multiple terminating hypotheses and multiple absorbing states, is used to investigate the performance of one- and two-step search schemes with absorbing false alarm occurrences. The analysis of the Overall Detection (Acquisition) Probability shows that the two-step scheme can provide better acquisition probabilities with comparable synchronization accuracy.

An overview of some recent advances in distributed information processing for control over wireless sensor networks is presented in this paper. Firstly, a taxonomy of fundamental control and communication schemes for these systems is introduced. Next, specific research issues are proposed and discussed with three prominent examples on distributed source coding with packet aggregation, distributed cooperative diversity and distributed cooperative localization. In regard to these examples, it is argued about some open research problems and suggestions for further investigations on joint control and communication design for distributed processing and control over wireless sensor networks.

This paper proposes an analytical framework for performance evaluation of TCP (transport control protocol) over adaptive wireless links. Specifically, we include adaptation of power, modulation format and error recovery strategy, and incorporate some features of wireless fading channels. This framework is then used to pursue joint optimization through maximization of an objective functional, that expresses a trade-off between achievable throughput and energy costs. A set of numerical results is reported, and it is seen that hybrid ARQ schemes may provide significant benefits in the optimization framework

Moving from the need for a simple and versatile method for outage computation in various contexts of interest in wireless communications, in this paper we propose a lognormal approximation for the linear combination of a set of lognormal random variables (RV) with one-sided random weights. The approximation is based on a generalization of the well known moment matching approximation (MMA) for the sum of lognormal RVs, and it allows quite simple handling of the power sum of interfering signals even in rather complicated scenarios. Specifically, composite multiplicative channel models with unequal parameters can be handled, and generic (unequal) correlation patterns for some channel components can be handled with reference to any pair of signals. At this stage of the computation, only moments of the random weights are required. The probability density function of the random weight for the useful signal component may be required in computing outage probability, and numerical methods may be only required to solve a single integral at this second stage. The suitability of the approximation is examined by evaluating outage performance for various values of system parameters in the context of interest of composite Nakagami-lognormal channels in reuse-based systems

In this paper we propose a polyphase processing solution for relaxing the strict timing constraints of all-digital ultra wide band (UWB) receiver architectures. The work is motivated by the fact that, while interleaved data acquisition systems have been investigated in the literature with the aim of mitigating the strict timing requirements imposed by the sampling theorem, less attention has been paid in analyzing efficient processing architectures aiming at reducing the overall computational complexity of UWB receiver architectures. Specifically, we evidence how to exploit the polyphase approach for designing efficient detection, synchronization and channel estimation structures

This paper proposes a general framework for analyzing the performance of ultra wide band (UWB) communication systems in a synchronous reference scenario. In this context the information flows, produced by various sources, are synchronously multiplexed to share the common radio resource. The analysis in mainly devoted to investigate the performance of differential UWB receiver architectures, with the signal plus (multiplexing) interference to noise ratio (SINR) and bit error rate (BER) being the parameters of interest. While the obtained results point out that typical channelization codes (i.e. Hadamard) do not seem to be adequate to mitigate multiplexing interference (MI), we identified exact expressions to completely remove MI. In this perspective, the developed framework turns out to be a fundamental setup to identify efficient code families that aims at optimizing the overall system performance

Moving from the need for a simple and versatile method for outage computation in various contexts of interest in wireless communications, in this paper we propose a lognormal approximation for the linear combination of a set of lognormal random variables (RV) with one-sided random weights. The approximation is based on a generalization of the well known moment matching approximation (MMA) for the sum of lognormal RVs, and it allows quite simple handling of the power sum of interfering signals even in rather complicated scenarios. Specifically, composite multiplicative channel models with unequal parameters can be handled, and generic (unequal) correlation patterns for some channel components can be handled with reference to any pair of signals. At this stage of the computation, only moments of the random weights are required. The probability density function of the random weight for the useful signal component may be required in computing outage probability, and numerical methods may be only required to solve a single integral at this second stage. The suitability of the approximation is examined by evaluating outage performance for various values of system parameters in some contexts of interest, namely spread spectrum systems and typical reuse-based systems with composite Rayleigh-lognormal and Nakagami-lognormal channels.

This paper proposes an investigation of binary and quaternary modulation schemes for ultra wide band systems using differential receiver architectures. The expressions for the signal to noise ratio (SNR) and bit error rate (BER) are derived taking into account the code effect, the trade-off between time correlation window width and front-end filter bandwidth. The analysis points out that the quaternary modulation scheme outperforms binary modulations in terms of BER.

SERAN is a two-layer (routing and MAC) protocol for wireless sensor networks in manufacturing plants. At both layers, SERAN combines a randomized and a deterministic approach. While the randomized component provides robustness over unreliable channels, the deterministic component avoids an explosion of packet collisions and allows our protocol to scale with network size. Our solution is based on a mathematical model that characterizes performance accurately without extensive simulations. SERAN is robust against node failures and clock drifts, supports data aggregation algorithms and is easily implementable in any of the existing hardware platforms. Although SERAN was designed for manufacturing plants applications, it can be used in any type of clustered topology. We consider a representative case study and we present simulation results to show SERAN efficiency

This paper proposes a log-normal approximation for the sum of on-off log-normal processes. An analytical approach is developed, that moves from the method early proposed by Wilkinson for approximating first order statistics of a sum of log-normal components, and extends to incorporate second order statistics and the presence of random weights in moments' matching. As a relevant application, the method is used to calculate in an effective and accurate way the parameters of the signal-to-(noise+interference) ratio (S I N R) in a power-controlled wideband wireless system, where the random weights are binary RVs and denote the activity status of each interfering source. A collection of numerical results is presented, where performance predicted by the analysis is compared to that obtained from simulation.

An analytical approach to derive the level crossing rate (LCR) and the average fade duration (AFD) for the signal-to-interference ratio (SIR) in a mobile radio system is proposed. The channel model is characterized by a log-normal shadowing component and a Rayleigh fast fading component on the useful link and on interfering links. Shadowing components are assumed to be cross-correlated. The approach can be divided in two steps. The first one mainly consists in extending Wilkinson's approximation method for the sum of log-normal random variables to the matching of second order statistics of randomly weighted log-normal processes. In particular, the latter approach is used in order to obtain a log-normal approximation for the ratio between total interference and the log-normal component of the useful signal strength. In the second step the SIR is expressed as the product of a Rayleigh process and a log-normal process, and the LCR and AFD are then obtained through the Rice's (1944) approach. Numerical results are presented in terms of LCR and AFD for various values of cross correlation parameters among shadowing components.

A novel methodology is proposed for computing the outage probability in mobile radio systems in the presence of log-normal shadowing. A relevant feature is that the proposed analysis assumes a general correlation for any pair of links. Various approaches are considered to compute the statistics of user signal-to-interference ratio (SIR), namely Schwartz and Yeh's method, Wilkinson's method, and Fenton's method. By a simple reformulation of the problem, these methods can be used to calculate in a straightforward way the parameters of the SIR. The accuracy of the methods is checked in a number of situations of interest. Moreover, when the same correlation is assigned to any pair of links, the novel analysis is more accurate than previously proposed approaches.

A theoretical framework is developed to analyze the user membership in cellular networks. The main interest is on code-division multiple-access (CDMA) networks, although the validity of the proposed approach is not restricted to these networks. The membership of a user terminal to a certain base station (BS) is established if the local mean attenuation to this BS is the lowest one among all surrounding BSs. The estimate of local mean attenuation on the radio links from a mobile terminal to each of the surrounding BSs is carried out through proper filtering of the sequences of received signal strength measurements taken on broadcast signals at regular time intervals. In CDMA networks, pilot channels can be considered, while broadcast control channels can be generically considered in narrow-band systems. A decision is made each time on whether the terminal is to be assigned to its "current" BS or if it would be better served by a different BS. Two performance measures are considered: the probability that the best BS is not selected and the average number of membership switchings per time unit. A channel model with log-normal shadowing and fast fading superimposed is considered. Analytical expressions for the above-mentioned performance measures are derived in a general system scenario. From numerical results, it is seen that a proper choice of filter parameters is required to achieve the lowest values for both performance measures. Moreover, these values are not negligible when the mobile terminal is close to a boundary cell region. The obtained results are considered to be of interest in handover and power control algorithms.

In this paper, the problem of computing cochannel interference statistics in signal strength measurements in mobile radio systems is presented. In a cellular environment with cross-correlated log-normal shadowings, extensions of Wilkinson's method and Schwartz and Yeh's (1982) method are proposed for evaluating the statistics of differences between signal strengths that a mobile terminal measures on the links to any pair of base stations in the presence of cochannel interferers. The derived statistics are then used in the performance analysis of relative signal strength handover algorithms. Results provided by the two methods are compared with simulation results, in order to assess their accuracy, and computational issues are addressed. From numerical results, it is also seen that handover algorithm performance has a noticeable dependence on both cross correlation among shadow fadings and the interference level. Finally, it is seen that previous approaches to derive cochannel interference statistics in the presence of log-normal shadowing can be obtained as particular cases.

The problem of allocating efficiently the power to the various classes of users in a multimedia CDMA wireless system is considered in the presence of imperfect power control. The quality of service requirement for each class of users is expressed in terms of the outage probability. It is seen that the reverse link capacity is maximized by a proper power sharing policy, which results to be a generalization of the one previously found in the presence of perfect power control.

In a multimedia CDMA wireless system, where various classes of users are characterized by different quality of service requirements and source rates, the capacity bound is derived. In a multi-cell environment, an approach is proposed to exploit the optimal policy of jointly assigning the power level and the base station to each user terminal. Non-uniform distributions of users can thus be accounted for in a straightforward way.

A general model for the analysis of outage intervals in mobile radio systems with macrodiversity is proposed. In a log-normal shadowing environment, reception diversity from two base stations is considered in the general case of different fading margins. Through a level-crossing analysis, the probability density function (PDF) of the outage interval is derived. It is seen that exact expressions can be obtained for the average outage occurrence rate and the average outage duration. The exact expressions are used to also improve the accuracy of the PDF at small values of the fading margins, by forcing the PDF to meet the exact average through a proper choice of its parameters. As a particular case, explicit solutions are derived for minimum duration outages.

The traffic performance of integrated cellular mobile and satellite networks is analyzed. Using a previously proposed traffic model for a hierarchical architecture, a parametric analysis is carried out in the ranges of interest for application scenarios of satellite systems under development (e.g. Iridium and Globalstar). In particular, the effect of the following parameters is considered for some constellations: (a) the ratio between the highest and the lowest value of the spatial traffic density in the area covered by a satellite spot; and (b) the percentage of the satellite spot area covered also by the underlying terrestrial cellular networks. A traffic capacity estimation is carried out for the generic satellite spot, using channel reservation (guard channels) for those users who directly access the satellite. Moreover, an improved traffic model is presented, which accounts for frequent inter-spot handovers in low Earth orbit satellite systems.

An analysis of the user membership in a cellular CDMA network is proposed. It is based on the estimate of the local mean attenuation on the radio links from a mobile terminal to each of the surrounding base stations. The estimate is carried out through proper filtering of the sequences of signal strength measurements performed on the received pilot signals. Two performance measures are considered: the probability that the best base station will not be selected, and the average number of membership switchings per time unit. Assuming a channel model with log-normal shadowing and fast fading superimposed, it is seen that a proper choice of the filter parameters is required to achieve the lowest values for these performance measures. The results obtained are of interest for handover and power control algorithms.

A performance analysis of packet cellular networks in the presence of shadowing is presented. Starting from the theories of level crossing and large excursions of Gaussian processes, a statistical characterization of occurrence and duration of fading intervals is first obtained. Then, by considering also the statistics of activity-inactivity intervals of the mobile terminal, the probability function of the sequences of dropped packets is derived. Results are presented in terms of fading intervals statistics and probability function of dropped packet sequences for voice sources, in the presence and in the absence of a terminal buffer. A radio link design approach is also proposed and a design example is discussed.

A traffic model of mobile integrated networks with hierarchical cellular coverages is presented. The model characterizes the traffic overflow from terrestrial cells to overlying satellite spots, accounting for inter-system handovers from the terrestrial component to the satellite one. In order to provide a uniform service quality degree over the whole covered area, a priority policy is adopted in the satellite resource management. Performance measures of the integrated system are derived in terms of blocking probability, forced termination probability and probability of non-completed call. Results are presented in terms of these performance measures at various values of spatial traffic density parameters. The possible model exploitation for the design of the integrated system is also pointed out.

The event of handing over a call from one base station to another in a cellular mobile radio network requests the cooperation of many system elements, with a consequent load of signalling traffic. Therefore, accurate design of handover procedures must be ensured, to avoid the occurrence of forced terminations and unnecessary handovers. This can be pursued by averaging the received power samples with a window of suitable shape and length, N, and by introducing a hysteresis cycle with margin H (dB). In the paper, a software simulator is described that allows the design of N and H considering the handover occurrence rate and the probability of unnecessary handover. Rectangular and exponential averaging window shapes have been considered.>

A urban cellular system providing a mixed coverage has been simulated, aiming at a proper trade-off between network capacity and probability of handover failure. In particular a single macrocell has been overlaid to a four-cluster microcell coverage, according to a hierarchical architecture. The system has been investigated in terms of handover performance, achieving a benefit from both handover requests at reserved channels for the overflow handover traffic at macrocell level.>