This paper introduces a novel joint user association and resource allocation framework to efficiently deal with eavesdropping attacks without requiring prior information about eavesdroppers. Specifically, the co-channel interference when reusing resource blocks is leveraged to disrupt the signal reception at eavesdroppers. To maximize the secure area, defined as the area where eavesdroppers cannot wiretap the channel due to co-channel interference, we first formulate the system by using the Markov decision process to capture the dynamics and uncertainty of mobile users and wireless communications. Then, a deep reinforcement learning (DRL)-based approach is proposed to obtain the joint optimal user association and resource allocation policy to utilize the co-channel interference and maximize the secure area. Extensive simulation results demonstrate that by intelligently associating users and allocating resource blocks to them, our proposed solution can help to effectively defeat eavesdropping attacks without requiring prior information of eavesdroppers which may not be readily available in practice. In addition, the proposed DRL-based algorithm can converge to the optimal policy quickly and achieve better performance compared to existing solutions.

Remote and home care, 24/7 monitoring, and other new procedures are modernizing the processes of professional care as well as enabling better self-monitoring capabilities for health and wellbeing enthusiastic. Due to the aging, societies all around the world are coming to lack of decent healthcare services. Thus, any relief in nursing work is preferred. Wireless technology will be an enabler to accelerate this paradigm change. Monitoring person's own vital signs is not tight to a specific location but data collection can be done real-time wherever and whenever. Also, numerous sensors can be used to collect appropriate vital data. Automated data collection enables continuous monitoring of health status or progress of certain symptom, but enables also efficient data post-processing and access to health data ubiquitously. European Telecommunications Standards Institute's (ETSI) SmartBAN is the newest wireless technology dedicated to body area networks to transfer vital information in reliable manner and with low power consumption. Not only used for outpatient, the SmartBAN is also available for use in different hospital, nursing home, training, etc. procedures.

Abstract Densification of networks through heterogeneous cells deployment is considered a key technology to satisfy the huge traffic growth in future wireless systems. In addition to achieving the required communication capacity and efficiency, another significant challenge arises from the broadcast nature of wireless channels: vulnerability to wiretapping. Physical-layer security is envisaged as an additional level of security to provide confidentiality of radio communications. Typical characteristics of the wireless channel (noise, interference) can be exploited to keep a message confidential from potential eavesdroppers. In particular, heterogeneous networks (HetNet) have inherent security features: while the legitimate user can benefit of the HetNet architecture, the eavesdropper is strongly affected by the inter-cell interference. This paper presents an overview of HetNets intrinsic security benefits, mainly focusing on users association and resource allocation policies. In particular, allocation of radio resources is a poorly investigated topic when related to information security. However, in systems with a large radio resource reuse like HetNets, co-channel interference can be suitably exploited to resist to the eavesdropper. This paper presents a new framework for radio resources allocation using reinforcement learning (Q-learning) to increase the security level in HetNets. A coordinated scheduling among different cells using the same radio resources is proposed based on the exploitation of the spatial information. The goal is to optimize the security at physical layer. The reinforcement learning approach represents a feasible and efficient solution to the proposed problem.

Nowadays, a rapid, easy, and convenient access to our private information is essential to carry out both personal and professional activities. In most cases, this information is sensitive and can be stolen due to its importance and the lack of security protocols. In this study we propose a time–invariant cryptographic key generation mechanism based on electroencephalogram (EEG) signals. We employed Discrete Wavelet Transform and autoencoders to extract the biometric features from the EEG signals. Using these features, we construct a scheme to generate secure seeds that can be used as inputs for secure hash functions and obtain cryptographic keys. The mechanism proposed preserves the privacy of the user, as the cryptographic key is generated for each new EEG signal received, avoiding the need of storing the key, previous EEG signals or any other information. Results show that the proposed mechanism is secure against random attacks, as a 0% of False Acceptance Rate is reported, while generating seeds with an entropy of 0.968 in less than 500 ms.

Intelligent Transportation Systems (ITS) aim at integration of innovative technologies in next-generation vehicles in order to increase the safety and efficiency standards of vehicular traffic fluxes. Although many sensors are currently available in modern cars, mutual data exchange between vehicles in real-time will be crucial in future smart vehicles, but this domain, and in particular bidirectional Vehicle-to-Vehicle (V2V) through Visible Light Communications (VLC), remain relatively unexplored yet. In this paper we present a system for bidirectional data transmission between vehicles through VLC. Specifically, we implement for the first time a bidirectional VLC link using real motorcycle headlights (HL) and rear lights (RL), and we provide a characterization of transmission performances under direct sunlight conditions in an outdoor scenario for realistic distances (up to 30 m) and relative positions between two vehicles. The performance of the VLC system has been evaluated in terms of Signal-to-Noise (SNR) maps and Packet Error Rate (PER), measured in various configurations and for different baudrates (28 kBaud / 57 kBaud). Our result show that a bidirectional error-free communication is possible between two consecutive vehicles for distances up to 12 m, whilst successful transmission could be observed up to 21 m. Finally, we compare our bidirectional intensity and PER data in realistic (flat) configuration against the predictions of a physical model which considers non-ideal orientations of the receiver stage through a novel, simple technique that could also be exploited in different VLC implementations. A very good agreement between the experimental data set and the model is found on the whole measurements grid.

Light-based positioning systems (LPS) are gaining significant attention as a means to provide localization with cm accuracy. Many of these systems estimate the object position based on the received light intensity, and work properly in `ideal' environments such as large open spaces without obstructions around the light-emitting diode (LED) and the receiver, where reflections are negligible. In more dynamic environments, such as indoor spaces with moving people and city roads with moving vehicles, materials cause a wide variety of reflections. This causes variations in the received light intensity and, as a consequence, gross localization errors in LPS. We propose a new multipath detection technique for improving LPS that does not require the knowledge of the channel impulse response and then, it is suited to be implemented in low-cost positioning receivers that use a single-pixel photodetector. To develop our technique, we (i) analyze the statistical properties of non-line-of-sight (NLOS) components, (ii) develop an automated testbed to study the reflections of different types of surfaces and materials, and (iii) design an algorithm to remove the NLOS components affecting the positioning estimate. Our experimental evaluation shows that, in complex environments, our methodology can reduce the localization error using LEDs up to 93%.

Emerging healthcare radio technologies are designed to operate in the 2.4GHz industrial, scientific and medical (ISM) band. Since both standardized (Bluetooth and Wi-Fi) and non-standardized (proprietary) devices use the same frequency band, the aggregate interference may significantly affect the performance of medical wireless systems. This paper characterizes the spatiotemporal spectrum occupancy and proposes models for the aggregate interference in hospital environments. In particular, time-frequency and cluster-based statistical models for the aggregate interference are developed based on network experimentation. The proposed models enable the design of wireless networks for e-health applications and medical services.

Indoor localization systems have become a hot topic of research in the last decade, driven by emerging location-based services as well as missing of a widely adopted localization technology for indoor environments. The large amount of research papers in literature on localization mainly focus on theory, system design or evaluation in non-industrial environments such as offices or healthcare spaces. This paper focuses on a detailed evaluation of a commercial ultra wideband (UWB) localization system in a harsh industrial environment. The experimental field tests have been carried out in a real working industrial galvanic process to come up with a concrete understanding about the performance of this accurate localization technology and thus its benefits/drawbacks for industrial applications.

Network secrecy is vital for a variety of wireless applications and can be accomplished by exploiting network interference. Recently, interference engineering strategies (IESs) have been developed to harness network interference, depending on the wireless environment (node distribution, transmission policy, and channel conditions). Typically, the node spatial distribution has been modeled according to a homogeneous Poisson point process for mathematical tractability. However, such a model can be inadequate for inhomogeneous (e.g., sensor and vehicular) networks. This paper develops a framework for the design and analysis of inhomogeneous wireless networks with intrinsic secrecy. Based on the characterization of the network interference and received signal-to-interference ratio for different receiver selection strategies. Local and global secrecy metrics are introduced for characterizing the level of intrinsic secrecy in inhomogeneous wireless networks from a link and a network perspective. The benefits of IESs are quantified by simulations in various scenarios, thus corroborating the analysis. Results show that IESs can elevate the network secrecy significantly.

The information-theoretic techniques can ensure security in communication regardless of the computational power of the attackers. The requirements for applying such techniques require: 1) an advantage over the eavesdroppers' quality of reception and 2) the location information on the eavesdropper. Traditionally, the performance of a secure communication link is measured using the metrics of secrecy capacity or outage probability, which are both related to the relative quality of the legitimate link compared with that of the eavesdropper link. In this paper, we present a new metric, called secrecy pressure, which measures the security level of the surface/environment where the legitimate link is embedded but is independent of the position of the eavesdropping node. The metric can be also visualized as a secrecy map. The analytical results show how the optimization of the secrecy pressure measure can lead to decide the optimum transmit antenna orientation and/or the position and power of an additional interfering node (friendly jammer).

The impressive growth of secrecy-sensitive wireless applications calls for methods to complement traditional cryptography. In particular, physical-layer security is attractive to enhance communication confidentiality by exploiting the characteristics of the wireless environment. Recent works on information-theoretic wireless network secrecy have shown how to exploit interference to enhance the level of information confidentiality for node spatial distribution according to a homogeneous Poisson point process. We propose a framework for design and analysis of inhomogeneous Poisson networks with maximum secrecy rate. We determine the effects of the inhomogeneous node spatial distribution on the secrecy metrics, which provide guidelines for network design.

Information-theoretical approaches can ensure security, regardless of the computational power of the attackers. Requirements for the application of this theory are: 1) assuring an advantage over the eavesdropper quality of reception and 2) knowing where the eavesdropper is. The traditional metrics are the secrecy capacity or outage, which are both related to the quality of the legitimate link against the eavesdropper link. Our goal is to define a new metric, which is the characteristic of the security of the surface/environment where the legitimate link is immersed, regardless of the position of the eavesdropping node. The contribution of this paper is twofold: 1) a general framework for the derivation of the secrecy capacity of a surface, which considers all the parameters that influence the secrecy capacity and 2) the definition of a new metric to measure the secrecy of a surface: the secrecy pressure. The metric can be also visualized as a secrecy map, analogously to weather forecast. Different application scenarios are shown: from “forbidden zone” to Gaussian mobility model for the eavesdropper. Moreover, the secrecy outage probability of a surface is derived. This additional metric can measure, which is the secrecy rate supportable by the specific environment.

The performance of wireless networks is fundamentally limited by interference [or, equivalently, the signal-to-interference ratio (SIR)]. In an attempt to characterize the interference as a direction-selective quantity and motivated by the useful analogy between classical propagation channels and wireless networks, we propose a novel network description framework, namely the interference azimuth spectrum (IAS). The IAS represents the distribution of interference in the angular domain and is parallel to the conventional power azimuth spectrum (PAS) used in propagation channels. We also extend this concept to the directional characterization of average achievable rate, assuming that interference is treated as noise. Provided with this analytical framework, we present the notion of local area outage, defined as the probability that a receiver is in the state of outage within a local area where both interference and desired signal are assumed to be wide-sense stationary (WSS). We further propose the geometry-based stochastic models (GBSMs) as a part of the IAS framework, where the interfering terminals are randomly distributed according to a specific probability density function (pdf) of their positions. The GBSMs are applicable to a wide variety of wireless network environments without and with interferer clustering. The proposed methodology would provide useful insight on the design and performance assessment of future networks, featured by opportunistic, randomized, and dense placement of nodes.

In this paper we present an experimental campaign which shows the interference levels experienced in a real city hospital in the ISM band as well as the performance of a wearable wireless ECG monitoring system. A typical city hospital usually has several medical and nonmedical devices which work at ISM frequency band. Other sources can be the surrounding private houses WiFi connections as well as the WiFi connection offered by modern hospital to the patients. All these sources can represent a high level of interference for a wearable/portable wireless monitoring system of vital signs. The wireless real-time ECG monitoring prototype which we have developed uses large bandwidth signal that occupies all the ISM band. The performance of the proposed hardware solution following the IEEE802.15.4a standard has been proven in a real situation by means of experimental trials in the emergency ward of a real city hospital.

Due to the enormous spreading of applied wireless networks, security is actually one of the most important issues for telecommunications. One of the main issue in the field of securing wireless information exchanging is the initial common knowledge between source and destination. A shared secret is normally mandatory in order to decide the encryption (algorithm or code or key) of the information stream. It is usual to exchange this common a priori knowledge by using a “secure” channel. A new modulation technique, able to encrypt the radio signal without any a priori common secret between the two nodes, was previously proposed by the authors [1]-[3]. The information is modulated, at physical layer, by the thermal noise experienced by the link between two terminals. A loop scheme is designed for unique recovering of mutual information. This contribution improves the previous works by exploring the real robustness of the proposed technique against the presence of DOS warriors and impairment of the radio channel, considering also implementation details, such as the bit integration time. Both the case of passive and active attacks have also been implemented and simulated by using the Matlab Simulink.

In order to evaluate the performance of emerging wireless systems such as relay, sensor, and mobile ad hoc networks with multihop coverage extensions, spatial-temporal network channel models are required. These models should include the directional characteristics of network information flows in order to exploit the spatial domain due to the deployment of advanced antenna systems. Furthermore, the models should be capable of handling non-stationary scenarios with dynamic evolution of network nodes. In an attempt to solve these two problems which have not been fully addressed in the existing literature, and motivated by the useful analogy between classical propagation channels and wireless networks, we propose a novel spatial-temporal network modeling framework, where the relevant figure-of-merit (FOM) may be received signal power, channel capacity, event detection error exponent, etc., depending on the network's type. Our methodology would be most useful for the design and analysis of future networks featured by decentralized, random, and dense placement of nodes.

In a Mobile Ad-hoc NETwork (MANET) where Mobile Nodes (MNs) self-organize in order to ensure the communication over radio links, routing protocols clearly play a significant role. In future MANETs, protocols should provide routing under full mobility, power constraints, fast time-varying channels and nodes subject to a high loading. In this paper a robust routing protocol, named DXFP (Distributed X-layer Fastest Path), is proposed. The protocol is based on a cross-layer metric which is robust against the time-variations of the network as far as topology (mobility), congestion of the nodes and channel quality (fading, power constraints) are concerned. All these features are integrated in a single physical cost, i.e., the network crossing time, which has to be minimized. Furthermore, several routes from source to destination are stored for a given data flow in order to efficiently face the disconnections which frequently occur in MANETs. It is shown that the DXFP protocol, though locally operating in a fully distributed way within the MNs, provides, for each data flow, the globally optimum routes according to the considered metric. The DXFP protocol has been compared with the two currently most used routing protocols for MANET, i.e. DSR (Dynamic Source Routing) and AODV (Ad hoc On-demand Distance Vector), showing significant improvements in performance and robustness.

Due to the enormous spreading of applied wireless networks, security is actually one of the most important issues for telecommunications. One of the main issue in the field of securing wireless information exchanging is the initial common knowledge between source and destination. A shared secret is normally mandatory in order to decide the encryption (algorithm or code or key) of the information stream. It is usual to exchange this common a priori knowledge by using a "secure" channel. Nowadays a secure wireless channel is not possible. In fact normally the common a priori knowledge is already established (but this is not secure) or by using a non-radio channel (that implies a waste of time and resource). This contribution deals with the proposal of a new modulation technique ensuring secure communication in a full wireless environment. The information is modulated, at physical layer, by the thermal noise experienced by the link between two terminals. A loop scheme is designed for unique recovering of mutual information. The probability of error/detection is analytically derived for the legal users and for the third unwanted listener. The proposed scheme has also been implemented in a Xilinx Virtex II FPGA. All the results show that the performance of the proposed scheme yields the advantage of intrinsic security, i.e., the mutual information cannot be physically demodulated (passive attack) or denied (active attack) by a third terminal, leading us to conclude that the proposed technique is really useful for private key distribution in every wireless network.

This paper proposes a new parameter for identifying the room typology when the receiver is in ultra wideband (UWB) indoor environments. The method proposed does not imply any estimation process at the received signal. The proposed parameter is not only able to clearly distinguish between line-of-sight (LOS) and non-line-of-sight (NLOS) conditions, but it is also capable of ordering the quality of the received signal in two different LOS or NLOS rooms, although the signal-to-noise-ratio (SNR) is the same. Moreover, this parameter is able to distinguish between LOS and NLOS macro groups clearly and, at the same time, to order conditions within these two macro groups (for example, clear LOS condition from Quasi-LOS, i.e., when an object partially shadows the link, etc.). The method proposed in this paper is based on the calculation of the kurtosis index of the sampled received signal. The kurtosis index can be successfully applied to the received signal in order to identify the typology of the link between transmitter and receiver (LOS, Quasi-LOS, high-NLOS, low-NLOS, extreme-low-NLOS). Results are achieved by both real measurements and simulations with IEEE802.15.3a and 4a channel models.

The standard IEEE 802.16 was originally conceived for targeting local and metropolitan area networks, for relatively small link distances. However, the significant deployment of novel wireless-based applications as well as the availability of advanced transmission techniques has suggested a possible extension of the standard-based systems to mountainous and isolated areas. From the propagation point of view, those demanding scenarios result in to non-line-of-sight, long delay spread, and very rich scattering radio environments. Nowadays, no channel models proposed in the literature are suitable for modeling 3.5 GHz transmission in such demanding scenarios. In this paper we propose a possible solution by analyzing and modifying the IST-WINNER model. According to the simulations, the novel channel model characterizes the strong peaks due to the reflection from a mountain and the interfering paths due to near scatterers. The combination of these paths creates a long delay spread that can be fatal for OFDM-based systems. Finally, in order to show the impact of the challenging scenario on the system performance, we present the results related to a system-level simulation using beamforming/MIMO techniques.

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 the proposal of a new parameter for channel identification in ultra wideband (UWB) indoor environments. The proposed method does not imply any estimation process to the received signal and it is able to clearly distinguish not only between LOS and NLOS conditions, but it is also able to order the quality of two different LOS or NLOS conditions, although the SNR is the same. The method proposed here is based on the kurtosis index calculation. Results were obtained by both real measurements and simulations with IEEE802.15.3a channel models.

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.

This paper investigates time of arrival (ToA) estimation methods for ultra-wide bandwidth (UWB) propagation signals. Different algorithms are implemented in order to detect the direct path in a dense multipath environment. In particular, suboptimal low-complex techniques based on peak detection are used to deal with partial overlap of signal paths. A comparison in terms of ranging accuracy, complexity, and parameters sensitivity to propagation conditions is carried out also considering a conventional technique based on threshold detection. The algorithms are tested on experimental data collected from a measurement campaign performed in a typical office building.

The multiband UWB approach is well-seen as one of the most promising technique for short range communications due to its compatibility towards 802.11 family. In this contribution we aim to present a multiband UWB system using cross-polarized antenna, a channel model taking into account also the mutual orientation of Tx and Rx antennas and, at last, several time-frequency codes for accessing the channel in a multi-piconets environment

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.

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.

In the third generation communication system, due to the average increase of the radio link bandwidth requirements and the power constraints at the mobile S-UMTS terminal, the system capacity will meet its physical limitations even in a moderated deployment scenario. In the 3GPP standard, due to the complexity constraints at the user equipment, the DTX implementation on the uplink channel is heavily limited. The transmission scheme presented in this paper is an extension of the traditional informative symbol set with a zero energy symbol. The silence symbols are integrated with the informative ones and delivered to the radio link layer for transmission. The paper presents a theoretical formulation of the optimum two-state receiver. Comparisons with the traditional single-states receiver are obtained with a theoretical approach and through computer simulations. In the latter case a real Globalstar-like S-UMTS environment show the better performances of the proposed scheme for fast varying sources.

Linear minimum mean square error (LMMSE) receivers are capable of suppressing multiple access interference and near-far occurrences in a code division multiple access (CDMA) system operating in multipath fading wireless channels. Their relative low complexity makes them suitable for both uplink and downlink receivers. Third generation receivers are mainly based on coherent detection. Carrier frequency, carrier phase, multipath profile, path delays as well as fading characteristics are important parameters to perform a coherent detection of transmitted symbols. Several multi-user receivers for direct-sequence CDMA systems have been proposed in previous years mainly with the assumption of perfect estimation of those parameters. The aim of this paper is to analyze and investigate the impact of channel estimation and synchronization errors on the LMMSE receivers performance. In particular, two different LMMSE schemes have been considered depending on the order in which the interference suppression and the multipath combining are performed. The pre-combining and the post-combining LMMSE receivers behavior in a multipath fading wireless channel when an imperfect parameters estimation is present into the detection process has been evaluated by using the asymptotic multiuser efficiency.