Indoor Positioning Systems (IPS) are crucial for location-based services and IoT. Ultra-Wideband (UWB) offers high precision but faces challenges from Non-Line-of-Sight (NLOS) conditions, which degrade accuracy. This paper introduces a machine learning model based on a Convolutional Neural Network (CNN) for NLOS vs. Line-of-Sight (LOS) classification in UWB systems. The proposed model operates by extracting relevant features from the Channel Impulse Response (CIR), rather than using CIR samples as in previous work, leading to a reduced computational complexity while maintaining high accuracy. The model was evaluated on an open source UWB dataset, showing a high classification performance and highlighting the potential role of deep learning in enhancing NLOS detection and potentially improving the reliability of positioning systems.

The Narrowband Internet of Things (NB-IoT) technology has an important role in the mobile cellular ecosystem, enabling massive Machine Type Communication (mMTC) services. NB-IoT propagation was preliminarily analyzed via a measurement campaign carried out in 2020 in the city of Oslo, Norway. This investigation resulted in Oslo-2020, the first NB-IoT-specific Alpha-Beta-Gamma (ABG) path loss (PL) model, which showed higher prediction accuracy compared to models developed for different technologies but often used for NB-IoT. In this paper, to further investigate NB-IoT PL in urban scenarios, we analyze new measurement campaigns performed in 2020-2021 and 2023 in the city of Rome, Italy. First, we use the 2020-2021 measurements to derive Rome-2021, a new NB-IoT-specific ABG PL model. We show that Rome-2021 preserves the statistical properties of Oslo-2020 (e.g., the Gaussianity of the PL exponent distribution across base stations), although the moments of the distributions are different due to city-specific environmental characteristics. We also use new data on signal losses due to outdoor-to-indoor propagation to refine the analysis of this scenario. Finally, we propose a methodology to combine Oslo-2020 and Rome-2021 into a more general model. Our methodology uses so-called Mixture Distributions (MDs), thus leveraging the shared statistical properties between Oslo-2020 and Rome-2021. By using the 2023 measurements, we show that our MD-based approach estimates PL model parameters with higher accuracy compared to Oslo-2020 and Rome-2021 models used separately, thus providing an effective solution for predicting NB-IoT urban PL in lack of site-specific measurements and information.

Fifth Generation (5G) networks are becoming the norm in the global telecommunications industry, and Mobile Network Operators (MNOs) are currently deploying 5G alongside their existing Fourth Generation (4G) networks. In this paper, we present results and insights from our large-scale measurement study on commercial 5G Non Standalone (NSA) deployments in a European country. We leverage the collected dataset, which covers two MNOs in Rome, Italy, to study network deployment and radio coverage aspects, and explore the performance of two use cases related to enhanced Mobile Broadband (eMBB) and Ultra-Reliable Low Latency Communication (URLLC). We further leverage a machine learning (ML)-based approach to model the Dual Connectivity (DC) feature enabled by 5G NSA. Our data-driven analysis shows that 5G NSA can provide higher downlink throughput and slightly lower latency compared to 4G. However, performance is influenced by several factors, including propagation conditions, system configurations, and handovers, ultimately highlighting the need for further system optimization. Moreover, by casting the DC modeling problem into a classification problem, we compare four supervised ML algorithms and show that a high model accuracy (up to 99%) can be achieved, in particular, when several radio coverage indicators from both access networks are used as input. Finally, we conduct analyses towards aiding the explainability of the ML models.

The lack of publicly available large-scale measurements has hindered the derivation of empirical path-loss (PL) models for Narrowband Internet of Things (NB-IoT). Therefore, simulation-based investigations currently rely on models conceived for other cellular technologies, which are characterized, however, by different available bandwidth, carrier frequency, and infrastructure deployment, among others. In this article, we take advantage of data from a large-scale measurement campaign in the city of Oslo, Norway, to provide the first empirical characterization of NB-IoT PL in an urban scenario. For the PL average term, we characterize Alpha-Beta-Gamma (ABG) and Close-In (CI) models. By analyzing multiple NB-IoT cells, we propose a statistical PL characterization, i.e., the model parameters are not set to a single constant value across cells, but are randomly extracted from well-known distributions. Similarly, we define the PL shadowing distribution, correlation over distance, and intersite correlation. Finally, we give initial insights on the outdoor-to-indoor propagation, using measurements up to deep indoor scenarios. The proposed models improve the PL estimation accuracy compared to the ones currently adopted in NB-IoT investigations, enabling more realistic simulations of urban scenarios similar to the sites covered by our measurements.

Widespread adoption of indoor positioning systems based on WiFi fingerprinting is at present hindered by the large efforts required for measurements collection during the offline phase. Two approaches were recently proposed to address such an issue: crowdsourcing and RSS radiomap prediction, based on either interpolation or propagation channel model fitting from a small set of measurements. RSS prediction promises better positioning accuracy when compared to crowdsourcing, but no systematic analysis of the impact of system parameters on positioning accuracy is available. This paper fills this gap by introducing ViFi, an indoor positioning system that relies on RSS prediction based on Multi-Wall Multi-Floor (MWMF) propagation model to generate a discrete RSS radiomap (virtual fingerprints). Extensive experimental results, obtained in multiple independent testbeds, show that ViFi outperforms virtual fingerprinting systems adopting simpler propagation models in terms of accuracy, and allows a seven-fold reduction in the number of measurements to be collected, while achieving the same accuracy of a traditional fingerprinting system deployed in the same environment. Finally, a set of guidelines for the implementation of ViFi in a generic environment, that saves the effort of collecting additional measurements for system testing and fine tuning, is proposed.

In overloaded Massive MIMO systems, wherein the number K of user equipments (UEs) exceeds the number of base station antennas M, it has recently been shown that non-orthogonal multiple access (NOMA) can increase performance. This paper aims at identifying cases of the classical operating regime K <; M, where code-domain NOMA can also improve the spectral efficiency of Massive MIMO. Particular attention is given to use cases in which poor favorable propagation conditions are experienced. Numerical results show that Massive MIMO with planar antenna arrays can benefit from NOMA in practical scenarios where the UEs are spatially close to each other.

Motivated by recent theoretical challenges for 5G, this study aims to position relevant results in the literature on code‐domain non‐orthogonal multiple access (NOMA) from an information‐theoretic perspective, given that most of the recent intuition of NOMA relies on another domain, that is, the power domain. Theoretical derivations for several code‐domain NOMA schemes are reported and interpreted, adopting a unified framework that focuses on the analysis of the NOMA spreading matrix, in terms of load, sparsity, and regularity features. The comparative analysis shows that it is beneficial to adopt extreme low‐dense code‐domain NOMA in the large system limit, where the number of resource elements and number of users grow unboundedly while their ratio, called load, is kept constant. Particularly, when optimum receivers are used, the adoption of a regular low‐dense spreading matrix is beneficial to the system achievable rates, which are higher than those obtained with either irregular low‐dense or dense formats, for any value of load. For linear receivers, which are more favourable in practice due to lower complexity, the regular low‐dense NOMA still has better performance in the underloaded regime (load ), while the irregular counterpart outperforms all the other schemes in the overloaded scenario (load ).

Spectral efficiency of low-density spreading non-orthogonal multiple access channels in the presence of fading is derived for linear detection with independent decoding and optimum decoding. The large system limit, where both the number of users and number of signal dimensions grow with fixed ratio, called load, is considered. In the case of optimum decoding, it is found that low-density spreading underperforms dense spreading for all loads. Conversely, linear detection is characterized by different behaviors in the underloaded versus overloaded regimes. In particular, it is shown that spectral efficiency changes smoothly as load increases. However, in the overloaded regime, the spectral efficiency of low-density spreading is higher than that of dense spreading.

Time reversal (TR) is an effective solution in both single user and multiuser communications for moving complexity from the receiver to the transmitter, in comparison to traditional postfiltering based on Rake receivers. Imperfect channel estimation may, however, affect pre‐ versus postfiltering schemes in a different way; this paper analyzes the robustness of time reversal versus All‐Rake (AR) transceivers, in multiple access communications, with respect to channel estimation errors. Two performance indicators are adopted in the analysis: symbol error probability and spectral efficiency. Analytic expressions for both indicators are derived and used as the basis for simulation‐based performance evaluation. Results show that while TR leads to slight performance advantage over AR when channel estimation is accurate, its performance is severely degraded by large channel estimation errors, indicating a clear advantage for AR receivers in this case, in particular when extremely short impulsive waveforms are adopted. Results however also show a stronger non‐Gaussianity of interference in the TR case suggesting that the adoption of a receiver structure adapted to non‐Gaussian interference might tilt the balance towards TR.

Traditionally paired with impulsive communications, time-hopping code-division multiple access (TH-CDMA) is a multiple access technique that separates users in time by coding their transmissions into pulses occupying a subset of Nschips out of the total N included in a symbol period, in contrast with the traditional direct-sequence CDMA (DS-CDMA), where Ns= N. This paper analyzes the TH-CDMA with random spreading, by determining whether peculiar theoretical limits are identifiable, with both optimal and suboptimal receiver structures, in particular in the archetypal case of sparse spreading, that is, Ns= 1. Results indicate that the TH-CDMA has a fundamentally different behavior than DS-CDMA, where the crucial role played by energy concentration, typical of TH, directly relates with its intrinsic uneven use of degrees of freedom.

This paper introduces a transmit beamforming strategy taking into account the positions of primary, secondary victim and intended secondary receivers, to achieve underlay secondary access in multihop cognitive radio networking. The transmit beamforming strategy defines a novel path optimization scheme that deviates from a preselected path given by the routing module, based on local information and according to a relay selection metric. This metric is designed to improve both coexistence with primary/secondary victim receivers and performance of the secondary cognitive network. Simulations compare the proposed strategy with a baseline solution that does not adopt beamforming, and with a strategy that applies beamforming on each hop without modifying the original path. Results show that the proposed strategy is capable of improving coexistence with primary/secondary victims, and highlight that a trade-off exists between the meeting of coexistence constraints and maximisation of secondary network performance.

Recent evolution in regulation of access to TV channels allocated in UHF frequencies (DVB-T) makes vacant channels (TV White Spaces - TVWS) available to wireless data services. While this opportunity is currently widely studied by the cognitive radio community for communications, the use of TVWS for indoor positioning is all but unexplored. Frequencies below 900 MHz are extremely appealing for positioning due to a more uniform signal propagation with respect to the ISM bands and a lower attenuation when passing through obstacles. This work focuses indeed on indoor positioning in the TVWS. A TVWS positioning system is proposed and compared against WiFi-based solutions, in terms of energy efficiency, operating range, and impact of network topology. Moreover, the formulation of a cognitive paradigm for optimal selection of the topology of Access Points and of network topology in a TVWS communication and positioning system is given. The proposed algorithm takes into account constraints related to positioning accuracy and communication performance. Results obtained analytically and by simulation show that favorable propagation conditions characterizing the TVWS frequencies, in conjunction with an optimized system organization and topology, lead to highly accurate positioning and improved energy efficiency over traditional schemes, thanks to lower transmit power levels. The proposed solution is therefore also appealing in light of recent trends towards green wireless communications.

In this paper we deal with the problem of minimizing the complexity of an IR-UWB system by the introduction of Time-Reversal, under a power constraint and fixing a reachable performance in terms of BER. An approximate trade-off in the choice of the number of taps at the transmitter and the number of fingers at the receiver is proposed.

In this paper we present the concept of cognitive satellite terrestrial radios (CSTR) for hybrid satellite-terrestrial systems (HSTS). The cognitive radio (CR) technology is being motivated by the radio regulatory bodies for efficient utilization of the radio spectrum. The future satellite ground terminals therefore need to integrate and co-exist with the spectrally crowded terrestrial wireless systems and hence we propose the idea of CSTR. The key issues are addressed and the concepts of developing CR based satellite ground terminals in HSTS for dynamic spectrum access on the ground are presented. Furthermore, the concept of 3D-Spatial reuse of the spectrum is also presented using the CSTR considering low elevated satellite ground stations. Two particular HSTS applications to illustrate the CSTR concept, a) the hybrid satellite-UWB (ultra wideband) communication system for personal area networks (PAN) with short range on ground communications, and b) the hybrid satellite-WRAN (wireless regional area networks) for long range on ground communications are presented. In both the applications the satellite uplink and the terrestrial radios adopt the CR functionalities. The key enabling technologies and their integrated architecture for the CSTR are also presented.

This work presents a traffic-based, mobility-aware clustering algorithm tailored for application scenarios typical of low data rate IEEE 802.15.4a networks and characterized by a hierarchical network organization. The proposed algorithm adapts to emerging traffic and mobility patterns in the network by selecting as cluster heads nodes that are the intended destinations for a large number of packets, and by associating to the same cluster nodes that send packets to the same destination. The performance of the proposed algorithm is compared by computer simulations with both a non-clustered approach and a clustering algorithm aiming at energy efficiency maximization, in a network of UWB nodes compliant to the 802.15.4a physical layer. Simulation results show that the proposed clustering algorithm improves both network throughput and energy efficiency in hierarchically organized low rate UWB networks.

Time hopping impulse radio commonly encodes data symbols by shifting the position of transmitted pulses over a time gap that is quantized within the inter pulse interval range. In this paper, we adopt a previously investigated coding scheme that considers real-valued codes, and as such introduces time hopping in a "fluid" way. We analyze the application of fluid time hopping to UWB sensor networks. For this purpose we consider a fluid time hopping implementation that is simplified to the maximum extent, in order for it to be appropriate for those networks that need a flexible and easily adjustable multiple access scheme. Fluid time hopping proves in fact to allow fast, detailed, and low-complexity spectrum management, as most suitable in self-organizing networks

Abstract Modeling the resource manager of an ultra wide band (UWB) network is the main object of this paper. The model is tested in two different application scenarios: (i) a UWB WLAN access network to a backbone where the resource management module is implemented at the access points (APs); (ii) a UWB ad hoc network for either local communications or data exchange among sensors, with peer‐to‐peer links with distributed management. The design must include a quality of service (QoS)‐aware strategy and must take into account coexistence issues raised by the use of UWB at the physical layer. Link quality is represented by the maximum end‐to‐end delay and minimum percentage of correct packets. From these parameters, the resource manager jointly selects the values of power and rate which must be adopted at the physical layer. In the model, radiated power by each device is supposed to be limited by an upper bound, reflecting thus the limitation imposed by regulation. QoS awareness and power constraints are satisfied, thanks to the implementation of an admission control function, which is centralized in the AP in the WLAN case and distributed in the ad hoc case. Major innovative aspects include: (i) taking into account UWB specific features; (ii) introducing QoS awareness based on network layer parameters rather than physical layer parameters; (iii) incorporating error protection functionalities for the optimization of transmission efficiency; (iv) considering both centralized and distributed resource management. Performance of the proposed resource manager module is evaluated in the presence of different classes of traffic, that is multimedia, voice, and data traffic. For each class of traffic, performance is expressed in terms of the maximum possible number of simultaneous connections for the WLAN case, and in terms of the effective achievable throughput for the ad hoc case. Results of simulations indicate that the behavior of the proposed scheme is strongly dependent upon the class of traffic in the WLAN scenario, while it is slightly affected by changes in traffic characteristics in the ad hoc case. Copyright © 2005 John Wiley & Sons, Ltd.

When considering applications requiring QoS it is crucial to adopt in the MAC adaptive resource allocation strategies in order to reduce system load. This paper proposes an analytical procedure for optimizing resource allocation in the case of mobile ultra wide band (UWB) users in an indoor environment. The proposed analysis incorporates both the user mobility model and the UWB time-varying channel model. The proposed resource allocation algorithm is based on an iterative algorithm which is capable of minimizing required capacity according to both the state of the channel and the requested QoS. Results of simulations show that within reasonable speed limits which can be quantified, the algorithm is capable of providing the system with an excellent fit of assigned resource vs. required QoS.

Pulse shaping in ultra-wide band (UWB) networks based on impulse radio (IR) is a viable way for adapting the power spectral density (PSD) of transmitted signals to spectral requirements. The proposed pulse shaping method is based on linear combination of a set of base waveforms obtained by differentiation of the Gaussian pulse. Strategies for selecting linear combination coefficients are proposed and approximation of emission masks for UWB indoor systems based on linear combination of the above base functions is analyzed. It is shown that linear combination of base waveforms fulfils spectral requirements with higher efficiency than that achieved by a single waveform. The adoption of pulse shaping in the reduction of multiuser interference (MUI) between different UWB networks is finally proposed and evaluated by means of simulations.

We address the problem of designing time hopping codes for impulse radio multiple access communication systems. Time hopping techniques are first reviewed, including a new code that Iacobucci and Di Benedetto (see Proc. International Symposium 3G Infrastructure and Services, Athens, Greece,July 200) proposed for time hopping, and performance in terms of cyclic correlation properties are given. Advantages and disadvantages of different time hopping codes in terms of resource assignment for multiple access communication systems are analyzed and discussed.

The traditional design of communication networks has rarely been able to focus on the optimization of global network properties. Ultra-wideband (UWB) radio is emerging as an attractive physical layer for wireless communication networks offering new opportunities for the principled design and optimization of network properties. We develop a framework for the principled design of UWB wireless networks based on a flexible cost function that can be tailored and scaled to a wide range of networks and applications, ranging from sensor networks to voice and data wireless networks. The function comprises cost terms associated with transmission, connection setup, interference, and quality-of-service. Multihop routing strategies are associated with admissible paths of minimal cost that are computable in linear time. The cost function together with the overall level of requests determine the dynamics of the connections and the equilibrium topology of the network. We report simulation results in the case of simple ring and square lattice networks.

Orthogonal frequency division multiplexing (OFDM) particularly suffers from the presence of nonlinearities since the signal amplitude is Rayleigh distributed. The degradation introduced by the nonlinear amplifier in the transmitter can be significantly reduced by using an analog cubic predistorter minimum mean square error (MMSE) predistorter proposed by the authors (see ibid., vol.43, no.12, p.2966, 1995).

Describes a new approach for designing analog cubic predistorters in view of minimizing nonlinear distortion introduced by the high power amplifier (HPA) in microwave radio links. The approach is based on a global mean squared error minimization between the input to the predistorter and the output of the power amplifier, rather than on the elimination of the cubic term. In this manner, two advantages are obtained. Firstly, the off-band distortion terms are reduced so that it is possible to eliminate the HF transmission filter. Secondly, the interference produced by the nonlinear distortion can be uniformly distributed over the entire constellation so that it is possible to reduce the back-off value of the HPA. Results of the application of the method proposed to some high spectrally efficient QAM systems, such as the 512-QAM system, are presented.

In this paper, the analysis of macro (prosodic) and micro (segmental) features is described for a workstation designed to improve the pronunciation of English, French and Italian by non-native speakers. The SPELL workstation is intended to be a teaching device aimed at intermediate ability foreign language learners. Audio and visual aids will be used to help students improve their general intelligibility within a basic teaching paradigm called DELTA (Demonstrate, Evaluate Listening, Teach and Assess). Prosodic analysis will apply to the features of intonation, stress and rhythm. A phonological approach is used for intonation which provides a well-structured system of contrasting units that correlate with discrete linguistic functions. A more limited approach to the prosodic phonology of stress and rhythm will be taught in the SPELL system by manipulating the relatively simple acoustic features of vowel quality and segmental duration. The micro feature analysis will focus on the segmental class of vowels. A distinctive feature approach is used to characterize non-native vowel pronunciation. Acoustic properties are sought which will be speaker-independent. © 1992.

A complete statistical model for italian vowels is presented. The classification method contains the adaptive procedure which makes possible the evolution of the regions characteristic of each vowel in the F1-F2 plane and the effectiveness of which has been verified in a previous work [1]. In this paper, each part of the algorithm is described in its theoretical detail and justified on the basis of an extended experimentation. Results are given proving the accuracy of the classifier for vowel segments independent of the context and prosody and dependent upon the context and prosody.

The examination of the diagrams showing the unnormalized formant frequencies in the F1-F2(first and second formant) plane of the vowels (in italian or other languages) shows an overlap of the regions characteristic of each vowel (vowel zones) caused mainly by the differences in the measurement and shape of the vocal tract among speakers. In this paper, a method is presented that makes possible the evolution of the vowel zones by using an adaptive procedure. At the beginning of the algorithm, the center of gravity of each vowel zone represents the mean characteristics for many speakers, when pronouncing each vowel. In the successive steps, the centers of gravity and the shape of the zones tend towards the ones characteristic of the specific speaker. Results are given that show this evolution both for male and female speakers, with the elimination of the overlap between the zones.