Aging and degradation of power cables in railway systems can lead to failures, posing significant safety and operational risks. This paper presents a novel Gramian Angular Field (GAF)-based Power Line Communication (PLC) sensing method for detecting cable aging in both in-train wiring and railway longitudinal power lines. By extracting Channel State Information (CSI) from PLC signals and encoding it into structured GAF representations, the method preserves temporal correlations and nonlinear dynamics while enhancing resilience to noise and transient disturbances. A machine learning-based classification model is then applied to analyze these representations, improving the detection of subtle degradation patterns. Experimental results demonstrate that this approach significantly enhances early-stage cable aging detection, offering a robust and adaptive solution for railway maintenance and safety.

This paper focuses on the parameterization of the multipath propagation model (MPM) for indoor broadband power line communications (PLC), which up to now has been established in an heuristic way. The MPM model was initially proposed in the PLC context for outdoor channels in the band up to 20 MHz, but its number of parameters becomes extremely large when used to model indoor channel frequency responses (CFR), which are much more frequency-selective than outdoor ones, and the band is extended to 80 MHz. This work proposes a fitting procedure that addresses this problem. It allows determining the model parameters that yield the best fit to each channel of a large database of single-input single-output (SISO) experimental measurements acquired in typical home premises of different European countries. Then, the statistics of the MPM parameters are analyzed. The study unveils the relation between the model parameters and the main characteristics of the actual CFR like the frequency selectivity and the average attenuation. It also estimates the probability density function (PDF) of each parameter and proposes a fitting distribution for each of them. Moreover, the relationship among the main parameters of the model, as well as their impact on the performance of PLC communication systems are also explored. Provided results can be helpful for the development of MPM-based models for indoor broadband PLC.

Probability density estimation from observed data constitutes a central task in statistics. In this brief, we focus on the problem of estimating the copula density associated with any observed data, as it fully describes the dependence between random variables. We separate univariate marginal distributions from the joint dependence structure in the data, the copula itself, and we model the latter with a neural network-based method referred to as copula density neural estimation (CODINE). Results show that the novel learning approach is capable of modeling complex distributions and can be applied for mutual information estimation and data generation.

In deep learning, classification tasks are formalized as optimization problems often solved via the minimization of the cross-entropy. However, recent advancements in the design of objective functions allow the usage of the $f$-divergence to generalize the formulation of the optimization problem for classification. We adopt a Bayesian perspective and formulate the classification task as a maximum a posteriori probability problem. We propose a class of objective functions based on the variational representation of the $f$-divergence. Furthermore, driven by the challenge of improving the state-of-the-art approach, we propose a bottom-up method that leads us to the formulation of an objective function corresponding to a novel $f$-divergence referred to as shifted log (SL). We theoretically analyze the objective functions proposed and numerically test them in three application scenarios: toy examples, image datasets, and signal detection/decoding problems. The analyzed scenarios demonstrate the effectiveness of the proposed approach and that the SL divergence achieves the highest classification accuracy in almost all the considered cases.

Estimating mutual information accurately is pivotal across diverse applications, from machine learning to communications and biology, enabling us to gain insights into the inner mechanisms of complex systems. Yet, dealing with high-dimensional data presents a formidable challenge, due to its size and the presence of intricate relationships. Recently proposed neural methods employing variational lower bounds on the mutual information have gained prominence. However, these approaches suffer from either high bias or high variance, as the sample size and the structure of the loss function directly influence the training process. In this paper, we propose a novel class of discriminative mutual information estimators based on the variational representation of the $f$-divergence. We investigate the impact of the permutation function used to obtain the marginal training samples and present a novel architectural solution based on derangements. The proposed estimator is flexible since it exhibits an excellent bias/variance trade-off. The comparison with state-of-the-art neural estimators, through extensive experimentation within established reference scenarios, shows that our approach offers higher accuracy and lower complexity.

In this article, we introduce a novel machine learning algorithm termed the S-parameters-based Human Detection Algorithm (S-PBHD). Designed to operate on radio frequency datasets transformed into an S-parameter multi-port channel matrix, our algorithm aims to detect human targets within indoor environments using distributed antennas. Central to the efficacy of this algorithm lies its preprocessing phase, which entails the extraction of critical components from the scattered radio field. This is achieved through the Para-Hermitian Eigenvalue Decomposition method, which effectively disentangles the complexities inherent in the S-parameter multi-port channel matrix.

This paper presents a dynamic digital pre-distortion (DPD) method for a current-steering digital-to-analog converter (CS-DAC). The novel proposed method is based on the inverse modelling of the system with a Volterra series expansion. It uses a memory structure often only used for DPD in power amplifiers (PA). The goal is to find a model to counteract the signal dependent non-linearities of charge injection from the switching activity of the converter with a limited parameter count. A priori knowledge of the non-linear behavior and architecture of the DAC is exploited. The proposed Volterra system consists of a first and third order kernel with a respective memory depth of one. This results in a total number of only 6 parameters that need to be estimated. This is sufficient to significantly attenuate the non-linear distortions and efficient in terms of memory usage and computational complexity. The paper compares three different methods for generating the inverse of the Volterra system and determines the performance difference between them. The evaluation of the proposed DPD is done via Spice simulations of a 14-bit CS-DAC using a lumped circuit model and Spectre simulations of a real 14-bit 16 nm DAC design. Narrow-band and broad-band discrete multi-tone (DMT) signals with a frequency of up to 684 MHz are considered. The results show a performance gain of the missing-tone-power-ratio (MTPR) of up to 8.4 dB for both model-based and circuit-based simulations based analysis, respectively.

Constant envelope orthogonal frequency division multiplexing (CE-OFDM) is a multi-carrier waveform with 0 dB peak-to-average power ratio (PAPR). This property enables the exploitation of multi-carrier waveforms with non-linear power amplifiers, avoiding the undesirable clipping effects. However, the existing channel estimation techniques designed for OFDM cannot be reused, since the use of a phase modulator makes CE-OFDM a non-linear waveform. Previous works assumed that the channel estimation process relies on the transmission of preambles, and the data symbols are equalized using a frequency domain equalizer (FDE). To avoid the overhead induced by preambles, a phase-domain injected training (PIT) is proposed, where the pilot sequence is embedded in the phase dimension of the data symbols. This novel approach does not waste time and/or frequency resources as in preamble-based schemes. Moreover, it does not require additional power for the training. The received symbols are averaged with a dual procedure, and owing to the particular structure of CE-OFDM, the channel estimates are recovered. Also, the analytical expression of the channel estimation mean squared error (MSE) is derived. Finally, several numerical results illustrate the performance of the proposal, showing that the MSE, bit error rate (BER) and achievable rate are improved, as compared to the existing works.

In this article, we consider the problem of fully-distributed detection of a source emitting a radio signal in a fast fading scenario. We consider that geographically distributed sensor nodes obtain energy measurements and compute cooperatively and in a distributed fashion a decision metric for detecting if the source is present or absent without the need of a fusion center. Since we assume that the sensing channels -from the source to the nodes-vary rapidly due to the nodes and/or the source mobility, we design an algorithm based on the statistical channel state information (S-CSI), instead of the instantaneous channel state information (I-CSI). Nevertheless, even in this scenario, the derived model has some unknown parameters (such as the source transmitted energy or the channel mean attenuation). Therefore, we follow the philosophy of the Generalized Likelihood Ratio Test (GLRT) theory and obtain a test statistic suitable for scenarios without a fusion center: the S-GLRT statistic. We compute its performance through Monte Carlo simulations, and find that S-GLRT overcomes other algorithms available in the literature which are frequently used in similar scenarios.

This paper presents a novel static digital pre-distortion (DPD) method for a current-steering digital-to-analog converter (CS-DAC). The proposed method utilizes the knowledge of the current cell array architecture to calculate the static mismatch currents of the cells. The mismatch values are stored in memory and added to the original input code to generate the new pre-distorted input word. The converter corrects the static error with its own current cells without incorporating an additional calibration DAC (CALDAC) or programmable current sources. This results in a reduction in area, power and simulation run times because of the simpler circuit design. An Overflow-Cell-Selection (OCS) is introduced as a novel solution to further enhance the static linearity of the converter. It also can be implemented as a software solution for already existing DAC designs which do not have an integrated DPD and lab/measurement equipment (e.g., arbitrary wave generator (AWG)). This poses as a strong differentiation factor compared to other state-of-the-art static DPD methods. The evaluation of the proposed DPD is done via simulations in MATLAB and on- chip measurements with a 14-bit CS-DAC in 16 nm. Single tone measurements show a performance gain of the total harmonic distortion (THD) of 12 dB.

Recent advancements in generative networks have shown that it is possible to produce real-world-like data using deep neural networks. Some implicit probabilistic models that follow a stochastic procedure to directly generate data have been introduced to overcome the intractability of the posterior distribution. However, the ability to model data requires deep knowledge and understanding of its statistical dependence-which can be preserved and studied in appropriate latent spaces. In this article, we present a segmented generation process through linear and nonlinear manipulations in the same-dimensional latent space where data are projected to. Inspired by the known stochastic method to generate correlated data, we develop a segmented approach for the generation of dependent data, exploiting the concept of copula. The generation process is split into two frames: one embedding the covariance or copula information in the uniform probability space, and the other embedding the marginal distribution information in the sample domain. The proposed network structure, referred to as a segmented generative network (SGN), also provides an empirical method to sample directly from implicit copulas. To show its generality, we evaluate the presented approach in three application scenarios: a toy example, handwritten digits, and face image generation.

This article presents a novel recursive smooth trajectory (RST) generation algorithm for application in robotics and in particular for unmanned aerial vehicles (UAVs). RST builds the trajectory recursively as a smooth polynomial path, thus a closed form trajectory satisfying any arbitrary dynamic limitation that translates into kinematic constraints (e.g., position, velocity, acceleration, etc.). Uncertainties and perturbations in the constraints are also discussed, modeled, and finally included in the calculation of the polynomial trajectory coefficients. Moreover, due to its recursive formulation, RST enables an immediate extension toward the solution of a trajectory optimization problem. In particular, it is shown that the minimum-snap piecewise polynomial trajectory can be interpreted as a special case of RST. The effectiveness of the proposed algorithm is demonstrated numerically via two illustrative scenarios. Its application to a UAV structure is also discussed to highlight the advantage of a smooth path over a piecewise one. Finally, the computational complexity and memory requirements are analyzed.

Cyclic block filtered multi-tone (CB-FMT) is a waveform that can be efficiently synthesized through a filter-bank in the frequency domain. Although the main principles have been already established, channel estimation has not been addressed yet. This is because of assuming that the existing techniques based on pilot symbol assisted modulation (PSAM), implemented in OFDM-like schemes, can be reused. However, PSAM leads to an undesirable loss of data-rate. In this paper, an alternative method inspired by the superimposed training (ST) concept, namely pilot pouring ST (PPST), is proposed. In PPST, pilots are superimposed over data taking advantage of the particular spectral characteristics of CB-FMT. Exploiting the sub-channel spectrum, the pilot symbols are poured in those resources unused for data transmission. This spectral shaping of pilots is also exploited at the receiver to carry out channel estimation, by enhancing those channel estimates that exhibit a low data interference contribution. Furthermore, a frequency domain resource mapping strategy for the data and poured pilot symbols is proposed to enable an accurate estimation in strongly frequency-selective channels. The parameters of the proposed scheme are optimized to minimize the channel estimation mean squared error (MSE). Finally, several numerical results illustrate the performance advantages of the proposed technique as compared to other alternatives.

In this study, the authors propose a novel architecture based on the combination of peak‐to‐average power ratio (PAPR) reduction with digital beamforming (BF) for mm‐wave massive multiple‐input multiple‐output (MIMO) systems. In order to keep the power amplifiers (PAs) working at the same input back‐off thus maximising the system power efficiency, they propose to perform time‐domain transmit beam‐steering by adding progressive time delays to the signals at each antenna element, while keeping the amplitude weights unitary. They show that these time delays can be obtained with a finite impulse response filter implementation of time‐domain fractional delay filter structures such as Lagrange interpolation polynomials. They also introduce an analysis on the PAPR of the interpolated signals, where they derive an upper bound to it and show that its value is similar to that of the signal at the input of the interpolation filters, showing the feasibility of the proposed method. In addition, they present a detailed analysis where they show that a significant reduction in computational complexity is obtained when compared to frequency‐domain BF. Simulation results validate that the novel proposed scheme combining PAPR reduction and digital BF offers high‐precision beam‐steering maintaining reduced PAPR in the delayed signals fed to the antennas.

An effective approach to enhance the data rate in narrowband power line communication (NBPLC) system is multicarrier modulation based on orthogonal frequency-division multiplexing (OFDM) and multiple-input multiple-output (MIMO) transmission over multiple power line phases. A key challenge for achieving reliable communication over MIMO-OFDM NBPLC is to mitigate the effects of the correlated non-stationary additive noise. In fact, substantial components of the noise in NBPLC systems exhibit a cyclostationary behavior with a period of half the AC cycle. Moreover, when MIMO transmission is adopted, an important issue that must be considered is the cross-correlation between the different phases. In this work, we propose to classify the cyclostationary noise into three classes, based on the evaluation of second order statistics. In addition, we derive estimates of the probability density functions for each of the three classes and show that while two of them exhibit a Gaussian behavior, the third one has an impulsive behaviour similar to the Middleton class-A noise. Simulation results show that the bit error rate (BER) of MIMO-OFDM NBPLC significantly changes between different classes of noise. Hence, we develop an algorithm for switching data delivery between MIMO-OFDM NBPLC and MIMO-OFDM wireless transmission in unlicensed frequency band that takes into account knowledge of the periodicity of the three classes of noises. The result is a hybrid MIMO-OFDM wireless/NBPLC system, which we refer to as, hybrid MIMO-OFDM WiNPLC. Our simulation results demonstrate BER improvement of the proposed hybrid system over individual MIMO-OFDM NBPLC or MIMO-OFDM wireless systems.

This paper proposes a time domain behavioral model for dynamic switching effects of a current-steering digital-to-analog converter (CS-DAC) which shortens the simulation run time while still providing reasonable accuracy. Instead of implementing it with commonly used behavioral models such as the Wiener model, the analysis framework is obtained with the switched state-space model (SSM) approach. With switched SSMs it is possible to directly incorporate element mismatches and parasitics from the design into the model. This provides greater flexibility to designers of data converters. The results of the proposed model are compared to transistor level simulations of the real design in the frequency domain. The achieved speedup factor is > 1000.

In this paper, we consider the identification of a smart grid network topology by means of admittance measurements performed at the network nodes. We show how the application of the transmission line theory allows the identification of the node-to-node connections. Thereby, a topology identification algorithm is presented. The identification error due to the network noise is reduced by performing repeated measurements, either at different time instants or over a set of frequencies, at each network node. The information is then fused by means of the total least square regression technique, which is also compared to a simpler estimator. A thorough analysis of the results is then presented, which shows good reliability of the proposed algorithm.

This paper proposes a synthetic statistical top-down MIMO power line communications channel model based on a pure phenomenological approach. The basic idea consists of directly synthesizing the experimental channel statistical properties to obtain an extremely compact model that requires a small set of parameters. The model is derived from the analysis of the in-home 2 × 3 MIMO PLC channel data set obtained by the European Telecommunications Standards Institute specialist task force 410 measurement campaign in the band 1.8-100 MHz. The challenge of modeling the channel statistical correlation, exhibited among the frequencies and between the MIMO modes, in compact form is tackled and it is shown that a small set of parameters can be used to reconstruct such a correlation behavior. The model is validated and compared with the measured channels, showing a good agreement in terms of average channel gain, root-mean-square delay spread, coherence bandwidth, and channel capacity distribution.

In recent decades, power line communication (PLC) has attracted considerable attention from the research community and industry, as well as from regulatory and standardization bodies. In this paper, we provide an overview of both narrowband and broadband systems, covering potential applications, regulatory and standardization efforts, and recent research advancements in channel characterization, physical layer performance, medium access, and higher layer specifications and evaluations. We also identify the areas of current and further study that will enable the continued success of PLC technology.

Welcome to the IEEE JSAC special issue on Power Line Communications and its Integration with the Networking Ecosystem. This special issue was motivated by the growth in maturity of power line communications (PLC) over the last ten years since the last JSAC special issue focusing on PLC in 2006. For this special issue, we hoped to receive papers showing the growth of PLC technology itself, and works showing applications and integration with the technology ecosystem.

The orthogonal design of a cyclic block filtered multititone modulation (CB-FMT) system is addressed. CB-FMT is a filter bank modulation scheme that uses frequency confined prototype pulses, similarly to FMT. Differently from FMT, where the linear convolution is used, the cyclic convolution is exploited in CB-FMT. This allows to efficiently implement the system via a concatenation of discrete Fourier transforms. The necessary and sufficient orthogonality conditions are derived in time domain and frequency domain. Then, these conditions are expressed in matrix form, and the prototype pulse coefficients are parameterized with hyper-spherical coordinates. The effect of a linear time-variant transmission medium is discussed. In such a scenario, the optimal filter bank orthogonal design is considered with the objective of maximizing either the in-band-to-out-band sub-channel energy ratio or the achievable rate. Numerical results and comparisons show the performance improvements attainable with several designed optimal pulses also with respect to the use of the baseline root-raised-cosine pulse.

Narrow-Band power line communications (NB-PLC) operate in portions of the 3-500 kHz spectrum and have to obey certain spectral masks for EMC and coexistence issues. Although orthogonal frequency division multiplexing (OFDM) allows simple spectrum management by switching on-off the subchannels, its poor sub-channel frequency selectivity translates into a poor spectrum usage. An agile use of the spectrum and higher spectral efficiency can be obtained with filter bank modulation. In particular, in this paper, we investigate the use of cyclic block filtered multitone (CB-FMT) modulation and compare it to pulse shaped OFDM (PS-OFDM) deployed in the G3-PLC and IEEE P1901.2 standards. The comparison shows that higher spectral efficiency and improved spectrum management can be achieved with CB-FMT.

The authors consider the secure transmission of information over power line communication (PLC) networks. The focus is on the secrecy guaranteed at the physical layer, named physical layer security (PLS). Although PLS has been deeply investigated for the wireless case, it is not the same for the PLC environment. Thus, starting from the knowledge in the wireless context, the authors extend the results to typical PLC scenarios. In particular, the PLC channel statistics is evaluated and a performance comparison among PLC and wireless channels is performed, in terms of secrecy rate distribution. For the PLC case, the secrecy rate distribution, under a total power constraint, is evaluated for both optimal and uniform power distributions in broadband channels. To provide experimental evidence, the authors consider channel measures obtained in an in‐home measurement campaign. The underlying network presents a tree topology, which introduces frequency and spatial correlation among channels, and suffers from the keyhole effect, generated by branches that depart from the same node. As shown by the numerical results, these effects can reduce the secrecy rate. Finally, the authors evaluate the secrecy rate region for the multi‐user broadcast channel considering both simulated channel realisations and experimental channel measures.

A statistical characterization of the in-home power line communication channel is performed from the study of a wide set of measured channels in the 1.8-100 MHz frequency band. The study provides new insights on (a) the relation between the line impedance and the channel frequency response (CFR), and (b) on the spatial relation between the channels that share either the transmitter or the receiver outlet. Furthermore, it confirms the validity of some results presented in the literature that are limited to the 30 MHz band. The study comprises the analysis of the average channel gain, the root-mean-square delay spread and the coherence bandwidth, as well as the relation between such quantities and the phase of the CFR. Closed-form expressions are provided to model the quantities and their relations. Finally, the coverage, i.e., the relation between the maximum achievable rate and the distance, as well as the achievable rate gain offered by the use of the frequency band up to 300 MHz, are studied.

A novel filter bank modulation scheme is proposed. This architecture is based on the Filtered Multitone (FMT) modulation concept where well frequency confined prototype pulses are deployed. However, in the proposed scheme linear convolutions are replaced by circular convolutions. We refer to this new scheme as Cyclic Block Filtered Multitone Modulation (CB-FMT). Both the synthesis and the analysis filter banks in CB-FMT can be efficiently implemented in the frequency domain via the concatenation of Fast Fourier Transforms (FFTs). Furthermore, it is possible to design the prototype pulse so that the system is orthogonal and it does not experience any inter-symbol and inter-carrier interference in ideal conditions. To cope with the interference introduced by a frequency selective fading medium, simple frequency domain equalization can be used. Numerical results show that CB-FMT can provide better performance than FMT and OFDM in frequency selective fading with comparable or lower complexity.

Households account for a significant fraction of overall energy consumption. Energy usage can be reduced by improving the efficiency of devices and optimizing their use as well as by encouraging people to change their behaviour towards a more sustainable lifestyle. In this study, we investigate patterns of domestic energy use in Carinthia (Austria) and Friuli-Venezia Giulia (Italy). In particular, we report the results of an online survey about electrical devices and their use in households. We outline typical scenarios in the two regions and discuss possible strategies to reduce the consumption of energy in these regions.

We investigate the statistics of the in-home power line communications channel in the broadband frequency range up to 300 MHz. The analysis is based on the results of an experimental measurement campaign in Italy during which we acquired more than 1300 channels. Firstly, we focus on the channel frequency response. We study the statistics of the amplitude (in dB). In particular, we infer the normal distribution of the quantity. Furthermore, we examine the statistics of the phase. Then, we study the line impedance. We investigate the statistics of the resistive and reactive component of the line impedance and their relation. Finally, we perform the joint analysis of the line impedance components and the amplitude of the channel frequency response.

We propose a random channel generator for in-home power line communications (PLC). We follow a statistical top-down approach and we model the multipath propagation effects of the PLC channel in the frequency domain. Then, we introduce the variability into the model, i.e., we let the parameters associated to the reflections be random, according to a certain statistics. Finally, we fit the model to the experimental data. We target the average path loss and root-mean-square (RMS) delay spread of the measured channels. According to this methodology, we show that the randomly generated channels are in good agreement with the experimental ones in terms of the main metrics.

We study the problem of determining the position of a node via the exploitation of 2-D angle of arrival estimation (azimuth and elevation), using orthogonal linear arrays. We also consider the presence of hardware impairments that include RF carrier frequency, phase, and DC offsets. We show that the algorithm is robust to the hardware impairments and it provides good performance for a wide range of distances from the receiver. Both the Cramer-Rao bound and simulation results are reported and they are compared with the root-MUSIC performance.

In this paper we consider the design of a linearly precoded MIMO transceiver based on filter bank (FB) modulation for transmission over broadband frequency selective fading channels. The modulation FB is capable of lowering the channel dispersion at sub-channel level. Nevertheless, the sub-channels experience some level of inter-symbol interference. Therefore, the pre-coder and the equalizer are designed exploiting the polynomial singular value decomposition (PSVD). In particular, we consider two types of FB system. The first system deploys maximal frequency confined pulses and it is referred to as filtered multitone (FMT) modulation, while the second uses maximal time confined pulses with rectangular impulse response, i.e., it corresponds to the conventional orthogonal frequency division multiplexing (OFDM) system. We compare the performance of the considered systems in terms of capacity over typical WLAN channels, showing that PSVD precoding with FMT can outperform the performance of precoded OFDM in the two-by-two antenna case especially for moderate to low SNRs.

We study the effect of phase noise in filter bank modulation systems. In particular, we analyze the FMT (Filtered Multitone) and the DMT (Discrete Multitone) system. While DMT uses a rectangular shape sub-channel pulse, the FMT system uses a frequency confined pulse. Approximated symbol error rate expressions for M-PSK and M-QAM constellations are derived for two types of receivers: the non-coherent receiver, and the one-tap coherent receiver. The results show that FMT with a root-raised-cosine pulse has some more robustness to phase noise w.r.t. DMT, although both systems are affected by phase noise especially with high order modulation.

We consider the use of a relay to provide capacity improvements and range extension for in-home power line communication networks. In particular, we focus on opportunistic relaying where the relay is exploited only if it provides improved capacity w.r.t. the use of direct transmission between the source and the destination. The relay applies a decode and forward scheme and the channel is shared in a time division multiple access mode. The performance is studied in statistically representative in-home power line communication (PLC) networks via the use of a statistical topology model together with the application of transmission line theory for the computation of the channel transfer function among network nodes. The statistical topology model allows determining the capacity improvements as a function of the relay position. Furthermore, we determine the optimal time slot duration for each considered relay configuration, as well as we propose the use of a globally optimal time slot duration that maximizes the average network capacity. The numerical results show that significant capacity improvement can be obtained via opportunistic relaying in in-home PLC networks. The gains are more significant for low SNR scenarios and for networks composed by sub-networks each connected to the main panel via a circuit breaker that introduces signal attenuation.

In this paper we propose a novel hybrid multicarrier architecture for wireless LAN (WLAN) applications. We refer to this architecture as hybrid filtered multitone (HFMT). Depending on the experienced channel condition, H-FMT switches between short orthogonal FMT (SO-FMT) modulation, and adaptive orthogonal frequency division multiplexing (A-OFDM). Extensive numerical results show that H-FMT could significantly improve the capacity and the robustness of the WLAN standard that deploys conventional OFDM. Furthermore, its efficient implementation has a complexity that is comparable to that of OFDM.

We consider the estimation of the direction of arrival (DoA) in the presence of hardware impairments that include the RF carrier frequency offsets, the phase offsets generated by an uncalibrated array, and the DC offset. The impairments model has been derived from the analysis of a hardware multiple antenna test-bed that uses direct down-conversion RF front-ends. The performance of the proposed algorithm has been investigated both analytically and via simulations. We show that the estimator provides good performance for a wide range of angles and it is robust to the hardware impairments.

The usual approach when designing an orthogonal frequency division multiplexing (OFDM) system, is to dimension the length of the cyclic prefix (CP) equal to the length of a typical "bad" (i.e., long) channel impulse response, so that both inter-symbol and inter-carrier interference are avoided for almost all channel realizations. However, such an approach does not maximize system capacity. It (a) wastes channel resources for relatively short channel impulse response realizations and (b) it is not necessarily optimal to completely eliminate interference. In this paper, we study the problem of designing the CP length for OFDM systems in a capacity-optimal way. To this end, we first present optimal and simplified metrics suitable to maximize capacity. Then, we apply those metrics and propose practical resource (bit-loading and OFDM sub-channel assignment) algorithms that include CP-length adaptation. We present numerical results for the example of a power line communication (PLC) OFDM system with typical indoor PLC channels that confirm the gains achievable with the proposed CP-length adaptation.

In this letter we study filtered multitone modulation (FMT) for broadband multiuser power line communications. We address the implementation problem, and we derive a novel efficient digital implementation of both the synthesis and the analysis filter bank. A simple fractionally spaced multiuser receiver is also proposed.

This paper presents further enhancements to a recently proposed air interface that concatenates an inner filtered multitone (FMT) modulator with transmission over multiple antennas, and an outer space-time cyclically prefixed discrete multitone (ST-CP- DMT) modulator with frequency domain data spreading. We focus on the uplink with asynchronous mobile devices. The contribution is threefold. Firstly, we show an efficient implementation of the transmitter. Secondly, we propose an efficient multiuser receiver architecture that requires a single polyphase filter bank and a concatenation of DFTs. Thirdly, we analyze time domain pre- equalization (TEQ) to shorten the equivalent channel impulse response between the FMT filter bank output and the ST-CP-DMT receiver. The proposed multiuser receiver outperforms the bank of synchronous single user receivers yet requiring less complexity. TEQ has the potentiality of improving performance in severely dispersive channels, and to increase transmission rate since the DMT stage can use shorter cyclic prefix (CP).

We address the challenges related to the development of very high speed power line communication (PLC) systems in the home environment. The development of such a technology is fundamental to realize the objective of reliably delivering new high speed services in the home environment in a network that integrates in a coordinated fashion also wireless systems. That is, an in-house network with the need of ldquonog new wiresrdquo. We start with an overview of the state of the art PLC technology, and then we describe our vision on application scenarios, and requirements. We address the problem related to transmission bandwidth, channel modeling, capacity evaluation as well as we describe novel advanced transmission technologies that enable reliable high speed transmission. We show that by enhancing current technology bandwidth up to 100 MHz, Gbps transmission is achievable.

In this paper we study the performance of Filtered Multitone (FMT) modulation systems in time-frequency selective fading channels. FMT generalizes the OFDM scheme through the deployment of a sub-channel shaping pulse. A general analysis framework is reported, and it is specialized to the case of using a sine pulse, a root-raised cosine pulse, and Gaussian pulse. Quasi-closed form expressions for the signal-to-interference (SIR) power ratio are derived. The results allow to benchmark the multitone system and understand how robust it is to frequency selective time-variant fading. We make a comparison with OFDM both in terms of SIR and bit-error-rate when single-tap subchannel equalization is used. It shows that FMT can have better performance than OFDM due to the better sub-channel spectral containment. We also discuss the usefulness of the SIR results on the design of the prototype pulse in a time-frequency selective fading channel.

We present a general analysis framework to analyze the performance of filtered multitone (FMT) modulation systems in time-frequency selective fading channels. FMT is a generalization of the OFDM scheme that deploys sub-channel shaping pulses. The results are specialized for several pulses: root-raised cosine, Gaussian, sine and rectangular (OFDM). They allow to benchmark the multitone system and understand how robust it is to frequency selective time-variant fading. An analysis both in terms of SIR and bit-error-rate is made. Remarks on the prototype pulse design are also reported. The better sub-channel spectral containment of FMT yields increased robustness compared to OFDM.

In this paper we analyze the performance of filtered multitone (FMT) modulation systems in time-frequency selective fading channels. FMT generalizes the OFDM scheme through the deployment of a sub-channel shaping pulse. A general analysis framework is presented, and it is specialized to the case of using a root-raised cosine pulse (FMT) and a rectangular pulse (OFDM). Quasi-closed form expressions for the signal-to-interference (SIR) power ratio are derived. The results allow to benchmark the multitone system and understand how robust it is to frequency selective time-variant fading. An analysis both in terms of SIR and bit-error-rate is made. It is shown that the better sub-channel spectral containment of the FMT yields better performance than OFDM.

We describe a powerline (PL) communication system that deploys wide band impulse modulation combined with direct sequence code division multiple access (DS-CDMA) to obtain a form of orthogonal modulation, and to allow for user multiplexing. Several novel frequency domain (FD) detection algorithms are proposed. They all have the capability of canceling the inter-code interference (ICI) and the multiple access interference (MAI) that is generated by the frequency selective PL channel. Practical estimation of the channel, and mitigation of impulse noise is also addressed. When channel coding is used, we also show that iterative techniques with feedback from the decoder better the channel estimation and detection performance. Simulation results prove that the scheme achieves high data rates in a PL channel in the presence of impulsive noise and MAI.

This paper deals with the design and implementation of a filtered multitone (FMT) modulation system. FMT generalizes the popular OFDM scheme through the deployment of subchannel shaping filters. We address the implementation problem and we describe (and compare in terms of complexity) two efficient implementation methods in the time domain (TD) and another one in the frequency domain (FD). We consider the design of the prototype pulse and we propose to synthesize it in the FD with a small number of frequency components. This allows to efficiently implement the FMT scheme through the FD architecture. A simple FD equalization scheme is also proposed and its performance is evaluated in typical wireless fading channels. The results show that FMT performs better than OFDM with and without channel coding

In this paper, we present a novel transmission technology approach for application in the asynchronous multiple-access wireless channel (uplink). It is based on the concatenation of an inner filtered multitone (FMT) modulator with transmission over multiple antennas, and an outer space-time cyclically prefixed discrete multitone (ST-CP-DMT) modulator. The inner modulator is used to efficiently realize frequency-division multiplexing of the users by partitioning the FMT subchannels among them. The outer modulator copes with the residual subchannel intersymbol interference and it further implements a form of transmit diversity. Frequency and space diversity is exploited via direct sequence (DS) data spreading across the DMT tones. The design parameters are flexible and are chosen to make the proposed air-interface robust to the time and frequency offsets between uplink users, as well as to the channel time-frequency selectivity. Furthermore, the ST-CP-DMT modulator with DS spreading provides sensible performance gains. In particular, it yields a diversity gain for the users that transmit at low rate and occupy a fraction of the overall spectrum.

In this paper we propose and investigate a frequency domain approach to channel estimation, and detection for ultra wide band (UWB) direct sequence code division multiple access (DS-CDMA) systems. The channel estimation and detection approach is single user based, and operates in the frequency domain. In the presence of multiple access interference (MAI) the algorithm is appropriately modified to include the capability of canceling the interference through the exploitation of its frequency domain correlation.

In this paper, we investigate the best attainable performance for filtered multitone modulation (FMT) in time-variant frequency-selective fading channels when optimal maximum-likelihood (ML) detection is deployed. FMT generalizes the popular orthogonal frequency division multiplexing (OFDM) scheme through the deployment of subchannel shaping filters. The performance limits are derived by extending to this multichannel context the matched filter bounding technique. We first conduct an exact calculation for the average and the distribution of the matched filter error rate bound. Then, we follow a numerical procedure that overcomes the problems of accuracy and ill conditioning in the implementation of the exact method. This study allows for an analytical treatment of the diversity effect on performance as a function of the time/frequency selectivity of the channel. It is found that FMT is a diversity transform that is capable of yielding coding gains and time/frequency diversity gains as a function of the subcarrier spacing and the subchannel filter shape.

This paper deals with synchronization, channel estimation, and detection in ultrawideband (UWB) biphase impulse-modulated systems. We address both the single-user scenario, and the multiuser scenario assuming a direct-sequence code-division multiple-access (DS-CDMA) scheme. The users' binary-codeword elements modulate short-duration pulses. Codewords span a transmission frame. Frames are separated by a guard time to cope with the channel time dispersion. The detection approach is single-user-based and it operates in the frequency domain (FD). The algorithm first acquires frame synchronization with the desired user. It runs a discrete Fourier transform (DFT), and it performs FD channel estimation for the desired user via a recursive least-squares (RLS) algorithm. Finally, detection is directly accomplished in the FD. Frame synchronization is achieved in the time domain with a two-step procedure that first acquires coarse timing, then finely estimates where the desired user's signal energy is located. In the presence of multiple-access interference (MAI), the algorithm is appropriately modified to include the capability of canceling the interference through the exploitation of its FD correlation. Simulation results show that the proposed approach exhibits fast convergence, and high performance with and without synchronous/asynchronous MAI.

In this paper, we study the effects of phase noise in a multicarrier system. We show that the phase noise introduces interference components, and we evaluate their second order statistics. The analysis is then applied to two particular multicarrier architectures: discrete multitone (DMT) modulation, and filtered multitone (FMT) modulation. For the DMT case, our results are in agreement with other related work that considers DMT only. For FMT modulation, we demonstrate that the phase noise power spectral density as well as the frequency response of the prototype filters play a key role on the resulting interference power value. Finally, we show that the analytical performance results are close to the simulation results.

Decoding of space-time codes in frequency-selective fading channels is considered. The approach is based on iterative soft-in soft-out equalization and decoding. It is applicable to space-time coded systems that deploy symbol/bit interleavers. We focus on the equalization stage by extending the Ungerboeck equalizer formulation to a multiple-input multiple-output time-variant channel. The resulting structure comprises a bank of matched filters, followed by an a posteriori probabilities calculator that runs the Bahl-Cocke-Jelinek-Raviv/maximum a posteriori algorithm with an appropriate metric. Simulation results are reported for space-time bit-interleaved codes designed over the enhanced data rates for GSM evolution (EDGE) air interface.

We consider a multitone multiple access wireless system where users are multiplexed by the assignment of sub-sets of the available tones. The information signals of distinct users are multicarrier modulated and propagate through asynchronous frequency selective fading channels, i.e., uplink. In this scenario intersymbol, intercarrier, and multiple access interference arise. We consider simple single user detection and study its performance in terms of outage probability. In particular we investigate the effect on outage probability of the choice of the sub-channel transmit filters and the tone allocation strategy.

Space-time coding over frequency selective time-varying fading channels is considered. The approach is based on deploying bit/symbol interleaved space-time codes. Decoding is based on the iterative concatenation of a soft-in soft-out MIMO equalizer with a soft-in soft-out decoder. The equalizer structure comprises a bank of matched filters followed by a maximum a posteriori processor with an appropriate metric. It does not require multiple receive antennas. Methods to reduce its complexity are devised. Finally, performance results are shown for ST bit-interleaved convolutional codes designed for the EDGE air interface with two transmit-single receive antennas.

Space-time coded architectures that deploy multiple transmit-receive antennas with interleaved space-time codes are considered. Decoding is based on the iterative concatenation of a demapping stage with a decoding stage. We describe several simplified demapping algorithms based on array processing methods that can include either soft or hard feedback information. These algorithms are particularly suited for application in space-time architectures that deploy bit-interleaved convolutional codes and transmission over block fading channels. Performance results show that space-time bit-interleaved convolutional codes with turbo array processing provide high coding and spatial/temporal diversity gains.

A space-time serial concatenated coding approach for spectrally efficient and reliable communications over fading channels is presented. The approach is based on bit-interleaved convolutionally coded modulation with multiple transmit antennas. The decoding problem of such a scheme is addressed in frequency selective fading channels, where an iterative procedure is proposed. At the first step a multiple-soft-in multiple-soft-out maximum a posteriori equalizer is deployed. Then, a soft-in soft-out maximum a posteriori convolutional decoder follows after deinterleaving. Soft information is exchanged between the decoder and the equalizer through multiple equalization and decoding iterations. A 2 bits/s/Hz system deploying two transmit antennas is presented. Simulation results show that, with just one receive antenna, few decoding iterations yield significant BER/FER gains in both frequency selective block fading and frequency selective fast fading over the uncoded system with dual receive diversity.