Francesco Benedetto

Dynamic LOS/NLOS Statistical Discrimination of Wireless Mobile Channels

This paper presents the problem of identifying whether a received signal at a base station is due to a line-of-sight (LOS) transmission or not (NLOS). This is a first step towards estimating the mobile stations location. We formulate the NLOS identification problem as a binary hypothesis test by exploiting the Rician factor estimation. In particular, results from wireless environments with simulated geometry showed that the new test can decide for a LOS or NLOS condition using a small amount of samples. Therefore, changes from NLOS to LOS propagation can also be tracked quickly. This information is of high significance for location purposes in a wireless cellular network since time-of-arrival (TOA) and time-difference-of-arrival (TDOA) information based on LOS connections can be weighted stronger in a location computing algorithm and hence can lead to higher positioning accuracy. Otherwise, if the connection is identified as NLOS it can be useful to adopt a 2-D signal processing (space-time processing) strategy with an antenna array, instead of using the high complexity of the TOA and TDOA methods.

Reliability of signal processing technique for pavement damages detection and classification using ground penetrating radar

Ground penetrating radar (GPR) signal processing is a nondestructive technique, currently performed by many agencies involved in road management and particularly promising for soil characteristics interpretation. The focus of this paper is to assess the reliability of an optimal signal processing algorithm for pavement inspection. Preliminary detection and subsequent classification of pavement damages, based on an automatic GPR analysis, have been performed and experimentally validated. A threshold analysis of the error is carried out to detect possible damages and check if they can be predicted, while a second threshold analysis determines the nature of the damage. An optimum detection procedure is performed. It implements the classical Neyman-Pearson radar test. All the settings needed by the procedure have been estimated from training sets of experimental measures. The overall performance has been evaluated by looking at the usual receivers operating characteristic. The results show that a reasonable performance has been achieved by exploiting the spatial correlation properties of the received signal, obtained from an appropriate analysis of GPR images. The proposed system shows that automatic evaluation of subgrade soil characteristics by GPR-based signal analysis and processing can be considered reliable in a number of experimental cases.

GPR applications for geotechnical stability of transportation infrastructures

Nowadays, severe meteorological events are always more frequent all over the world. This causes a strong impact on the environment such as numerous landslides, especially in rural areas. Rural roads are exposed to an increased risk for geotechnical instability. In the meantime, financial resources for maintenance are certainly decreased due to the international crisis and other different domestic factors. In this context, the best allocation of funds becomes a priority: efficiency and effectiveness of plans and actions are crucially requested. For this purpose, the correct localisation of geotechnically instable domains is strategic. In this paper, the use of Ground-Penetrating Radar (GPR) for geotechnical inspection of pavement and sub-pavement layers is proposed. A three-step protocol has been calibrated and validated to allocate efficiently and effectively the maintenance funds. In the first step, the instability is localised through an inspection at traffic speed using a 1-GHz GPR horn launched antenna. The productivity is generally about or over 300 Km/day. Data are processed offline by automatic procedures. In the second step, a GPR inspection restricted to the critical road sections is carried out using two coupled antennas. One antenna is used for top pavement inspection (1.6 GHz central frequency) and a second antenna (600 MHz central frequency) is used for sub-pavement structure diagnosis. Finally, GPR data are post-processed in the time and frequency domains to identify accurately the geometry of the instability. The case study shows the potentiality of this protocol applied to the rural roads exposed to a landslide.

GPR experimental evaluation of subgrade soil characteristics for rehabilitation of roads

One of the most crucial problem in roads rehabilitation regards the pavement damage. Usually it is easy to localize the damage, but it is always difficult to identify the causes. The rehabilitation can be compromised, if the cause is not removed. The GPR technique is used by many Agencies involved in roads management. It is nondestructive and it is promising for soil characteristics interpretation, such as moisture or density. A classification of pavement damage, based on GPR analysis, is already performed and experimentally validated. The causes of damage are often referable to water intrusion in subgrade or clay intrusion in sandy subgrade. This is why we principally investigate how the moisture and the soil density influence the dielectric constant. The outcomes of a laboratory experimental survey are here discussed. Different soils have been considered. The GPR responses of each soil have been investigated, considering different moistures. The dielectric properties are highly correlated with the water content and the water status in soil. A significant correlation between dielectric properties and soil density is shown; this correlation is not so relevant as the previous. Any generalization is not reliable, but the study proves that the GPR evaluation of subgrade characteristics is possible.

A self-synchronizing method for asynchronous code acquisition in band-limited spread spectrum communications

This paper addresses the problem of initial synchronization of pseudo-noise code. A new code acquisition technique for spread-spectrum communication systems using band-limited chip waveforms is presented. Unlike conventional power detector based on testing the estimated maximum of the ambiguity function, the devised detector exploits a fast parabolic interpolation, running on three estimated ambiguity samples in the neighborhood of the coarse estimate. Performance analysis is carried out in comparison with conventional detector. Mathematical expressions for the probability of false alarm and detection are derived. They are numerically evaluated, under operating settings, by a reduced Tayloriquests expansion up to the second order. The theoretical results, substantiated by computer simulations, have evidenced that the devised method is well suited for asynchronous spread-spectrum communications. In particular, the acquisition performance depends on the actual offset between the received and the reference code waveforms, which are randomly distributed (in chip-asynchronous systems) within one sampling period. In fact, the parabolic interpolation technique outperforms the conventional detector for a wide range of code offsets because it is able to self-synchronize the testing variable around the true offset.

Remote Sensing of Soil Moisture Content by GPR Signal Processing in the Frequency Domain

This paper presents a method, based on ground penetrating radar (GPR) signal processing in the frequency domain, to estimate moisture content in a porous medium without preventive calibration. Several indicators based on high order moments are extracted from the GPR spectra and their dependency on the moisture content is evaluated. Experimental results confirm the theoretical expectations and show the effectiveness of the proposed approach to estimate soil moisture content.

A Unified Approach for Time-Delay Estimators in Spread Spectrum Communications

This paper addresses the problem of time-delay estimation and proposes an effective time-delay estimator for spread-spectrum communications. The main contribution of our work is twofold: first, we define a new objective function that analytically expresses the performance of different estimation criteria. Second, we introduce a new estimator that outperforms the conventional approaches. In particular, we develop a unified approach, deriving the performance trends of several time-delay estimators by one parametric closed form expression. Furthermore, we propose a new estimator that exploits a fast interpolation, running on few samples in the neighborhood of the coarse estimate, i.e. the (abscissa of the) estimated maximum of the ambiguity function. Mathematical expressions for bias and variance of the estimation error are derived and numerically evaluated by reduced Taylors expansions up to the second order. The theoretical results, substantiated by computer simulations, have evidenced that the devised method is well suited for spread-spectrum satellite communications.

A New Test for Initial Code Acquisition of Correlated Cells

This paper proposes a new testing procedure, namely, the twin test, for performance improvements of initial code acquisition, taking into account several correlated cells at once. We derive a closed-form expression to analytically express the system probabilities in terms of a new function: the extended modified generalized-Q (EMGQ) function. The analytical results, which are substantiated by computer simulations, show that the twin test can offer better performance than the conventional scheme based on the cell-by-cell detection, with a negligible increase in the computational complexity of the system.

A Blind Equalization Algorithm Based on Minimization of Normalized Variance for DS/CDMA Communications

This paper proposes a blind equalizer that pursues the maximization of a novel objective function. It consists of the ratio between the square of the mean signal power and the variance of the signal power. In this paper, important prepositions are first mathematically stated. The devised equalizer is asymptotically equivalent to the well-known constant-modulus algorithm (CMA) and the Kurtosis maximization algorithm (KMA) because they pursue the same ldquoRicianityrdquo criterion already employed in the ldquoRayleigh-nessrdquo test for spread-spectrum code acquisition. The performance of the addressed equalizers is then investigated by focusing on direct-sequence code-division multiple-access (DS/CDMA) communication environments in a downlink scenario. In particular, we have evidenced the effectiveness of the presented equalizer in the numerical examples in terms of robustness against the effect of interference, as well as in terms of convergence rate, in spite of a small amount of extra processing.

A Fast Time-Delay Estimator of PN Signals

This work proposes an effective time-delay estimator for PN satellite signals, exploiting a fast triangular interpolator, running on three estimated ambiguity samples in the neighborhood of the coarse estimate. Performance analysis (theory and simulation) is carried out in comparison with conventional approaches based on the interpolation, usually carried out by (time-consuming) narrow-band over-sampling or (fast) fitting of few samples of a smoothed function of the ambiguity function around its maximum. The theoretical results, substantiated by computer simulations, have evidenced that the devised method outperforms the conventional estimator for all the timing offsets and is well suited for satellite spread-spectrum communications.