1,721,089 research outputs found
Time domain estimation of MT impedance tensor
No full textThe spectral analysis of magnetotelluric (MT) data for impedance tensor estimation requires the stationarity of measured magnetic (H) and electric (E) fields. However, it is well known that noise biases time-domain tensor estimates obtained via an iterative search by a descent algorithm to determine the least-mean-square residual between measured and estimated E data obtained from H data. To limit the noise that slows down, or even prevents convergence, the steepest descent step size is based upon the statistics of the residual. The time-domain technique is applied to data sets from the EMSLAB Juan de Fuca project as well as to data from a southern Italian site. -from Autho
2-D phase unwrapping and phase aliasing
No full textThe phase of complex signals is measured modulo-2Ï (wrapped phase); continuous-phase information is obtained by adding properly chosen multiples of 2Ï shift to the wrapped phase. Unwrapping searches for the 2Ï combinations that minimize the discontinuity of the unwrapped phase as only the unwrapped phase can be analyzed and interpreted by further processing. The key problem of phase unwrapping is phase aliasing, a condition mainly caused by rapid phase variations. The extension of the one-dimensional (1-D) phase unwrapping algorithms to a two-dimensional (2-D) domain by 1-D slicing gives unsatisfactory results even in the presence of low-phase aliasing, whereas 2-D phase unwrapping deals with the complete problem, overcoming the limitations of 1-D unwrapping. The 2-D unwrapped phase is obtained as the solution of a variational problem that minimizes the differences between the gradients of the wrapped and unwrapped phase. -from Autho
Adaptive optical processing for wideband hybrid beamforming
No full textMultiuser centralized radio access networks (C-RANs) need to adapt to time-varying radio environments, and adaptation is advantageously split between remote antenna units (RAUs) and centralized baseband units (BBUs) to minimize the required fronthaul throughput. To this end, hybrid beamforming to spatially multiplex signals to/from a pool of users is split between RAU and BBU, and optical analog signal processing can be performed at the RAU. The goal here is to reduce the number of fronthaul channels and the corresponding number of analog/digital converters at the BBU in wideband (>100 MHz) millimeter wave (mmWave) radio communication. An algorithm for hybrid beamforming design is developed, and shown to approach the performance of ideal digital beamforming with a number of fronthaul channels comparable to the number of simultaneously served users rather than with the number of array elements. To cope with the radio-access of multiple users, optical analog processing is made adaptive by tuning delay lines built with optical ring resonators (ORRs). The tunability of analog beamforming by means of thermo-optic phase shifters is designed for time-varying configuration compliant to the 5G new radio specifications and the performance degradation of beamforming transients due to the tunability of optical components is assessed
Multi-layer detection/tracking for monostatic ground penetrating radar
No full textIn monostatic ground penetrating radar (GPR) the interfaces profile can be estimated from echoes amplitude and time of delay (TOD) using a layer stripping inversion algorithm. Our aim is to establish a reliable processing sequence for layer stripping inversion by estimating echoes TOD that keeps into account the layers lateral continuity, and by tracking the corresponding interfaces. Here we propose first an algorithm for multitarget tracking and then we describe the application of detection/tracking to 1 ns pulse monostatic GPR. The system is used to estimate layer thicknesses of asphalt and concrete in pavement profiling. Detection/tracking shows a better recognition capability of the lateral continuity in near surface interfaces with respect to algorithms that employ only local detection of echoes
Analog MIMO Radio-Over-Copper Downlink with Space-Frequency to Space-Frequency Multiplexing for Multi-User 5G Indoor Deployments
Full text linkRadio access network (RAN) centralization is at the basis of current mobile networks, in which BaseBand Units (BBUs) and radio antenna units (RAUs) exchange over the FrontHaul (FH) digitized radio-frequency signals through protocols such as the common public radio interface. However, such architecture, as it stands, does not scale to the demands of multiple-antennas 5G systems, thus leading to drastic RAN paradigm changes. Differently from digital RAN architectures, we propose to overcome bandwidth/latency issues due to digitization by employing an all-analog FH for multiple-antenna RAUs based on the analog radio-over-copper (A-RoC) paradigm. The A-RoC is an alternative/complementary solution to FH for the last 200 m, such as for indoor, to reuse existing local area network (LAN) cables with remarkable economic benefits. Although LAN cables contain 4 twisted-pairs with up to 500 MHz bandwidth/ea., their usage is limited by cable attenuation and crosstalk among pairs. This paper demonstrates that a judicious mapping of each radio-frequency signal of each antenna onto a combination of cable pair-frequency allocations, referred to as space-frequency to space-frequency multiplexing, optimized together with the design of the digital precoding at the BBU, substantially mitigates the cable impairments. The LAN cables can be exploited for last 100-200 m analog transport FH to meet the requirements of 5G indoor networks
Multitarget detection/tracking of echoes with known waveform: algorithm and applications
No full textCancelling directional EM noise in magnetoteilurics
No full textThe prospecting of densely urbanized areas by the measurement of magnetic and electric natural fields is severely hampered by electromagnetic (EM) noise. Active manâmade EM noise sources can generally be considered fixed in space, thus affecting the magnetotelluric (MT) signals of a measuring site mainly along their polarization directions. Taking advantage of the impulsive nature of polarized EM noise, a timeâdomain directional noise cancelling (DNC) technique is proposed. The comparison of noisy data with data predicted, using a low noise reference signal or with data interpolated whenever no reference is available, allows the detection of the most likely noise sources with prevailing directional patterns using a Bayes's criterion. The DNC approach is general and can be adapted, depending on the reference signal used (singleâsite or remoteâreference). In field data, hodograms of the prediction residuals basically confirm the directional noise model assumed in DNC. An example is presented in which the DNC technique has been applied to a singleâsite MT survey carried out in northern Italy, where the signal was heavily corrupted by noise with prevailing directional properties due to the densely urbanized area. MT apparent resistivities and phases obtained at the site of the survey before and after DNC are presented and discussed. Copyright © 1995, Wiley Blackwell. All rights reserve
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