0000000000585142
AUTHOR
G. Garbo
showing 27 related works from this author
MUSIC-based modal channel estimation for wideband OFDM-OQAM
2008
Orthogonal frequency division multiplexing based on offset quadrature amplitude modulation (OFDM-OQAM) over wideband frequency selective multipath channels suffers from inter-symbol interference (ISI) and inter-carrier interference (ICI) that degrade its performance. Channel estimation and equalization are needed to combat these interferences. In this paper a novel channel estimator for passband OFDM-OQAM signaling over wideband multipath channels, which is based on multiple signal classification (MUSIC) with the Spatial Smoothing technique is presented. Numerical simulation results are presented in the low number of subcarriers, i.e. wideband, scenario.
Simple method for limiting delay of optimized interleavers for turbo-codes
2000
An iterative interleaver growth algorithm is extended to allow the delay and required memory of designed interleavers to be halved with negligible performance loss. The original algorithm is efficient for two-component parallel concatenated turbo-codes with given constituent encoders that are optimum with regard to a cost function satisfying some mild conditions. However, it is only actually optimum if the selected set of patterns is representative of low-weight turbo-codewords. The new interleaver uses all terminating error patterns having an input weight not greater than a fixed IWX and single-coder output weight not greater than WX is proposed.
Self-validating bundles for flexible data access control
2016
Modern cloud-based services offer free or low-cost content sharing with significant advantages for the users but also new issues in privacy and security. To protect sensitive contents (i.e., copyrighted, top secret, and personal data) from the unauthorized access, sophisticated access management systems or/and decryption schemes have been proposed, generally based on trusted applications at client side. These applications work also as access controllers, verifying specific permissions and restrictions accessing user’s resources. We propose secure bundles (S-bundles), which encapsulate a behavioral model (provided as bytecode) to define versatile stand-alone access controllers and encoding/d…
Wireless OFDM-OQAM with a small number of subcarriers
2008
Orthogonal frequency division multiplexing based on offset quadrature amplitude modulation (OFDM-OQAM) is a multicarrier signaling technique which trades off robustness for spectral efficiency when compared to conventional OFDM with a cyclic prefix. In this paper, a novel matrix model for passband OFDM-OQAM signaling with a small number of subcarriers over a multipath frequency selective fading channel is presented. Specifically, in OFDM-OQAM a frequency selective channel is divided into many smaller but still frequency selective overlapping channels, so approximating the frequency response of a subchannel by the channel frequency response sampled at the subcarrier frequency may be inadequa…
An Improved Detection Technique for Cyclic-Prefixed OFDM
2010
A novel Orthogonal Frequency Division Multiplexing detection technique compatible to standard (e.g. Wireless LAN) transmitters is proposed. It features enhanced error-rate performance with flexible computational complexity and robustness to imperfect channel estimation. It is based on exploitation of the redundancy available in the cyclic prefix after cancellation of interference from the preceding block. In order to show the effectiveness of our proposal, an analysis of computational complexity and a number of comparisons to the standard per-subcarrier receiver and a previously existing method in terms of error rates are reported.
An OFDM Receiver Exploiting Multipath Diversity
2008
We propose a novel receiver structure, to be employed with standard Orthogonal Frequency Division Multiplexing transmitters, capable of exploiting the multipath diversity of wireless channels. The proposed technique is based on cancellation of inter-block interference arising in the guard interval and linear detection techniques. It features a low implementation complexity and is easily generalized to MIMO systems and non-linear detection techniques.
Statistical analysis of RaptorQ failure probability applied to a data recovery software
2014
In this work, we have implemented a data recovery software integrating the most recent rateless codes, i.e., RaptorQ codes. Thanks to the above-mentioned software, it is possible to recover data loss occurring on several kinds of network conditions. We have performed a statistical analysis of failure probabilities at several configurations of RaptorQ parameters. We have found a good agreement with the theoretical values of a random linear fountain code over Galois Field GF(256). Moreover, we have shown that the probability of having a certain number of failed decoded source blocks - when sending a fixed size file - follows a Poisson distribution.
Efficient Simulation of Orthogonal Multicarrier Transmission over Multipath Fading Channels
2011
Filterbank orthogonal multicarrier transmission schemes, such as OFDM/OQAM, are currently under intense study for their spectral efficiency and suitability for the physical layer of Cognitive Radio. Nonetheless, the mathematical description of the signal is cumbersome, and closed form expressions for performance figures are not available, so performance analysis on fading channels has to be performed by means of simulations. We propose an algorithm for simulating the received signal over multipath frequency selective fading channels, based on Taylor series expansion of the channel transfer function. The proposed method is compared to the state-of-the-art FFT-based method in terms of computa…
A simple joint estimation-detection technique for OFDM systems
2005
In this work a simple approach for the joint estimation-detection in a frequency selective severe fading environment of OFDM signals adopting PSK constellations is presented. A linear predictor of suitable order is adopted for the channel estimation in the frequency domain. The predictor coefficients are estimated on the basis of a sample estimation of the autocorrelation of the channel frequency response, aided by a preliminary differential decoding, in a blockwise manner. The detection technique proposed here is based on a simple tree search where a small number of best survivor paths are maintained at each step. Despite the simplicity of above detection approach, the simulation results s…
Image-based MRI Gradient Estimation
2017
In order to reduce geometric distortion phenomena in MR images, every MRI system main magnet undergoes a shimming process. Since this process aims at optimizing magnetic field homogeneity within a so-called uniformity sphere, image quality outside this sphere is neglected. Since the fields vary smoothly in space, MR signal-to-noise ratio is still non-zero just outside the uniformity region, but correction of MR image distortion fails due to lack of magnetic field knowledge outside it. We propose a novel algorithm for measuring all the fields involved in the generation of images. Our proposal is based on exploitation of the distortion which can be observed in images of a known phantom. The p…
Error mitigation using RaptorQ codes in an experimental indoor free space optical link under the influence of turbulence
2015
In free space optical (FSO) communications, several factors can strongly affect the link quality. Among them, one of the most important impairments that can degrade the FSO link quality and its reliability even under the clear sky conditions consists of optical turbulence. In this work, the authors investigate the generation of both weak and moderate turbulence regimes in an indoor environment to assess the FSO link quality. In particular, they show that, due to the presence of the turbulence, the link experiences both erasure errors and packet losses during transmission, and also compare the experimental statistical distribution of samples with the predicted Gamma Gamma model. Furthermore,…
Diagonal space time hadamard codes with erasure decoding algorithm
2005
A major challenge in the area of space time (ST) codes is to find codes suitable for efficient decoding, thus overcoming the problem of many existing ST code designs which require maximum-likelihood (ML) decoding. A solution could be to apply single-input single-output (SISO) channel codes and theory over temporal channel fading to the multi-input single-output (MISO) code construction and classical suboptimum decoding methods. For these purposes, an ST code construction which allows the use of efficient decoding algorithms is described. We propose a concatenated code, where the inner code is the diagonal ST Hadamard (D-STH) code with Paley constructions and the outer code is an algebraic b…
Interference Cancellation for LoRa Gateways and Impact on Network Capacity
2021
In this paper we propose LoRaSyNc (LoRa receiver with SyNchronization and Cancellation), a second generation LoRa receiver that implements Successive Interference Cancellation (SIC) and time synchronization to improve the performance of LoRa gateways. Indeed, the chirp spread spectrum modulation employed in LoRa experiences very high capture probability, and cancelling the strongest signal in case of collisions can significantly improve the cell capacity. An important feature of LoRaSyNc is the ability to track the frequency and clock drifts between the transmitter and receiver, during the whole demodulation of the interfered frame. Due to the use of low-cost oscillators on end-devices, a s…
Rateless Codes Performance Tests On Terrestrial FSO Time-Correlated Channel Model
2012
Free Space Optics (FSO) links are affected by several impairments: optical turbulence, scattering, absorption, and pointing. In particular, atmospheric optical turbulence generates optical power fluctuations at the receiver that can degrade communications with fading events, especially, in high data rate links. A way to mitigate FSO link outages can be to add a coding to communications. Nevertheless, in order to study innovative solutions (software or hardware) and to improve the FSO link performance it needs accurate testing models. In this paper we describe an accurate time-correlated channel model able to predict random temporal fluctuations of optical signal irradiance caused by optical…
Recovery Capabilities of Rateless Codes on Simulated Turbulent Terrestrial Free Space Optics Channel Model
2013
Free Space Optics (FSO) links are affected by several impairments: optical turbulence, scattering, absorption, and pointing. In particular, atmospheric optical turbulence generates optical power fluctuations at the receiver that can degrade communications with fading events, especially in high data rate links. Innovative solutions require an improvement of FSO link performances, together with testing models and appropriate channel codes. In this paper, we describe a high-resolution time-correlated channel model able to predict random temporal fluctuations of optical signal irradiance caused by optical turbulence. Concerning the same channel, we also report simulation results on the error mi…
An Improved Receiver Architecture for Cyclic-Prefixed OFDM
2009
A novel Orthogonal Frequency Division Multiplexing receiver architecture to be employed with standard (e.g. Wireless LAN) transmitters is proposed. It features enhanced error-rate performance with flexible computational complexity and robustness to imperfect channel estimation. It is based on exploitation of the redundancy available in the cyclic prefix after cancellation of interference from the previous block. In order to show the effectiveness of our proposal, a number of comparisons to the standard per-subcarrier receiver and a previously existing method are reported.
Joint LMMSE equalizer for HSDPA in full-rate space time transmit diversity schemes
2005
This contribution presents a joint linear minimum mean square error (LMMSE) equalizer for full-rate space-time transmit diversity multi-code schemes based on W-CDMA, featuring two and four transmit antennas. Specifically, high-rate, high load systems are targeted, in order to analyze the high speed downlink packet access (HSDPA) of 3GPP Release 6. We derive an equivalent transmission scheme to equalize the received sufficient statistic in a single stage. To reduce the effects of multipath and multiuser interference, and to provide spatial and frequency diversity at the receiver, an LMMSE equalizer is employed. Computer simulations confirm that the proposed schemes achieve robust performance…
A study on spectral optimisation in partial response CPM signals
1995
An optimisation technique for the minimisation of the effective bandwidth in partial response CPM signals is described. The minimum Euclidean distance is used as optimisation constraint because the bit error probability is a function of this parameter for high values of signal to noise ratio. The procedure has been implemented for a correlation length corresponding to two signalling intervals. The optimisation problem leads to a system of two nonlinear differential equations for the pulse shape, together with some boundary conditions. Numerical solution of the differential equations has been performed; initial conditions have been adjusted, to satisfy the boundary conditions using an iterat…
A fully automated method for accurate measurement of geometrical distortion in magnetic resonance imaging of a 3D-lattice phantom
2019
Abstract This paper describes an automated method for extracting the apparent positions of fiducial points from 2D or 3D images of a phantom. We consider a 3D-lattice phantom for two main reasons: first, ease of manufacture and isotropy of its structure with respect to coordinate projections; second, a connected structure allowing to uniquely assess the adjacency relationship between fiducial points even if geometric distortions arising from main magnet inhomogeneity and gradient fields non-linearity is severe as observed in open-bore systems. In order to validate our proposed method and compare different choices for the parameters of our phantom (i.e. number and distance between grids and …
The structure of the state representation of shift invariant controllable and observable group codes
2000
AbstractIn this paper an investigation on the structure of the canonical trellis section of shift invariant, l-controllable and m-observable group codes is carried out. Necessary and sufficient conditions for a set of group homomorphisms in order that they represent the trellis section of this class of codes are established.
Orthogonal Multicarrier Transmission with Modal Channel Estimation
2009
A novel multi-carrier orthogonal transmission scheme is presented. While being simpler to implement, it has a spectral efficiency and design parameters similar to those of Orthogonal Frequency Division Multiplexing based on Offset Quadrature Amplitude Modulation (OFDM/OQAM). A parametric channel estimation technique is subsequently reported. The proposed technique is based on an algorithm obtained from classic Multiple Signal Classification (MUSIC) by relaxation of the hypothesis on the number of measurements with respect to the number of sensors. Numerical simulations show that our proposal outperforms previous works in this field.
MUSIC-LS Modal Channel Estimation for an OFDM-OQAM System
2008
Orthogonal frequency division multiplexing based on offset quadrature amplitude modulation (OFDM-OQAM) signaling over frequency selective multipath channels shows inter-symbol interference (ISI) and Inter-Channel Interference (ICI) that degrade its performance. Channel equalization and channel estimation are needed to combat these intrinsic interferences. In this paper a novel modal channel estimator based on the MUltiple signal classification (MUSIC) and least squares (LS) algorithms for a wideband passband OFDM-OQAM signaling over static multipath channels is presented. The effects of the frequency selective channel on the received signal are described considering a wideband OFDM-OQAM sys…
Search for scalar leptoquarks from Z$^0$ decays
1992
We have searched for pair produced scalar leptoquarks each decaying to a quark and a charged lepton in a sample of 116 000 hadronic Z0 events produced at LEP. No candidate was detected and cross section and branching ratio limits are set for the above process at 95% CL. Mass limits are found to be about 42 GeV/c2 depending only slightly on the models used and a coupling times branching ratio exclusion line is drawn for a scalar leptoquark with a free coupling. We have also probed the mass region above 45 GeV/c2 for a singly produced scalar leptoquark and set limits on the cross section and the coupling lambda(2)/4-pi up to 60 GeV.
Fading mitigation coding techniques for space to ground free space optical communications
2014
In this manuscript, a Geostationary satellite-toground Free Space Optics (FSO) downlink channel model has been implemented, which is able to predict temporal irradiance fluctuations caused by scintillation at a wide range of turbulence conditions and for different values of the zenith angle. In order to mitigate fading events that occur in FSO communications, we have also tested the performance of three different families of Rateless Codes (Luby Transform, Raptor and RaptorQ) into our model and found that RaptorQ is the best candidate to mitigate errors in FSO links. Keywords— Optical Wireless Communications; Space-toGround FSO links, time-series, rateless codes; fading mitigation
Design of efficient codes for the AWGN channel based on decomposable binary lattices
1998
This work is concerned with the use of binary decomposable lattice codes over the QAM Gaussian channel. First, we investigate the structure of such class of lattices: we derive consistency conditions for the binary codes appearing in their decomposition and express their nominal coding gain and some bounds for their error coefficient in terms of the parameters of the component codes. Then we describe a general multistage bounded‐distance decoding algorithm with low complexity and we evaluate its performance. Finally, we develop a design example and report the corresponding simulation results; as a reference some comparisons with standard TCM codes are also presented.
Channel Impairment Effects on TPRC for Multicode V-BLAST with CD-SIC
2006
In third generation communication systems currently in standardization process, a number of multi-antenna schemes, derived from the well-known Bell Labs layered space-time (BLAST) approach, are being considered in order to improve performance in both communication reliability and system throughput. Among these schemes there is growing interest on schemes with feedback to aid the transmitter side (usually the Base Station) in adapting the transmission parameters, as modulation and coding rate and/or antenna/code power allocation, to the channel conditions. One of the proposed schemes is the Transmission Power Ratio Control (TPRC) for Multi-code Vertical-BLAST (with code domain serial interfe…
A software receiver phase lock loop analysis and design to implement adaptive phase tracking using a finite impulse response loop filter
2009
In this paper we analyze the design of a digital Phase Lock Loop (PLL) for a Global Navigation Satellite System (GNSS) software receiver. Even if the topic of phase tracking has been widely studied, we found it useful to provide a short walkthrough for the design of a PLL in a real software receiver, avoiding to introduce the common theoretical phase-based model and aiming to the practical implementation of a system that deals with frequencies. Nonetheless, our analysis and design will grow away from the canonical approach, in the way that we will not resort to analog filter theory. The result is a PLL which is more reactive than the ones usually found in literature and that implements a si…