Santiago Zazo - Academia.edu (original) (raw)

Papers by Santiago Zazo

To better utilize the capacity of the twisted-pair access networks, operators deploying very high... more To better utilize the capacity of the twisted-pair access networks, operators deploying very high-speed digital subscriber line (VDSL) systems need accurate parameters for power back-off (PBO). However, VDSL standards give almost no guidance on how these parameters should be established for a particular network. In this paper we present a new technique for optimizing PBO parameters for a cable bundle, which is based on the Nelder-Mead simplex search algorithm. In this way each operator can easily calculate PBO parameters that match its actual access network down to the individual cable bundle. Using the properties of the PBO, as defined in the VDSL standard, we show how a normalized FEXT coupling can replace the knowledge of the individual couplings during the optimization of the PBO parameters. By simulations based on measured cable data we show that our approach using cable bundle unique PBO (CUPBO) achieves a significant improvements compared to the performance achieved with the ordinary PBO.

This paper investigates common-mode propagation in shielded twisted pair cables. The common mode ... more This paper investigates common-mode propagation in shielded twisted pair cables. The common mode exhibits great potential for improving the throughput in emerging wireline systems. The design of corresponding transmission schemes over multipair copper cables requires accurate knowledge of the channel properties. We present measurement and modeling results and investigate the feasibility of using standard differential- mode models for data fitting in multiconductor transmission-line modelling of common-mode paths.

Page 1. 1 A Multistage Deflation Algorithm for Blind Source Separation based on Order Statistics.... more Page 1. 1 A Multistage Deflation Algorithm for Blind Source Separation based on Order Statistics.* Yolanda Blanco Archilla, Santiago Zazo , José Manuel Páez Borrallo Grupo GAPS-SSR; ETS Ingenieros Telecomunicación (Universidad Politécnica de Madrid). ...

Page 1. BLIND SEPARATION OF HYBRID MIXTURES THROUGH ICA WITH OS Yolanda Blanco Archilla, Santiago... more Page 1. BLIND SEPARATION OF HYBRID MIXTURES THROUGH ICA WITH OS Yolanda Blanco Archilla, Santiago Zazo , José Manuel Páez Borrallo Grupo GAPS-SSR; ETS Ingenieros Telecomunicación (Universidad Politécnica de Madrid). ...

The main goal of this paper is to review the fundamental ideas of the method called “ICA with OS”... more The main goal of this paper is to review the fundamental ideas of the method called “ICA with OS”. We review a set of alternative statistical distances between distributions based on the Cumulative Density Function (cdf). In particular, these gaussianity distances provide new cost functions whose maximization perform the extraction of one independent component at each successive stage of a new proposed deflation ICA procedure. These measures are estimated through Order Statistics (OS) that are consistent estimators of the inverse cdf. The new Gaussianity measures improve the ICA performance and also increase the robustness against outliers compared with the traditional ones.

Neurocomputing, 2003

In this paper we propose and analyze a set of alternative statistical distances between distribut... more In this paper we propose and analyze a set of alternative statistical distances between distributions based on the cumulative density function instead of traditional probability density function. In particular, these new Gaussian distances provide new cost functions whose maximization performs the extraction of one independent component at each successive stage of a de ation ICA procedure. The new Gaussianity measures improve the ICA performance and also increase the robustness against outliers in comparison with traditional ones.

In this work we deal with the design and simulation of a complete multi-carrier modem alternative... more In this work we deal with the design and simulation of a complete multi-carrier modem alternative to the recommended one (single-carrier) for the high frequency data link standard (known as HFDL) for communications between ground stations and civil aircraft. We show how the multicarrier modem offers a better performance, from the bit error rate point of view, even in the case of very short interleaving procedure, fulfilling, at the same time, the timing constraints imposed by the TDMA structure of the HFDL system

This paper discusses a novel method called 'ICA with OS' ('Independent Component Analysis with Or... more This paper discusses a novel method called 'ICA with OS' ('Independent Component Analysis with Order Statistics') to solve the vital problem of Blind Source Separation. The key of the procedure is a new alternative Gaussianity measure estimated by Order Statistics of the cdf (cumulative density function) instead of the common pdf (probability density function) moments. The maximization of this measure performs the extraction of one source in each of the successive stages of a deflation procedure based on Givens rotations.

Most of the current synchronization schemes used for the ForwardlDownlink MC-CDMA ( Multi-Carrier... more Most of the current synchronization schemes used for the ForwardlDownlink MC-CDMA ( Multi-Carrier Code Division Multiple Access ) Systems are not suitable for the ReverseAJplink case. The technique proposed in this paper gives a new way to estimate the time-frequency synchronization parameters in an uplink MC-CDMA System, take under consideration that all the users reach the base station in an asynchronous mode. The proposed scheme combines the CDMA insertion mode for different spreading codes for all the users, and the SS-MC-MA ( Spread Spectrum Multi-Carrier Multiple Access) mode as an insertion technique for the offset correction sequences. The insertion of pilots and offset correction sequences for each user are located at different carriers and obey to the non-overlapping principle with the rest of the user's position.

Sensors, 2009

The improvement in the transmission range in wireless applications without the use of batteries r... more The improvement in the transmission range in wireless applications without the use of batteries remains a significant challenge in identification applications. In this paper, we describe a heterogeneous wireless identification network mostly powered by kinetic energy, which allows the localization of animals in open environments. The system relies on radio communications and a global positioning system. It is made up of primary and secondary nodes. Secondary nodes are kinetic-powered and take advantage of animal movements to activate the node and transmit a specific identifier, reducing the number of batteries of the system. Primary nodes are battery-powered and gather secondary-node transmitted information to provide it, along with position and time data, to a final base station in charge of the animal monitoring. The system allows tracking based on contextual information obtained from statistical data.

In this paper, the distribution of pilot symbols in the time-frequency lattice of a multicarrier ... more In this paper, the distribution of pilot symbols in the time-frequency lattice of a multicarrier system for HF communications has been analysed. The pilot density of an OFDM modem based on the HFDL standard can be reduced, so the data rate can be about 3600 bit/s. An hexagonal pilot pattern has been proposed and compared with rectangular geometries. Hexagonal distribution of the pilots is optimum in terms of sampling efficiency and it provides better performance in terms of BER

Multiple Access Interference (MAI) imposes serious limitation to the MC-CDMA systems' performance... more Multiple Access Interference (MAI) imposes serious limitation to the MC-CDMA systems' performance in uplink channel. In our proposal we are considering a system where orthogonal users' codes are based on Prolate Spheroidal Functions (PSF), specifically those denominated Periodic Discrete Prolate Spheroidal Sequences (PDPSS). These codes have the property concentrating signal energy in the desired time interval and gives the possibility to avoid Inter Symbol Interference (ISI) for a certain number of users without introducing the guard interval between consecutive symbols. Furthermore, it is also possible to avoid completely MAI for a certain number of active users in the uplink channel. Even in the case when this limit is passed, MAI is below the standard MC-CDMA schemes. Preliminary simulations presented here demonstrate this affirmation.

An efficient channel estimation algorithm for OFDM in wireless applications has been proposed. Tw... more An efficient channel estimation algorithm for OFDM in wireless applications has been proposed. Two-dimensional pilot-symbol assisted modulation (2D-PSAM) is employed in coherent OFDM for channel estimation and it is based on inserting known symbols spreaded throughout the 2D time-frequency grid. These scattered symbols are employed to perform an estimation of the channel's frequency response. At a first stage, if certain requirements are fulfilled, channel estimation in frequency dimension can be carried out with an efficient DFT-based algorithm, which provides an accurate estimation at time positions where pilot symbols are included. In the second step, linear interpolation is performed in the time direction. This scheme has been proven to be very successful in multicarrier HF communications systems

This paper is concerned with the application of pre-rake processing in the up link of a DS-CDMA s... more This paper is concerned with the application of pre-rake processing in the up link of a DS-CDMA system for a Wireless Local Loop (WLL) scenario with Time Division Duplex (TDD) access. It is well known that rake processing allows optimum time diversity gain in a multipath channel. And alternative approach, known as pre-rake processing, exploits the channel reciprocity in TDD systems in the up and down links to perform the optimum combination at the transmitter with the consequent receiver simplification. Typically, the prerake works at the base station, transmitting all users information with their particular pre-distortion. In this paper we explore other possibility, that is, each user performs its own pre-distortion, in order to simplify the synchronization and multiuser detection at the base station. Several simulations show its feasibility in comparison with standard multiuser detection techniques.

Electronics Letters, 2000

111 orlhogonid Iiaqncncy ilivisim innlliplcxing. OFDM. pilalsymbol distrihulinn can hc v i e d as... more 111 orlhogonid Iiaqncncy ilivisim innlliplcxing. OFDM. pilalsymbol distrihulinn can hc v i e d as a 2D sampliiig ~m h l c m rcliilcd 10 llic cliiiiiiicl Cvcilocncy rcip~msc. Cul-rcnl pilot piillci-as

Bursty data transmission over OFDM systems requires rapid time-frequency synchronization using a ... more Bursty data transmission over OFDM systems requires rapid time-frequency synchronization using a desirable short-time training sequence. Several sophisticated methods provide frame and carrier recovery in two symbols. We formulate these methods with a common notation and this leads us to address an oversampled scheme which allows synchronization in only one symbol. In our proposal, the limit of the acquisition range for the carrier frequency offset can be extended to ±N the subcarrier spacing instead of ±1 the subcarrier spacing as previous methods. Discussions about its robustness against channel and noise are included and supported by several representative computer simulations

Performance of a modem designed for HF communications is presented in this contribution. The aim ... more Performance of a modem designed for HF communications is presented in this contribution. The aim was to attain the real time communication for interactive voice transmission. Therefore, powerful coding for error protection and long interleaving was not permitted. Frequency selective HF channel was converted into a set of frequency flat channels with MultiCarrier modulation, Orthogonal Frequency Division Multiplex (OFDM). Spread Spectrum Technique (SST) was applied to improve modem's performance. This technique takes advantage of frequency diversity, as one symbol is transmitted (spreaded) over larger number of subcarriers (N), and more symbols (N) are transmitted simultaneously. Use of SS techniques permits us to perform advanced signal processing in receiver and further enhance modem's performance. We applied Multi User Detector (MUD) in receiver, denoting as "virtual users" the symbols transmitted simultaneously with different spreading codes. For data transmission, when delay is not restricted, coding and interleaving can be incorporated, improving drastically the performance.

This paper is concerned with the reduction of both self interference due to multipath, and multiu... more This paper is concerned with the reduction of both self interference due to multipath, and multiuser interference due to multiple access for synchronous DS-CDMA communications over frequency-selective fading channels. The general structure of these detectors consists of a bank of matched filters, a linear transformation that operates on the matched filter outputs, and a set of threshold devices. The goal of the present work is related with a single sensor multiuser detection providing a Multiuser + Self Inbference (h4UI+Sr) cancellation in order to improve the expected behavior of classical schemes. This interfkence canceller exploits the well known Generalized Side Lobe Canceller (GSLC) scheme based on the canonical representation for the desired user linear detector. The orthogonality condition between both components is imposed by the proper design of the blocking matrix in terms of the interference subspace span.

Neurocomputing, 2003

Sensors, 2009

Electronics Letters, 2000