Santiago Zazo | Universidad Politécnica de Madrid (original) (raw)

Papers by Santiago Zazo

Research paper thumbnail of ALTERNATIVE STATISTICAL GAUSSIANITY MEASURE USING THE CUMULATIVE DENSITY FUNCTION

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Research paper thumbnail of Nonparametric Boxed Belief Propagation for Localization in Wireless Sensor Networks

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Research paper thumbnail of SENSOR LOCALIZATION USING GENERALIZED BELIEF PROPAGATION IN NETWORK WITH LOOPS

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Research paper thumbnail of Sensor localization using nonparametric generalized belief propagation in network with loops

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Research paper thumbnail of Optimized edge appearance probability for cooperative localization based on tree-reweighted nonparametric belief propagation

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Research paper thumbnail of DFT-based channel estimation in 2D-pilot-symbol-aided OFDM wireless systems

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

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Research paper thumbnail of A new multichannel blind equalization criterium based on a generalized Rayleigh quotient

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Research paper thumbnail of Pilot patterns for channel estimation in OFDM

Electronics Letters, 2000

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Research paper thumbnail of Advanced OFDM-CDMA HF modem with self-interference cancellation

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Research paper thumbnail of A Heterogeneous Wireless Identification Network for the Localization of Animals Based on Stochastic Movements

Sensors, 2009

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Research paper thumbnail of Reduced interference MC-CDMA system using Discrete Prolate codes

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.

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Research paper thumbnail of Efficient pilot patterns for channel estimation in OFDM systems over HF channels

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

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Research paper thumbnail of A multiple access/self interference canceller receiver for DS-CDMA multiuser detection over fading channels

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Research paper thumbnail of Spread Spectrum OFDM Modem for HF Voice-Band Link over Fading Channels

European Transactions on Telecommunications, 2000

This paper deals with the application of spread spectrum techniques to MultiCarrier HF modems. OF... more This paper deals with the application of spread spectrum techniques to MultiCarrier HF modems. OFDM modems are a special option for the transmission over the high dispersive HF medium in front of single carrier modems. Our present contribution is now focused on the application of Spread Spectrum techniques to improve its fading robustness. The transmission bandwidth is the standard voice band channel in the HF band where the spread spectrum characteristic means that one symbol is transmitted over N times the spectrum in the classical N-OFDM scheme. The motivation of this idea is the observation of the OFDM modems behaviour over fading channels with deep nulls showing a quite different performance between carriers: those in the vicinity of deep nulls provide a much higher Bit Error Rate (BER) than others far away of the nulls. Our proposal intends to spread different symbols over all the subcarriers simultaneously in order to homogenize performances. This approach, performed by orthogonal codes, shows an evident link with MC-CDMA techniques. In addition, Multi User Detection (MUD) strategies as Interference Cancellation (IC) with coherent detection are also applied in order to improve its performance.

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Research paper thumbnail of Pre-RAKE and multiuser detection techniques in UTRA-TDD 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. An 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 pre-RAKE works at the base station, transmitting all users information with their particular pre-distortion. In this paper we explore another 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

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Research paper thumbnail of Uplink acquisition of synchronization parameters in MC-CDMA systems

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Research paper thumbnail of Order statistics: a new approach to the problem of blind source separation

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Research paper thumbnail of Analysis of a new frequency synchronization scheme in OFDM systems

Signal Processing, 2001

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Research paper thumbnail of Blind multichannel equalization using a novel subspace method

IEEE Transactions on Signal Processing, 2000

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Research paper thumbnail of ALTERNATIVE STATISTICAL GAUSSIANITY MEASURE USING THE CUMULATIVE DENSITY FUNCTION

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Research paper thumbnail of Nonparametric Boxed Belief Propagation for Localization in Wireless Sensor Networks

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Research paper thumbnail of SENSOR LOCALIZATION USING GENERALIZED BELIEF PROPAGATION IN NETWORK WITH LOOPS

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Research paper thumbnail of Sensor localization using nonparametric generalized belief propagation in network with loops

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Research paper thumbnail of Optimized edge appearance probability for cooperative localization based on tree-reweighted nonparametric belief propagation

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Research paper thumbnail of DFT-based channel estimation in 2D-pilot-symbol-aided OFDM wireless systems

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

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Research paper thumbnail of A new multichannel blind equalization criterium based on a generalized Rayleigh quotient

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Research paper thumbnail of Pilot patterns for channel estimation in OFDM

Electronics Letters, 2000

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Research paper thumbnail of Advanced OFDM-CDMA HF modem with self-interference cancellation

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Research paper thumbnail of A Heterogeneous Wireless Identification Network for the Localization of Animals Based on Stochastic Movements

Sensors, 2009

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Research paper thumbnail of Reduced interference MC-CDMA system using Discrete Prolate codes

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.

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Research paper thumbnail of Efficient pilot patterns for channel estimation in OFDM systems over HF channels

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

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Research paper thumbnail of A multiple access/self interference canceller receiver for DS-CDMA multiuser detection over fading channels

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Research paper thumbnail of Spread Spectrum OFDM Modem for HF Voice-Band Link over Fading Channels

European Transactions on Telecommunications, 2000

This paper deals with the application of spread spectrum techniques to MultiCarrier HF modems. OF... more This paper deals with the application of spread spectrum techniques to MultiCarrier HF modems. OFDM modems are a special option for the transmission over the high dispersive HF medium in front of single carrier modems. Our present contribution is now focused on the application of Spread Spectrum techniques to improve its fading robustness. The transmission bandwidth is the standard voice band channel in the HF band where the spread spectrum characteristic means that one symbol is transmitted over N times the spectrum in the classical N-OFDM scheme. The motivation of this idea is the observation of the OFDM modems behaviour over fading channels with deep nulls showing a quite different performance between carriers: those in the vicinity of deep nulls provide a much higher Bit Error Rate (BER) than others far away of the nulls. Our proposal intends to spread different symbols over all the subcarriers simultaneously in order to homogenize performances. This approach, performed by orthogonal codes, shows an evident link with MC-CDMA techniques. In addition, Multi User Detection (MUD) strategies as Interference Cancellation (IC) with coherent detection are also applied in order to improve its performance.

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Research paper thumbnail of Pre-RAKE and multiuser detection techniques in UTRA-TDD 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. An 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 pre-RAKE works at the base station, transmitting all users information with their particular pre-distortion. In this paper we explore another 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

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Research paper thumbnail of Uplink acquisition of synchronization parameters in MC-CDMA systems

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Research paper thumbnail of Order statistics: a new approach to the problem of blind source separation

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Research paper thumbnail of Analysis of a new frequency synchronization scheme in OFDM systems

Signal Processing, 2001

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Research paper thumbnail of Blind multichannel equalization using a novel subspace method

IEEE Transactions on Signal Processing, 2000

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