Santiago Zazo | Universidad Politécnica de Madrid (original) (raw)
Papers by Santiago Zazo
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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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Electronics Letters, 2000
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Sensors, 2009
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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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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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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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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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Signal Processing, 2001
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IEEE Transactions on Signal Processing, 2000
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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
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
Electronics Letters, 2000
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
Sensors, 2009
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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.
Bookmarks Related papers MentionsView impact
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
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
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.
Bookmarks Related papers MentionsView impact
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
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
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Signal Processing, 2001
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IEEE Transactions on Signal Processing, 2000
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