Inaki Berenguer

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—A method to improve the performance of multiple -input–multiple-output systems is to employ a large number of antennas and select the optimal subset depending on the specific channel realization. A simple antenna-selection criterion is to choose the antenna subset that maximizes the mutual information. However, when the receiver has finite complexity(More)
— Orthogonal Frequency Division Multiplexing (OFDM) significantly reduces receiver complexity in wireless broadband systems and therefore has recently been proposed for use in wireless broadband multi-antenna (MIMO) systems. The performance of maximum likelihood detector in MIMO-OFDM system is optimal, however, its complexity , especially with higher order(More)
Cooperative diversity systems have been recently proposed as a solution to provide spatial diversity for terminals where multiple antennas are not feasible to be implemented. As in MIMO systems, space-time codes can be used to efficiently exploit the increase in capacity provided in cooperative diversity systems. In this paper we propose a two-layer linear(More)
We consider transmit antenna subset selection in spatial multiplexing systems. In particular, we propose selection algorithms aiming to minimize the error rate when linear detectors are used at the receiver. Previous work on antenna selection has considered capacity and post-processing SNR selection criteria. However, in this work we consider a geometrical(More)
— This paper develops a framework for the efficient maximum-likelihood decoding of lattice codes. Specifically we apply it to the spherical Lattice Space-Time (LAST) codes recently put forward by El Gamal et al. that have been proven to achieve the optimal diversity-multiplexing tradeoff of MIMO channels. Our solution addresses the so-called boundary(More)
In this paper we propose a systematic procedure for designing minimum-error-rate lattice (space-time) codes. By employing stochastic optimization techniques we design lattice (space-time) codes with minimum error rate when maximum likelihood (ML) detection is employed. Our design methodology can be tailored to optimize lattice (space-time) codes for any(More)
—In this paper, we propose a systematic procedure for designing spherical lattice (space–time) codes. By employing sto-chastic optimization techniques we design lattice codes which are well matched to the fading statistics as well as to the decoder used at the receiver. The decoders we consider here include the optimal albeit of highest decoding complexity(More)
—A new framework for efficient exact Maximum-Likelihood (ML) decoding of spherical lattice codes is developed. It employs a double-tree structure: The first is that which underlies established tree-search decoders; the second plays the crucial role of guiding the primary search by specifying admissible candidates and is our present focus. Lattice codes have(More)
Nonlinear precoding schemes for downlink time-division duplex – CDMA systems over multipath fading channels, are considered. First, the capacity results of a downlink CDMA system with either multiuser detection or precoding, were obtained and compared. It is seen that the two schemes exhibit similar capacity regions for both sum rate and maximum equal rate,(More)