E. Martos-Naya

Bio: E. Martos-Naya is an academic researcher. The author has contributed to research in topics: Synchronization & MIMO. The author has an hindex of 3, co-authored 5 publications receiving 18 citations.

Low Complexity Synchronization and Frequency Equalization for OFDM Systems

Abstract: This paper shows an efficient implementation of symbol synchronization and frequency equalization algorithms for OFDM (orthogonal frequency division multiplexing) based systems. The aim is to have a low complexity realization that can be implemented on a FPGA (Field Programmable Gate Array), to obtain an area-efficient receiver. The algorithms are described theoretically, and hardware considerations about their implementation are discussed. Furthermore, the proposed methods have been tested on a real-time FPGA platform.

Analysis of MIMO Beamforming with Channel Response Variations Over the Frame Interval

Abstract: Important throughput improvements in multiple- input multiple-output (MIMO) fading channels can be obtained by merging beamforming at the transmitter and maximal ratio combining (MRC) at the receiver. However, to attain these performance gains it is important to obtain accurate channel state information (CSI). For this purpose a channel estimation technique is used at the receiver: channel prediction to feed back to the transmitter for beamforming, and channel interpolation for MRC at the receiver. In this paper, the impact of imperfect channel prediction on bit error probability (BEP) is analyzed in Rayleigh fading, taking into account the channel response variations over the frame interval. An exact closed-form expression for BEP is obtained, and we evaluate this expression assuming both time-variant and time-invariant channel models. These results indicate that the BEP performance degrades on the order of 1.5 dB due to channel variations.

Hardware Implementation of a Correlation-based Synchronization Algorithm for Wireless OFDM

Abstract: In the world of wireless communications, OFDM is one of the most used multicarrier techniques today. The main reasons for that are the multipath immunity that provides and the easy implementation of FFT, but OFDM systems are sensitive to timing synchronization errors. This paper shows a novel synchronization algorithm for the IEEE 802.16-2004 standard. The proposed method performs frame detection and determines the beginning of the data frame, by using a combination of auto and cross correlation techniques. Besides, a FPGA implementation of the developed algorithm is achieved in order to evaluate its performance on a real system.

A Random Matrix Model for $\kappa$-$\mu$ Shadowed Fading

Abstract: This paper shows that the proposed Rician shadowed model for multi-antenna communications allows for the unification of a wide set of models, both for multiple-input multiple output (MIMO) and single-input single output (SISO) communications. The MIMO Rayleigh and MIMO Rician can be deduced from the MIMO Rician shadowed, and so their SISO counterparts. Other SISO models, besides the Rician shadowed proposed by Abdi et. al., are included in the model, such as the $\kappa$-$\mu$ defined by Yacoub, and its recent generalization, the \mbox{$\kappa$-$\mu$} shadowed model. Moreover, the SISO \mbox{$\eta$-$\mu$} and \mbox{Nakagami-$q$} models can be seen as particular cases of the MIMO Rician shadowed. The literature already presents the probability density function (pdf) of the Rician shadowed Gram channel matrix in terms of the well-known gamma-Wishart distribution. We here derive its moment generating function in a tractable form. Closed-form expressions for the cumulative distribution function and the pdf of the maximum eigenvalue are also carried out.

Zero-Outage Delay-Aware Adaptive Modulation for Flat Fading Channels

Abstract: We present an adaptive modulation policy that provides delay-throughput balance for data packet transmission over flat fading channels. The proposed policy is based on uninterrupted data transmission (zero-outage) and achieves low packet-delay while satisfies certain average BER constraints. Such delay and BER control is not an obstacle to achieve an average spectral efficiency close to that obtained by maximum spectral efficiency adaptation policies. Both continuous and discrete rate adaptation are considered.

Achievable Throughput Optimization in OFDM Systems in the Presence of Interference and its Application to Power Line Networks

Abstract: The aim of this paper is to study the bit-loading and power allocation problem in the presence of interference (Inter-carrier Interference (ICI) and Inter-Symbol Interference (ISI)) in Orthogonal Frequency Division Multiplexing (OFDM) systems. ISI and ICI significantly degrade the performance of OFDM systems and make the resource management optimized without the assumption of interference less efficient. To solve this problem, an initial solution based on the greedy approach is proposed in this paper. Then, several reduced complexity approaches, which yield a little degradation compared to the initial solution, have been developed. Simulation results presented in the context of Power Line Communication (PLC) show that the performance of proposed algorithms is tight with their upper bound. Moreover, these algorithms efficiently improve the system performance as compared to the constant power water-filling allocation algorithm as well as maximum power allocation algorithm.

Performance of Dualbeam MIMO for Millimeter Wave Indoor Communication Systems

Abstract: Millimeter wave (MMW) communication provides high data rates for the personal area networks with the availability of 57---64 GHz unlicensed spectrum, in indoor environment. Multipath fading being pre-dominant in indoor, multi input multi output (MIMO) technology is considered to be the ideal choice compared with the existing systems. As spatial diversity in both transmit and receive enhances the diversity gain, the performance of the system is further enhanced by introducing transmit beamforming based antenna beam diversity. In classical $$2\times 2$$ 2 × 2 MIMO, a diversity gain of 4 is achieved, whereas in this work, space time block code matrix of code rate 1/2 and dualbeam $$2\times 2$$ 2 × 2 MIMO with diversity gain 8 is considered. Dualbeam is generated by antenna array with four elements per array with out of phase feed configuration. The weight vector of the beamforming network is out of phase as to reduce the interference between the beams. The dualbeam transmitter is designed with unknown channel state information. Training symbols are transmitted to train and track the channel statistics at the receiver. The proposed work is carried out for MMW indoor system. The indoor channel is modeled using Triple Saleh–Valenzuela (TSV) model that takes into account both time of arrival and the angle of arrival information of the rays. Channel estimation is done for classical MIMO and the above proposed model in both Rayleigh and TSV channel. The orthogonal beams facilitate linear processing in the receiver. Hence maximum ratio combiner with maximum likelihood decoder is used in the receiver to decode the transmitted data. Classical MIMO and dualbeam MIMO are evaluated with respect to bit error rate and channel models. An improved diversity order is achieved with dualbeam MIMO compared to classical MIMO, with a power gain of 1.6 dB. The dualbeam MIMO using TSV is found to perform better compared to dualbeam MIMO using Rayleigh in the low Energy per bit to Noise level $$(\hbox {E}_{\mathrm{b}}/\hbox {N}_{0})$$ ( E b / N 0 ) with a power gain of 2 dB.

Adaptive Modulation for MIMO Systems with Channel Prediction Errors

Abstract: The performance of multiple-input multiple-output (MIMO) systems using spatial multiplexing is analyzed under channel prediction errors. We derive exact closed-form expressions for the conditional and average bit error rate (BER) for both fixed and adaptive modulation. We apply our analysis to design a rate adaptation policy that optimally adapts antenna use between beamforming and spatial multiplexing. Our results indicate that the prediction error degrades BER in MIMO systems with spatial multiplexing much more than in MIMO systems with beamforming due to the self-interference that arises from channel coupling. In particular, if interference between eigenchannels is high, spatial multiplexing should not utilize the weakest eigenchannels. In our policy, beamforming is used when prediction error is high to avoid interference, whereas multiplexing is used when it is low to achieve the maximum multiplexing gain. We show that this policy improves performance over prior adaptive policies that have been proposed in the literature.

SER for Optimal Combining in the Presence of Multiple Correlated Co-Channel Interferers

Abstract: Symbol error rate (SER) performance has been analyzed for a receive diversity system in the presence of multiple interferers and noise over fading channels. Both unequal power interferers and correlated interferers have been considered. The derived approximate SER expressions are easy to evaluate and are applicable to any QAM constellation and arbitrary number of receive antennas and interferers. Further, the impact of correlation between interferer channels is studied and it is shown that correlation behaves like partial interference alignment.