Abdelhakim Youcef

Bio: Abdelhakim Youcef is an academic researcher from University of Bordeaux. The author has contributed to research in topics: Bit error rate & White noise. The author has an hindex of 2, co-authored 3 publications receiving 10 citations. Previous affiliations of Abdelhakim Youcef include Institut Mines-Télécom.

Adaptive frequency-domain equalization for underwater acoustic communications

Abstract: In this paper, frequency-domain equalization approach is proposed to deal with the intersymbol interference in underwater acoustic communications. To track the time-varying underwater acoustic channel, an adaptive algorithm is considered using overlap-and-save method. This technique makes it possible to remove the overhead due to the transmission of cyclic prefix over each block of data, such as in usual frequency-domain equalization systems. We compare both schemes through simulations to select the best one. The transmission scheme is validated in the Atlantic Ocean over a distance up to 2 kilometers in shallow water with high data rate single carrier QPSK communications (10 kbps). The receiver includes an efficient timing recovery tracking scheme followed by equalization. The results of simulations and experiments are evaluated in terms of bit error rate (BER) and mean square error (MSE).

Errors-in-variables identification of noisy moving average models

Abstract: In this paper, we propose to address the moving average (MA) parameters estimation issue based only on noisy observations and without any knowledge on the variance of the additive stationary white Gaussian measurement noise. For this purpose, the MA process is approximated by a high-order AR process and its parameters are estimated by using an errors-in-variables (EIV) approach, which also makes it possible to derive the variances of both the driving process and the additive white noise. The method is based on the Frisch scheme. One of the main difficulties in this case is to evaluate the minimal AR-process order that must be considered to have a "good" approximation of the MA process. To this end, we propose a way based on K-means method. Simulation results of the proposed method are presented and compared to existing MA-parameter estimation approaches.

Single Carrier Frequency Division Multiple Access for Underwater Acoustic Communications

Abstract: A single-carrier frequency division multiple access (SC-FDMA) scheme for transmission through underwater acoustic channel is proposed in this paper. A uniform distributed mode is used for the subcarrier mapping at the transmitter side. A single user scenario is considered where empty subcarriers between each two successive occupied subcarriers are considered as a guard interval. This enables to increase the receiver robustness against Doppler spread compared to traditional single-carrier transmission schemes. Adaptive linear frequency-domain equalization is considered at the receiver. Results show that the proposed scheme outperforms the single-carrier frequency-domain equalization transmission scheme (SC-FDE) in terms of bit error rate (BER) and mean square error (MSE).

Bayesian Iterative Channel Estimation and Turbo Equalization for Multiple-Input–Multiple-Output Underwater Acoustic Communications

Abstract: This article investigates a robust receiver scheme for a single carrier, multiple-input–multiple-output (MIMO) underwater acoustic (UWA) communications, which uses the sparse Bayesian learning algorithm for iterative channel estimation embedded in Turbo equalization (TEQ). We derive a block-wise sparse Bayesian learning framework modeling the spatial correlation of the MIMO UWA channels, where a more robust expectation–maximization algorithm is proposed for updating the joint estimates of channel impulse response, residual noise, and channel covariance matrix. By exploiting the spatially correlated sparsity of MIMO UWA channels and the second-order a priori channel statistics from the training sequence, the proposed Bayesian channel estimator enjoys not only relatively low complexity but also more stable control of the hyperparameters that determine the channel sparsity and recovery accuracy. Moreover, this article proposes a low complexity space-time soft decision feedback equalizer (ST-SDFE) with successive soft interference cancellation. Evaluated by the undersea 2008 Surface Processes and Acoustic Communications Experiment, the improved sparse Bayesian learning channel estimation algorithm outperforms the conventional Bayesian algorithms in terms of the robustness and complexity, while enjoying better estimation accuracy than the orthogonal matching pursuit and the improved proportionate normalized least mean squares algorithms. We have also verified that the proposed ST-SDFE TEQ significantly outperforms the low-complexity minimum mean square error TEQ in terms of the bit error rate and error propagation.

DFT-Precoded MIMO OFDM Underwater Acoustic Communications

Abstract: The discrete Fourier transform (DFT) precoded orthogonal frequency-division multiplexing (OFDM) has been adopted as the uplink transmission technique in the long-term evolution terrestrial communication standard, for its lower peak-to-average power ratio (PAPR) and similar receiver complexity, compared with the standard OFDM. However, its application in the underwater acoustic (UWA) communications remains doubtful, mainly for the lack of systematic studies as well as sufficient experimental verifications. This paper provides a comprehensive investigation on the DFT-precoded OFDM UWA communication with a multiple-input–multiple-output (MIMO) configuration, and corroborates its superiority for implementing a practical UWA communication modem. The DFT precoding is applied on the data symbols to achieve a lower PAPR than that of the standard OFDM, and it is optional for the pilot symbols. The frequency-domain turbo equalization (FDTE) technique, especially suitable for interference-intensive scenarios, is employed on the receiver side to combat the intersymbol interference (ISI) and the multiplexing interference. Experimental results are provided to demonstrate the performance of the proposed transceiver scheme. It is shown reliable communication is achieved for the two-transducer transmission with a QPSK modulation and the one-transducer transmission with a 16QAM modulation, even without running any iteration for the FDTE. With the help of turbo iterations, a two-transducer transmission with a 16QAM modulation also achieves a satisfactory performance.

Orthogonal Chirp Division Multiplexing for Underwater Acoustic Communication.

Abstract: The objective of this study is to investigate a novel Underwater Acoustic Communication (UWAC) system based on a modulated chirp signal termed as Orthogonal Chirp Division Multiplexing (OCDM). Originating from the Fresnel transform, OCDM uses chirp signals to exploit the multipath diversity of the channel, achieving a good robustness against frequency fading, especially in the underloaded scenario where only a subset of the available waveforms is modulated. The implementation of the OCDM system for the UWAC scenario is described, and the performance results over an experimental water tank and realistic replayed underwater channel are compared against the traditional Orthogonal Frequency Division Multiplexing (OFDM) transmission scheme.