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Author

Ahmad Gomaa

Other affiliations: Cairo University, Broadcom, MediaTek  ...read more
Bio: Ahmad Gomaa is an academic researcher from University of Texas at Dallas. The author has contributed to research in topics: Orthogonal frequency-division multiplexing & Fading. The author has an hindex of 12, co-authored 41 publications receiving 414 citations. Previous affiliations of Ahmad Gomaa include Cairo University & Broadcom.

Papers
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Journal ArticleDOI
TL;DR: A novel approach based on compressive sensing theory to estimate and mitigate asynchronous narrow-band interference in orthogonal frequency division multiplexing systems with multiple transmit and/or multiple receive antennas and proposes a novel technique for estimating the desired signal's channel in the presence of unknown NBI.
Abstract: In this paper, we present a novel approach based on compressive sensing theory to estimate and mitigate asynchronous narrow-band interference (NBI) in orthogonal frequency division multiplexing systems with multiple transmit and/or multiple receive antennas. We consider the practical scenarios where one or multiple asynchronous NBI signals experience fast fading and/or frequency-selective fading channels. Furthermore, we propose a novel technique for estimating the desired signal's channel in the presence of unknown NBI. Our approach does not require any prior information about the NBI. Simulation results demonstrate the effectiveness of our proposed techniques in mitigating NBI and approaching the interference-free performance limit over practical ranges of NBI power levels, spectral widths, and mobility levels.

74 citations

Journal ArticleDOI
TL;DR: Analytical and numerical results demonstrate that the direct mode can outperform the amplify-and-forward mode even under moderate levels of uncompensated I/Q imbalance.
Abstract: We analyze the outage performance of half-duplex amplify-and-forward relaying in an OFDM system with MRC detection in the presence of I/Q imbalance and compare it with that of the direct transmission mode. Both analytical and numerical results demonstrate that the direct mode can outperform the amplify-and-forward mode even under moderate levels of uncompensated I/Q imbalance. The cross-over I/Q imbalance levels are determined analytically to be inversely proportional to the cube of the signal constellation size. In addition, we present a low-complexity receiver-based digital baseband I/Q imbalance compensation scheme for the amplify-and-forward mode and analyze its EVM performance. Furthermore, we derive accurate analytical approximations for the EVM performance as a function of relay location and I/Q imbalance level with and without compensation.

59 citations

Journal ArticleDOI
TL;DR: This paper formulates greedy and convex-optimization-based solutions for sparse FIR linear equalizer tap vectors given a maximum allowable loss in the decision-point signal-to-noise ratio and extends this formulation to decision feedback equalizers and multiple-antenna systems.
Abstract: In this paper, we propose a new framework for the design of sparse finite impulse response (FIR) equalizers. We start by formulating greedy and convex-optimization-based solutions for sparse FIR linear equalizer tap vectors given a maximum allowable loss in the decision-point signal-to-noise ratio. Then, we extend our formulation to decision feedback equalizers and multiple-antenna systems. This is followed by further generalization to the channel shortening setup which is important for communication systems operating over broadband channels with long channel impulse responses. We propose a novel approach to design a sparse target impulse response. Finally, as an application of current practical interest, we consider self far-end crosstalk cancellation on vectored very high-speed digital subscriber line systems for cellular backhaul networks.

36 citations

Journal ArticleDOI
TL;DR: This analysis reveals an interesting design tradeoff between the peak-to-average power ratio of a training sequence and the increase in channel estimation mean squared error over the ideal case when these two impairments are not present.
Abstract: In this paper, we design MMSE-optimal training sequences for multi-user MIMO-OFDM systems with an arbitrary number of transmit antennas and an arbitrary number of training symbols. It addresses spectrally-efficient uplink transmission scenarios where the users overlap in time and frequency and are separated using spatial processing at the base station. The robustness of the proposed training sequences to residual carrier frequency offset and phase noise is evaluated. This analysis reveals an interesting design tradeoff between the peak-to-average power ratio of a training sequence and the increase in channel estimation mean squared error over the ideal case when these two impairments are not present.

32 citations

Proceedings ArticleDOI
01 Dec 2010
TL;DR: A novel algorithm based on compressive sensing (CS) theory to estimate narrow band interference (NBI) signals experiencing time-varying frequency-selective fading channels in orthogonal frequency division multiplexing (OFDM) systems with negligible performance loss is proposed.
Abstract: We propose a novel algorithm based on compressive sensing (CS) theory to estimate narrow band interference (NBI) signals experiencing time-varying frequency-selective fading channels in orthogonal frequency division multiplexing (OFDM) systems. In addition, we investigate the case of asynchronous jamming where there is a frequency offset between the NBI and desired signals. Furthermore, we propose a reduced-complexity implementation for our proposed algorithm with negligible performance loss. Finally, we show that our proposed approach can be applied to both cyclic-prefix and zero-padding OFDM systems. Simulation results show the effectiveness of our proposed algorithm in mitigating NBI.

22 citations


Cited by
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01 Jan 2016
TL;DR: The table of integrals series and products is universally compatible with any devices to read and is available in the book collection an online access to it is set as public so you can get it instantly.
Abstract: Thank you very much for downloading table of integrals series and products. Maybe you have knowledge that, people have look hundreds times for their chosen books like this table of integrals series and products, but end up in harmful downloads. Rather than reading a good book with a cup of coffee in the afternoon, instead they cope with some harmful virus inside their laptop. table of integrals series and products is available in our book collection an online access to it is set as public so you can get it instantly. Our book servers saves in multiple locations, allowing you to get the most less latency time to download any of our books like this one. Merely said, the table of integrals series and products is universally compatible with any devices to read.

4,085 citations

Journal ArticleDOI
TL;DR: This paper derives new closed-form expressions for the exact and asymptotic OPs, accounting for hardware impairments at the source, relay, and destination, and proves that for high signal-to-noise ratio (SNR), the end- to-end SNDR converges to a deterministic constant, coined the SNDR ceiling, which is inversely proportional to the level of impairments.
Abstract: Physical transceivers have hardware impairments that create distortions which degrade the performance of communication systems. The vast majority of technical contributions in the area of relaying neglect hardware impairments and, thus, assume ideal hardware. Such approximations make sense in low-rate systems, but can lead to very misleading results when analyzing future high-rate systems. This paper quantifies the impact of hardware impairments on dual-hop relaying, for both amplify-and-forward and decode-and-forward protocols. The outage probability (OP) in these practical scenarios is a function of the effective end-to-end signal-to-noise-and-distortion ratio (SNDR). This paper derives new closed-form expressions for the exact and asymptotic OPs, accounting for hardware impairments at the source, relay, and destination. A similar analysis for the ergodic capacity is also pursued, resulting in new upper bounds. We assume that both hops are subject to independent but non-identically distributed Nakagami-m fading. This paper validates that the performance loss is small at low rates, but otherwise can be very substantial. In particular, it is proved that for high signal-to-noise ratio (SNR), the end-to-end SNDR converges to a deterministic constant, coined the SNDR ceiling, which is inversely proportional to the level of impairments. This stands in contrast to the ideal hardware case in which the end-to-end SNDR grows without bound in the high-SNR regime. Finally, we provide fundamental design guidelines for selecting hardware that satisfies the requirements of a practical relaying system.

370 citations

Journal ArticleDOI
TL;DR: An efficient ML DOA estimator based on a spatially overcomplete array output formulation that surpasses state-of-the-art methods largely in performance, especially in demanding scenarios such as low signal-to-noise ratio (SNR), limited snapshots and spatially adjacent signals.
Abstract: The computationally prohibitive multi-dimensional searching procedure greatly restricts the application of the maximum likelihood (ML) direction-of-arrival (DOA) estimation method in practical systems. In this paper, we propose an efficient ML DOA estimator based on a spatially overcomplete array output formulation. The new method first reconstructs the array output on a predefined spatial discrete grid under the sparsity constraint via sparse Bayesian learning (SBL), thus obtaining a spatial power spectrum estimate that also indicates the coarse locations of the sources. Then a refined 1-D searching procedure is introduced to estimate the signal directions one by one based on the reconstruction result. The new method is able to estimate the incident signal number simultaneously. Numerical results show that the proposed method surpasses state-of-the-art methods largely in performance, especially in demanding scenarios such as low signal-to-noise ratio (SNR), limited snapshots and spatially adjacent signals.

187 citations

Journal ArticleDOI
TL;DR: It is demonstrated that under some mild spectral separation condition, it is possible to exactly recover all frequencies by solving an atomic norm minimization program, as long as the sample complexity exceeds the order of rlogrlogn.
Abstract: This paper is concerned with estimation of two-dimensional (2-D) frequencies from partial time samples, which arises in many applications such as radar, inverse scattering, and super-resolution imaging. Suppose that the object under study is a mixture of r continuous-valued 2-D sinusoids. The goal is to identify all frequency components when we only have information about a random subset of n regularly spaced time samples. We demonstrate that under some mild spectral separation condition, it is possible to exactly recover all frequencies by solving an atomic norm minimization program, as long as the sample complexity exceeds the order of rlogrlogn. We then propose to solve the atomic norm minimization via a semidefinite program and provide numerical examples to justify its practical ability. Our work extends the framework proposed by Tang for line spectrum estimation to 2-D frequency models.

183 citations

Journal ArticleDOI
TL;DR: Simulations demonstrate that the proposed APSP approach can provide substantial performance gains in terms of achievable spectral efficiency over the conventional phase shift orthogonal pilot approach in typical mobility scenarios.
Abstract: We propose adjustable phase shift pilots (APSPs) for channel acquisition in wideband massive multiple-input multiple-output (MIMO) systems employing orthogonal frequency division multiplexing (OFDM) to reduce the pilot overhead. Based on a physically motivated channel model, we first establish a relationship between channel space-frequency correlations and the channel power angle-delay spectrum in the massive antenna array regime, which reveals the channel sparsity in massive MIMO-OFDM. With this channel model, we then investigate channel acquisition, including channel estimation and channel prediction, for massive MIMO-OFDM with APSPs. We show that channel acquisition performance in terms of sum mean square error can be minimized if the user terminals' channel power distributions in the angle-delay domain can be made nonoverlapping with proper pilot phase shift scheduling. A simplified pilot phase shift scheduling algorithm is developed based on this optimal channel acquisition condition. The performance of APSPs is investigated for both one symbol and multiple symbol data models. Simulations demonstrate that the proposed APSP approach can provide substantial performance gains in terms of achievable spectral efficiency over the conventional phase shift orthogonal pilot approach in typical mobility scenarios.

171 citations