Sajid Ahmed

Sajid Ahmed
Information Technology University · Department of Electrical Engineering

PhD

About

68
Publications
12,372
Reads
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1,459
Citations
Additional affiliations
January 2012 - June 2017
King Abdullah University of Science and Technology
Position
  • Researcher
October 2008 - January 2012
University of Edinburgh
Position
  • Research Associate
October 2005 - October 2007
Queen's University Belfast
Position
  • Research Associate

Publications

Publications (68)
Article
Full-text available
This study shows an approach for classifying road users using a 24-GHz millimeter-wave radar. The sensor transmits multiple linear frequency–modulated waves, which enable range estimation and Doppler-shift estimation of targets in the scene. We aimed to develop a solution for localization and classification, which yielded the same performance when...
Preprint
Full-text available
In conventional radar, the transmission of the same waveform is repeated after a predefined interval of time called pulse-repetition-interval (PRI). This technique helps to estimate the range and Doppler shift of targets and suppress clutter. In dual-function radar communication (DFRC), different waveforms are transmitted after each PRI. Thus, each...
Article
Full-text available
Electrocardiogram (ECG) signals represent the electrical activity of the human hearts and consist of several waveforms (P, QRS, and T). The duration and shape of each waveform and the distances between different peaks are used to diagnose heart diseases. In this work, to better analyze ECG signals, a new algorithm that exploits two-event related mo...
Article
Full-text available
In this paper, we propose studying the disease spread mechanism in the atmosphere as an engineering problem. Aerosol transmission is the most significant mode among the viral transmission mechanisms that do not include physical contact, where airflows carry virus-laden droplets over long distances. Throughout this work, we study the transport of th...
Preprint
Full-text available
In this paper, we propose studying the disease spread mechanism in the atmosphere as an engineering problem. Aerosol transmission is the most significant mode among the viral transmission mechanisms that do not include physical contact, where airflows carry virus-laden droplets over long distances. Throughout this work, we study the transport of th...
Article
In the phased-array radar signals from each antenna are transmitted at the same carrier frequency, which yields narrowly focused only angle dependent beampattern. In contrast, in the frequency-diverse-array (FDA) radar signals from antenna array are generally transmitted at linearly increasing frequencies that yields range, time, and angle dependen...
Article
In this work, we propose a reduced dimension and low complexity algorithm to estimate the direction-of-arrival (DOA), direction-of-departure (DOD) and the Doppler shift of a moving target for a multiple-input-multiple-output (MIMO) radar. We derive two cost functions based on two different objective functions. We solve each of the derived cost func...
Article
Full-text available
Exhaled breath can be used in retrieving information and creating innovative communication systems. It contains several volatile organic compounds and biological entities that can act as health biomarkers. For instance, the breath of an infected human contains a nonnegligible amount of pathogenic aerosol that can spread or remain suspended in the a...
Article
Full-text available
Due to an increasing demand in channel capacity and bandwidth, there has been a growing interest in the millimeter wave (mmWave) spectrum [1]-[3]. Many researchers overcame the challenges of implementing extremely high frequency systems and secured large bandwidths comparable to that of fiber optics [4]. The mmWave spectrum offers numerous advantag...
Preprint
Full-text available
Exhaled breath can be used in retrieving information and creating innovative communication systems. It contains several volatile organic compounds (VOCs) and biological entities that can act as health biomarkers. For instance, the breath of infected human contains a nonnegligible amount of pathogenic aerosol that can spread or remain suspended in t...
Article
In multiple-input multiple-output radar, to localize a target and estimate its reflection coefficient, a given cost function is usually optimized over a grid of points. The performance of such algorithms is directly affected by the grid resolution. Increasing the number of grid points enhances the resolution of the estimator but also increases its...
Article
The simultaneous lobing technique, also known as monopulse technique, has been widely used for fast target localisation and tracking purposes. Many works focused on accurately localising one or two targets lying within a narrow beam centred around the monopulse antenna boresight. In this study, a new approach is proposed, which uses the outputs of...
Article
In multiple-input multiple-out (MIMO) radar, for desired transmit beampatterns, appropriate correlated waveforms are designed. To design such waveforms, conventional MIMO radar methods use two steps. In the first step, the waveforms covariance matrix, R, is synthesized to achieve the desired beampattern. While in the second step, to realize the syn...
Article
Full-text available
Conventional algorithms used for parameter estimation in colocated multiple-input-multiple-output (MIMO) radars require the inversion of the covariance matrix of the received spatial samples. In these algorithms, the number of received snapshots should be at least equal to the size of the covariance matrix. For large size MIMO antenna arrays, the i...
Conference Paper
The estimation of angular-location and range of a target is a joint optimization problem. In this work, to estimate these parameters, by meticulously evaluating the phase of the received samples, low complexity sequential and joint estimation algorithms are proposed. We use a single-input and multiple-output (SIMO) system and transmit frequency-mod...
Conference Paper
In this paper, we consider a bistatic multiple-input multiple-output (MIMO) radar. We propose a reduced complexity algorithm to estimate the direction-of-arrival (DOA) and direction-of-departure (DOD) for moving target. We show that the calculation of parameter estimation can be expressed in terms of one-dimensional fast-Fourier-transforms which dr...
Article
To change the transmit beampattern, single antenna radar requires a change of antenna while multiple antenna array radar, such as phased-array, require amplitude/phase tapers, which are hardware components. Therefore, there is a genuine demand that the parameters of future radar systems be controlled through a software without changing any hardware...
Article
To change the transmit beam pattern, single antenna radar requires a change of antenna while multiple antenna array radar, such as phased-array, require amplitude/phase tapers, which are hardware components. Therefore, there is a genuine demand that the parameters of future radar systems be controlled through a software without changing any hardwar...
Research
Full-text available
In multiple-input multiple-output radar systems, it is usually desirable to steer transmitted power in the region-of-interest. To do this, conventional methods optimize the waveform co- variance matrix, R, for the desired beampattern, which is then used to generate actual transmitted waveforms. In this pa- per, we provide a low complexity closed-fo...
Article
In multiple-input multiple-output (MIMO) radar, to estimate the reflection coefficient, spatial location, and Doppler shift of a target, maximum-likelihood (ML) estimation yields the best performance. For this problem, the ML estimation requires the joint estimation of spatial location and Doppler shift, which is a two dimensional search problem. T...
Article
Multiple-input multiple-output (MIMO) radar works on the principle of transmission of independent waveforms at each element of its antenna array and is widely used for surveillance purposes. In this work, we investigate MIMO radar target localization problem with compressive sensing. Specifically, we try to solve the problem of estimation of target...
Article
Full-text available
In this paper, a new detector is proposed for an amplify-and-forward (AF) relaying system. The detector is designed to minimize the symbol-error-rate (SER) of the system. The SER surface is non-linear and may have multiple minimas, therefore, designing an SER detector for cooperative communications becomes an optimization problem. Evolutionary base...
Article
Full-text available
In this paper, a new detector is proposed for amplify-and-forward (AF) relaying system. The detector is designed to minimize the symbol-error-rate (SER) of the system. The SER surface is non-linear and may have multiple minimas, therefore, designing a SER detector for cooperative communications becomes an optimization problem. Evolutionary based al...
Article
Full-text available
Correlated waveforms have a number of applications in different fields, such as radar and communication. It is very easy to generate correlated waveforms using infinite alphabets, but for some of the applications, it is very challenging to use them in practice. Moreover, to generate infinite alphabet constant envelope correlated waveforms, the avai...
Article
Compared to phased-array, multiple-input multiple-output (MIMO) radars provide more degrees-of-freedom (DOF) that can be exploited for improved spatial resolution, better parametric identifiability, lower side-lobe levels at the transmitter/receiver, and design variety of transmit beampatterns. The design of the transmit beampattern generally requi...
Article
Full-text available
Compared to phased-array, multiple-input multiple- output (MIMO) radars provide more degrees-of-freedom (DOF) that can be exploited for improved spatial resolution, better parametric identifiability, lower sidelobe levels at the transmitter/receiver, and design variety of transmit beampatterns. The design of the transmit beampattern generally requi...
Article
Full-text available
In multiple-input multiple-output (MIMO) radar settings, it is often desirable to transmit power only to a given location or set of locations defined by a beampattern. Transmit waveform design is a topic that has received much attention recently, involving synthesis of both the signal covariance matrix, ${bf R}$, as well as the actual waveforms. Cu...
Conference Paper
Full-text available
In multiple-input multiple-output (MIMO) radar setting, it is often desirable to design correlated waveforms such that power is transmitted only to a given set of locations, a process known as beampattern design. To design desired beam-pattern, current research uses iterative algorithms, first to synthesize the waveform covariance matrix, R, then t...
Article
Full-text available
Multiple-input multiple-output (MIMO) radar has better parametric identifiability but compared to phased-array radar, it shows loss in signal-to-noise ratio due to noncoherent processing. To exploit the benefits of both MIMO radar and phased array, a waveform covariance matrix is proposed. To generate the proposed covariance matrix, the values of t...
Article
In this work, we propose a relatively low-complexity iterative algorithm for the detection of transmitted symbols at the uplink of a multiple-input multiple-output (MIMO) orthogonal frequency-division multiple-access (OFDMA) system. The algorithm allows distinct frequency-offsets (FO)s between each user and the base-station (BS). FOs cause inter-ca...
Conference Paper
In this work to exploit the benefits of both multiple-input multiple-output (MIMO)-radar and phased-array a waveform covariance matrix is proposed. Our analytical results show that the proposed covariance matrix yields gain in signal-to-interference-plus-noise ratio (SINR) compared to MIMO-radar while the gain in SINR is close to phased-array and r...
Conference Paper
In this work, an algorithm for the multiple-input multiple-output (MIMO) radar is proposed. It has low computational complexity compared to the available schemes, and relatively low side-lobe-levels in the receive beampattern compared to the phased-array and MIMO-radar. In the proposed algorithm, the received signal vector of MIMO-radar is divided...
Conference Paper
The design of waveforms with specified auto- and cross-correlation properties has a number of applications in multiple-input multiple-output (MIMO) radar, one of them is the desired transmit beampattern design. In this work, an algorithm is proposed to generate quadrature phase shift-keying (QPSK) waveforms with required cross-correlation propertie...
Conference Paper
Multiple input multiple output (MIMO) radars have many advantages over their phased-array counterparts: improved spatial resolution; better parametric identifiably and greater flexibility to acheive the desired transmit beampattern. The desired transmit beampatterns using MIMO-radar requires the waveforms to have arbitrary auto- and cross-correlati...
Article
Multiple-input multiple-output (MIMO) radars have many advantages over their phased-array counterparts: improved spatial resolution; better parametric identifiably and greater flexibility to design the transmit beampattern. The design of the transmit beampatterns generally requires the waveforms to have arbitrary auto- and cross-correlation propert...
Article
Full-text available
Multiple-input multiple-output (MIMO) radars have many advantages over their phased-array counterparts: improved spatial resolution; better parametric identifiably and greater flexibility to design the transmit beampattern. The design of the transmit beampatterns generally requires the waveforms to have arbitrary auto-and cross-correlation properti...
Conference Paper
Designing transmit beampattern with MIMO radars generally requires the waveforms to be able to have arbitrary cross-correlation values. In contrast to the available algorithms, the proposed technique provides a closed-form solution for the synthesis of covariance matrix, R, of the waveforms to obtain desired beampattern match. To synthesis R the co...
Conference Paper
A method for generating constant envelope (CE) waveforms to realise a given covariance matrix for a closely spaced MIMO radar system is proposed. In contrast to available algorithms, the technique provides closed form solutions for finding the required waveforms and suggests that waveforms can be chosen from finite alphabets such as binary-phase sh...
Article
MIMO-radars have many advantages over the phased-array radars, such as high spatial resolution, better parametric identifiably and much flexibility to design transmit beampattern. The design of transmit beampatterns using MIMO radar generally requires the waveforms to have arbitrary auto-and cross-correlation. The synthesis of the waveform correlat...
Conference Paper
In this work, we propose an iterative algorithm for the detection of transmitted symbols at the uplink of an orthogonal frequency-division multiple access (OFDMA) system. The algorithm allows distinct frequency-offsets (FO)s from each user that cause self- and multiple-access-interference. The proposed algorithm squeezes the interference of subcarr...
Article
Full-text available
In this work, we propose an iterative algorithm for the detection of transmitted symbols at the uplink of an orthogonal frequency-division multiple access (OFDMA) system. The algorithm allows distinct frequency-offsets (FO)s from each user that cause multiple-access and self interference. The proposed algorithm squeezes the interference of subcarri...
Article
In this paper, we investigate two reduced-complexity iterative soft interference cancellation minimum mean square error (SIC-MMSE) receivers for frequency-selective multiple-input-multiple-output (MIMO) channels. In the first receiver, the extrinsic information is exchanged between the SIC-MMSE equalizer and the channel decoding stages at each iter...
Article
The authors propose a three-node full diversity cooperative protocol, which allows the retransmission of all symbols. By allowing multiple nodes to transmit simultaneously, relaying transmission only consumes limited bandwidth resource. To facilitate the performance analysis of the proposed cooperative protocol, the lower and upper bounds of the ou...
Conference Paper
Full-text available
In recent years, due to the low complexity nature of the turbo processing and excellent bit-error-rate (BER) performance, designing turbo-like receivers for frequency-selective MIMO channels has been of great research interest. The performance gain in turbo decoders is due to an extrinsic information transfer (EXIT) process between the detection an...
Article
In this paper, a reduced-complexity soft-interference-cancellation minimum mean-square-error (SIC-MMSE) iterative equalization method for severe time-dispersive multiple-input-multiple-output (MIMO) channels is proposed. To mitigate the severe time dispersiveness of the channel, a single carrier with cyclic prefix is employed, and the equalization...
Conference Paper
Full-text available
In this work, we show a new method which can directly encode an I (in-phase) and Q (quadrature-phase) baseband data stream onto a circularly polarized (CP) microwave signal. Here I and Q components are fed directly into a two port CP antenna in order to yield right hand circular polarized (RHCP) or left hand circular polarized (LHCP) waveforms each...
Conference Paper
The application of turbo principle in designing receivers for multiple-input multiple-output (MIMO) wireless systems not only achieves practical complexity receiver systems but also near optimal performances for many of the next generation systems. In particular, our recent research has shown that significant performance can be achieved by using a...
Conference Paper
Full-text available
In this paper, we study the bit-error-rate (BER) performance of a novel method of signal detection whereby the signal is modulated by polarization rotation. The method combines two oppositely sensed circularly polarized signals to generate a linearly polarized wave with a spatial tilt angle determined by the phase difference between the two circula...
Conference Paper
In this paper, a spectrally efficient protocol for cooperative transmit diversity is proposed. By allowing multiple nodes to transmit simultaneously, relaying transmission only consumes limited bandwidth resource. To facilitate the performance analysis, the lower and upper bounds of the outage probability are first developed. Then the high signal-t...
Conference Paper
Full-text available
In this work, reduced complexity minimum mean squared error (MMSE) iterative equalization methods for a multiple-input multiple-output (MIMO) frequency selective channel are proposed. To combat the severe time dispersiveness of the channel OFDM is incorporated. Use of OFDM simplifies the challenging problem of equalization in a MIMO system, due to...
Article
Full-text available
Orthogonal frequency division multiplexing (OFDM) requires an expensive linear amplifier at the transmitter due to its high peak-to-average power ratio (PAPR). Single carrier with cyclic prefix (SC-CP) is a closely related transmission scheme that possesses most of the benefits of OFDM but does not have the PAPR problem. Although in a multipath env...
Article
Channel gains and frequency offsets are estimated in a multiple input and multiple output (MIMO) scenario, allowing for more than one path between the transmit and the receive antennas, with each path possibly having a different frequency offset. Such a scenario may arise due to Doppler shift associated with various multipaths. Here, the general ca...
Article
This is an article from the journal, IEEE Transactions on Communications [© IEEE]. It is also available at: http://ieeexplore.ieee.org/ Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to server...
Conference Paper
In a multi-path channel an orthogonal frequency division multiplexing (OFDM) system is very robust to frequency selective fading, but it is sensitive to the time selective fading of the mobile channel. Time selectivity of the channel causes inter-carrier-interference (ICI) in OFDM, thereby degrading the performance significantly and increasing the...
Article
Full-text available
In this work, we focus upon the estimation of the channel parameters of a multiple input and multiple output (MIMO) model, allowing for more than one path between the trans-mit and the receive antennas, with each path possibly having different frequency offsets (FOs). Such a scenario may arise due to Doppler shifts associated with various multipath...
Article
Full-text available
Time selectivity of the channel causes inter-carrier inter-ference (ICI) in orthogonal frequency division multiplexing (OFDM), thereby degrading the system performance signif-icantly and increasing the computational complexity of the receiver. On the other hand, time selectivity introduces tem-poral diversity that can be exploited to improve the pe...

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