arXiv subjects

Ahmad Bazzi

Publications and source records attributed to Ahmad Bazzi.

45 records · Page 3Linked to original sources

arXiv2023

Secure Full Duplex Integrated Sensing and Communications

The following paper models a secure full duplex (FD) integrated sensing and communication (ISAC) scenario, where malicious eavesdroppers aim at intercepting the downlink (DL) as well as the uplink (UL) information exchanged between the dual functional radar and communication (DFRC) base station (BS) and a set of communication users. The DFRC BS, on the other hand, aims at illuminating radar beams at the eavesdroppers in order to sense their physical parameters, while maintaining high UL/DL secrecy rates. Based on the proposed model, we formulate a power efficient secure ISAC optimization framework design, which is intended to guarantee both UL and DL secrecy rates requirements, while illuminating radar beams towards eavesdroppers. The framework exploits artificial noise (AN) generation at the DFRC BS, along with UL/DL beamforming design and UL power allocation. We propose a beamforming design solution to the secure ISAC optimization problem. Finally, we corroborate our findings via simulation results and demonstrate the feasibility, as well as the superiority of the proposed algorithm, under different situations. We also reveal insightful trade-offs achieved by our approach.

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arXiv2023

Deep Learning-based Estimation for Multitarget Radar Detection

Target detection and recognition is a very challenging task in a wireless environment where a multitude of objects are located, whether to effectively determine their positions or to identify them and predict their moves. In this work, we propose a new method based on a convolutional neural network (CNN) to estimate the range and velocity of moving targets directly from the range-Doppler map of the detected signals. We compare the obtained results to the two dimensional (2D) periodogram, and to the similar state of the art methods, 2DResFreq and VGG-19 network and show that the estimation process performed with our model provides better estimation accuracy of range and velocity index in different signal to noise ratio (SNR) regimes along with a reduced prediction time. Afterwards, we assess the performance of our proposed algorithm using the peak signal to noise ratio (PSNR) which is a relevant metric to analyse the quality of an output image obtained from compression or noise reduction. Compared to the 2D-periodogram, 2DResFreq and VGG-19, we gain 33 dB, 21 dB and 10 dB, respectively, in terms of PSNR when SNR = 30 dB.

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arXiv2023

Chirp Spread Spectrum-based Waveform Design and Detection Mechanisms for LPWAN-based IoT -- A Survey

LoRa is a widely adopted method of utilizing chirp spread spectrum (CSS) techniques at the physical (PHY) layer to facilitate low-power wide-area network (LPWAN) connectivity. By tailoring the spreading factors, LoRa can achieve a diverse spectral and energy efficiency (EE) levels, making it amenable to a plethora of Internet-of-Things (IoT) applications that rely on LPWANs. However, a primary drawback of LoRa is its relatively low data data rate. Despite this, there has been a dearth of research dedicated to enhancing the data transfer capabilities of LoRa until recently, when a plethora of CSS-based PHY layer alternatives to LoRa for LPWANs was proposed. This survey, for the first time, presents a comprehensive examination of the waveform design of these CSS-based PHY layer alternatives, proposed between \(2019\) and \(2022\). A total of fifteen alternatives to LoRa are analyzed. This study delves deeply into the waveform design of alternatives to LoRa. The CSS schemes studied in this study are classified into three categories: single chirp, multiple chirps, and multiple chirps with index modulation, based on the number of activated frequency shifts activated for un-chirped symbols. The transceiver architecture of these schemes is thoroughly explicated. Additionally, we propose coherent/non-coherent detection mechanisms for specific schemes that have not been previously documented in the literature. We also provide some key insights and recommendations based on the performance of the schemes. The performance of the schemes is evaluated based on metrics such as EE, spectral efficiency, the bit-error-rate (BER) in additive white Gaussian noise, and BER in the presence of phase and frequency offsets. Finally, we highlight some open research issues and future research directions in this field.

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arXiv2023

Robust Integrated Sensing and Communication Beamforming for Dual-functional Radar and Communications: Method and Insights

This work presents a novel robust beamforming design dedicated for dual-functional radar and communication (DFRC) base stations (BSs) in the context of integrated sensing and communications (ISAC). The architecture is intended for circumstances with imperfect channel state information (CSI). Our suggested approach demonstrates several tradeoffs for joint radar-communication deployment. Due to the DFRC nature of the design, the beamformer can simultaneously point towards an intended target, while optimizing communication quality of service. We unveil several insights regarding closed form expressions, as well as optimality of the proposed beamformer. Lastly, simulation results demonstrate the effectiveness of the proposed ISAC beamformer.

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arXiv2023

On Integrated Sensing and Communication Waveforms with Tunable PAPR

We present a novel approach to the problem of dual-functional radar and communication (DFRC) waveform design with adjustable peak-to-average power ratio (PAPR), while minimizing the multi-user communication interference and maintaining a similarity constraint towards a radar chirp signal. The approach is applicable to generic radar chirp signals and for different constellation sizes. We formulate the waveform design problem as a non convex optimization problem. As a solution, we adopt the alternating direction method of multipliers (ADMM), hence iterating towards a stable waveform for both radar and communication purposes. Additionally, we prove convergence of the proposed method and analyze its computational complexity. Moreover, we offer an extended version of the method to cope with imperfect channel state information (CSI). Finally, we demonstrate its superior performance through simulations, in comparison to state-of-the-art radar-communication waveform designs.

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arXiv2023

On Outage-based Beamforming Design for Dual-Functional Radar-Communication 6G Systems

This article studies and derives beamforming design in a dual-functional radar-communication (DFRC) multiple-input-multiple-output system. We focus on a scenario, where the DFRC base station communicates with downlink communication users, with imperfect channel state information knowledge, and performs target detection, all via the same transmit signal. Through careful relaxation procedures, we arrive at a suitable and novel optimization problem, which maximizes the radar output power in the Bartlett sense, under probabilistic outage signal-to-interference-and-noise ratio constraints. Theoretical analysis proves optimality of the solution given by the relaxed version of the problem, as well as closed-form solutions in certain scenarios. Finally, the achieved performances and trade-offs of the proposed beamforming design are demonstrated through numerical simulations.

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arXiv2022

RIS-Enabled Passive Radar towards Target Localization

In this paper, we study a communication-centric integrated sensing and communication (ISAC) approach, where an access point (AP) communicates with users, while a passive radar (PR) is present in the environment. We investigate the deployment of a reconfigurable intelligent surface (RIS) to enable the PR to localize a target. We derive an optimization problem for updating the phase shifters of the RIS per epoch. Due to the limited information at the PR, such as unknown payload information and unknown number of targets in the scene, we propose two methods capable of performing joint angle of arrival estimation and detection of the targets. We demonstrate the superior performance of the methods onto the proposed setting through numerical simulations, in comparison to a no-RIS baseline scheme.

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arXiv2022

Dual-Mode Time Domain Multiplexed Chirp Spread Spectrum

We propose a dual-mode (DM) time domain multiplexed (TDM) chirp spread spectrum (CSS) modulation for spectral and energy-efficient low-power wide-area networks (LPWANs). DM-CSS modulation that uses both the even and odd cyclic time shifts has been proposed for LPWANs to achieve noteworthy performance improvement over classical counterparts. However, its spectral efficiency (SE) is half of the in-phase and quadrature (IQ)-TDM-CSS scheme that employs IQ components with both up and down chirps, resulting in a SE that is four times relative to Long Range (LoRa) modulation. Nevertheless, the IQ-TDM-CSS scheme only allows coherent detection. Furthermore, it is also sensitive to carrier frequency and phase offsets, making it less practical for low-cost battery-powered LPWANs for Internet-of-Things (IoT) applications. DM-CSS uses either an up-chirp or a down-chirp. DM-TDM-CSS consists of two chirped symbols that are multiplexed in the time domain. One of these symbols consisting of even and odd frequency shifts (FSs) is chirped using an up-chirp. The second chirped symbol also consists of even and odd FSs, but they are chirped using a down-chirp. It shall be demonstrated that DM-TDM-CSS attains a maximum achievable SE close to IQ-TDM-CSS while also allowing both coherent and non-coherent detection. Additionally, unlike IQ-TDM-CSS, DM-TDM-CSS is robust against carrier frequency and phase offsets.

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arXiv2022

Dual-Mode Chirp Spread Spectrum Modulation

In this letter, we propose dual-mode chirp spread spectrum (DM-CSS) modulation for low-power wide-area networks. DM-CSS is capable of achieving a higher spectral efficiency (SE) relative to its counterparts, such as Long Range (LoRa) modulation. Considering the same symbol period, the SE in DM-CSS are augmented by: (i) simultaneously multiplexing even and odd chirp signals; (ii) using phase shifts of \(0\) and \(π\) radians for both even and odd chirp signals; and (iii) using either up-chirp or down-chirp signal. The SE increases by up to \(116.66\%\) for the same bandwidth and spreading factor relative to LoRa. We present a complete transceiver architecture along with non-coherent detection process. Simulation results reveal that DM-CSS is not only more spectral efficient but also more energy efficient than most classical counterparts. It is also demonstrated that DM-CSS is robust to phase and frequency offsets.

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