Ahmad Dhaini | American University of Beirut (original) (raw)

Papers by Ahmad Dhaini

IEEE Access, 2018

Keratoconus is a progressive eye disease that may lead to significant loss of visual acuity. Corn... more Keratoconus is a progressive eye disease that may lead to significant loss of visual acuity. Corneal cross-linking (CXL) is a surgical procedure that halts the progression of keratoconus. One commonly used clinical indicator of CXL success, albeit being an indirect one, is the presence and depth of stromal demarcation line. In addition, corneal haze beyond the demarcation line can be an ominous sign of loss of corneal transparency, which is a much dreaded side effect of CXL. To date, ophthalmologists evaluate the presence and depth of the demarcation line and grade corneal haze using slit lamp biomicroscopy and/or optical coherence tomography (OCT). Interpreting the output of the former is very biased at best, while analyzing the information presented by the latter is time consuming, potentially error prone, and observer dependent. In this paper, we propose the first method that employs image analysis and machine learning to automatically detect and measure corneal haze and demarcation line presence and depth in OCT images. The automated method provides the user with haze statistics as well as visual annotation, reflecting the shape and location of the haze and demarcation line in the cornea. Our experimental results demonstrate the efficacy and effectiveness of the proposed techniques visa -vis manual measurements in a much faster, repeatable, and reproducible manner. INDEX TERMS Medical image analysis, optical coherence tomography, keratoconus, crosslinking, corneal haze.

Journal of Communications, May 1, 2012

Maximizing the optical network unit's (ONU) sleep time is an effective approach for achieving max... more Maximizing the optical network unit's (ONU) sleep time is an effective approach for achieving maximum energy conservation in green Ethernet passive optical networks (EPONs). While overlapping downstream and upstream ONU transmissions can maximize the ONU sleep time, it jeopardizes the quality of service (QoS) performance of the network, especially for downstream traffic in case the overlapping is based on the upstream time slot. In this paper, we study the downstream traffic performance in green EPONs under the limited service discipline and the upstream-based overlapped time window. Specifically, we first derive the expected mean packet delay, and then present a closed-form expression of the ONU sleep time, setting identical upstream/downstream transmission cycle times based on a maximum downstream traffic delay requirement. With the proposed system model, we present a novel downstream bandwidth allocation scheme for energy conservation in green EPONs. Simulation results verify the proposed model and highlight the advantages of our scheme over conventional approaches.

Journal of Optical Communications and Networking, Jun 9, 2010

IEEE Communications Magazine, 2011

Ethernet passive optical networks (EPONs) are being designed to deliver multiple services and app... more Ethernet passive optical networks (EPONs) are being designed to deliver multiple services and applications, such as voice communications (VoIP), standard and high-definition video (STV and HDTV), video conferencing (interactive video) and data traffic access network. However, most of the current work focuses on inter-ONU dynamic bandwidth allocation (DBA) algorithms. In this paper, we concentrate on the intra-ONU bandwidth allocation for

IEEE Communications Magazine, Aug 1, 2015

Journal of Lightwave Technology, Oct 15, 2014

Journal of Lightwave Technology, Jul 1, 2007

Ethernet passive optical networks (EPONs) are designed to deliver services for numerous applicati... more Ethernet passive optical networks (EPONs) are designed to deliver services for numerous applications such as voice over Internet protocol, standard and high-definition video, video conferencing (interactive video), and data traffic. Various dynamic bandwidth allocation and intra-optical network unit (ONU) scheduling algorithms have been proposed to enable EPONs to deliver differentiated services for traffic with different quality of service (QoS) requirements. However, none of these protocols and schedulers can guarantee bandwidth for each class of service nor can they protect the QoS level required by admitted real-time traffic streams. In this paper, we propose the first framework for per-stream QoS protection in EPONs using a two-stage admission control (AC) system. The first stage enables the ONU to perform flow admission locally according to the bandwidth availability, and the second stage allows for global AC at the optical line terminal. Appropriate bandwidth allocation algorithms are presented as well. An event-driven simulation model is implemented to study the effectiveness of the proposed schemes in providing and protecting QoS. Index Terms-Access networks, admission control, ethernet passive optical network (EPON), quality of service (QoS). I. INTRODUCTION T HE Ethernet passive optical network (EPON) [1] represents the convergence of inexpensive and ubiquitous Ethernet equipment with low-cost fiber infrastructure. It is viewed as an attractive solution for the broadband access network bottleneck; EPON is a point-to-multipoint access network with no active elements in the signal's path from source to destination. It has been standardized by the IEEE 802.3ah Working Group [4], and it comprises one optical line terminal (OLT, at the Central Office) and a number of optical network units (ONUs) and provides broadband video, data, and voice services to end customers. EPON systems currently deploy only one channel for downstream traffic and another channel for upstream traffic. In the downstream, Ethernet frames are broadcast by the OLT and are selectively received by each ONU.

Cloud computing has been the killer technology for offering dynamically scalable infrastructure t... more Cloud computing has been the killer technology for offering dynamically scalable infrastructure to modern Internet applications. However, cloud networks can be a burden for latency-sensitive applications such as Tactile Internet, which can't afford the high delay due to communication with remote cloud servers. In this paper, we exploit content distribution networks deployed by Internet service providers, and next-generation passive optical networks to construct agile, programmable and scalable Optical CLoud Distribution Networks (OCLDN). With OCLDN, a software defined networking (SDN)-based mini-cloud data center is installed at the central office, which includes a cloud-based tactile steering server, and supports all types of cloud applications. To meet the stringent quality-of-service (QoS) requirements for new and existing services, we propose a new Dynamic Wavelength and Bandwidth Allocation scheme, which employs the Water-Filling technique and advanced intra- ONU scheduling. Extensive simulations are performed; results highlight the effectiveness of the proposed scheme in supporting the new types of services without impairing the QoS demands for new and legacy data services.

The global network energy consumption is increasing at an alarming rate due to proliferation of t... more The global network energy consumption is increasing at an alarming rate due to proliferation of the Internet and its increasing bandwidth-intensive applications. In this paper, we propose an energy efficient Access/In-Building architecture that features energy efficient customer premises equipment (CPE) design in conjunction with an energy efficient access network protocol, and in-building optical/wireless integration using Radio-over-Fiber. We analyze the energy consumption of the proposed architecture and show that the use of these technologies could lead to up to 50% energy savings compared to the architectures that employ legacy technologies.

Optical Flow Switching (OFS) is promised to be an efficient solution for large Internet data tran... more Optical Flow Switching (OFS) is promised to be an efficient solution for large Internet data transfers. In this paper, we introduce UltraFlow Access, a novel optical access network architecture that offers dual-mode service to its end-users: IP and OFS. With UltraFlow Access, we design and implement a new control plane and a novel dual-mode network stack to ensure efficient connection setup, and reliable and optimal data transmission. Experimental testbed results demonstrate concurrent error-free transmission of 10 Gbps per-wavelength OFS and 1.25 Gbps conventional IP, delivered over the same infrastructure.

Journal of Optical Communications and Networking, Nov 21, 2013

Electrical packet switching is well known as a flexible solution for small data transfers, wherea... more Electrical packet switching is well known as a flexible solution for small data transfers, whereas optical flow switching (OFS) might be an effective solution for large Internet file transfers. The UltraFlow project, a joint effort of three universities, Stanford, Massachusetts Institute of Technology, and University of Texas-Dallas, aims at providing an efficient dual-mode solution (i.e., IP and OFS) to the current network. In this paper, we propose and experimentally demonstrate UltraFlow Access, a novel optical access network that enables dual-mode service to the end users: IP and OFS. The new architecture cooperates with legacy passive optical networks (PONs) to provide both IP and novel OFS services. The latter is facilitated by a novel optical flow network unit (OFNU) that we have proposed, designed, and experimentally demonstrated. Different colored and colorless OFNU designs are presented, and their impact on the network performance is explored. Our testbed experiments demonstrate concurrent bidirectional 1.25 Gbps IP and 10 Gbps per-wavelength Flow error-free communication delivered over the same infrastructure. The support of intra-PON OFS communication, that is, between two OFNUs in the same PON, is also explored and experimentally demonstrated. Index Terms-Dual-mode transmission; Optical access network; Optical flow switching (OFS); Passive optical network (PON).

Journal of Lightwave Technology, May 1, 2011

Research and development on optical networks generally and on Passive Optical Networks (PON) part... more Research and development on optical networks generally and on Passive Optical Networks (PON) particularly have matured considerably. The exponential increase in the demand for bandwidth has exposed many challenges in the "last mile" that remains the bottleneck in broadband access networks. Currently, Ethernet PON has emerged as the most inexpensive panacea, providing more bandwidth than Cable Modems and Digital Subscriber Lines. Nevertheless, providing fair and efficient Quality of Service (QoS) has always been a major issue due to the un-deterministic nature of Time Division Multiple Access (TDMA) technology and the limited 1 Gbps channel speed that EPON relies on; unlike backbone networks that uses the Wavelength Division Multiplexing (WDM) technology. This book instruments these challenges and issues and offers effective solutions. More specifically, it presents an upgrade from a TDM-PON to a Hybrid TDM/WDM-PON and proposes and validates the first framework that enables for per-stream QoS protection in EPON using a new fair QoS scheduler. The book addresses professionals in optical and access networks. It is also directed towards researchers who would like to get a novel fragrance of EPONs.

First and foremost, I wish to express my sincere thanks and gratitude to my thesis supervisor, Pr... more First and foremost, I wish to express my sincere thanks and gratitude to my thesis supervisor, Prof. Pin-Han Ho, for his expert guidance, help, and support throughout my research work. Professor Ho's boundless enthusiasm and persistent commitment to high quality research have extremely contributed to this thesis. I would also like to thank my collaborators, Prof. Xiaohong Jiang and Prof. Gangxiang Shen, for their constructive comments on major parts of this work. I must also thank my colleagues and friends Jean-Paul, Marko, James, Emad, as well as my kind office-mates Amir and Helen for their friendships and discussions who have taught me many things during my studies. I thank all the staff members in the Electrical and Computer Engineering (ECE) Department for their kind and warm assistance. I also thank the Faculty of Engineering and Computer Science at University of Waterloo, for their superb teaching environment. I thank Prof. Johnny Wong, Prof. Zhou Wang, and Prof. Paul Ward for serving on my thesis examining committee, and for their kind and constructive comments. I am also very thankful to Prof. Suresh Subramaniam for serving as the external thesis examiner and for his great observations and comments. It is a great honor to have you all as my thesis committee. My warmest appreciation goes to all my great friends for their support and love during my Ph.D. studies. The list is too long to be accommodated¨. However, I must especially thank Michelle, Jalal, Imad, Benjamin, Khoder, Sandra, and Hussein for always being there for me. Words cannot describe how lucky and honored I am to have you guys in my life. My deepest gratitude and love go to my dear sisters, brother, father, and dearly beloved mother whom with their endless giving love and support throughout my life made everything possible.

ABSTRACT Energy efficiency is rapidly becoming an important requirement for modern networks. In t... more ABSTRACT Energy efficiency is rapidly becoming an important requirement for modern networks. In this paper, we discuss the physical limits to the power consumption of wireless and optical transmission. We show that there is an optimum cell size that results in the least power consumption in optical/wireless in-building networks and explain why. We then discuss the principles that govern the design of in-building Radio-over-Fiber (RoF) distribution networks. We use theoretical models to analyze the impact of key design factors on the energy consumption of point-to-point RoF links and how their adverse effects can be mitigated. Finally, we compare the energy consumption of several key in-building optical/wireless architectures based on several different RoF technologies, and demonstrate that centralized architectures based on RoF links can be substantially more energy efficient than baseband-over-fiber (BoF) architectures in network capacity-limited scenarios, when designed properly. Our findings also show that RoF-based architectures are energy efficient for cell sizes less than 10m.

Radio-over-Fiber (RoF) based network architectures would allow centralization of signal processin... more Radio-over-Fiber (RoF) based network architectures would allow centralization of signal processing and signal conditioning functions and simple, cost-effective remote units at the cell site. RoF technology results in remote units with few components, however, certain aspects of the technology may inadvertently lead to high power consuming components. In this paper, we experimentally investigate the effect of electrical-optical-electrical (E/O/E) loss and signal bandwidth on the energy consumption of analog and digitized RoF (ARoF and DRoF) links. We also analyze the energy efficiency of multiple services on a single RoF distribution network. Our results show that E/O/E loss significantly degrades the energy efficiency of the ARoF links. DRoF is robust to the E/O/E loss on the optical link but is affected by the loss due to reconstruction of the radio frequency signal at higher Nyquist zones. We also show that increasing the bandwidth improves the energy efficiency. Finally, we demonstrate that the extra energy savings from having multiple services on a single RoF link depends on the wireless environment.