Ieee Transactions on Intelligent Transportation Systems, Nov 13, 2013
This paper presents a concise yet comprehensive description of a multi-channel Vehicle-to-Infrast... more This paper presents a concise yet comprehensive description of a multi-channel Vehicle-to-Infrastructure (V2I) communication system. Existing mathematical models for such a system overlook some of its essential behavioural characteristics such as the reneging, force-termination and ultimately blocking of service requests. Thus, the reported performance results obtained from these models seem to be unrealistically overoptimistic. Accordingly, in this paper, a multi-server queueing model is proposed for the purpose of accurately capturing the dynamics of the above-mentioned communication system and evaluating its performance. The proposed model is renowned for its complexity and the nonexistance of closed-form analytical expressions that characterize its fundamental performance metrics. Hence, approximations were exploited as a mean to enhance this model's mathematical tractability. Simulations are conducted in the context of a realistic scenario with the objective of validating the proposed approximate model, verifying its accuracy and characterizing the system's performance in terms of several new metrics. The simulations' results indicate a cataclysmic service request blocking probability in the range of 65% to 85%.
The contemporary problem of scheduling the recharge operations of electric vehicles (EVs) has gai... more The contemporary problem of scheduling the recharge operations of electric vehicles (EVs) has gained a lot of research attention. This is particularly true given the governmental and industrial confidence in a bright future for EVs accompanied with the widespread installation of an enormous number of charging stations across the world. As such, this paper addresses the delay-optimal scheduling of charging EVs at several Charging Stations (CSs) each with multiple charging outlets. At first, a centralized optimization framework is formulated using an Integer Linear Problem (ILP) that accounts for the delayed arrival of EVs to CSs and the randomness in the requested recharge time interval. Simulation results showed the efficacy of the ILP model when compared to na\"{i}ve as well as sophisticated scheduling heuristics. Next, motivated by the scalability issues of the ILP model, this paper then proposes a distributed game-theoretical approach where each EV communicates its selected CS and iterates on modifying its strategy until all EVs converge to selecting an appropriate CS that minimizes their waiting times for receiving services. The distributed game-theoretical approach recorded promising results especially when compared to the well-known Shortest Job First scheduling algorithm. Further, unlike the other approaches which normally are centralized and suited for offline scheduling, the game-based method is suited for online scheduling since it is played at anytime a batch of EVs requests charging services. The running time of the game is remarkably small and outperforms all other heuristics and its convergence to Nash equilibrium is guaranteed after only small number of iterations.
Relay-assisted Free Space Optical (FSO) systems
were proposed as a means for remedying the effect... more Relay-assisted Free Space Optical (FSO) systems were proposed as a means for remedying the effects of the various atmospheric impairments on the quality of the FSO signal. Conventional relay-assisted FSO systems are however designed around two basic assumptions: a) relays are buffer-free, and b) relays are stationary. This paper proposes to improve the performance of the existing relay-assisted FSO systems by relaxing both of these highly restrictive assumptions through the integration of Unmanned Aerial Vehicles (UAVs) as bufferaided moving relays into the conventional relay-assisted FSO systems. Specifically, two possible simple integration scenarios are proposed and analyzed through simulation. The obtained simulation results demonstrate the great potential associated with the proposed highly promising, innovative, hybrid FSO architecture. Given that high performance gains are observed under small buffer sizes, it becomes conceivable to employ the buffer-aided moving relaying UAVs to serve a variety of other purposes. This includes, for instance, having these UAVs oversee the operation of amateur drones for potential misbehavior or wrongdoing within the area of their deployment.
Elsevier Journal of Pervasive and Mobile Computing, 2015
This paper presents a concise yet comprehensive description of a multi-channel Vehicleto-Infrastr... more This paper presents a concise yet comprehensive description of a multi-channel Vehicleto-Infrastructure (V2I) communication system. Existing mathematical models for such a system overlook some of its essential behavioural characteristics such as the reneging, force-termination and ultimately blocking of service requests. A multi-server queueing model with First-In–First-Out (FIFO) service policy is proposed for the purpose of accurately capturing the dynamics of the above-mentioned communication system and evaluating its performance. Approximations were exploited as a mean to enhance this model’s mathematical tractability. Simulations are conducted in the context of a realistic scenario with the objective of validating the proposed approximate model, verifying its accuracy and characterizing the system’s performance in terms of several new metrics. The reported results indicate a cataclysmic access request blocking probability ranging from 66% to 85%. An Access Request Deadline-Aware (ARDA) service policy is then proposed to reduce the blocking probability and improve the system’s response time. Indeed ARDA achieved an improvement over FIFO of almost 70% in terms of the overall blocking probability and 22% to 66% in terms of the system’s response time.
Recent advances in optical networking technologies are setting the foundation for the next-genera... more Recent advances in optical networking technologies are setting the foundation for the next-generation data-centric networking paradigm, an``Optical Internet''. This work addresses one of the most challenging issues facing today's service providers and data vendors; how will the SONET/SDH-based legacy infrastructure currently in place make a graceful transition to the next generation networking paradigm?
INTERCHANGING THE SEARCH SPACE BETWEEN THE LOGICAL AND PHYSICAL LAYERS IN FUTURE IP OPTICAL NETWO... more INTERCHANGING THE SEARCH SPACE BETWEEN THE LOGICAL AND PHYSICAL LAYERS IN FUTURE IP OPTICAL NETWORKS Antonis Hadjiantonis, Ahmad Khalil, and MA Ali Dept. of Electrical Engineering The City College ...
Dynamic bandwidth allocation and grant scheduling are important factors when designing passive op... more Dynamic bandwidth allocation and grant scheduling are important factors when designing passive optical networks. In this paper, we investigate the problem of optimal scheduling and bandwidth allocation in next generation 10G-EPON coexisting with 1G WDM-PONs. We propose a network architecture for providing this coexistence and derive an ILP model for offline joint scheduling and bandwidth assignment for 10G-TDM and 1G-WDM ONUs. To address the scalability of the ILP model, we introduce a Tabu Search based heuristic for efficiently obtaining near optimal solutions. We further explore the tradeoff which exists in terms of delay, scheduling length, and channel utilization, when separate or the same DBA modules are used for 1G-and 10G-ONUs.
Ieee Transactions on Intelligent Transportation Systems, Mar 15, 2013
"This paper presents an in-depth investigation on the feasibility of Dynamic Spe... more "This paper presents an in-depth investigation on the feasibility of Dynamic Spectrum Access (DSA) in vehicular environments. We present a comprehensive description of the DSA-based Vehicle-to-Infrastructure (V2I) communication as it takes place in the context of a scenario where spectral resources are limited. Founded on top of this description is a queueing model whose primary objectives are to capture and characterize the dynamics of this type of communication systems as well as to assess its performance in terms of several classical metrics. Simplicity, and tractability distinguish the proposed model herein from existing models in the literature. Extensive simulations and numerical analysis are conducted for the purpose of validating the proposed model as well as to evaluate the performance of DSA-based communication and highlight its limitations."
Ieee Osa Journal of Optical Communications and Networking, 2009
At present there is a strong worldwide push toward bringing fiber closer to individual homes and ... more At present there is a strong worldwide push toward bringing fiber closer to individual homes and businesses. Another evolutionary step is the cost-effective all-optical integration of fiber-based access and metro networks. STARGATE (IEEE Commun. Mag., vol. 45, no. 5, pp. 50-56, May 2007) is an alloptical access-metro architecture that does not rely on costly active devices, e.g., optical cross connects or fixed wavelength converters, and allows low-cost passive optical network (PON) technologies to follow low-cost Ethernet technologies from Ethernet PON (EPON) access into metro networks, resulting in significantly reduced cost and complexity. It uses an overlay island of transparency with optical bypassing capabilities. We first propose optical network unit architectures and discuss several technical challenges, which allow STARGATE EPONs (SG-EPONs) to evolve in a pay-as-you-grow manner while providing backward compatibility with legacy infrastructure and protecting previous investment. Second, and considering all the hardware constraints, we present the corresponding dynamic bandwidth allocation algorithm for effective resource management in these networks and investigate their performances (delay, throughput) through simulation experiments.
Ieee Transactions on Intelligent Transportation Systems, Sep 1, 2012
The performance of vehicular data networks (VDNs) is highly dependent on vehicular traffic. Exist... more The performance of vehicular data networks (VDNs) is highly dependent on vehicular traffic. Existing studies on VDNs consider custom-developed traffic models that mimic real-life vehicular traffic behavior and prepare the ground for accurate VDN performance evaluation. Traffic evolution is affected by numerous random events. Some developed models are microscopic. They independently consider some possible factors (e.g., weather, road geometry, and drivers' skills). These microscopic models are complex, and their implementations may be costly. Other models are macroscopic. They revolve around only the following three major traffic parameters: 1) density; 2) flow; and 3) speed. The majority of such existing models are unrealistic, because they are based on restrictive assumptions tailored to their enclosing study. Comparing the performance of VDN protocols becomes adequate if and only if these protocols are all developed on top of the same traffic model. Unfortunately, the opposite is true. Hence, the design of a generic traffic model that serves as a basis for future studies on VDNs is equally urgent and important. This paper presents a comprehensive and traffic-theory-inspired macroscopic description of vehicular traffic behavior over roadway facilities that operate under free-flow traffic conditions. Accordingly, a simple and tractable macroscopic traffic model is proposed. Extensive simulations are conducted to verify the validity of the proposed model and its high accuracy.
This paper addresses the problem of dynamically provisioning both low-speed<xref rid="fn1"type="f... more This paper addresses the problem of dynamically provisioning both low-speed<xref rid="fn1"type="fnote"><footnote id="fn1"> A low-speed connection is a connection request with only a fraction of a wavelength capacity.</footnote></xref> unicast and multicast connection requests in mesh-based wavelength division multiplexing (WDM) optical networks. Several routing/provisioning schemes to dynamically provision both unicast and multicast connection requests are presented. In addition, a constraint-based grooming strategy is devised to utilize the overall network resources as efficiently as possible. Based on this strategy, several different sequential multicast grooming heuristics are first presented. Then, we devise a hybrid grooming approach and combine it with sequential approaches to achieve a grooming scheme that is biased toward serving multicast traffic demands in comparison with all other sequential grooming approaches. To achieve our objective, we decompose the problem into four subproblems: 1) routing problem; 2) light-tree-based logical-topology-design problem; 3) provisioning problem; and 4) traffic-grooming problem. The simulation results of the proposed schemes are compared with each other and with those of conventional nongrooming approaches. To the best of our knowledge, this is the first detailed paper to address and examine the problem of grooming dynamic multicast traffic demands.
In multihop, multi-rate wireless networks, simultaneous transmissions can interfere with one anot... more In multihop, multi-rate wireless networks, simultaneous transmissions can interfere with one another to impair the transmission quality and prevent correct frame reception. Achieving high network performance (e.g. throughout and energy consumption) in such networks therefore requires a balance between the spectrum spatial reuse and the transmission quality. To achieve this trade-off, a decentralised control algorithm is proposed that allows a sender -receiver pair, using the IEEE 802.11 four-way access method, to dynamically adjust the transmit power and rate for their frames according to the level of interference in the network. Specifically, the scheme is based on the interplay between two approaches: physical carrier sensing and virtual carrier sensing approach to achieve this optimal trade-off. The algorithm outlines the rules for performing power and rate assignment so that higher performance is obtained. A realistic analytical model is presented to study the performance of the proposed heuristic; analytical results show that the algorithm proposed by the authors, indeed, finds the balance between spatial reuse and transmission quality through its appropriate search for the suitable transmission parameters. Simulation results for different topologies are used to demonstrate the significant throughput and energy gains that can be obtained by the proposed scheme.
We investigate the problem of grant scheduling in multichannel optical access networks using a sc... more We investigate the problem of grant scheduling in multichannel optical access networks using a scheduling theoretic approach. The network we consider is a novel cost-effective Ethernet Passive Optical Network (EPON) that is designed to operate with STARGATE [2] or any evolutionary MAN. We show that the problem can modeled using an Open Shop model and we present a formulation for the joint scheduling and wavelength assignment problem as a Mixed Integer Linear Program (MILP) whose objective is to reduce the length of a scheduling period. Since the problem is shown to be NP-Hard, we introduce a Tabu Search based heuristic for solving the joint problem. Different other heuristics are also introduced and their performances are compared with those of Tabu and MILP. Results indicate that by appropriately scheduling transmission grants and assigning wavelengths, substantial consistent improvements may be obtained in the network performance.
Abstract Current restoration signaling is a two-phase messaging,procedure between the sender and ... more Abstract Current restoration signaling is a two-phase messaging,procedure between the sender and the receiver and depends heavily on the message propagation delays during the recovery process and the cross-connect switching times. Offset time (OT) based restoration was proposed,in [C. Assi, Y. Ye, S. Dixit, M. Ali. Control and management protocols for survivable optical mesh networks, IEEE Journal of Lightware Technology, November 2003.] to address the impact of these parameters and upper bound (OT-UB) expressions were derived. However, our closer investigation showed,that as the network conditions change (e.g. increasing the number,of wave-length channels per link) the benefits this restoration paradigm offer rapidly diminish, thereby rendering the argument of avoiding conventional restoration signaling inappropriate. In this paper, we propose a more accurate model to estimate the OT of each failed connection using a time-driven scheduling procedure. We also study the applicability of the proposed,recovery protocol under double link failures assumption,and we propose extensions to the protocol. We evaluate our proposal through simulation experiments,and we show,that substantial restoration gain can be achieved under varying network conditions. q 2005 Elsevier B.V. All rights reserved. Keywords: Optical networks; Shared mesh restoration; Protocols; Dual failures; Simulations
Advanced wireless technologies are, nowadays, being exploited as means for intelligent transporta... more Advanced wireless technologies are, nowadays, being exploited as means for intelligent transportation management and on-the-road driving assistance. However, the recent synergic efforts in both industry and academia are symptomatic of a paradigm shift in Intelligent Transportation Systems. Today's vehicles, being equipped with computerized modules and wireless devices, characterize themselves by a revolutionary smart personality. In particular they can carry and distribute information, they inter-communicate and are capable of communicating with other stationary units deployed along roadways. Most importantly, they can sense. Ultimately, the transportation infrastructure embraces versatile wireless communication systems with the objective of provisioning Wireless Access in Vehicular Environments (WAVE). In order to catalyze the realization of this objective, the U.S. Federal Communications Commissions (FCC) has allocated 75 MHz of spectrum for Dedicated Short Range Communications (DSRC). The Institute of Electrical and Electronics Engineers (IEEE) has specifically tailored the 802.11p standard to regulate access to this spectrum. The IEEE 1609.4 protocol allows for multi-channel access and is currently being standardized. Alternatively, researchers have engaged in the design of scheduling policies for the purpose of increasing the spectrum access efficiency and optimizing the performance of vehicular networks in terms of several classical metrics. The recently emerging spectrum scarcity problem has lead numerous investigations on the potential exploitation of cognitive radios as well as the feasibility of Vehicular Dynamic Spectrum Access (VDSA) schemes with the objective of: a) enhancing spectrum utilization and b) improving the network's throughput and response time. This paper sheds the light over the latest advancements in each of the above-mentioned research sectors and highlights pending open issues in each of them. Vehicular Networks Intermittently Connected Networks Legacy Wireless Networks D e l a y T o l e r a n t N e t w o r k i n g Overlay INTERNET CORE Figure 1: Network interaction diagram.
We discuss a wavelength-division-multiplexed-based passive-optical-network (PON) architecture tha... more We discuss a wavelength-division-multiplexed-based passive-optical-network (PON) architecture that allows for incremental upgrade from single-channel time-division multipleaccess PONs in order to provide higher bandwidth in the access network. Various dynamic-wavelength and bandwidth-allocation algorithms (DWBAs) for wave-division multiplexed PON are presented; they exploit both interchannel and intrachannel statistical multiplexing in order to achieve better performance, especially when the load on various channels is not symmetric. Three variants of the DWBA are presented, and their performance is compared. While the first variant incurs larger idle times (and, hence, poor performance), the other two algorithms achieve better but different performance with critical dissimilarities. Our analysis also focuses on the fair assignment of excessive bandwidth in the upstream direction to highly loaded optical network units. We compare the performance of DWBA to another algorithm that relies on static-channel allocation. Furthermore, a study is presented wherein the number of wavelengths increases, and a comparison with interleaved polling with adaptive cycle time is shown. We use extensive simulations throughout this paper.
Ethernet Passive Optical Networks (EPONs) are considered the most promising solutions for upgradi... more Ethernet Passive Optical Networks (EPONs) are considered the most promising solutions for upgrading the current congested access networks to enable the delivery of broadband integrated services. Although current EPON architectures are economically feasible, they are however bandwidth limited. In this paper, we discuss a simple upgrade architecture from EPON to WDM-PON. We present various Dynamic Wavelength and Bandwidth Allocation algorithms (DWBAs) that exploit both inter-channel and intra-channel statistical multiplexing in order to achieve good performance. We use extensive simulation experiments to validate our reasoning.
2015 IEEE Wireless Communications and Networking Conference (WCNC), 2015
Vehicular Ad hoc Networks have been receiving significant interest during the past years as they ... more Vehicular Ad hoc Networks have been receiving significant interest during the past years as they support both safety and non-safety applications for passengers commuting onboard smart vehicles. Vehicles may communicate with each others for the purpose of sharing information. Moreover, they may be privileged by Broadband Internet access as well as other services provisioned by stationary Roadside Units (RSUs) deployed along the roadways. When a vehicle leaves the coverage range of an RSU, it enters a dark area. However, it may still maintain connectivity with the RSU through multi-hop communication with other cooperative vehicles serving as intermediate relays.
Ieee Transactions on Intelligent Transportation Systems, Nov 13, 2013
This paper presents a concise yet comprehensive description of a multi-channel Vehicle-to-Infrast... more This paper presents a concise yet comprehensive description of a multi-channel Vehicle-to-Infrastructure (V2I) communication system. Existing mathematical models for such a system overlook some of its essential behavioural characteristics such as the reneging, force-termination and ultimately blocking of service requests. Thus, the reported performance results obtained from these models seem to be unrealistically overoptimistic. Accordingly, in this paper, a multi-server queueing model is proposed for the purpose of accurately capturing the dynamics of the above-mentioned communication system and evaluating its performance. The proposed model is renowned for its complexity and the nonexistance of closed-form analytical expressions that characterize its fundamental performance metrics. Hence, approximations were exploited as a mean to enhance this model's mathematical tractability. Simulations are conducted in the context of a realistic scenario with the objective of validating the proposed approximate model, verifying its accuracy and characterizing the system's performance in terms of several new metrics. The simulations' results indicate a cataclysmic service request blocking probability in the range of 65% to 85%.
The contemporary problem of scheduling the recharge operations of electric vehicles (EVs) has gai... more The contemporary problem of scheduling the recharge operations of electric vehicles (EVs) has gained a lot of research attention. This is particularly true given the governmental and industrial confidence in a bright future for EVs accompanied with the widespread installation of an enormous number of charging stations across the world. As such, this paper addresses the delay-optimal scheduling of charging EVs at several Charging Stations (CSs) each with multiple charging outlets. At first, a centralized optimization framework is formulated using an Integer Linear Problem (ILP) that accounts for the delayed arrival of EVs to CSs and the randomness in the requested recharge time interval. Simulation results showed the efficacy of the ILP model when compared to na\"{i}ve as well as sophisticated scheduling heuristics. Next, motivated by the scalability issues of the ILP model, this paper then proposes a distributed game-theoretical approach where each EV communicates its selected CS and iterates on modifying its strategy until all EVs converge to selecting an appropriate CS that minimizes their waiting times for receiving services. The distributed game-theoretical approach recorded promising results especially when compared to the well-known Shortest Job First scheduling algorithm. Further, unlike the other approaches which normally are centralized and suited for offline scheduling, the game-based method is suited for online scheduling since it is played at anytime a batch of EVs requests charging services. The running time of the game is remarkably small and outperforms all other heuristics and its convergence to Nash equilibrium is guaranteed after only small number of iterations.
Relay-assisted Free Space Optical (FSO) systems
were proposed as a means for remedying the effect... more Relay-assisted Free Space Optical (FSO) systems were proposed as a means for remedying the effects of the various atmospheric impairments on the quality of the FSO signal. Conventional relay-assisted FSO systems are however designed around two basic assumptions: a) relays are buffer-free, and b) relays are stationary. This paper proposes to improve the performance of the existing relay-assisted FSO systems by relaxing both of these highly restrictive assumptions through the integration of Unmanned Aerial Vehicles (UAVs) as bufferaided moving relays into the conventional relay-assisted FSO systems. Specifically, two possible simple integration scenarios are proposed and analyzed through simulation. The obtained simulation results demonstrate the great potential associated with the proposed highly promising, innovative, hybrid FSO architecture. Given that high performance gains are observed under small buffer sizes, it becomes conceivable to employ the buffer-aided moving relaying UAVs to serve a variety of other purposes. This includes, for instance, having these UAVs oversee the operation of amateur drones for potential misbehavior or wrongdoing within the area of their deployment.
Elsevier Journal of Pervasive and Mobile Computing, 2015
This paper presents a concise yet comprehensive description of a multi-channel Vehicleto-Infrastr... more This paper presents a concise yet comprehensive description of a multi-channel Vehicleto-Infrastructure (V2I) communication system. Existing mathematical models for such a system overlook some of its essential behavioural characteristics such as the reneging, force-termination and ultimately blocking of service requests. A multi-server queueing model with First-In–First-Out (FIFO) service policy is proposed for the purpose of accurately capturing the dynamics of the above-mentioned communication system and evaluating its performance. Approximations were exploited as a mean to enhance this model’s mathematical tractability. Simulations are conducted in the context of a realistic scenario with the objective of validating the proposed approximate model, verifying its accuracy and characterizing the system’s performance in terms of several new metrics. The reported results indicate a cataclysmic access request blocking probability ranging from 66% to 85%. An Access Request Deadline-Aware (ARDA) service policy is then proposed to reduce the blocking probability and improve the system’s response time. Indeed ARDA achieved an improvement over FIFO of almost 70% in terms of the overall blocking probability and 22% to 66% in terms of the system’s response time.
Recent advances in optical networking technologies are setting the foundation for the next-genera... more Recent advances in optical networking technologies are setting the foundation for the next-generation data-centric networking paradigm, an``Optical Internet''. This work addresses one of the most challenging issues facing today's service providers and data vendors; how will the SONET/SDH-based legacy infrastructure currently in place make a graceful transition to the next generation networking paradigm?
INTERCHANGING THE SEARCH SPACE BETWEEN THE LOGICAL AND PHYSICAL LAYERS IN FUTURE IP OPTICAL NETWO... more INTERCHANGING THE SEARCH SPACE BETWEEN THE LOGICAL AND PHYSICAL LAYERS IN FUTURE IP OPTICAL NETWORKS Antonis Hadjiantonis, Ahmad Khalil, and MA Ali Dept. of Electrical Engineering The City College ...
Dynamic bandwidth allocation and grant scheduling are important factors when designing passive op... more Dynamic bandwidth allocation and grant scheduling are important factors when designing passive optical networks. In this paper, we investigate the problem of optimal scheduling and bandwidth allocation in next generation 10G-EPON coexisting with 1G WDM-PONs. We propose a network architecture for providing this coexistence and derive an ILP model for offline joint scheduling and bandwidth assignment for 10G-TDM and 1G-WDM ONUs. To address the scalability of the ILP model, we introduce a Tabu Search based heuristic for efficiently obtaining near optimal solutions. We further explore the tradeoff which exists in terms of delay, scheduling length, and channel utilization, when separate or the same DBA modules are used for 1G-and 10G-ONUs.
Ieee Transactions on Intelligent Transportation Systems, Mar 15, 2013
&amp;amp;quot;This paper presents an in-depth investigation on the feasibility of Dynamic Spe... more &amp;amp;quot;This paper presents an in-depth investigation on the feasibility of Dynamic Spectrum Access (DSA) in vehicular environments. We present a comprehensive description of the DSA-based Vehicle-to-Infrastructure (V2I) communication as it takes place in the context of a scenario where spectral resources are limited. Founded on top of this description is a queueing model whose primary objectives are to capture and characterize the dynamics of this type of communication systems as well as to assess its performance in terms of several classical metrics. Simplicity, and tractability distinguish the proposed model herein from existing models in the literature. Extensive simulations and numerical analysis are conducted for the purpose of validating the proposed model as well as to evaluate the performance of DSA-based communication and highlight its limitations.&amp;amp;quot;
Ieee Osa Journal of Optical Communications and Networking, 2009
At present there is a strong worldwide push toward bringing fiber closer to individual homes and ... more At present there is a strong worldwide push toward bringing fiber closer to individual homes and businesses. Another evolutionary step is the cost-effective all-optical integration of fiber-based access and metro networks. STARGATE (IEEE Commun. Mag., vol. 45, no. 5, pp. 50-56, May 2007) is an alloptical access-metro architecture that does not rely on costly active devices, e.g., optical cross connects or fixed wavelength converters, and allows low-cost passive optical network (PON) technologies to follow low-cost Ethernet technologies from Ethernet PON (EPON) access into metro networks, resulting in significantly reduced cost and complexity. It uses an overlay island of transparency with optical bypassing capabilities. We first propose optical network unit architectures and discuss several technical challenges, which allow STARGATE EPONs (SG-EPONs) to evolve in a pay-as-you-grow manner while providing backward compatibility with legacy infrastructure and protecting previous investment. Second, and considering all the hardware constraints, we present the corresponding dynamic bandwidth allocation algorithm for effective resource management in these networks and investigate their performances (delay, throughput) through simulation experiments.
Ieee Transactions on Intelligent Transportation Systems, Sep 1, 2012
The performance of vehicular data networks (VDNs) is highly dependent on vehicular traffic. Exist... more The performance of vehicular data networks (VDNs) is highly dependent on vehicular traffic. Existing studies on VDNs consider custom-developed traffic models that mimic real-life vehicular traffic behavior and prepare the ground for accurate VDN performance evaluation. Traffic evolution is affected by numerous random events. Some developed models are microscopic. They independently consider some possible factors (e.g., weather, road geometry, and drivers' skills). These microscopic models are complex, and their implementations may be costly. Other models are macroscopic. They revolve around only the following three major traffic parameters: 1) density; 2) flow; and 3) speed. The majority of such existing models are unrealistic, because they are based on restrictive assumptions tailored to their enclosing study. Comparing the performance of VDN protocols becomes adequate if and only if these protocols are all developed on top of the same traffic model. Unfortunately, the opposite is true. Hence, the design of a generic traffic model that serves as a basis for future studies on VDNs is equally urgent and important. This paper presents a comprehensive and traffic-theory-inspired macroscopic description of vehicular traffic behavior over roadway facilities that operate under free-flow traffic conditions. Accordingly, a simple and tractable macroscopic traffic model is proposed. Extensive simulations are conducted to verify the validity of the proposed model and its high accuracy.
This paper addresses the problem of dynamically provisioning both low-speed<xref rid="fn1"type="f... more This paper addresses the problem of dynamically provisioning both low-speed<xref rid="fn1"type="fnote"><footnote id="fn1"> A low-speed connection is a connection request with only a fraction of a wavelength capacity.</footnote></xref> unicast and multicast connection requests in mesh-based wavelength division multiplexing (WDM) optical networks. Several routing/provisioning schemes to dynamically provision both unicast and multicast connection requests are presented. In addition, a constraint-based grooming strategy is devised to utilize the overall network resources as efficiently as possible. Based on this strategy, several different sequential multicast grooming heuristics are first presented. Then, we devise a hybrid grooming approach and combine it with sequential approaches to achieve a grooming scheme that is biased toward serving multicast traffic demands in comparison with all other sequential grooming approaches. To achieve our objective, we decompose the problem into four subproblems: 1) routing problem; 2) light-tree-based logical-topology-design problem; 3) provisioning problem; and 4) traffic-grooming problem. The simulation results of the proposed schemes are compared with each other and with those of conventional nongrooming approaches. To the best of our knowledge, this is the first detailed paper to address and examine the problem of grooming dynamic multicast traffic demands.
In multihop, multi-rate wireless networks, simultaneous transmissions can interfere with one anot... more In multihop, multi-rate wireless networks, simultaneous transmissions can interfere with one another to impair the transmission quality and prevent correct frame reception. Achieving high network performance (e.g. throughout and energy consumption) in such networks therefore requires a balance between the spectrum spatial reuse and the transmission quality. To achieve this trade-off, a decentralised control algorithm is proposed that allows a sender -receiver pair, using the IEEE 802.11 four-way access method, to dynamically adjust the transmit power and rate for their frames according to the level of interference in the network. Specifically, the scheme is based on the interplay between two approaches: physical carrier sensing and virtual carrier sensing approach to achieve this optimal trade-off. The algorithm outlines the rules for performing power and rate assignment so that higher performance is obtained. A realistic analytical model is presented to study the performance of the proposed heuristic; analytical results show that the algorithm proposed by the authors, indeed, finds the balance between spatial reuse and transmission quality through its appropriate search for the suitable transmission parameters. Simulation results for different topologies are used to demonstrate the significant throughput and energy gains that can be obtained by the proposed scheme.
We investigate the problem of grant scheduling in multichannel optical access networks using a sc... more We investigate the problem of grant scheduling in multichannel optical access networks using a scheduling theoretic approach. The network we consider is a novel cost-effective Ethernet Passive Optical Network (EPON) that is designed to operate with STARGATE [2] or any evolutionary MAN. We show that the problem can modeled using an Open Shop model and we present a formulation for the joint scheduling and wavelength assignment problem as a Mixed Integer Linear Program (MILP) whose objective is to reduce the length of a scheduling period. Since the problem is shown to be NP-Hard, we introduce a Tabu Search based heuristic for solving the joint problem. Different other heuristics are also introduced and their performances are compared with those of Tabu and MILP. Results indicate that by appropriately scheduling transmission grants and assigning wavelengths, substantial consistent improvements may be obtained in the network performance.
Abstract Current restoration signaling is a two-phase messaging,procedure between the sender and ... more Abstract Current restoration signaling is a two-phase messaging,procedure between the sender and the receiver and depends heavily on the message propagation delays during the recovery process and the cross-connect switching times. Offset time (OT) based restoration was proposed,in [C. Assi, Y. Ye, S. Dixit, M. Ali. Control and management protocols for survivable optical mesh networks, IEEE Journal of Lightware Technology, November 2003.] to address the impact of these parameters and upper bound (OT-UB) expressions were derived. However, our closer investigation showed,that as the network conditions change (e.g. increasing the number,of wave-length channels per link) the benefits this restoration paradigm offer rapidly diminish, thereby rendering the argument of avoiding conventional restoration signaling inappropriate. In this paper, we propose a more accurate model to estimate the OT of each failed connection using a time-driven scheduling procedure. We also study the applicability of the proposed,recovery protocol under double link failures assumption,and we propose extensions to the protocol. We evaluate our proposal through simulation experiments,and we show,that substantial restoration gain can be achieved under varying network conditions. q 2005 Elsevier B.V. All rights reserved. Keywords: Optical networks; Shared mesh restoration; Protocols; Dual failures; Simulations
Advanced wireless technologies are, nowadays, being exploited as means for intelligent transporta... more Advanced wireless technologies are, nowadays, being exploited as means for intelligent transportation management and on-the-road driving assistance. However, the recent synergic efforts in both industry and academia are symptomatic of a paradigm shift in Intelligent Transportation Systems. Today's vehicles, being equipped with computerized modules and wireless devices, characterize themselves by a revolutionary smart personality. In particular they can carry and distribute information, they inter-communicate and are capable of communicating with other stationary units deployed along roadways. Most importantly, they can sense. Ultimately, the transportation infrastructure embraces versatile wireless communication systems with the objective of provisioning Wireless Access in Vehicular Environments (WAVE). In order to catalyze the realization of this objective, the U.S. Federal Communications Commissions (FCC) has allocated 75 MHz of spectrum for Dedicated Short Range Communications (DSRC). The Institute of Electrical and Electronics Engineers (IEEE) has specifically tailored the 802.11p standard to regulate access to this spectrum. The IEEE 1609.4 protocol allows for multi-channel access and is currently being standardized. Alternatively, researchers have engaged in the design of scheduling policies for the purpose of increasing the spectrum access efficiency and optimizing the performance of vehicular networks in terms of several classical metrics. The recently emerging spectrum scarcity problem has lead numerous investigations on the potential exploitation of cognitive radios as well as the feasibility of Vehicular Dynamic Spectrum Access (VDSA) schemes with the objective of: a) enhancing spectrum utilization and b) improving the network's throughput and response time. This paper sheds the light over the latest advancements in each of the above-mentioned research sectors and highlights pending open issues in each of them. Vehicular Networks Intermittently Connected Networks Legacy Wireless Networks D e l a y T o l e r a n t N e t w o r k i n g Overlay INTERNET CORE Figure 1: Network interaction diagram.
We discuss a wavelength-division-multiplexed-based passive-optical-network (PON) architecture tha... more We discuss a wavelength-division-multiplexed-based passive-optical-network (PON) architecture that allows for incremental upgrade from single-channel time-division multipleaccess PONs in order to provide higher bandwidth in the access network. Various dynamic-wavelength and bandwidth-allocation algorithms (DWBAs) for wave-division multiplexed PON are presented; they exploit both interchannel and intrachannel statistical multiplexing in order to achieve better performance, especially when the load on various channels is not symmetric. Three variants of the DWBA are presented, and their performance is compared. While the first variant incurs larger idle times (and, hence, poor performance), the other two algorithms achieve better but different performance with critical dissimilarities. Our analysis also focuses on the fair assignment of excessive bandwidth in the upstream direction to highly loaded optical network units. We compare the performance of DWBA to another algorithm that relies on static-channel allocation. Furthermore, a study is presented wherein the number of wavelengths increases, and a comparison with interleaved polling with adaptive cycle time is shown. We use extensive simulations throughout this paper.
Ethernet Passive Optical Networks (EPONs) are considered the most promising solutions for upgradi... more Ethernet Passive Optical Networks (EPONs) are considered the most promising solutions for upgrading the current congested access networks to enable the delivery of broadband integrated services. Although current EPON architectures are economically feasible, they are however bandwidth limited. In this paper, we discuss a simple upgrade architecture from EPON to WDM-PON. We present various Dynamic Wavelength and Bandwidth Allocation algorithms (DWBAs) that exploit both inter-channel and intra-channel statistical multiplexing in order to achieve good performance. We use extensive simulation experiments to validate our reasoning.
2015 IEEE Wireless Communications and Networking Conference (WCNC), 2015
Vehicular Ad hoc Networks have been receiving significant interest during the past years as they ... more Vehicular Ad hoc Networks have been receiving significant interest during the past years as they support both safety and non-safety applications for passengers commuting onboard smart vehicles. Vehicles may communicate with each others for the purpose of sharing information. Moreover, they may be privileged by Broadband Internet access as well as other services provisioned by stationary Roadside Units (RSUs) deployed along the roadways. When a vehicle leaves the coverage range of an RSU, it enters a dark area. However, it may still maintain connectivity with the RSU through multi-hop communication with other cooperative vehicles serving as intermediate relays.
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Papers by Chadi Assi
were proposed as a means for remedying the effects of the
various atmospheric impairments on the quality of the FSO
signal. Conventional relay-assisted FSO systems are however
designed around two basic assumptions: a) relays are buffer-free,
and b) relays are stationary. This paper proposes to improve
the performance of the existing relay-assisted FSO systems by
relaxing both of these highly restrictive assumptions through
the integration of Unmanned Aerial Vehicles (UAVs) as bufferaided
moving relays into the conventional relay-assisted FSO
systems. Specifically, two possible simple integration scenarios
are proposed and analyzed through simulation. The obtained
simulation results demonstrate the great potential associated
with the proposed highly promising, innovative, hybrid FSO
architecture. Given that high performance gains are observed
under small buffer sizes, it becomes conceivable to employ the
buffer-aided moving relaying UAVs to serve a variety of other
purposes. This includes, for instance, having these UAVs oversee
the operation of amateur drones for potential misbehavior or
wrongdoing within the area of their deployment.
(V2I) communication system. Existing mathematical models for such a
system overlook some of its essential behavioural characteristics such as the reneging,
force-termination and ultimately blocking of service requests. A multi-server queueing
model with First-In–First-Out (FIFO) service policy is proposed for the purpose of accurately
capturing the dynamics of the above-mentioned communication system and evaluating
its performance. Approximations were exploited as a mean to enhance this model’s
mathematical tractability. Simulations are conducted in the context of a realistic scenario
with the objective of validating the proposed approximate model, verifying its accuracy
and characterizing the system’s performance in terms of several new metrics. The reported
results indicate a cataclysmic access request blocking probability ranging from 66% to 85%.
An Access Request Deadline-Aware (ARDA) service policy is then proposed to reduce the
blocking probability and improve the system’s response time. Indeed ARDA achieved an
improvement over FIFO of almost 70% in terms of the overall blocking probability and 22%
to 66% in terms of the system’s response time.
were proposed as a means for remedying the effects of the
various atmospheric impairments on the quality of the FSO
signal. Conventional relay-assisted FSO systems are however
designed around two basic assumptions: a) relays are buffer-free,
and b) relays are stationary. This paper proposes to improve
the performance of the existing relay-assisted FSO systems by
relaxing both of these highly restrictive assumptions through
the integration of Unmanned Aerial Vehicles (UAVs) as bufferaided
moving relays into the conventional relay-assisted FSO
systems. Specifically, two possible simple integration scenarios
are proposed and analyzed through simulation. The obtained
simulation results demonstrate the great potential associated
with the proposed highly promising, innovative, hybrid FSO
architecture. Given that high performance gains are observed
under small buffer sizes, it becomes conceivable to employ the
buffer-aided moving relaying UAVs to serve a variety of other
purposes. This includes, for instance, having these UAVs oversee
the operation of amateur drones for potential misbehavior or
wrongdoing within the area of their deployment.
(V2I) communication system. Existing mathematical models for such a
system overlook some of its essential behavioural characteristics such as the reneging,
force-termination and ultimately blocking of service requests. A multi-server queueing
model with First-In–First-Out (FIFO) service policy is proposed for the purpose of accurately
capturing the dynamics of the above-mentioned communication system and evaluating
its performance. Approximations were exploited as a mean to enhance this model’s
mathematical tractability. Simulations are conducted in the context of a realistic scenario
with the objective of validating the proposed approximate model, verifying its accuracy
and characterizing the system’s performance in terms of several new metrics. The reported
results indicate a cataclysmic access request blocking probability ranging from 66% to 85%.
An Access Request Deadline-Aware (ARDA) service policy is then proposed to reduce the
blocking probability and improve the system’s response time. Indeed ARDA achieved an
improvement over FIFO of almost 70% in terms of the overall blocking probability and 22%
to 66% in terms of the system’s response time.