Integrating device-to-device (D2D) cooperation with mobile edge computing (MEC) for computation offloading has proven to be an effective method for extending the system capabilities of low-end devices to run complex applications. This can be realized through efficient computing data offloading and yet enhanced while simultaneously using multiple wireless interfaces for D2D, MEC and cloud offloading. In this work, we propose user-centric real-time computation task offloading and resource allocation strategies aiming at minimizing energy consumption and monetary cost while maximizing the number of completed tasks. We develop dynamic partial offloading solutions using the Lyapunov drift-plus-penalty optimization approach. Moreover, we propose a task admission solution based on support vector machines (SVM) to assess the potential of a task to be completed within its deadline, and accordingly, decide whether to drop from or add it to the user’s queue for processing. Results demonstrate high performance gains of the proposed solution that employs SVM-based task admission and Lyapunov-based computation offloading strategies. Significant increase in number of completed tasks, energy savings, and cost reductions are resulted as compared to alternative baseline approaches.

In this paper, the problem of Quality-of-Service (QoS) differentiation is studied in the context of Buffer-Aided (BA) cooperative Free Space Optical (FSO) communication systems. This is particularly true since the existing relevant literature overlooked the possibility of preferential treatment of data packets based on their delay requirements. Inspired by this observation, this paper proposes to classify the data packets emanating from the source node into either Delay Tolerant (DT) packets or Non Delay Tolerant (NDT) ones and to service these packets according to this classification at the relay node. Priority queueing is first introduced in the relay's buffer with a view to improving the delay experienced by NDT packets. Class of service mutation is then proposed as a starvation mitigation strategy to better manage the interesting dynamics resulting from the co-existence of packets having different QoS requirements in the same buffer. The various performance measures of interest for the explored QoS-aware communication system are both evaluated mathematically based on a Markov chain analysis and validated through extensive simulations. An asymptotic analysis is also carried out highlighting the dependence of the performance on the system parameters in an intuitive manner.

This work targets the performance analysis of buffer-aided (BA) Free-Space Optical (FSO) relaying with a single decode-and-forward (DF) relay. In particular, we study the impact of activating the direct source-destination link on the system performance. Based on a Markov chain analysis, we derive closed-form expressions for the system outage probability (OP) and average packet delay (APD). Moreover, we carry out an asymptotic analysis and evaluate the achievable diversity order. Results show that while activating the direct link reduces the APD in all scenarios, this activation might either increase or decrease the diversity order depending on the relay position.

In this paper, we analyze multi-hop free-space optical (FSO) communications in the context of decode-and-forward serial relaying, where the relays are equipped with finite-size buffers. Based on a Markov chain analysis, we derive closed-form asymptotic expressions for the system outage probability (OP) and average packet delay (APD) for an arbitrary number of relays N, and an arbitrary buffer size L. The closed-form evaluation links the system performance to the various network parameters in a simple and intuitive manner, and it is useful for offering clear insight on the impact of the relay placement and the selection of the buffer size for practical FSO systems. We prove that buffer-aided multi-hop systems can reap a diversity gain that ranges from [(Nτ/2)] + 1 to Nτ+ 1 compared with multi-hop buffer-free systems while the asymptotic APD values can range from Nτto (L - 1)Nτfor L ≥ 2. Our analysis also highlights the optimal solutions capable of concurrently minimizing the OP and APD.

In this paper, we consider the problem of relay-assisted free space optical (FSO) communications in the case where the relays are equipped with buffers of finite size. The high directivity of the FSO links clearly distinguishes cooperative FSO networks from their radio frequency (RF) counterparts thus motivating the design of FSO-specific buffer-aided (BA) cooperative protocols. We propose three novel decode-and-forward relaying protocols that are adapted to the nature of FSO transmissions and are capable of achieving different levels of tradeoff between outage probability, average packet delay and system complexity: 1) the BA selective relaying protocol that can be implemented in the presence of channel state information (CSI) and that outperforms the RF max-link protocol with a reduced delay; 2) the BA all-active relaying protocol that can be implemented in the absence of CSI and constitutes the simplest protocol with the best delay performance at the expense of a degraded outage performance; and 3) the BA load-balanced selective protocol where supplementary FSO communications are triggered along the inter-relay links for a more balanced distribution of the packets among the buffers. While the last protocol incurs the highest signaling complexity, it results in significant performance gains with a delay that is comparable to that of the BA selective protocol. A Markov chain analysis is adopted for evaluating the system outage probability and the average packet delay where the corresponding state transition matrices are derived in the cases of both symmetrical and asymmetrical networks.

This paper presents a consice yet comprehensive description of a DSA-based Vehicle-to-Infrastructure (V2I) communication system operating under spectral scarcity conditions. Existing mathematical models for such a system overlook some but essential ones of its behavioural characteristics. Thus, these models' reported performance results seem to be unrealistically overoptimistic. In this paper, a simulation study is conducted in the context of a real-life scenario. As opposed to the existing studies, the study herein aims at providing more insights into the dynamics of this type of communication systems and assessing its performance in terms of several new metrics.

Delay-optimal data delivery in Vehicular Intermittently Connected Networks (VICNs) is challenging since vehicular traffic is affected by numerous recurring and completely random events. Some of these events cause breakdowns and jams while others subserve traffic stability. Researchers observed that mobile vehicles might be wisely exploited to connect two isolated, Stationary Roadside Units (SRUs). In this context, the design of effective delay-minimal data relaying strategies is receiving significant attention. However, many existing such schemes either do not adequately model vehicular traffic behaviours or adapt typical Internet packet-like forwarding protocols to VICNs. In contrast, this manuscript presents a concise, yet comprehensive study of vehicular traffic states based on which a "comme-il-faut" vehicular traffic model is established. This model captures the fundamental traffic characteristics and enables the selection of appropriate distributions for vehicular flow and speeds that parallel the realistic measurements made by traffic theorists. These distributions constitute the basis of a novel Probabilistic Bundle Release Scheme with Bulk Bundle Release (PBRS-BBR) that is proposed with the objective to minimize the average bundle delivery delay. An analytical queueing model is formulated to assess the performance of PBRS-BBR under medium-to-light vehicular traffic. Extensive simulations are conducted to prove the model's validity and accuracy.

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.

The use of vehicular infrastructure to establish connectivity between isolated stationary Information Relay Stations is an appealing application of Terrestrial Delay-Tolerant Networking. A source opportunistically releases data bundles to vehicles that randomly enter its range. In turn, those vehicles store the received bundles, carry and deliver them to their intended destination. It follows that a contemporaneous source- destination end-to-end path does not exist. Consequently, bundles experience longer queueing periods at the source. Under such circumstances, the end-to-end bundle delivery delays become several orders of magnitude higher than those experienced in traditional wireless networks. In this context, bundle delivery delay minimization emerges as a challenging problem that has not been adequately addressed in the open literature. This paper proposes a simple Probabilistic Bundle Relay Strategy with Bulk Bundle Release (PBRS-BBR) that aims at minimizing the average end-to-end bundle delivery delay while capturing the essence of vehicular delay-tolerant networking in that it revolves around minimal network information knowledge. A queueing model is formulated to represent stationary sources operating under PBRS-BBR. This model is mathematically analyzed and validated through extensive simulations that gauge its merit.

A persisting major challenge in Vehicular Delay- Tolerant Networks (VDTNs) is the delay minimization of data delivery when communicating nodes are stationary, arbitrarily deployed along roadsides and considerably apart that they cannot establish direct communication between each other. A source opportunistically releases bundles of data to cooperating vehicles passing by, hoping that they will successfully deliver them to the intended destination. Several complex strategies that tackle this problem have been proposed in the open literature. Nevertheless, these strategies often implicitly assume complete network knowledge. In this paper, we propose a rather simple Probabilistic Bundle Relay Strategy (PBRS) that relaxes the availability of complete network information. A queuing model is formulated to represent VDTN stationary sources where PBRS is deployed. We introduce the bundle release probability parameter which expresses the likelihood that a bundle is released by the source to a vehicle passing by. The proposed model is studied analytically and theoretical expressions of its characteristic parameters are all derived. In particular, we compute the time it takes to release a head-of-line bundle (referred to as the bundle's service time). Moreover, the model is validated through a simulation study that gauges its merit. The simulation results show that even with partial network knowledge the proposed queueing model can guarantee acceptable bundle delivery delay.

One of the major challenges for optical network operators is related to realizing profitable networks that preserve the overall satisfaction of their end customers. This necessitates ensuring a controlled network resource usage while decreasing connection blocking probability. However, optical networks are witnessing the introduction of an increasing number of new services, each having different requirements. As such, the evolution towards resource efficient connection setup management strategies that provide differentiated call-blocking probability becomes inevitable. Building on the previous observation, we propose in this paper a novel connection setup management strategy. This latter aims to differentiate the blocking probability among different classes of lightpath requests, while avoiding the starvation of the lower class lightpaths. The main idea behind our proposal is to privilige higher class lightpaths via preemption and to protect the lower class lightpaths through rerouting. In this manner, the proposed strategy serves the double objective of minimizing the overall connection blocking probability and of realizing quality of service (QoS) differentiation. The previous claim is asserted through our simulation results that gauge the main benefits behind our proposed connection setup strategy. The simulation results drawn from the National Science Foundation Network (NSFNET) and the European Optical Network (EON) show that the proposed strategy achieves both differentiated and low blocking probabilities.

In this paper, we consider the problem of space-time (ST) coding with pulse position modulation (PPM). While all the existing ST block codes necessitate rotating the phase or amplifying the amplitude of the transmitted symbols, the proposed scheme can be associated with unipolar PPM constellations without introducing any additional constellation extension. In other words, full transmit diversity can be achieved while conveying the information only through the time delays of the modulated signals transmitted from the different antennas. The absence of phase rotations renders the proposed scheme convenient for low- cost carrier-less multiple-input-multiple-output (MIMO) time- hopping ultra-wideband (TH-UWB) systems and for MIMO free-space optical (FSO) communications with direct detection. In particular, we propose two families of minimal-delay ST block codes that achieve a full transmit diversity order with PPM. Designate by n the number of transmit antennas and by M the number of modulation positions. For a given set of values of (n, m), the first family of codes achieves a rate of 1 symbol per channel use (PCU) which is the highest possible achievable rate when no constellation extensions are introduced. The second family of codes can be applied with a wider range of (n, m) at the expense of a reduced rate given by: R=1/n+n-1/n log2(M-1)/n log2(M).

The worldwide network domain tendency to evolve towards dynamic quality of service (QoS) enabled optical networks is imminent. In such an evolution, improving connection setup conditions is considered to be one of the major requirements. This paper proposes a novel connection setup management approach. The rationale behind this proposal lies in considering the optical connection setup time requirement as a (timely increasing) priority indicator during the setup/provisioning process. From this viewpoint, we adapt the well known earliest deadline first (EDF) scheduling discipline to the particular case of optical connection setup management, which consists in giving highest priority to the connection request having the shortest setup time requirement. Another originality of this paper stems from the proposal of a computational method for the assessment of optical connection setup success probability under the proposed management approach. The latter parameter, that is the connection setup success rate, is an important indicator for both optical operators and clients.

A plethora of packet-scheduling algorithms have been proposed in the literature in order to meet the stringent time constraints of real time flows at an IP router level. In this regard, the so-called EDF algorithm attracted special attention since it is prominent for optimally managing flows with strict time constraints. However, EDF is complex and expensive as far as implementation is concerned, especially when compared with the standard FIFO algorithm. As a main contribution in this paper, we therefore propose a novel hybrid scheduling approach, which combines the optimality of EDF and the simplicity of FIFO. This approach allows reducing EDF's implementation complexity while making efficient use of its optimal flow management. Our simulation results underline the benefits behind such a proposal.

Optical networks are becoming an inevitable technology in the next generation Internet. Optical WDM networks require a control network for automatic and rapid configuration. A control plane is under standardization by the Internet Engineering Task Force (IETF) under the name generalized multiprotocol label switching (GMPLS). However, this control plane is unaware of the specifications of the services to be enforced. This work presents a policy-based management architecture adapted to an emerging kind of optical networks called hybrid photonic networks. Contributing to network flexibility, we present extensions to the management plane of these transparent wavelength and switching capable networks that provide the means to leverage their inherent capabilities. The proposed management architecture would provide optical network operators with the possibility to provision optical services, defined through high level service contracts, in an efficient and dynamic way.

One of the major concerns of optical network operators is related to improving the availability of services provided to their highest-class clients through the use of different protection schemes. However, the majority of the work concerning protection schemes considered the primary connections as equally important when contending for the use of the backup resources. As a first contribution we therefore propose an improvement of the existing shared protection schemes through the introduction of relative priorities among the different primary connections contending for the access to the protection path. Moreover, as a second contribution, we propose to include a novel service differentiation parameter, the service disruption rate of a connection, to provide differentiated services in a WDM mesh network, and we motivate the use of such a parameter with numerical examples. As a third contribution, we present a mathematical model for both the classical protection schemes and for the proposed priority-aware scheme. As a key distinguishing feature from existing literature we derive explicit analytic expressions for the average availability and service disruption rate resulting from the deployment of such schemes. By solving these models we then evaluate numerically the benefits of the service differentiation feature introduced in our scheme as well as the impact of the service disruption rate as service differentiator.

This document presents provisioning strategies for emerging hybrid optical networks. The idea is to make use of policy-based management that guides the behavior of a network through high-level declarative directives. In this regard and in the context of hybrid optical networks, policy rules are employed as the main means to extend the functionality of the control system and to complement its role in order to achieve the service provisioning.