Tamer Khattab

Quality-of-service mechanisms in IP-over-WDM networks

Classical approaches to QoS provisioning in IP networks are difficult to apply in all-optical networks. This is mainly because there is no optical counterpart to the store-and-forward model that mandates the use of buffers for queuing packets during contention for bandwidth in electronic packet switches. Since plain IP assumes a best effort service model, there is a need to devise mechanisms for QoS provisioning in IP over wavelength-division multiplexing networks. Such mechanisms must consider the physical characteristics and limitations of the optical domain. This article presents a classification and survey of proposals for QoS provisioning and enforcement in IP-over-WDM networks. The different QoS proposals surveyed cover three major optical switching methods: wavelength routing, optical packet switching, and optical burst switching.

Cognitive Relaying in Wireless Sensor Networks: Performance Analysis and Optimization

The anticipated increase in the density of the deployed wireless sensor networks calls for spectrum sharing through unlicensed access to licensed spectrum. The key technology for spectrum sharing in this scenario is cognitive radio networks. Cognitive relaying scenarios, where a cognitive (unlicensed) user provides relaying services to a licensed (primary) user, have been proposed before as a method to increase chances of spectrum white spaces. In this paper, we develop a wireless sensor network framework containing a cognitive user (sensor node), with delay sensitive data and limited power budget. The cognitive user offers relaying capability to the primary traffic when the primary connection fails to deliver. The cognitive user utilizes a scheduling mechanism that grants priority to relayed traffic over its own traffic. In our framework, the cognitive user is allowed to control the volume of the relayed traffic through an admission control parameter. The objective of the sensor node (cognitive user) is to minimize its traffic delay, subject to certain power budget allowed for relaying the primary traffic. Our key contributions in this work are the development of the aforementioned framework, the establishment of a mathematical formalization for this problem, the derivation of mathematical expressions for average power consumption and average packet delay, and the solution for the developed optimization problem by finding a value for the admission control parameter that minimizes delay while satisfying power budget constraints.

Statistics of general order selection in correlated Nakagami fading channels

In this letter, the cumulative distribution function (and hence outage probability) of the r-th order signal-to-noise ratio from a set of n correlated Nakagami fading branches is studied. Numerical results are presented to illustrate the effect of fading correlation and the fading severity parameter. The accuracy of a simple exchangeable approximation is also examined.

Optical CDMA for All-Optical Sub-Wavelength Switching in Core GMPLS Networks

Generalized multi-protocol label switching (GMPLS) is a multipurpose control-plane paradigm that extends the MPLS scheme allowing switching without recognizing packet boundaries. In this paper, we present a novel extension that exploits a new physical layer for switching in optical GMPLS. The proposed extension is achieved through adding an optical code switching layer, or code switch capable (CSC) layer, to the existing label mapping layers. Our proposal enables finer granularity at sub-wavelength level in all-optical GMPLS core switches, resulting in significant enhancements to traffic isolation capabilities for all-optical GMPLS core switches. We employ mathematical analysis to derive performance bounds for the proposed scheme, from both the labeling capacity and network throughput points of view. We use our analytical model to derive several optimum operating points for the network, and show that our techniques significantly improve the overall performance of all-optical core networks

On the coexistence of a primary user with an energy harvesting secondary user: a case of cognitive cooperation

In this paper, we consider a cognitive scenario where an energy harvesting secondary user shares the spectrum with a primary user. The secondary source helps the primary source in delivering its undelivered packets during periods of silence of the primary source. The primary source has a queue for storing its data packets, whereas the secondary source has two data queues: a queue for storing its own packets and the other for storing the fraction of the undelivered primary packets accepted for relaying. The secondary source is assumed to be a battery-based node, which harvests energy packets from the environment. In addition to its data queues, the secondary user has an energy queue to store the harvested energy packets. The secondary energy packets are used for primary packets decoding and data packets transmission. More specifically, if the secondary energy queue is empty, the secondary source can neither help the primary source nor transmit a packet from the data queues. The energy queue is modeled as a discrete-time queue with Markov arrival and service processes. Because of the interaction of the queues, we provide inner and outer bounds on the stability region of the proposed system. We investigate the impact of the energy arrival rate on the stability region. Numerical results show the significant gain of cooperation.Copyright

On spectrum sharing between energy harvesting cognitive radio users and primary users

This paper investigates the maximum throughput for a rechargeable secondary user (SU) sharing the spectrum with a primary user (PU) plugged to a reliable power supply. The SU maintains a finite energy queue and harvests energy from natural resources and primary radio frequency (RF) transmissions. We propose a power allocation policy at the PU and analyze its effect on the throughput of both the PU and SU Furthermore, we study the impact of the bursty arrivals at the PU on the energy harvested by the SU from RF transmissions. Moreover, we investigate the impact of the rate of energy harvesting from natural resources on the SU throughput. We assume fading channels and compute exact closed-form expressions for the energy harvested by the SU under fading. Results reveal that the proposed power allocation policy along with the implemented RF energy harvesting at the SU enhance the throughput of both primary and secondary links.

A Degrees of Freedom-Optimal Scheme for SISO X Channel with Synergistic Alternating CSIT

In this paper, the degrees of freedom (DoF) of the two-user single input single output (SISO) X channel are investigated. Three cases are considered for the availability of channel state information at the transmitters (CSIT); perfect, delayed, and no-CSIT. A new achievable scheme is proposed to elucidate the potency of interference creation-resurrection (IRC) when the available CSIT alternates between these three cases. For some patterns of alternating CSIT, the proposed scheme achieves 4/3 DoF, and hence, coincides with the information theoretic upper bound on the DoF of the X channel with perfect and instantaneous CSIT. The CSIT alternation patterns are investigated where the patterns that provide extraordinary synergistic gain and dissociative ones are identified.

Optical GMPLS networks with code switch capable layer for sub-wavelength switching

We propose a novel extension to the label mapping space in GMPLS networks by exploiting further physical layer properties. The proposed extension, OC-GMPLS (optical code enabled GMPLS), is a modified version of the standard GMPLS. OC-GMPLS relies on adding an optical CDMA code switching layer called code switch capable (CSC) layer to the existing label mapping layers. OC-GMPLS provides a larger label mapping space and enhances the QoS capabilities for optical networks through increasing the granularity of traffic identification. In our extension, we use Manchester signaling to allow for more robust clock recovery while providing enhanced performance over conventional on-off keying (OOK) schemes. We also provide a reference architecture for the label switching layers in our OC-GMPLS architecture capable of performing labelling through optical CDMA. We analyze the performance of the proposed scheme and show that our proposal significantly enhances the overall network performance.

On the Higher Order Statistics of the Channel Capacity in Dispersed Spectrum Cognitive Radio Systems Over Generalized Fading Channels

This work is devoted to the study of dispersed spectrum cognitive radio (CR) systems over independent and nonidentically distributed (i.n.i.d.) generalized fading channels. More specifically, this is performed in terms of the high-order statistics (HOS) of the channel capacity over η-μ fading channels. A generic analytic expression is derived for the corresponding nth statistical moment, which is subsequently employed for deducing exact closed-form expressions for the first four moments. Using these expressions, important statistical metrics, such as the amount of dispersion, amount of fading, skewness, and kurtosis, are derived in closed form and can be efficiently used in providing insights on the performance of dispersed CR systems. The obtained numerical results reveal interesting outcomes that could be useful for the channel selection, either for sharing or aggregation in heterogeneous networks, which is the core structure of future wireless communication systems.

Energy-efficient cooperative relaying protocol for full-duplex cognitive radio users and delay-aware primary users

This paper considers a network in which a primary user (PU) may cooperate with a cognitive radio (CR) user for transmission of its data packets. The PU is assumed to be a buffered terminal operating in a time-slotted fashion. We develop an energy-efficient protocol that involves cooperation and coordination between primary and secondary users. To satisfy certain quality-of-service requirements, users share time slot duration and frequency bandwidth. Moreover, the secondary user (SU) may leverage the primary feedback channel. The proposed protocol is designed such that the secondary rate is maximized and the primary queueing delay is maintained less than the queueing delay in case of non-cooperative PU. In addition, the proposed protocol guarantees the stability of the primary queue and maintains the average energy emitted by the CR user below a certain predefined value that depends on the application. The proposed protocol provides more robust and potentially continuous service for SUs compared to the conventional practice in cognitive networks where SUs transmit in the spectrum holes and silence sessions of the PUs. We include primary source burstiness and sensing errors to the analysis of the proposed cooperative cognitive protocol. Numerical results show the beneficial gains of the cooperative protocol in terms of SU rate and PU throughput, PU queueing delay, and PU average energy savings.