Mohamed Abd rabou Kalil

Increasing spectrum capacity for ad hoc networks using cognitive radios: an analytical model

In this letter, an analytical model to evaluate the performance of ad hoc devices equipped with cognitive radio capabilities, is investigated. By applying cognitive radio technology, the ad hoc devices will utilize the unused spectrum of the existing legacy systems in an opportunistic manner in addition to using the unlicensed spectrum. Therefore, the network throughput will be increased. The results show that the performance is improved in terms of blocking and dropping probabilities.

Analysis of Opportunistic Spectrum Access in Cognitive Ad Hoc Networks

Cognitive radio (CR) is a promising technology for increasing the spectrum capacity for ad hoc networks. Based on CR, the unlicensed users will utilize the unused spectrum of the licensed users in an opportunistic manner. Therefore, the average spectrum usage will be increased. However, the sudden appearance of the licensed users forces the unlicensed user to vacate its operating channel and handoff to another free one. Spectrum handoff is one of the main challenges in cognitive ad hoc networks. In this paper, we aim to reduce the effect of consecutive spectrum handoff for cognitive ad hoc users. To achieve that, the licensed channels will be used as operating channels and the unlicensed channels will be used as backup channels when the primary user appears. Therefore, the number of spectrum handoff will be reduced, since unlicensed bands are primary user free bands. A Markov chain model is presented to evaluate the proposed scheme. Performance metrics such as blocking probability and dropping probabilities are obtained. The results show that the proposed scheme reduces all the aforementioned performance metrics.

Spectrum handoff reduction for cognitive radio ad hoc networks

Spectrum handoff is one of the main challenges in cognitive radio ad hoc networks. Spectrum handoff occurs when the owner of the spectrum or the primary user (PU) appears in the same channel that is already occupied by a secondary user (SU). In this case, the SU should vacate this channel and determine another free one. This process may continue till SU finishes its transmission. Spectrum handoff has a negative impact on the performance of SU in terms of delay and link maintenance; therefore the number of handoffs should be reduced. Opportunistic Spectrum Access with Backup channels (OSAB) is a new spectrum access concept for managing and increasing the spectrum capacity for ad hoc networks. Reducing the number of spectrum handoffs is one of the main features of OSAB. This is achieved by utilizing the unlicensed channels as backup channels in case of the appearance of the PUs. In this paper, an extensive mathematical model is presented to evaluate the performance of the OSAB in terms of the link maintenance probability and the expected number of spectrum handoffs. Numerical results show that OSAB outperforms the classical opportunistic spectrum access concept in terms of the aforementioned performance metrics.

SWITCH: A Multichannel MAC Protocol for Cognitive Radio Ad Hoc Networks

Cognitive radio (CR) technology will empower wireless devices with the capabilities to dynamically exploit opportunities in both licensed and unlicensed spectra. Thus, the spectrum shortage problem that occurs due to the ever-increasing of wireless devices can be handled. In CR ad hoc network, a secondary user (SU) is allowed to utilize a channel of the primary system provided the channel is idle from primary user (PU) activity. In this environment, the way the SU copes with a sudden appearance of the PU is the most important feature of distributed CR-MAC protocols. In this paper, a multichannel CR-MAC protocol, which reacts efficiently to PU appearance, is developed. The new protocol is named opportunistic Spectrum access WITh backup CHannel (SWITCH). The SWITCH protocol is a decentralized, asynchronous, and contention-based MAC protocol for CR ad hoc networks. The proposed protocol operates over both licensed and unlicensed spectra. In addition, the concept of backup channel is introduced and employed to make the SU extremely robust to the appearance of PUs. The simulation results show that SWITCH accomplishes 91% throughput gain over other CR-MAC protocols.

Adaptive Discrete Particle Swarm Optimization for Cognitive Radios

The adaptation of transmission parameters is a basic and essential process for efficient communication in Cognitive Radios (CR). However, the dynamic nature of wireless channels and the number of transmission parameters to be optimized in such systems adds more complexity to the adaptation process. The Genetic Algorithm (GA) is a well-known evolutionary algorithm for adaptation and optimization of CR systems. However, the convergence speed in GA is low. Recently, Particle Swarm Optimization (PSO) has been used in the CR systems to reduce the computational cost of GA. In this paper, we propose an Adaptive Discrete PSO (ADPSO) algorithm for adaptation of transmission parameters and achievement of Quality of Service (QoS) requirements of a CR node using multi-objective optimization. Simulation results show that ADPSO has faster convergence speed and high fitness values compared to GA and the conventional PSO.

Lha: logical hierarchical addressing protocol for mobile ad-hoc networks

A mobile Ad-hoc network (MANET) is an autonomous system of mobile routers that are self-organizing and decentralized without any need for infrastructure support. While much effort has been made to handle seamless handoff by developing routing algorithms, other fundamental issues such as dynamic and fast addressing mechanisms were neglected. In the paper, we present a new address auto-configuration protocol named Logical Hierarchical Addressing (LHA) which is designed to work in MANET. The proposed protocol allows nodes to get a unique address fast and dynamically. LHA efficiently supports merging and partitioning of networks. We present an analytical model to investigate the performance of LHA and compare it with the token-based protocol. Our results show that the LHA protocol reduces the latency to obtain an IP address by 50%.

crSimulator: A discrete simulation model for cognitive radio ad hoc networks in OMNeT ++

Cognitive Radio is an exciting new technology for efficient use of radio spectrum. Research on cognitive radio has for a large part, focused on physical layer issues such as robust spectrum sensing and radio environment characterization. The networking of cognitive radio nodes is equally important however as new protocols need to be developed to cope with physical layer dynamics. The lack of a widely used and open source simulation platform has been a hindrance in this regard. In this paper, we present crSimuiator, which is a discrete simulation model for cognitive radio ad hoc networks in OMNeT++. We present the core concepts, major requirements, architectural model of cognitive radio nodes, and the implementation details of crSimulator. The crSimulator model effectively captures the physical layer level dynamics and facilitates higher layers protocol research. The model is validated with an implementation of cognitive radio MAC protocol having spectrum sensing and handover features together with a node architecture designed to operate in ad hoc networks.

Implementation and evaluation of a practical SDR testbed

Software defined radios provide a perfect playground for researchers to experiment with current and future wireless communication systems. However, the benefits, especially for communication protocols, largely depend on non-functional requirements (i.e. temporal behavior) that have to be met by the system architecture. In this paper, we share our experience with a flexible SDR framework named Iris. We present an implementation of a Send-and-Wait Automatic Repeat reQuest (ARQ) protocol as well as a virtual network driver component which, in conjunction with Iris, form the core of our software defined radio networking testbed. To verify the practical suitability of the testbed and to evaluate the performance of the protocol, we are conducting end-to-end throughput and delay benchmarks.

Self-organized common control channel design for Cognitive Radio Ad Hoc Networks

Cognitive Radio Ad Hoc Network (CRAHN) is an emergent paradigm in wireless communications that brings the promise of mitigating the well-known scalability problems of classical Mobile Ad Hoc Networks (MANETs). By integrating in its architecture novel dynamic spectrum access algorithms, the CRAHN is expected to increase usage efficiency of available spectrum resources. However, the performance of such algorithms, distributed and cooperative in its nature, is tightly coupled with the existence of a signaling layer, or common control channel (CCC), that is established between neighboring Cognitive Radios (CRs). In this paper we propose a Distributed Consensus Algorithm to address the problem of distributed CCC allocation in CRAHNs. The proposed solution defines a token ring architecture for the CCC and introduces an additional feature, the token-embedded pilot-tone, used by the consensus algorithm to derive a channel quality metric. Through a simulation study of the Distributed Consensus Algorithm, we evaluate its performance for different network scenarios; the results show a significant increase of network capacity and spectrum efficiency when compared to a sequence-based rendezvous scheme.

An architecture for Cognitive Radio ad-hoc network nodes

Cognitive Radio (CR) is considered to be the future of wireless communication. However, for a practical realization of CR, there is a need for an integrated, extensible and flexible architecture with well-defined interfaces and support for real-time adaptations. This article presents a novel architecture for CR nodes operating in an ad-hoc network scenario. Based on a highly reconfigurable software defined radio, it incorporates a Cognitive Resource Manager used for optimization, decision making and learning as well as a database-driven knowledge base called Distributed Resource Map. In contrast to other research in this field, this work focuses on practical feasibility, combines multiple hot topics in the CR domain and considers them holistically. We present implementation details and conclude the paper with intermediate results obtained in our networking testbed.