In a cognitive radio network (CRN), two nodes have a rendezvous when they tune to the same channel simultaneously. Providing rendezvous guarantee between any pair of nodes is essential because a rendezvous is necessary for communication. Some existing works claim that rendezvous guarantee can be provided by using a dedicated common control channel to negotiate the channel being used. A serious problem of these mechanisms is that a globally available channel may not exist. Some channel hopping protocols try to provide a rendezvous guarantee without using a common control channel. However, these solutions may suffer from a poor number of rendezvous or uneven channel utilization. In this paper, we propose a novel distributed channel hopping protocol: Quorum and Latin square channel hopping (QLCH). The QLCH scheme efficiently provides rendezvous guarantee by utilizing the concept of quorum systems and Latin squares. The former is utilized to guarantee balanced rendezvous among nodes, whereas the latter is adopted to share the rendezvous among channels. QLCH efficiently provides fast rendezvous guarantee and can cooperate with other channel hopping protocols to enhance network throughput. Analytical and simulation results verify the improvement of QLCH. For example, when there are 30 flows using 11 channels in a CRN, the achieved time to rendezvous of QLCH is 9.84 times lower than that of the existing protocol SYNC-ETCH, whereas the achieved network throughput of QLCH is 362% higher than that of the existing protocol, i.e., Quorum-based channel hopping (L-QCH).

A Fast Rendezvous-Guarantee Channel Hopping Protocol for Cognitive Radio Networks

Wireless sensor networks have been established for a wide range of applications in adversarial environments, which makes secure communication between sensor nodes a challenging issue. To achieve high level of security, each pair of nodes must share a secret key in order to communicate with each other. Because of the random deployment of sensors, a set of keys must be pre-distributed, so that each sensor node is assigned a set of keys from a key pool before the deployment. The keys stored in each node must be carefully selected to increase the probability of key share between two neighboring nodes. In this paper, we consider a hybrid key pre-distribution scheme based on the balanced incomplete block design. We present a new approach for choosing key pool in the hybrid symmetric design that improves the connectivity and scalability of the network. We also introduce an extension to the proposed approach to detract memory usage and improve resilience. Experimental results verify the performance and applicability of our approach. Copyright © 2014 John Wiley & Sons, Ltd.

Application-specific hybrid symmetric design of key pre-distribution for wireless sensor networks

Key distribution is one of the most challenging security issues in wireless sensor networks. To achieve a high level of security, each pair of nodes must share a secret key in order to communicate with each other. Recently, many researchers have used combinatorial designs as key pre-distribution scheme in wireless sensor networks. In this paper, we describe a new construction of a design in combinatorial algebraic called residual design and use it for key establishment. This is the first time for application of residual design. Our approach is a highly scalable key management scheme for wireless sensor networks which provides a good secure connectivity. We show that the basic mapping from residual design to key pre-distribution has an extremely high network scalability while this mapping does not have high resilience. Therefore, we present a new approach for key pre-distribution based on residual design that improves the resilience of the network while maintaining connectivity and high scalability. We also explain that the computational cost and storage overhead is low. Performance and security properties of the proposed scheme are studied both analytically and computationally to compare our scheme to main existing schemes. The obtained results show that at equal key-ring size, our scheme provides better scalability with high connectivity and resilience.

A Novel Scalable Key Pre-distribution Scheme for Wireless Sensor Networks Based on Residual Design

Wireless sensor networks as the key infrastructure of the new networking paradigm are vulnerable against different kinds of attacks. Therefore, ensuring a secure communication between the sensor nodes is important. 
One of the most critical issues in this regard is the key distribution mechanism. Due to the random deployment of the sensors in the target area, key pre-distribution is a promising approach, in which a list of keys, so-called key-ring, is pre-distributed to each sensor node before deployment. To establish a secure communication, two nodes must share a common key from their key-rings. In this paper, we consider a hybrid key pre-distribution approach based on the symmetric design. We propose a new scheme, which is a modification of the hybrid symmetric design in order to improve the connectivity and resilience. Considering the trade-off between resilience and connectivity, we introduce a new parameter based on the application requirement. The experimental results and analytical analysis approve the efficiency of our proposed approach and introduced parameter.

Key-management scheme for wireless sensor networks based on merging blocks of symmetric design

Combinatorial designs are powerful mathematical tools with comprehensive and simple algebraic structures. Recently, many researchers have used combinatorial designs as key predistribution schemes in wireless sensor networks WSNs. Previous studies on security of WSNs are mainly concentrated on those networks containing nodes with the same capabilities. Further, investigations reveal that high reliability and lifetime on networks can be achieved through hierarchical heterogeneous wireless sensor networks, where a small number of sensor nodes have more energy, memory, and transmission capability. Inspired by scheme due to Lee and Stinson, we propose a key predistribution scheme for a clustered heterogeneous WSN using transversal designs. This proposed scheme assigns key chains to sensor nodes before deployment and separates key pool of each cluster by adding a pseudo-random generated number after deployment. The performance evaluation and security analysis show that our proposed scheme can provide better security with significant reductions on communication overhead and storage space than other key management schemes without compromising connectivity. Copyright © 2014 John Wiley & Sons, Ltd.

Key Predistribution Scheme for Clustered Hierarchical Wireless Sensor Networks based on Combinatorial Designs

Correct scheduling of the project is the necessary condition for the project success. In traditional models, the activities duration times are deterministic and known. In real world however, accurate calculation of time for performing each activity is not possible and is always faced with uncertainty. In this paper, the duration of each activity is estimated by the experts as linguistic variables and the said variables are represented in fuzzy numbers form using the fuzzy theory. Estimating the project accomplishment duration and determining the project critical path will be possible through resolving a fuzzy linear programming model. For solving model, Fuzzy Critical Path Method Algorithm (FCPMA) is introduced that uses fuzzy numbers ranking. In none of this method steps the defuzzification of the fuzzy numbers occurs, and the project accomplishment duration is gained in trapezoidal fuzzy number. Finally the performance of the introduced algorithm is shown using an application example.

N Shahsavari Pour

Papers

Calculating the Project Network Critical Path in Uncertainty Conditions