In this paper we address the problem of secure multicast of data streams over a multihop wireless ad hoc network. We propose a dynamic multicast group management protocol that aims at solving problems that are specific to ad hoc networks such as mobility, unreliable links, and cost of multihop communication.The main idea is to have group members actively participate to the security of the multicast group, therefore reducing the communication and computation load on the source. Since the group security is distributed among the group members, we propose a service right certificate, to verify that a node is authorized to join the group, and also a corresponding revocation mechanism. We simulated our protocol within the ns-2 environment under various mobility, group size, and group dynamic scenarios. Our simulation results indicate that the communication cost and join delay of the protocol scale well when the group dynamic and nodes mobility increase. We have implemented the basic protocol in our ad hoc network testbed. We also proposed an extension to the basic secure multicast tree using multi-link capability combined with a k-out-of-N coding approach.
This paper presents a dual-band, polarization independent FSS for ISM and Wi-Fi shielding. The proposed structure has a band-stop characteristic for 2.5 and 5.1 GHz with a fractional bandwidth of 42% and 7%, respectively. The substrate of the FSS is a transparent material having a permittivity value of 2.77 and a thickness value of 1.48 mm, which provides band-pass characteristics for visible spectrum. The design, fabrication, and measurement of FSS were conducted for TM and TE polarizations; and satisfactory agreement was obtained
In this letter, the particle swarm optimization has been applied to calculate the optimized length and width of rectangular microstrip antennas. The inputs to the problem are the dielectric constant and thickness of the substrate; together with the desired resonant frequency; the outputs are the optimized length and width; where the antennas are considered to be electrically thin. The results are in good agreement with the results (experimental and calculated by other heuristics) in the literature.
A multilayer ultra-wideband frequency selective surface (FSS), which filters the frequency range between 3.38 and 4.66GHz is presented. The proposed structure having a transparent substrate allows the light pass through itself, while it filters the electromagnetic waves at the frequency band of interest; and it has a bandwidth of 1.28 GHz. For the FSS structure, a transparency level of 52.5% obtained with a fractional bandwidth value of 32%. The structure is examined layer by layer; and the proposed FSS structures are evaluated in terms of bandwidth and transparency level
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