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Kuala Selangor, Malaysia

Mahdi S.A.,University Putra Malaysia | Othman M.,University Putra Malaysia | Ibrahim H.,University Putra Malaysia | Desa J.M.,Telekom Research and Development | Sulaiman J.,Universiti Malaysia Sabah
Journal of Computer Science

Mobile ad hoc network security is a new area for research that it has been faced many difficulties to implement. These difficulties are due to the absence of central authentication server, the dynamically movement of the nodes (mobility), limited capacity of the wireless medium and the various types of vulnerability attacks. All these factor combine to make mobile ad hoc a great challenge to the researcher. Mobile ad hoc has been used in different applications networks range from military operations and emergency disaster relief to community networking and interaction among meeting attendees or students during a lecture. In these and other ad hoc networking applications, security in the routing protocol is necessary to protect against malicious attacks as well as in data transmission. The goal of mobile ad hoc security is to safeguard the node's operation and ensure the availability of communication in spite of adversary nodes. The node operations can be divided into two phases. The first phase is to discover the route (s) path. The second phase is to forward the data on the available discovered routes. Both stages need to protect from attacks; so many protocols have been proposed to secure the routing and data forwarding. This is a review study to mobile ad hoc protocols for securing routing as well as protocols for securing packets forwarding. Furthermore, it will present the characteristics and the limitations for each protocol and attributes. © 2013 Science Publications. Source

Kanesan T.,Aston University | Kanesan T.,Telekom Research and Development | Le S.T.,Aston University | Roque D.,CNRS GIPSA Laboratory | Ellis A.D.,Aston University
Optics Express

In this paper, we propose to increase residual carrier frequency offset tolerance based on short perfect reconstruction pulse shaping for coherent optical-orthogonal frequency division multiplexing. The proposed method suppresses the residual carrier frequency offset induced penalty at the receiver, without requiring any additional overhead and exhaustive signal processing. The Q-factor improvement contributed by the proposed method is 1.6 dB and 1.8 dB for time-frequency localization maximization and out-of-band energy minimization pulse shapes, respectively. Finally, the transmission span gain under the influence of residual carrier frequency offset is ̃62% with out-of-band energy minimization pulse shape. © 2014 Optical Society of America. Source

Mustafa F.,University of Technology Malaysia | Parimon N.,University of Technology Malaysia | Hashim A.M.,University of Technology Malaysia | Abd Rahman S.F.,University of Technology Malaysia | And 2 more authors.
Superlattices and Microstructures

A Schottky diode was designed and fabricated on an n-AlGaAs/GaAs high electron mobility transistor (HEMT) structure for RF power detection. The processing steps used in the fabrication were the conventional steps used in standard GaAs processing. Current-voltage measurements showed that the devices had rectifying properties with a barrier height of 0.5289-0.5468 eV. The fabricated Schottky diodes detected RF signals well and their cut-off frequencies up to 20 GHz were estimated in direct injection experiments. To achieve a high cut-off frequency, a smaller Schottky contact area is required. The feasibility of direct integration with the planar dipole antenna via a coplanar waveguide transmission line without insertion of matching circuits was discussed. A higher cut-off frequency can also be achieved by reducing the length of the coplanar waveguide transmission line. These preliminary results represent a breakthrough as regards direct on-chip integration technology, towards the realization of a ubiquitous network society. © 2009 Elsevier Ltd. All rights reserved. Source

Begum M.,Multimedia University | Begum M.,Bangladesh Atomic Energy Commission | Rahman A.K.M.M.,Multimedia University | Rahman A.K.M.M.,Bangladesh Atomic Energy Commission | And 5 more authors.
Applied Radiation and Isotopes

Important thermoluminescence (TL) properties of five (5) different core sizes Ge-doped optical fibers have been studied to develop new TL material with better response. These are drawn from same preform applying different speed and tension during drawing phase to produce Ge-doped optical fibers with five (5) different core sizes. The results of the investigations are also compared with most commonly used standard TLD-100 chips (LiF:Mg,Ti) and commercial multimode Ge-doped optical fiber (Yangtze Optical Fiber, China). Scanning Electron Microscope (SEM) and EDX analysis of the fibers are also performed to map Ge distribution across the deposited region. Standard Gamma radiation source in Secondary Standard Dosimetry Lab (SSDL) was used for irradiation covering dose range from 1Gy to 10Gy. The essential dosimetric parameters that have been studied are TL linearity, reproducibility and fading. Prior to irradiation all samples ~0.5cm length are annealed at temperature of 400°C for 1h period to standardize their sensitivities and background. Standard TLD-100 chips are also annealed for 1h at 400°C and subsequently 2h at 100°C to yield the highest sensitivity. TL responses of these fibers show linearity over a wide gamma radiation dose that is an important property for radiation dosimetry. Among all fibers used in this study, 100μm core diameter fiber provides highest response that is 2.6 times than that of smallest core (20μm core) optical fiber. These fiber-samples demonstrate better response than commercial multi-mode optical fiber and also provide low degree of fading about 20% over a period of fifteen days for gamma radiation. Effective atomic number (Zeff) is found in the range (13.25-13.69) which is higher than soft tissue (7.5) however within the range of human-bone (11.6-13.8). All the fibers can also be re-used several times as a detector after annealing. TL properties of the Ge-doped optical fibers indicate promising applications in ionizing radiation dosimetry. © 2014 Elsevier Ltd. Source

Rajbhandari S.,University of Oxford | Ghassemlooy Z.,Northumbria University | Haigh P.A.,University College London | Haigh P.A.,Czech Technical University | And 2 more authors.
Journal of Lightwave Technology

This paper experimentally investigates the performance of different modulation schemes under the atmospheric turbulence conditions for free space optical communication links. The experiments were carried out in a dedicated and controlled indoor atmospheric chamber. The turbulence environment was created by introducing hot air, while the temperature profile was monitored throughout the chamber to maintain a constant environment. By evaluating the error performance of different modulation schemes under identical conditions, it was observed that pulse position modulation offers the best performance, followed by subcarrier intensity modulation under weak turbulence environments. © 2014 IEEE. Source

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