Metal-Coated <100>-Cut GaAs Coupled to Tapered Parallel-Plate Waveguide for Cherenkov-Phase-Matched Terahertz Detection: Influence of Crystal Thickness

The influence of crystal thickness of metal-coated <100>-cut GaAs (M-G-M) on Cherenkov-phase-matched terahertz (THz) pulse detection was studied. The M-G-M detectors were utilized in conjunction with a metallic tapered parallel-plate waveguide (TPPWG). Polarization-sensitive measurements were carried out to exemplify the efficacy of GaAs in detecting transverse magnetic (TM)- and transverse electric (TE)-polarized THz waves. The reduction of GaAs’ thickness increased the THz amplitude spectra of the detected TM-polarized THz electro-optic (EO) signal due to enhanced electric field associated with a more tightly-focused and well-concentrated THz radiation on the thinner M-G-M. The higher-fluence THz beam coupled to the thinner M-G-M improved the integrated intensity of the detected THz amplitude spectrum. This trend was not observed for TE-polarized THz waves, wherein the integrated intensities were almost comparable. Nevertheless, good agreement of spectral line shapes of the superposed TM- and TE-polarized THz-EO signals with that of elliptically polarized THz-EO signal demonstrates excellent polarization-resolved detection capabilities of M-G-M via Cherenkov-phase-matched EO sampling technique.     

Optimization of Broadband Smooth-Wall Circular Horn Antennas

This paper presents the optimization and characterization of broadband circular horn antennas with smooth walls. These antennas are simpler and easier to manufacture than corrugated horns. They work by converting the incoming fundamental mode to a mode mixture, whose total field corresponds to a Gaussian beam pattern at the aperture. The geometry of the horn is found by an optimization algorithm. While smooth-wall horn antennas have been designed for many years, they are inherently band limited because they rely on a correct multimode interference in the aperture to match the total field to a Gaussian distribution. The presented method achieves significantly larger bandwidths by allowing the Gaussian beam parameters, and thus the required mode spectrum in the aperture, to vary with the frequency. Together with an appropriate mirror optics, a receiver system with a bandwidth of more than 3 octaves could be realized.     

Timeout Period Analysis to Detect Black Hole Attack in Multihop Wireless Ad Hoc Networks

A novel approach is proposed to estimate the timeout period used in wireless ad hoc networks in order to detect misbehaving nodes that make black hole attacks. Timeout period is an acceptable time frame for a node to forward a packet and is used to judge if the node is behaving properly. To avoid misjudgment and false alarms, the accuracy of the estimate of the timeout period is very important. Our method is based on the IEEE 802.11 MAC protocol and Dynamic Source Routing protocol. The main contribution of this paper is proposing a queuing analysis to calculate the mean and maximum delay per hop implementing the 95-percentile of medium access waiting time. In addition, a new technique is introduced that can be applied to determine the mean number of hops in flooding-based ad hoc networks, taking into account edge effects. For each proposed model, analytical results are compared with results obtained from simulations and the validity of the models is confirmed by observing the close relationship between the results.     

Performance Analysis of Privacy Protection System During Data Transfer in MANETs

The openness of a Mobile Adhoc network (MANET) makes it vulnerable to various attacks that can breach privacy, and this demands a privacy protection system. In this paper, we propose a privacy protection system with flexible and adaptable policies to protect privacy during data transfer based on application and context attributes. We also provide the performance analysis model to test the suitability of policies for maintaining privacy, which is essential for the real-time implementation of this system in a resource-limited MANET. Finally, the proposed privacy protection system is compared with previous works using simulations, and the results obtained show the effectiveness of the proposed privacy protection system.     

Structural Modeling and Performance Analysis of Rotary Circuit in Directional Drilling Rig Based on Load Sensing Technology

Aim at improving the energy saving and transmission efficiency of directional drilling rig, the load sensing technology and constant-pressure variable technique are adopted to enable the system to provide the required pressure and flow rate according to the load variation. In order to research the dynamic characteristics of hydraulic control systems, the background and working principle of the load sensing technology were introduced. The dynamic mathematical model of load sensing system is established based on the hydraulic principle. The directional drilling rig mainly consists of two basic circuits: rotary circuit and feed circuit. The dynamic characteristics of rotary circuit are mainly studied. In addition, the hydraulic system of kilometres directional rig is simulated with the software of AMESim. The simulation results show that the load sensing pump could output its required flow and outlet pressure adapted to the load pressure in real time, thus effectively improving the efficiency of the hydraulic system. Furthermore, to verify the validity of the mathematical model and the simulation analysis, an experimental platform of the load sensing hydraulic system was built. The dynamic performance test of load sensing hydraulic system was performed by using the platform. The experimental results demonstrated that the load sensing hydraulic system could output its required flow and pressure when the working condition changed. Finally, they also illustrate the validity of the proposed approach.     

A Distributed Management Method Based on the Artificial Fish-Swarm Model in Cloud Computing Environment

Recently, there are some problems in the centralized management, such as centralized management, heavy burden, excessive number of virtual machine migration, lack of mutual cooperation mechanism between nodes, can’t adapt to the cluster of change. The existing distributed management methods exist between the nodes have less cooperation mechanism and only simple communication, quality of service is no obvious improvement, system can save energy consumption is not obvious. According to the behavior characteristics of the fish, this paper presents an artificial fish to achieve mutual cooperation of nodes in the distributed management method.     

Honeypot Based Black-Hole Attack Confirmation in a MANET

Many solutions are proposed to identify or prevent the attacks in a Mobile Ad hoc Network. However, sometimes these systems detect false attacks. This could lead to loss of resources in a mobile ad hoc network and cause a downgrade in quality of service. Hence mobile ad hoc networks need a system to confirm the attack before taking further actions. In our work presented in this paper, we propose an attack confirm system for a malicious attacker, called the Black-hole attacker. We present our Black-hole attack Confirmation System, which identifies and confirms the black-hole attack in a mobile ad hoc network using honeypot. The honeypot intelligently identifies all the possible types of black-hole attack using the Black-hole Attack tree, and confirms the attack using the Attack History Database. Together, the Black-hole Attack tree, and Attack History Database aid the honeypot in reducing the false alarms in the mobile ad hoc network. We have simulated the proposed system in several mobile ad hoc network environments of varying sizes of nodes and applications. On several occasions the results have demonstrated that the proposed system is efficient in confirming the black-hole attack and saving the resources and minimizing the path re-establishment.     

Recursive least squares identification methods for multivariate pseudo-linear systems using the data filtering

This paper concerns the parameter identification methods of multivariate pseudo-linear autoregressive systems. A multivariate recursive generalized least squares algorithm is presented as a comparison. By using the data filtering technique, a multivariate pseudo-linear autoregressive system is transformed into a filtered system model and a filtered noise model, and a filtering based multivariate recursive generalized least squares algorithm is developed for estimating the parameters of these two models. The proposed algorithm achieves a higher computational efficiency than the multivariate recursive generalized least squares algorithm, and the simulation results prove that the proposed method is effective.     

Optimal energy-delay tradeoff for opportunistic spectrum access in cognitive radio networks

Cognitive radio (CR) has been considered as a promising technology to enhance spectrum efficiency via opportunistic transmission at link level. Basic CR features allow secondary users (SUs) to transmit only when the licensed channel is not occupied by primary users (PUs). However, waiting for an idle time slot may lead to large packet delays and high energy consumption. We further consider that the SU may decide, at any moment, to use another dedicated way of communication (4G) in order to transmit his packets. Thus, we consider an Opportunistic Spectrum Access (OSA) mechanism that takes into account packet delay and energy consumption. We formulate the OSA problem as a Partially Observable Markov Decision Process (POMDP) by explicitly considering the energy consumption as well as packets’ delay, which are often ignored in existing OSA solutions. Specifically, we consider a POMDP with an average reward criterion. We derive structural properties of the value function and we show the existence of optimal strategies in the class of the threshold strategies. For implementation purposes, we propose online learning mechanisms that estimate the PU activity and determine the appropriate threshold strategy on the fly. In particular, numerical illustrations validate our theoretical findings.