Wireless Networks

With the continuous development of new energy power generation and smart grid, Power Electronic Transformer (PET) has a good prospect for development because of its remarkable advantages. Based on the topology of AC/DC/AC, the modulation strategy with dual-PWM (Pulse Width Modulation) is adopted to control the operation of power electronic transformers in this paper. The PET structure consists of three units: importation portion, isolation portion and output portion. Model building and analyzing both at the input and output terminals are achieved step by step. And the simulation of the whole PET system with dual-PWM is accomplished with MATLAB/ Simulink. The simulation results show the control system stability and output voltage regulation precision are improved with feed-forward voltage decoupling vector control system. The correctness and effectiveness of the control strategy are demonstrated through the simulation. PETs play an important role in enhancing power supply reliability for Power Grid and promoting the new energy power generation development.

A mobile ad-hoc network (MANET) is composed of mobile nodes without any infrastructure where member nodes easily can leave or join the network. This issue provides a dynamic topology network such that providing quality of service and multicast services are very challenging tasks. The majority of applications of MANETs are in rapid deployment and dynamic reconfigurations. For these reasons, in this paper, we present an efficient fuzzy logic based multicast routing scheme to adaptively manage the network resources without any prior knowledge about network traffic. Every source node self-organizes the multicast session by using average end to end delay and packet delivery ratio parameters in order to dynamically adjust its own sending rate. The proposed method is a novel framework for multicast services such that it can be deployed by both tree-based and mesh-based multicast routing protocols. In addition, The proposed method uses a cross-layer technique to efficiently manage the congestion. The results show high improvement in terms of number of the retransmissions, delay, packet delivery ratio and overhead compared to the existing multicast schemes.

In wireless sensor networks, a sensor node communicates with a small set of neighbour sensor nodes and with the base station through a group leader or a cluster head. However, in some occasions, a sensor node required to move in the sensor networks. The node has to change its own position with the requirement of applications. Considering this phenomena, in this paper, we propose to design an angular function and private key management system authenticated by group leader for the transmission of a node. In the proposed scheme, the group is divided into sectors. The motion of the node is related with the angles to the group leader, which is the basis of our proposal. The nodes movement and activity should be tracked. The proposed scheme attains high connectivity and security with the help of the directional transreceiver. The lifetime of a node is increased, and it enables a node to move through the network and to transmit data to its neighbors.

Advances in both telecommunications and Information technology have improved the way users do business online. Android, an open-source mobile operating system, is becoming an attractive target for cyber criminals to exploit due to its predefined permission model. Without classification, the mobile operating system permits installation of mobile applications of all kinds, including Trojans, thus making its trustworthiness into question. In this paper, we present a security system called collaborative policy-based security scheme (CSS) that permits users to customize the access permissions of Android applications during runtime. The proposed CSS security scheme validates the trustworthiness of each application before being installed. The experimental results show that the proposed CSS successfully detects all malicious applications with a run-time overhead of 2.7%.

We propose and analyaze a distributed control law that will maintain prescribed local properties of a wireless ad hoc network in the presence of node mobility, MAC layer power control and link fades. The control law uses a simple and intuitive power adaptation mechanism. We consider as an example the topology requirement of maintaining the out-degrees of each node at prescribed values and keeping the in-degree close to the out-degree. The topology objective is achieved by adapting the transmission power based only on local information. This power adaptation algorithm is analyzed using the o.d.e. approach to stochastic approximation. Simulation results verify the analysis and demonstrate its effectiveness. We also study the ability of the proposed objective to maintain connectivity. Although many heuristics are described in the literature to maintain local topological properties, the algorithm proposed in this paper is the first one that has proven convergence properties.

To satisfy the needs of wireless data networking, study group 802.11 was formed under IEEE project 802 to recommend an international standard for Wireless Local Area Networks (WLANs). A key part of standard are the Medium Access Control (MAC) protocol needed to support asynchronous and time bounded delivery of data frames. It has been proposed that unslotted Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) be the basis for the IEEE 802.11 WLAN MAC protocols. We conduct performance evaluation of the asynchronous data transfer protocols that are a part of the proposed IEEE 802.11 standard taking into account the decentralized nature of communication between stations, the possibility of “capture”, and presence of “hidden” stations. We compute system throughput and evaluate fairness properties of the proposed MAC protocols. Further, the impact of spatial characteristics on the performance of the system and that observed by individual stations is determined. A comprehensive comparison of the access methods provided by the 802.11 MAC protocol is done and observations are made as to when each should be employed. Extensive numerical and simulation results are presented to help understand the issues involved.

Wireless communications are vulnerable to signal jamming attacks. Spread spectrum mitigates these attacks by spreading normal narrowband signals over a much wider band of frequencies and forcing jammers who do not know the spreading pattern to expend much more effort to launch the attack. In broadcast systems, however, jammers can easily find out the spread pattern by compromising just a single receiver. Several group-based ideas have been proposed to deal with compromised receivers; they can tolerate up to t malicious receivers by adding 2t extra copies for each broadcast message. In this paper, we propose a novel scheme with random channel sharing. This scheme reduces the communication cost from 2t to (1 + p)t extra copies, where p determines the channel sharing probability (0 < p < 1). In addition, it does not increase the hardware complexity as it does not require a receiver to operate on multiple channels at the same time.

In wireless sensor networks, sensors at different locations in the field use different energy levels to propagate sensing data back to the sink or base station. This causes unbalanced energy usage among sensors and also lowers the network lifetime. Currently there are several techniques to mitigate this problem, such as deploying multiple sinks, adding more sensors on heavy traffic areas, or managing the size of clusters depending on the distance from sensor to sink. In this paper, we propose a distributed algorithm and protocol called Multipath Energy Balancing (MEB) to mitigate unbalanced energy usage in clustered wireless sensor networks using multi-path and multi-hop, with a transmission power control approach. The network field is divided into regions, where the ratio of inter-region transmission traffic from all cluster head sensors in one region to other cluster head sensors in the two regions in front can be pre-computed and pre-programmed into the sensors to ease sensor deployment. To further prolong network lifetime, we also present a simple heuristic algorithm to procrastinate cluster formation and routing. Simulation results show that MEB can balance energy much better than Energy-efficient Clustering (EC) and Balancing Energy Consumption (BEC) solutions. It also has a longer network lifetime than EC and BEC protocols, especially when the required cluster size is small. Procrastinating cluster formation and routing also can further improve the network lifetime.

The construction of smart city has become the frontier trend of city development. Smart education shows the inner beauty of smart city, and smart education is the connotation extension of educational informatization. At present, smart education has become an important symbol of education modernization worldwide, which is an important way to improve the quality and efficiency of education, cultivate innovative talents, and is the inevitable choice to realize the leap-forward development of education. Furthermore, preschool education is a critical period for the rapid development of children's nervous system. Education in this period plays a decisive role in children's development and is also a necessary condition for their development of intelligence and potential. However, traditional teaching cannot guarantee the fun of children's teaching activities. According to the characteristics of multi-sensory, immersive, and interactive virtual reality (VR) technology, VR is introduced into the live demonstration application of preschool education. Since VR video contains information in all directions of a scene, its data volume is much larger than that of traditional video, and different panoramic video projection layout schemes have a great impact on the quality of video. To solve this problem, a continuous layout method based on octahedral projection is proposed, which eliminates the internal discontinuous edges and has good boundary continuity. Experimental results show that the layout method proposed in this paper has good performance in both video quality and computing cost, which provides power for VR technology in the live demonstration of preschool education, and increases the immersion and comfort of children when watching VR videos.