基于零折射率超材料的高定向性微带天线

研究了一种基于平面网格状零折射率超材料的高定向性微带天线.利用超材料结构的平均效应实现了在10.24 GHz处介电常数为零,进而实现了超材料的折射率为零.实验结果表明,利用零折射率超材料对波束产生汇聚作用,使微带天线的定向性明显增强,E面、H面半功率波束宽度分别收缩了56.67°和26.60.,侧向辐射明显减弱,天线的...     

A parallel implementation of seeker optimization algorithm for designing circular and concentric circular antenna arrays

In this paper, a parallel version of seeker optimization algorithm (SOA) is proposed for designing circular and concentric circular antenna arrays with the low sidelobe levels at a fixed beamwidth. The SOA is a relatively new evolutionary optimization algorithm based on the concept of simulating the act of humans’ intelligent search with their memory, experience, and uncertainty reasoning. In this work, The SOA has been parallelized by benefiting from its dividable population form. The numerical results show that the design of circular and concentric circular antenna arrays using the parallel SOA provides good sidelobe levels with a fixed beamwidth. The quality of results obtained by the parallel SOA is checked by comparing with those of several evolutionary algorithms in the literature.     

A compact energy harvesting multiband rectenna based on metamaterial complementary split ring resonator antenna and modified hybrid junction ring rectifier

This article presents an improved wireless energy harvesting multiband rectifying antenna. The proposed design is based on an original optimized bidirectional complimentary split ring resonator (CSRR) metamaterial multiband antenna and a modified hybrid junction ring rectifier with four rectifying branches. It harvests the ambient radiofrequency radiations at GSM, 1.8 GHz; UMTS, 2.1 GHz; WiFi, 2.45 GHz; and 4G‐2.6 GHz GSM bands. The created prototypes are printed on a 1.57‐mm‐thickness FR4 substrate and achieve the needed dimensional optimization in both antenna and rectifier. The CSRR antenna accomplished a maximum harvesting realized gain of 2.41, 2.26, 1.58, and 2.69 dB on the aforementioned frequency bands, respectively, 63.75% of antenna size reduction, and 23.62% rectifier size reduction regarding the conventional designs. The hybrid ring junction is used to independently match the subrectifiers at each frequency band. The realized rectenna has been accurately tested in both controlled and outdoor environments, achieving a 67.6% peak efficiency at 1.8 GHz frequency band for an input power level of 10 dBm. It powered up a digital batteryless watch in the outdoor experiment.     

A novel space-borne antenna anti-jamming technique based on immunity genetic algorithm-maximum likelihood

1 Introduction For satellite or extraterrestrial communications, Pattern synthesis in antenna arrays is a key technique to restrain strong interference from the ground and air. Some methods first estimate the Directions Of Arrival (DOA) of the interferences, and then restrain them. Over the years, several high-resolution algorithms have been proposed, including the maximum likelihood (ML) method, MUltiple SIgnal Classification (MUSIC), Esti-mation of Signal Parameters via Rotational …     

A novel initial ranging algorithm for OFDMA systems using smart antenna

To improve the capacity of initial ranging （IR） users simultaneously accessing into network and enhance the performance of the IR, a novel IR algorithm is presented for the orthogonal frequency division multiple access systems with the smart antenna. The beamforming weight vectors provided by the antenna array are introduced for the IR users, and the procedures of the multiuser parameter estimation and the interference cancellation are designed. The proposed method can improve the accuracy of the channel estimation of active paths and efficiently reduce the residual multiple access interference. Simulation results show that the proposed method has a much better performance than the available successive multiuser detection and interference cancellation algorithm and accommodates more active ranging users simultaneously accessing into a cell.     

A novel multi-channel MAC protocol with directional antenna for enhancing spatial reuse and bandwidth utilization in WLANs

This paper aims at developing an efficient MAC protocol for wireless LAN by considering multi-channel and directional antennae. Extending IEEE 802.11 to a multi-channel environment not only exploits the bandwidth utilization but also reduces the degree of contentions. Involving directional antennae in designing multi-channel MAC protocol additionally increases the spatial reuse, allowing more parallel communications. This study proposes an efficient Multi-Channel MAC protocol with a Directional Antenna (MCDA) for WLAN. Since each station is only equipped with a single antenna, communicating pairs that progress their communications on data channels cannot maintain the channel usage information which is only obtained from the control channel, raising the channel collision problem. The proposed protocol adopts the channel switch sequence (CSS) mechanism to cope with the channel collision problem and to reduce message exchange overhead for switching channels. According to the state management, MCDA then controls directional antenna transmitting data on a selected channel to exploit the opportunities of spatial reuse, and to maintain fairness among communicating pairs. Simulation results show that the proposed MCDA protocol maintains the fairness and significantly improves bandwidth utilization and throughput.     

A novel approach to improving search efficiency in unstructured peer-to-peer networks

The decentralized peer-to-peer (P2P) technique has been widely used to implement scalable file sharing systems. It organizes nodes in a system into a structured or unstructured network. The advantages of the unstructured P2P systems are that they have lower maintenance complexity and can better adapt to node heterogeneity as well as network dynamics. However, the search process in unstructured systems is not as efficient as in structured P2P systems because the same search message may go through a node multiple times. To facilitate the complex search and improve the search efficiency, we propose a novel approach of assigning identifications to nodes in an unstructured system. Our method can prevent a node from receiving duplicate search messages and retain the low maintenance overhead for the system. The performance evaluations demonstrate that the proposed approach can improve the search efficiency of unstructured P2P systems while keeping the maintenance overhead at a comparable or even lower level, compared with the traditional unstructured systems.     

A novel histogram transformation to improve the performance of thresholding methods in edge detection

The gradient image is used to detect edge points, and the gradient histogram is a typical case of a unimodal histogram. It is well-documented that bi-modal thresholding methods (such as the Otsu method) detect edges poorly. Therefore, specific unimodal thresholding methods are used to detect edge points. However, unimodal thresholding methods (such as the Rosin method) sometimes obtain very noisy results. In this paper, we propose a histogram transformation to improve the performance of some thresholding methods. Using the Berkeley Segmentation Dataset, we present quantitative performance results in an edge detection task to show that our transformation improves the performance of the Otsu and Rosin methods. Our histogram transformation can be used by any histogram thresholding method, but the performance of the method, using the transformed histogram, will depend of the criterion used by this method.     

A novel modular Q-learning architecture to improve performance under incomplete learning in a grid soccer game

Multi-agent reinforcement learning methods suffer from several deficiencies that are rooted in the large state space of multi-agent environments. This paper tackles two deficiencies of multi-agent reinforcement learning methods: their slow learning rate, and low quality decision-making in early stages of learning. The proposed methods are applied in a grid-world soccer game. In the proposed approach, modular reinforcement learning is applied to reduce the state space of the learning agents from exponential to linear in terms of the number of agents. The modular model proposed here includes two new modules, a partial-module and a single-module. These two new modules are effective for increasing the speed of learning in a soccer game. We also apply the instance-based learning concepts, to choose proper actions in states that are not experienced adequately during learning. The key idea is to use neighbouring states that have been explored sufficiently during the learning phase. The results of experiments in a grid-soccer game environment show that our proposed methods produce a higher average reward compared to the situation where the proposed method is not applied to the modular structure.     

Utility of a novel error-stepping method to improve gradient-based parameter identification by increasing the smoothness of the local objective surface: A case-study of pulmonary mechanics

Accurate model parameter identification relies on accurate forward model simulations to guide convergence. However, some forward simulation methodologies lack the precision required to properly define the local objective surface and can cause failed parameter identification.