Xidian University

About: Xidian University is a education organization based out in Xi'an, China. It is known for research contribution in the topics: Antenna (radio) & Computer science. The organization has 32099 authors who have published 38961 publications receiving 431820 citations. The organization is also known as: University of Electronic Science and Technology at Xi'an & Xīān Diànzǐ Kējì Dàxué.

Modified T-shaped planar monopole antennas for multiband operation

Abstract: In this paper, we propose a novel modified T-shaped planar monopole antenna in that two asymmetric horizontal strips are used as additional resonators to produce the lower and upper resonant modes. As a result, a dual-band antenna for covering 2.4- and 5-GHz wireless local area network (WLAN) bands is implemented. In order to expand the lower band, a multiband antenna for covering the digital communications systems, personal communications systems, Universal Mobile Telecommunications Systems, and 2.4/5-GHz WLAN bands is also developed. Prototypes of the multiband antenna have been successfully implemented. Good omnidirectional radiation in the desired frequency bands has been achieved. The proposed multiband antenna with relatively low profile is very suitable for multiband mobile communication systems

Flexible Data Access Control Based on Trust and Reputation in Cloud Computing

Abstract: Cloud computing offers a new way of services and has become a popular service platform. Storing user data at a cloud data center greatly releases storage burden of user devices and brings access convenience. Due to distrust in cloud service providers, users generally store their crucial data in an encrypted form. But in many cases, the data need to be accessed by other entities for fulfilling an expected service, e.g., an eHealth service. How to control personal data access at cloud is a critical issue. Various application scenarios request flexible control on cloud data access based on data owner policies and application demands. Either data owners or some trusted third parties or both should flexibly participate in this control. However, existing work hasn't yet investigated an effective and flexible solution to satisfy this demand. On the other hand, trust plays an important role in data sharing. It helps overcoming uncertainty and avoiding potential risks. But literature still lacks a practical solution to control cloud data access based on trust and reputation. In this paper, we propose a scheme to control data access in cloud computing based on trust evaluated by the data owner and/or reputations generated by a number of reputation centers in a flexible manner by applying Attribue-Based Encryption and Proxy Re-Encryption. We integrate the concept of context-aware trust and reputation evaluation into a cryptographic system in order to support various control scenarios and strategies. The security and performance of our scheme are evaluated and justified through extensive analysis, security proof, comparison and implementation. The results show the efficiency, flexibility and effectiveness of our scheme for data access control in cloud computing.

Switchable broadband terahertz absorber/reflector enabled by hybrid graphene-gold metasurface.

Abstract: Numerous studies have been made to design switchable terahertz absorber for the application of amplitude modulator. However, it is still a challenge to achieve large modulation range while maintaining broad bandwidth. Here, we propose a switchable broadband absorber/reflector in the low-terahertz regime. By utilizing a hybrid graphene-gold metasurface on SiO2/pSi/PDMS substrate with an aluminum back, an excellent absorption across 0.53–1.05 THz with a wide incident angles for both TE and TM polarizations is achieved. By controlling the voltage across gold electrode and pSi, the chemical potential of graphene can be changed correspondingly. When the chemical potential of graphene varied from 0eV to 0.3eV, the state of the proposed structure can be switched from absorption (>90%) to reflection (>82%) over the whole operation bandwidth. Electric field intensity and surface loss density of the proposed absorber under different chemical potential are given to have a physical insight of the mechanisms. The switchable absorber/reflector can enable a wide application of high performance terahertz devices, such as active camouflage, imaging, modulators and electro-optic switches.

Efficient Fair Conditional Payments for Outsourcing Computations

Abstract: The outsourcing computations in distributed environments suffer from the trust problems between the outsourcer and the workers All existing solutions only assume the rational lazy-but-honest workers In this paper, we first introduce the rational lazy-and-partially-dishonest workers in the outsourcing computation model In addition, we propose a new fair conditional payment scheme for outsourcing computation that is only based on traditional electronic cash systems The proposed construction uses a semitrusted third party T to achieve the fairness and efficiency However, T is only involved in the protocol in the exceptional case, namely in the case of disputes Moreover, since neither the secret sharing/splitting scheme nor the cut-and-choose protocol is used for the generation or verification of the payment token, our solution clearly outperforms the existing schemes in terms of efficiency

Peak-to-Average Power Ratio Reduction of OFDM Signals With Nonlinear Companding Scheme

Abstract: Companding transform is a simple and efficient method in reducing the Peak-to-Average Power Ratio (PAPR) of Orthogonal Frequency Division Multiplexing (OFDM) systems. In this paper, a novel nonlinear companding scheme is proposed to reduce the PAPR and improve Bit Error Rate (BER) for OFDM systems. This proposed scheme mainly focuses on compressing the large signals, while maintaining the average power constant by properly choosing transform parameters. Moreover, analysis shows that the proposed scheme without de-companding at the receiver can also offer a good BER performance. Finally, simulation results show that the proposed scheme outperforms other companding scheme in terms of spectrum side-lobes, PAPR reduction and BER performance.