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.

Advanced spectrum sharing in 5G cognitive heterogeneous networks

Abstract: Spectrum utilization, energy consumption, and cost efficiency are three key performance metrics that should be jointly investigated in developing a sustainable 5G system. Advanced spectrum sharing can enhance both the spectral efficiency and energy efficiency in a cost-effective manner, which is expected to perform much better than conventional networks. In this article, we survey cognitive and cooperative spectrum sharing, and classify a multi-level spectrum exploitation, coordination, and utilization framework from both technical and economic perspectives. We specifically concentrate on spectrum trading and leasing, spectrum mobility, relaying, routing, and harvesting. Finally, a spectrum flowing scheme is proposed for 5G cognitive heterogeneous cellular networks, which improves both spectral and energy efficiency.

Optimal Placement of Cloudlets for Access Delay Minimization in SDN-Based Internet of Things Networks

Abstract: Given the highly dynamic traffic loads of mobile Internet of Things (IoT) devices and their stringent quality-of-service requirements, i.e., access delay particularly, as well as the heterogeneous infrastructures among IoT networks, it is a nontrivial task to efficiently deploy cloudlets among large number of access points (APs) in IoT networks, especially for the access delay and network reliability, since different placement schemes would produce various network performances. To combat this issue, we are motivated to investigate in details the optimal placement of cloudlets to minimize the average access delay by applying software-defined networking (SDN) techniques to provide flexible and programmable management for cloudlets deployment in IoT networks with considering the complicated queuing process at numerous SDN-based APs. An enumeration-based optimal placement algorithm (EOPA) is first proposed as benchmark. Then we propose a ranking-based near-optimal placement algorithm (RNOPA) which is able to dynamically adapt to mobile IoT devices and their traffic loads, by treating each AP as a single server queue and adopting an efficient ranking mechanism. As corroborated by extensive simulation results, RNOPA reports access delay very close to that of EOPA. Note that RNOPA outperforms the famous ${K}$ -medians clustering algorithm (KMCA) in both of average cloudlet access delay and reliability, while at the cost of a much lower computational complexity than KMCA.

Compact Triband ACS-Fed Monopole Antenna Employing Open-Ended Slots for Wireless Communication

Abstract: A compact triband asymmetric coplanar strip (ACS)-fed printed monopole antenna employing open-ended slots for wireless communication is presented. The proposed antenna is composed of an ACS-fed monopole and two special open-ended slots, which occupies a very compact size of 27.5 × 13 mm2. By carefully selecting the lengths and positions of these slots, good dual stopband rejection characteristic can be achieved. The three obtained bands of 2.35-2.53, 3.34-3.85, and 5.05-6.28 GHz can successfully cover the WLAN and WiMAX operation bands. The principle and key parameters of the slot in producing notched band are analyzed in detail. The measured results demonstrate that the proposed antenna has good omnidirectional radiation patterns with reasonable gains across the operating bands, which is suitable to be integrated within the portable device for wireless communication.

Adsorption of CO2 at ZnO: A Surface Structure Effect from DFT+U Calculations

Abstract: A complete understanding of the carbon dioxide (CO2) interaction with zinc oxide (ZnO) is a basis for the development of new ZnO-containing materials for catalytic fixation of CO2 into useful chemicals such as methanol. In this work, the density functional theory plus U (DFT+U) method coupled with periodic boundary conditions has been employed to investigate the adsorption of CO2 molecules on five relevant exposed surfaces of ZnO in an effort to capture the surface chemistry of the adsorbed molecules. Through our calculations, we demonstrated that the CO2 adsorption is sensitive to the oxide surface structure. The activation of CO2 by ZnO via the carbonate-ion formation requires the presence of empty surface Zn–O pairs. It was found that the binding strength of CO2 follows the order of ZnO(0001) ≤ ZnO(0001) ZnO(1120) > ZnO(0001)/ZnO(0001) > ZnO(1121)). The co...