Security enhancement using a novel two-slot cooperative NOMA scheme

In this letter, we propose a novel cooperative non-orthogonal multiple access (NOMA) scheme to guarantee the secure transmission of a specific user via two time slots. During the first time slot, the base station (BS) transmits the superimposed signal to the first user and the relay via NOMA. Meanwhile, the signal for the first user is also decoded at the second user from the superimposed signal due to its high transmit power. In the second time slot, the relay forwards the signal to the second user while the BS retransmits the signal for the first user as interference to disrupt the eavesdropping. Due to the fact that the second user has obtained the signal for the first user in the first slot, the interference can be eliminated at the second user. To measure the performance of the proposed cooperative NOMA scheme, the outage probability for the first user and the secrecy outage probability for the second user are analyzed. Simulation results are presented to show the effectiveness of the proposed scheme

A novel spectrum sharing scheme assisted by secondary NOMA relay

In this letter, a two-slot secondary non-orthogonal multiple access (NOMA) relay is used to assist spectrum sharing, where the primary transceivers with long distance communicate through the relay. First, the information for the primary receiver (PR) and secondary receivers (SRs) is transmitted via the NOMA relay. Then, the information for PR is re-transmitted to it through a selected SR to improve its quality of service using maximal-ratio combining, while the next data for PR is sent from the primary transmitter (PT) to the NOMA relay simultaneously. The power allocation solution is derived for the NOMA relay. Simulation results have shown the effectiveness of the proposed scheme

Secure primary transmission assisted by a secondary full-duplex NOMA relay

In this correspondence, secure primary transmission is proposed by using a multi-antenna secondary full-duplex non-orthogonal multiple access (NOMA) relay in cognitive radio (CR) networks. First, the primary signal is transmitted from the primary transmitter to the relay. Artificial noise is generated by using part of the antennas at the relay to disrupt eavesdropping, without affecting the primary transmission. Then, superimposed signals are transmitted from the relay to the primary receiver (PR) and secondary receivers (SRs) via NOMA. The primary security is guaranteed by the modified decoding order and beam forming optimization, which is converted to convex and solved by an iterative algorithm. Simulation results are presented to show the effectiveness of the proposed scheme in guaranteeing the primary security in CR networks

Caching D2D connections in small-cell networks

Small-cell network is a promising solution to high video traffic. However, with the increasing number of devices, it cannot meet the requirements from all users. Thus, we propose a caching device-to-device (D2D) scheme for small-cell networks, in which caching placement and D2D establishment are combined. In this scheme, a limited cache is equipped at each user, and the popular files can be prefetched at the local cache during off-peak period. Thus, dense D2D connections can be established during peak time aided by these cached users, which will reduce the backhaul pressure significantly. To do this, first, an optimal caching scheme is formulated according to the popularity to maximize the total offloading probability of the D2D system. Thus, most edge users can obtain their required video files from the caches at users nearby, instead from the small-cell base station. Then, the sum rate of D2D links is analyzed in different signal-to-noise ratio (SNR) regions. Furthermore, to maximize the throughput of D2D links with low complexity, three D2Dlink scheduling schemes are proposed with the help of bipartite graph theory and Kuhn-Munkres algorithm for low, high and medium SNRs, respectively. Simulation results are presented to show the effectiveness of the proposed scheme

Microwave-Assisted Synthesis of Co/CoOx Supported on Earth-Abundant Coal-Derived Carbon for Electrocatalysis of Oxygen Evolution

The evident demand for hydrogen as the ultimate energy fuel for posterity calls for the development of low-cost, efficient and stable electrocatalysts for water splitting. Herein, we report the synthesis of Co/CoOx supported on coal-derived N-doped carbon via a simple microwave-assisted method and demonstrate its application as an efficient catalyst for the oxygen evolution reaction (OER). With the optimal amount of cobalt introduced into the N-doped coal-derived, the developed catalyst achieved overpotentials of 0.370 and 0.429 V during water oxidation at current densities of 1 mA cm(-2) and 10 mA cm(-2), respectively. There was no noticeable loss in the activity of the catalyst during continuous galvanostatic polarization at a current density of 10 mA cm(-2) for a test period of 66 h. The synergistic interaction of the Co/CoOx moieties with the pyridinic and pyrollic nitrogen functional groups in the N-doped carbon, as well with the other heteroatoms species in the pristine coal favored enhancement of the OER electrocatalytic performance. (C) The Author(s) 2019. Published by ECS

China's mitigating climate change

행사명 : KDIS-WBI-CAG Policy Foru

A Synthetic Fusion Rule for Salient Region Detection under the Framework of DS-Evidence Theory

Saliency detection is one of the most valuable research topics in computer vision. It focuses on the detection of the most significant objects/regions in images and reduces the computational time cost of getting the desired information from salient regions. Local saliency detection or common pattern discovery schemes were actively used by the researchers to overcome the saliency detection problems. In this paper, we propose a bottom-up saliency fusion method by taking into consideration the importance of the DS-Evidence (Dempster–Shafer (DS)) theory. Firstly, we calculate saliency maps from different algorithms based on the pixels-level, patches-level and region-level methods. Secondly, we fuse the pixels based on the foreground and background information under the framework of DS-Evidence theory (evidence theory allows one to combine evidence from different sources and arrive at a degree of belief that takes into account all the available evidence). The development inclination of image saliency detection through DS-Evidence theory gives us better results for saliency prediction. Experiments are conducted on the publicly available four different datasets (MSRA, ECSSD, DUT-OMRON and PASCAL-S). Our saliency detection method performs well and shows prominent results as compared to the state-of-the-art algorithms

Interaction between Organic Compounds and Catalyst Steers the Oxidation Pathway and Mechanism in the Iron Oxide-Based Heterogeneous Fenton System

In the past decades, extensive efforts have been devoted to the mechanistic understanding of various heterogeneous Fenton reactions. Nevertheless, controversy still remains on the oxidation mechanism/pathway toward different organic compounds in the classical iron oxide-based Fenton reaction, largely because the role of the interaction between the organic compounds and the catalyst has been scarcely considered. Here, we revisited the classic heterogeneous ferrihydrite (Fhy)/H2O2 system toward different organic compounds on the basis of a series of degradation experiments, alcohol quenching experiments, theoretical modeling, and intermediate analysis. The Fhy/H2O2 system exhibited highly selective oxidation toward the group of compounds that bear carboxyl groups, which tend to complex with the surface Fe(III) sites of the Fhy catalyst. Such interaction results in a nonradical inner sphere electron transfer process, which seizes one electron from the target compound and features negligible inhibition by the radical quencher. In contrast, for the oxidation of organic compounds that could not complex with the catalyst, the traditional HO· process makes the main contribution, which proceeds via hydroxyl addition reaction and could be readily suppressed by the radical quencher. This study implies that the interaction between the organic compounds and the catalyst plays a decisive role in the oxidation pathway and mechanism of the target compounds and provides a holistic understanding on the iron oxide-based heterogeneous Fenton system