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Co-DDTMA : Cooperative Distributed TDMA for Vehicular Networks
Zhen Chen,Zhengyu Liu,Jianghong Han,Songhua Hu,Yang Lu 보안공학연구지원센터 2016 International Journal of Future Generation Communi Vol.9 No.2
In recent years, Vehicular Ad Hoc Networks (VANET) has experienced a rapid development due to the advancement of wireless communication technologies, and now emerges as a promising way to provide road safety, traffic efficiency and infotainment applications. However, it is a challenge to design a reliable and efficient Medium Access Control (MAC) protocol for VANET due to its frequent topology changes and unreliable wireless links. Cooperative communication, on the other hand, can enhance the reliability of wireless links by exploiting the broadcast nature of the wireless communication. A cooperative scheme for MAC is proposed for VANET in this paper, referred to as Cooperative Distributed TDMA (Co-DTDMA). In the Co-DTDMA, neighboring nodes utilize its idle slots for cooperatively retransmitting a packet which has failed to reach the destination. Since the cooperative retransmission is conducted in node's own idle slot, the proposed scheme does not interrupt the normal transmission. Both theoretical analysis and simulation results demonstrate that the proposed scheme greatly increases the probability of successful packet transmission and decreases the packet transmission delay.
Hua Ye,Hongyu Wu,Liangyuan Chen,Songhua Ma,Kaifeng Zhou,Guobing Yan,Jiazhong Shen,Dongcheng Chen,Shi‑Jian Su 대한금속·재료학회 2018 ELECTRONIC MATERIALS LETTERS Vol.14 No.2
A series of new small molecules based on symmetric electron-acceptor of 1,3,4-oxadiazole moiety or its asymmetric isomerof 1,2,4-oxadiazole unit were successfully synthesized and applied to solution-processable blue phosphorescent organic lightemittingdiodes for the first time, and their thermal, photophysical, electrochemical properties and density functional theorycalculations were studied thoroughly. Due to the high triplet energy levels (ET, 2.82–2.85 eV), the energy from phosphorescentemitter of iridium(III) bis[(4,6-difluorophenyl)-pyridinate-N,C2′]picolinate (FIrpic) transfer to the host molecules couldbe effectively suppressed and thus assuring the emission of devices was all from FIrpic. In comparison with the para-modeconjugation in substitution of five-membered 1,3,4-oxadiazole in 134OXD, the meta-linkages of 1,2,4-isomer appending withtwo phenyl rings cause the worse conjugation degree and the electron delocalization as well as the lower electron-withdrawingability for the other 1,2,4-oxadiazole-based materials. Noting that the solution-processed device based on 134OXD containing1,3,4-oxadiazole units without extra vacuum thermal-deposited hole/exciton-blocking layer and electron-transportinglayer showed the highest maximum current efficiency (CEmax) of 8.75 cd/A due to the excellent charge transporting ability of134OXD, which far surpassed the similar devices based on other host materials containing 1,2,4-oxadiazole units. Moreover,the device based on 134OXD presented small efficiency roll-off with current efficiency (CE) of 6.26 cd/A at high brightnessup to 100 cd/m2. This work demonstrates different nitrogen and oxygen atom orientations of the oxadiazole-based hostmaterials produce major impact on the optoelectronic characteristics of the solution-processable devices.