Browsing by Author "Chang, Che-Yu"

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Novel hybrid light-emitting devices based on MAPbBr(3) nanoplatelets:PVK nanocomposites and zinc oxide nanorod arrays
(2018-01-01)
Wang, Szu-Ping
;
Chang, Chun-Kai
;
Yang, Sheng-Hsiung
;
Chang, Che-Yu
;
Chao, Yu-Chiang
In this research, we demonstrate inverted perovskite light-emitting devices (PeLEDs) based on zinc oxide nanorod arrays (ZnO NAs) as the electron transport layer and methylammonium lead bromide nanoplatelets (MAPbBr(3) NPLs) as the emissive material for the first time. The polyethyleneimine ethoxylated (PEIE) was inserted between the ZnO NAs and the MAPbBr(3) NPLs layer to reduce the energy barrier and improve the electron injection efficiency. Besides, different weight ratios of poly(N-vinylcarbazole) (PVK) were blended with MAPbBr(3) NPLs to make evenly dispersed nanocomposite films, thereby enhancing the performance of devices. Meanwhile, the photoluminescence of MAPbBr(3) NPLs:PVK nanocomposite film was increased due to reduced self-quenching and prolonged carrier lifetime. Inverted PeLEDs with the configuration of ITO/PEIE-modified ZnO NAs/MAPbBr(3) NPLs: PVK/TFB/Au were fabricated and evaluated, using TFB as the hole transport layer. The current density of the devices containing PVK matrix was significantly suppressed compared to those without PVK. Herein, the best device revealed a max brightness of 495 cd m(-2) and a low turn-on voltage of 3.1 V that shows potential use in light-emitting applications.
QoS/QoE Support for H.264/AVC Video Stream in IEEE 802.11ac
(2017-12-01)
Chang, Che-Yu
;
Yen, Hsu-Chun
;
Lin, Chun-Cheng
;
Deng, Der-Jiunn
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工業工程與管理學系
The H.264 video compression technique enjoys the merit of good video quality with high compression rate; therefore, it has been widely applied in delivering video content. In IEEE 802.11ac wireless local area networks, enhanced distributed channel access (EDCA) is the primarily adopted access control mechanism for multimedia traffic transmission. However, the performance is degraded due to the unpredictable delay caused by its inefficient backoff procedure. To achieve high quality of service/experience, this paper proposes a multipolling controlled access (MPCA) scheme to guarantee the latency in delivering important video frames while reducing transmission overhead. We also propose a cross-layer designed quality adjustment strategy to maximize the visual experience. Furthermore, the downlink multi-user multiple-input-multiple-output feature in IEEE 802.11ac is exploited to enhance the reliability of MPCA. Theoretical analysis is provided to show high efficiency of MPCA. Simulation results indicate that MPCA has higher throughput, lower packet delay, lower packet loss, and higher peak signal-to-noise ratio than the EDCA.