Jong-Hyo Lee

Dynamic power management in Wi-Fi Direct for future wireless serial bus

AbstractThis paper presents a performance analysis of Wi-Fi Direct power management schemes and exploits their problems to design a novel, enhanced power management for future wireless USB (WSB) applications. Wi-Fi Direct will become a key technology for the support of future WSB services that require high standards of service quality and power efficiency at the same time. To provide this, Wi-Fi Direct defines two power management schemes, opportunistic power save mode and notice-of-absence. Even though each scheme has its own characteristics and advantages, specification does not have any definition of how to select the schemes and its parameters based on the type of WSB application being serviced. We analyze the properties of the two power management schemes of Wi-Fi Direct, and discover that their performance can greatly vary depending on the number and type of WSB applications that is being transmitted in the network. To solve this problem, we propose a novel power saving algorithm that can dynamically change the power management of Wi-Fi Direct. Our work is extensively evaluated using the Wi-Fi Direct module implemented in the NS-3 simulator.

Microstructure and electrical properties of magnetic tunneling junctions: Ta/NiFe/IrMn/M/Al-oxide/M/NiFe (M=Co, NiFe, CoFe)

Abstract The microstructure and electrical properties of the Ta/NiFe/IrMn/M/Al-oxide/M/NiFe (M=Co, NiFe, CoFe) ferromagnetic tunnel junctions with different Al-oxide thickness were investigated. The CoFe junction showed the highest magnetoresistance (MR) ratio of 32% at room temperature with the insulation layer of Al (15 A)-oxide, but also had the highest junction resistance of 34 kΩ (junction area of 200×200 μm) out of the three electrodes. The Co junction had the lowest resistance with reasonably high MR ratio of 24%. Cross-sectional transmission electron microscopy of the junctions showed that the increasing insulation thickness resulted in the rapid increased roughness at the top electrode/Al-oxide interface and the subsequent reduction of the MR ratio for all three electrodes materials. We have demonstrated that the MR effect is not only dictated by the intrinsic properties of the FM electrode materials, but also by the thickness and the microstructure of the oxide layer, which could be utilized to optimize the electrical properties of the ferromagnetic tunneling junction.