Ok-Seon Lee

Hard Handoff Scheme Exploiting Uplink and Downlink Signals in IEEE 802.16e Systems

We consider hard handoff scheme based on uplink and downlink signals in IEEE 802.16e systems. To exploit the channel reciprocity in TDD systems, the proposed scheme triggers handoff initiation process using uplink signal. A serving base station monitors uplink traffic signal and triggers handoff process when the uplink signal strength or SINR becomes less than the predetermined level. This process can prevent mobile stations from periodically monitoring and reporting downlink signals of neighbor base stations at the non-handoff region. In the handoff decision process, the proposed scheme exploits not only uplink signal but also downlink signal as the handoff criteria to reduce ping-pong and outage probability. To efficiently combine uplink and downlink signal levels, the proposed scheme adopt an uplink and downlink joint hysteresis to determine a handoff direction. Using the joint hysteresis can reduce the outage probability compared with using uplink and downlink hysteresis independently. We evaluate the performance of the proposed scheme using computer simulation. The simulation results show that the proposed algorithm has better performance than the conventional mobile assisted handoff scheme of IEEE 802.16e in terms of the average number of handoff and the outage probability during handoff

A handover time negotiation mechanism for seamless service in IEEE 802.16E

IEEE 802.16e specification adopted that a target base station (BS) transmits Fast_Ranging_IE() to the upcoming handover MS to reduce the handover interruption time. However, the handover interruption time can be increased if the MS fails to receive Fast_Ranging_IE() because the channel release time between the MS and the serving BS is increased more than the estimated handover time due to the queuing delay and the handover message loss. In this paper, we propose the handover time negotiation mechanism to receive Fast_Ranging_IE() exactly. The proposed mechanism helps the serving BS and neighbor BSs to negotiate and share the estimated handover time information each other. To determine the estimated handover time, we considers the queuing delay in wireless and wired network, and the delay due to the handover message loss. The simulation results show that the receiving failure ratio of Fast_Ranging_IE() is reduced about 94% and handover interruption time of 95% users is less than 150 m sec when the proposed mechanism is applied to IEEE 802.16e system. Therefore, the proposed mechanism helps the IEEE 802.16e system to support the seamless service for the real-time applications.

The Study on Parameters Affecting Depth-Wise Photo-Curing Process Based on Interaction Between Light and Metal Surface

This paper deals with the depth-wise photo-curing phenomenon which is commonly found in lithography process for semiconductor packaging and printed circuit board. The depth-wise curing is affected also by temperature rise by absorption of irradiation wave at the surface of substrate. The generated heat accelerates curing reaction and final degree of curing increases more that those without temperature rise.