김동우 교수

In code division multiple access (CDMA) mobile networks, transmitted power is controlled to provide each user an acceptable connection by limiting the interference seen by other users. Previous work has focused on finding a power assignment that maximizes the minimum carrier-to-interference ratio where the transmission rate of each user is known and fixed. In future mobile networks, however, fluctuations in mobiles' transmission rate should be considered in designing power control algorithms. In

In this study a robust two-phase nonboiling heat transfer correlation for turbulent flow (Re SL > 4000) in vertical tubes with different fluid flow patterns and fluid combinations was developed using experimental data available from the literature. The correlation presented herein originates from a careful analysis of the major nondimensional parameters affecting two-phase heat transfer. This model takes into account the appropriate contributions of both the liquid and gas phases, using the resp

Various distributed carrier-to-interference (C/I) balancing procedures have been developed to cope with implementational drawbacks of centralized power-control schemes. However, it would be inevitable for these distributed schemes to lose some system performance compared to a centralized one since they control their power level based on only the local C/I measurements. An efficient distributed power-control (DPC) scheme is proposed to maximize the system performance. A distributed C/I balancing

When a mobile newly arrives and seeks admission in power-controlled cellular/personal communications services (PCS) systems, interactive call admission control guides the evolution of the power transmitted by the new mobile in order to protect the transmission quality of ongoing calls from dropping below a desired level. In addition, it eventually decides whether the new mobile should be accepted or rejected without errors. However, existing interactive call admission algorithms incur high netwo

Traditional downlink power control methods for code-division multiple-access (CDMA) cellular systems allocate individual power levels to the different users of a given cell according to their relative needs, while assuming the amount of total power transmitted by each base to be constant. If this amount is not controlled, it is impossible to reduce unnecessary interference and, as a result, to achieve an optimal power control performance. In this paper, we address rather a simple convergent algo

Given limited supply of approved vaccines and constrained medical resources, design of a vaccination strategy to control a pandemic is an economic problem. We use time-series and panel methods with real-world country-level data to estimate effects on COVID-19 cases and deaths of two key elements of mass vaccination - time between doses and vaccine type. We find that new infections and deaths are both significantly negatively associated with the fraction of the population vaccinated with at least

The mobile transmitter power control algorithms that need to exchange the tract information on link gains, interference levels, or signal-to-interference ratio (SIR) between transmitters and receivers have been proved to converge to a unique fixed power allocation. However, such exact exchange requires an excessive bandwidth for signalling traffic. In practical systems, only 1 bit is sent back to each transmitter. The 0-1 binary feedback is used by the transmitter either to increase or to decrea

In CDMA mobile networks, variations in the transmit power level of the pilot signal may control the coverage area of the cells. When traffic load in a specific cell is sharply increasing, reducing the pilot power in that cell and, as a result, letting some mobiles near the cell boundary make an handoff to the neighbor cells and reallocating the reduced power to traffic channels will balance the load and keep adequate signal quality. However, too much decrease in pilot power may result in introdu

In this paper, we discuss capacity unbalance between uplink (mobile-to-base) and downlink (base-to-mobile) in future code division multiple access (CDMA) radio networks where both narrow-band and wide-band CDMA systems are coexisted. Since the two links are not operated in an identical condition, their capacities are unequal and either of the links determines the whole system capacity. The purpose of this paper is to examine which link limits the system capacity and what are the limiting factors

Recently, the magnetorheological (MR) polishing process has been examined asa new ultra-precision polishing technology for micro parts in MEMS applications. In theMR polishing process, the magnetic force plays a dominant role. This method uses MRfluids which contains micro abrasives as a polishing media. The objective of the presentresearch is to shed light onto the material removal mechanism under various slurryconditions for polishing and to investigate surface characteristics, including shape

With signal-to-interference ratio (SIR) based call admission control, a newly arriving call is accepted only if the received SIR is greater than an admission threshold. Since a large threshold often leads to unnecessary denials of the admission requests, the threshold should be selected within a certain upper bound. In this paper, the upper bounds of the admission threshold is provided, which achieves a prespecified level of admission-denying rate in power-controlled DS-CDMA mobile systems.