• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.30 no.9A
• /
• pp.803-813
• /
• 2005

This paper explores the throughput performance of CSMA/CA-based DCF protocol over frequency-selective, slow Ricean fading channels with both the $E_{b}/N_{o}$ and BER at the MAC layer in the 802.1 la wireless LAN. By exploring the throughput of DCF protocol with the data rate of 6Mbps, 12 Mbps, 24 Mbps and 54 Mbps, we find the fact that the higher the $E_{b}/N_{o}$ be and the less the BER be, the higher the throughput be.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.13 no.2
• /
• pp.261-266
• /
• 2009

We analyze the performances of the DCF, which is the medium access control protocol of IEEE 802.11 WLAN, assuming normal traffic condition. There have been much less research efforts under the normal condition than those under the saturated one. This paper proposes an analytical method of approximating the transmission attempt rate under normal condition as proportional to that under saturated condition. In result, we show that we can obtain the transmission attempt rate and the packet collision probability which quickly converge using iterative computations of relatively simple equations, and using these results we derive the network throughput and medium access delay. Numerical results show that our method is much less complex than those based on the Markov Chain while it can predict the performances quite accurately.

• The Journal of the Korea Contents Association
• /
• v.11 no.11
• /
• pp.34-41
• /
• 2011

The MAC of IEEE 802.11 WLAN to control data transmission uses two control methods called DCF and PCF. The DCF uses BEB backoff algorithm based on CSMA/CA. The BEB backoff algorithm shows excellent performance relatively in situation that competition between stations is less, but its performance is decreases as the competition increases. This paper proposes and analyses mathematically an enhanced backoff algorithm. To reduce the collision probability, the proposed algorithm increases the contention window to maximum after collision and decreases the contention window smoothly after successful transmission. To prove efficiency of proposed algorithm, simulations are conducted and analyzed.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.41 no.12
• /
• pp.1811-1813
• /
• 2016

DCF (Distributed Coordination Function) resolves the channel contention problem in a distributed manner by forcing nodes to randomly choose a waiting time in a contention window. However, since the size of a contention is limited, the collision probability increases with the number of sending nodes. To resolve the problem, in this paper, we propose a transmission control method based on the minority game (MG). Each node can determine autonomously whether to send or not without message exchanges with other nodes to maximize its profit. Through simulation studies, we verify that the proposed method can improves the performance of DCF in terms of collision probability in a congestion situation.

• Journal of Korea Technology Innovation Society
• /
• v.9 no.1
• /
• pp.84-102
• /
• 2006

This paper compares four models to value a biotechnology R&D project; option tree model, dynamic discounted cash flow(DCF) model, and option thinking DCF model with general DCF model. Real Options, especially 6-folded option tree model yields boner estimate of value than values using other methods. According to sensitivity analysis, sales of final products, number of investigational new drug developments(INDs) and success rates of each stage are key factors for the value of biotechnology R&D investment.

• Asia-Pacific Journal of Business Venturing and Entrepreneurship
• /
• v.12 no.4
• /
• pp.15-24
• /
• 2017

The major goal of this paper falls on developing new rational valuation model, to help companies and investors in the early stage of growth as to preparing and negotiating valuation of investment, by applying new reasonable discount indexes of calculating Discount Cash Flow in valuation of the start-up which has been recognized the critical fatal flaws of DCF with them. There are three specific studies done in this paper. First, this paper found the solid and viable bases of rational discount indexes as to applying DCF in valuing companies in the early growth stage with reviewing the previous studies including Berkus method, Scorecard Method, and Risk factor Summation method classified the most effective tools of valuing pre-revenue generating companies. Second, this paper quoted and analyzed the previous models and studies, so called, 'DCF-Prime' of applying DCF method as to value companies in the early growth stage by taking all risk factors innate to the companies in the early growth stage as the discount rate Beta coefficient. Third, this paper propose more viable and solid valuation models, so called, 'DCF-Plus'of combing all validated valuation factors in Berkus, Scorecard, and Risk Factor Summation methods into applying separate discount bracket after DCF Valuation over the companies in the early growth stage instead of taking them as the factors of discount rate, beta coefficient, like the previous model of DCF-Prime. DCF-Plus mainly developed in this paper will not only provide more rational valuation bases as to investment negotiation between companies and investors in the early growth stage, but also providing more accountable guidelines to companies in the early growth as to prepare investment raising and accelerating their company's value by themselves.

• KOREAN JOURNAL OF CROP SCIENCE
• /
• v.42 no.2
• /
• pp.166-172
• /
• 1997

This experiment was carried out to clarify the effect of the deep water irrigation on dry-seeded rice cultivation at the three different water managements-deep continuous flooding(DCF), water saving irrigation(WSI), ordinary irrigation(OI). The highest tillering numbers per $m^2$ of rice were 551, 466 and 455 in OI, WSI and DCF, respectively. The tillering number of rice plants were significantly reduced in DCF. Heading date was delayed and the total chlorophyll content in leaf after heading was higher in DCF than those in other irrigation methods. For the characteristics associated with lodging, the culm length in DCF was slightly elongated and the diameter of culm in DCF was thicker than that in WSI and OI. The breaking weight and bending moment in DCF also were higher than those in others. As the result, although the culm length in DCF was long, the lodging index was comparatively low. The panicle length in DCF was longer than in OI and WSI. The spikelet number per $m^2$ and 1,000-grain weight were the most in WSI, while panicle number, ripened grain ratio and grain weight were not significantly different. Longer panicle length and more spikelet number resulted in higher yielding capacity in DCF.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.35 no.6A
• /
• pp.577-584
• /
• 2010

In this paper, a cooperative MAC protocol that is reliable over bad wireless channel environments and thus can enhance the system performance much more is proposed. Its performance is evaluated with the computer simulation. The system throughput and average waiting delay are used as performance measures. According to numerical results, the proposed MAC protocol provides better system throughput by 24% than the traditional rDCF scheme. From the average waiting delay point of view, when the number of terminals is small, the proposed MAC protocol has the better performance in an average view-point than the rDCF scheme. However, when the number of terminals is large, the proposed MAC protocol provides a little worse performance than the rDCF scheme. That is because, when the number of terminals is large, the dominant factor affecting the system performance is channel contention procedure, which results in lots of collisions. However, if the queuing delays in the waiting buffers are included for calculating the average waiting delay, then the total system delay will be smaller than the rDCF scheme.

• Journal of Advanced Navigation Technology
• /
• v.8 no.1
• /
• pp.65-72
• /
• 2004

A basic access method using for IEEE 802.11a wireless LANs is the DCF method that is based on the CSMA/CA. But, Since IEEE 802.11 MAC layer uses original backoff algorithm (Exponential backoff method), when collision occurs, the size of contention windows increases the double size. Hence, packet transmission delay time increases and efficiency is decreased by original backoff scheme. In this paper, we have analyzed TCP packet transmission time of IEEE 802.11 MAC DCF protocol for wireless LANs using a proposed enhanced backoff algorithm. From the results, in OFDM/quadrature phase shift keying channel (QPSK), we can achieve that the transmission time in wireless channel decreases as the TCP packet size increases and based on the data collected, we can infer the correlation between TCP packet size and total message transmission time, allowing for an inference of the optimal packet size in the TCP layer.

• Biomedical Science Letters
• /
• v.15 no.2
• /
• pp.119-126
• /
• 2009

This study investigated the effect of Corni Fructus(Cornus officinalis Sieb. et Zucc.) extract on hyperglycemia and renal function in streptozotocin-induced diabetic rats. Male Sprague-Dawley rats were divided into three groups including normal control(NC), diabetic control(DC), and diabetic treatment with Corni Fructus(DCF). Over a 4-week experimental period, Corni Fructus aqueous extract was administered orally at 500 mg/kg BW/day. The final fasting serum glucose, serum urea nitrogen, triglyceride, urinary total protein level, and relative weight of the left kidney in the DCF group were significantly lower than the DC group. Serum insulin level in the DCF group was higher than the DC group by 23%. The renal xanthine oxidase and superoxide dismutase activities in the DCF group were significantly lower than the DC group. The renal catalase activity in the DCF group was significantly higher than the DC group. In conclusion, these results indicated that Corni Fructus can reduce glucose level and prevent or retard the development of diabetic complication via its antioxidative effect and protecting against diabetic renal damage in streptozotocin-induced diabetic rats.