• Journal of the Korean Institute of Telematics and Electronics S
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• v.35S no.10
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• pp.42-51
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• 1998

This paper suggests a congestion control scheme for CL (ConnectionLess) overlay network using the feedback loops between CL user and CL server, between CL servers, and between end-to-end CL users, and the header translation table of CL server. The CL overlay network for CBDS(Connectionless Broadhand Data Service) defined by ITU-T((International Telecommunication Union-Telecommunication) consists of CL servers which route frames and links which connect between CL user and CL server or between CL servers. In the CL overlay network, two kinds of congestion, CL link congestion and CL server congestion, may occur. We considered the schemes to solve the congestion. link-by-link method[18] has used the ABR feedback loops of ATM layer between CL user and CL server or between CL servers, and the congestion table using header translation table of CL server. As in congestion of output virtual channel this method has an effect on all the traffic transmitting through the link, then it has an effect on the traffic that has not caused the congestion. As a result, the link utilization of output virtual channel that does not bring the congestion and outputs the traffic is decreased. To overcome this drawback of link-by-link, we proposed the hybrid method that are using the ABR feedback loops of link-by-link method, the feedback loop between CL users in end-to-end, the congestion table using and the header translation table. This scheme deals with teh congestion immediately by link-by-link loops and the header translation table, and then regulates the sending rate of CL user that causes the congestion by end-to-end loop.

• Korean Journal of Optics and Photonics
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• v.12 no.2
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• pp.135-142
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• 2001

Recently, plastic optical fiber draws a lot of attention as a new transmission medium for local area network (LAN) and home network applications. As PMMA based GI-POF (Graded Index Plastic Optical Fiber) has very low loss at about 500 nm and 650 nm wavelengths, it is very important to have a compact ultra short optical pulse source at these wavelength windows. In this paper, we have investigated detailed characteristics of gain switched laser system by using a commercially available low cost RF devices and an InGaAlP Fabry Perot semiconductor laser operating at 650 nm wavelength. The shortest optical 'pulse obtained was 33 psec with 1 GHz repetition rate. Depending on the DC bias current and the modulation frequency, the FWHM and the pulse energy of the gain switched pulses show 33.3-82.8 psec and 0.97-9.69 pI respectively. Also, the spectral bandwidths for CW and gain switched operations are 0.44 nm and 1.50 nm. We believe that these results are quite useful for high bit rate optical transmission applications with PMMA based plastic optical fibers in addition to estimate properties of ultra fast optical components and electro-optic devices. vices.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.5A
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• pp.401-407
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• 2009

The multi-band (MB) ultra-wideband (UWB) communication system divides its available frequency spectrum in 3.1 to 10.6GHz into 16 sub-bands, which leads to inherent disparities between carrier frequencies of each sub-band. For instance, the highest carrier frequency is 2.65 times higher than the lowest one. Since the propagation loss is proportional to the square of the transmission frequency, the propagation loss on the sub-band having the highest carrier frequency is approximately 7 times larger than that on the sub-band having the lowest carrier frequency, which results in disparities between received signal powers on each sub-band. In this paper, we propose a novel correlation scheme for frequency hopping (FH) MB UWB communications, where the correlation time is adaptively adjusted relative to the sub-band, which reduces the disparity between the received signal energies on each sub-band. Such compensation for lower received powers on sub-bands having higher carrier frequency leads to an improvement on the total average bit error rate (BER) of the entire FH MB UWB communication system. We analyze the performance of the proposed correlation scheme in Nakagami fading channels, and it is shown that the performance gain provided by the proposed correlator is more significant as the Nakagami fading index n increases (i.e., better channel conditions).

• 전자공학회논문지 IE
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• v.47 no.4
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• pp.39-47
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• 2010

This paper proposes a numerical analysis to prove that the performance of the differential phase detections (DPDs) with the decision feedback, such as the decision feedback DPD (DF-DPD) and the DPD with recursively generated phase reference (DPD-RGPR), approach the performance of the coherent detection with differential decoding. The conventional differential phase detection for M-ary DPSK can make the receiver architecture simple, while it can make the bit-error rate (BER) performance poor because of the previous noisy phase as a reference phase. To improve the BER performance of the conventional differential detection, multiple symbol differential detection methods, including DF-DPD and DPD-RGPR, have been proposed. However, the studies on the analysis and on the comparison of these methods have been little performed. Then, this paper mathematically intends to analyze and compare the performance of the DPDs with the decision feedback. The analysis results show that the DPDs with the decision feedback can have the performance equal to that of the coherent detection with differential decoding and be available for the noncoherent detection in the improved performance. Considering the hardware complexity, the DPD RGPR with the simple detection process by using the recursively generated phase reference can be more simply implemented than the DF-DPD based on the architecture whose complexity increases according to the increasing detection length.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.16 no.4
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• pp.180-195
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• 2011

A balanced trophic model for Sinjido marine ecosystem was constructed using ECOPATH model and data obtained 1994 in the region. The model integrates available information on biomass and food spectrum, and analyses ecosystem properties, dynamics of the main species populations and the key trophic pathways of the system, and then compares these results with those of other marine environments. The model comprises 17 groups of benthic algae, phytoplankton, zooplankton, gastropoda, polychaeta, bivalvia, echinodermata, crustacean, cephalopoda, goby, flatfish, rays and skates, croaker, blenny, conger, flatheads, and detritus. The model shows trophic levels of 1.0~4.0 from primary producers and detritus to top predator as flathead group. The model estimates total biomass(B) of 0.1 $kgWW/m^2$, total net primary production(PP) of 1.6 $kgWW/m^2/yr$, total system throughput(TST) of 3.4 $kgWW/m^2/yr$ and TST's components of consumption 7%, exports 43%, respiratory flows 4% and flows into detritus 46%. The model also calculates PP/TR of 0.012, PP/B of 0.015, omnivory index(OI) of 0.12, Fin's cycling index(FCI) of 0.7%, Fin's mean path length(MPL) of2.11, ascendancy(A) of 4.1 $kgWW/m^2/yr$ bits, development capacity(C) of 8.2 $kgWW/m^2/yr$ bits and A/C of 51%. In particular this study focuses the analysis of mixed trophic impacts and describes the indirect impact of a groupb upon another through mediating one based on 4 types. A large proportion of total export in TST means higher exchange rate in the study region than in semi enclosed basins, which seems by strong tidal currents along the channels between islands, called Sinjido, Choyakdo and Saengildo. Among ecosystem theory and cycling indices, B, TST, PP/TR, FCI, MPL and OI are shown low, indicating the system is not fully mature according to Odum's theory. Additionally, high A/C reveals the maximum capacity of the region is small. To sum up, the study region has high exports of trophic flow and low capacity to develop, and reaches a development stage in the moment. This is a pilot research applied to the Sinjido in terms of trophic flow and food web system such that it may be helpful for comparison and management of the ecosystem in the future.

• Journal of the Korea Organic Resources Recycling Association
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• v.19 no.4
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• pp.97-105
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• 2011

A wide diversity of liquid fertilizers and composts produced from the livestock manure in Korea is commonly applied to agricultural lands as an alternative of chemical fertilizers. However, their effects on the crop production and environmental impacts are still vague. The current study was investigated the property changes of paddy soils in sandy loam and silty loam treated with 1) control (no treatment), 2) chemicals, 3) storage liquid fertilizer and 4) SCB liquid fertilizer located in Gyeong-gi province, Korea. The chemical properties of soils in sandy loam and silty loam before the treatment were similar with the ones in the average paddy fields in Korea. Contrary to this, the amount of available phosphorus in sandy loam was higher than the one in the average paddy fields. The number of living organisms in sandy loam and silty loam treated with storage liquid fertilizer and SCB liquid fertilizer were higher than the ones in sandy loam and silty loam with no-treatment and chemicals. Significant difference (P<0.05) among the treatments and no-treatment was observed in sandy loam rather than in silty loam. The amounts of heavy metals were the highest in both sandy loam and silty loam treated with storage liquid fertilizer and SCB liquid fertilizer. The comparison of heavy metals showed that the ones in silty loam were little bit higher than sandy loam. The leaf lengths and dry weights of rices were increased over time, however, no significant difference was observed among each treament. In addition, the rice yield in sandy loam treated with SCB liquid fertilizer was higher than the ones in sandy loam. The highest rice yield was obtained from sandy loam treated with chemicals, but there was no significant difference between storage liquid fertilizer and SCB liquid fertilizer. While the rate of nutrient absorption by rices was the highest in sandy loam and silty loam treated with chemicals, there was no significant difference in sandy loam and silty loam treated with livestock liquid manure.