• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.36 no.6C
• /
• pp.376-383
• /
• 2011

Since the first arrival path may not be the strongest path of UWB(Ultra Wide Band) multipath channels, this makes ToA(Time-of-Arrival) estimation becomes a challengeable issue. Furthermore, because of ultra bandwidth of received signals, the compressed sensing theory is employed to reduce the complexity caused by very high Nyquist sampling rate in coherent UWB receivers. In this paper, we propose a ToA estimation scheme which provides precise estimation performance, while exploiting the benefits of compressed sensing-based UWB receivers. Simulation results show that the proposed scheme can outperform other low complexity schemes in a wide range of signal-to-noise ratios.

• The Journal of the Convergence on Culture Technology
• /
• v.8 no.1
• /
• pp.531-536
• /
• 2022

This paper compared the performance of the parametric method and the nonparametric method when estimating the distribution for the tail of the distribution with heavy tails. For the parametric method, the generalized extreme value distribution and the generalized Pareto distribution were used, and for the nonparametric method, the kernel density estimation method was applied. For comparison of the two approaches, the results of function estimation by applying the block maximum value model and the threshold excess model using daily fine dust public data for each observatory in Seoul from 2014 to 2018 are shown together. In addition, the area where high concentrations of fine dust will occur was predicted through the return level.

• Journal of KIISE:Information Networking
• /
• v.34 no.6
• /
• pp.505-513
• /
• 2007

Vertical handoff is a new type of handoff in wireless networks. It is issued when a mobile node moves over overlapping wireless networks with each proving a different access bandwidth, transmission latency, and coverage. By issuing the vertical handoff, the mobile node can obtain better network bandwidth. In the sense of TCP throughput, however, the vertical handoff does not always produce positive performance gain, so sometimes it is better for the mobile node to stay at lower bandwidth providing network rather than to select and move to higher bandwidth providing network. In this paper, we analyze TCP throughput for vertical handoff, and propose a new handoff decision scheme which can estimate TCP throughput at the moment of vertical handoff. Based on the estimation, a mobile node can decide to issue vertical handoff to produce better TCP throughput, and we verify the results by simulations.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.40 no.12
• /
• pp.9-17
• /
• 2003

In this paper we proposea method for estimating the bandwidth in next-generation If network. Especially, we concentrate on the edge routers accommodating the VoIP connections as well as a group of data connections. Bandwidth dimensioning is carried out at call level and packet level for voice traffic in the next-generation IP network. The model incorporates the statistical estimation approach at a call level for obtaining the number of voice connections simultaneously in the active mode. The call level model incorporates a statistical technique to compute the statistics of the number of active connections such as the mean and variance of the simultaneously connected calls in the network. The packet level model represents a load map for voice and data traffic by using non-preemptive M/G/1 queuing model with strict priority for voice over data buffer, From the proposed traffic model, we can derive a graph for upper bounds on the traffic load in terms of bandwidth for voice and data connections. Via numerical experiments we illustrate the implication of the work.

• The Journal of the Acoustical Society of Korea
• /
• v.27 no.3
• /
• pp.119-128
• /
• 2008

This paper analyzes the relationship between two representative statistical methods for bandwidth extension (BWE): Gaussian Mixture Model (GMM) and Hidden Markov Model (HMM) ones, and compares their performances. The HMM method is a memory-based system which was developed to take advantage of the inter-frame dependency of speech signals. Therefore, it could be expected to estimate better the transitional information of the original spectra from frame to frame. To verify it, a dynamic measure that is an approximation of the 1st-order derivative of spectral function over time was introduced in addition to a static measure. The comparison result shows that the two methods are similar in the static measure, while, in the dynamic measure, the HMM method outperforms explicitly the GMM one. Moreover, this difference increases in proportion to the number of states of HMM model. This indicates that the HMM method would be more appropriate at least for the 'blind BWE' problem. On the other hand, nevertheless, the GMM method could be treated as a preferable alternative of the HMM one in some applications where the static performance and algorithm complexity are critical.

• Journal of Korea Water Resources Association
• /
• v.53 no.8
• /
• pp.597-604
• /
• 2020

Muskingum, a hydrologic channel flood routing, is a method of predicting outflow by using the relationship between inflow, outflow, and storage. As many studies for Muskingum model were suggested, parameters were gradually increased and the calculation process was complicated by many parameters. To solve this problem, an optimization algorithm was applied to the parameter estimation of Muskingum model. This study applied the Advanced Nonlinear Muskingum Model considering continuous flow (ANLMM-L) to Wilson flood data and Sutculer flood data and compared results of the Linear Nonsingum Model incorporating Lateral flow (LMM-L), and Kinematic Wave Model (KWM). The Sum of Squares (SSQ) was used as an index for comparing simulated and observed results. Exponential Bandwidth Harmony Search with Centralized Global Search (EBHS-CGS) was applied to the parameter estimation of ANLMM-L. In Wilson flood data, ANLMM-L showed more accurate results than LMM-L. In the Sutculer flood data, ANLMM-L showed better results than KWM, but SSQ was larger than in the case of Wilson flood data because the flow rate of Sutculer flood data is large. EBHS-CGS could be appplied to be appplicable to various water resources engineering problems as well as Muskingum flood routing in this study.

• Journal of the Korean Data and Information Science Society
• /
• v.14 no.2
• /
• pp.247-255
• /
• 2003

Hypothesis testing for the equality of two distributions were considered. Nonparametric kernel density estimates were used for testing equality of distributions. Cross-validatory choice of bandwidth was used in the kernel density estimation. Sampling distribution of considered test statistic were developed by resampling method, called the bootstrap. Small sample Monte Carlo simulation were conducted. Empirical power of considered tests were compared for variety distributions.

• Proceedings of the Korean Information Science Society Conference
• /
• 2004.10c
• /
• pp.112-114
• /
• 2004

최근에 널리 사용되고 있는 IEEE 802.l1b의 QoS보장은 중요한 기술적 이슈가 되고 있다. IEEE 802.l1b의 QoS를 보장하기 위한 정책을 효율적으로 수립하기 위해서는 현재 채널에서의 사용 가능한 대역폭을 예측할 수 있어야 한다. 본 논문은 기존에 제시 되었던 IEEE 802.l1b의 채 널 saturation 대역폭 모델을 확장하여 채널 상태의 모니터링을 기반으로 한 현재 의 채널에서 사용 가능한 대역폭의 예측 모델을 제안한다. 또한 실제 무선 환경을 구현하여 실험한 결과와 제안한 모델에서의 결과 비교를 통해 제안한 모델이 채널의 가용 대역폭을 효과적으로 예측할 수 있음을 확인하였다.

• Proceedings of the Korean Information Science Society Conference
• /
• 2004.10c
• /
• pp.175-177
• /
• 2004

무선망에서의 TCP 성능은 않은 연구가 되어 왔지만 손실율이 큰 경우의 TCP의 성능은 아직도 개선의 여지가 많다. 본 논문은 두 가지 점에서 새로운 TCP를 제안한다. 첫째, 혼잡제어(Congestion Control)와 손실제어(Loss Recovery)가 분리(Decoupled)되었다. 기존의 연구들은 무선손실과 혼잡손실을 구분하여야 한다는 점에는 많은 연구를 해왔지만 무선 손실에 대하여 어떻게 대처할 것 인가에 관한 문제는 상대적으로 간과하였다. 둘째, 기종의 TCP-Westwood와 TCP-Jersey에서 사용되는 ABE(Available Bandwidth Estimation)가 무선네트워크에 의해 발생하는 패킷 손실로 인해 부정확해지는 것을 지적하고 새로운 ABE방법을 제시한다. 시뮬레이션을 통하여 우수한 성능을 보여주었다.

• Proceedings of the IEEK Conference
• /
• 2001.06a
• /
• pp.5-8
• /
• 2001

SSB(Single Sideband) modulation scheme is high bandwidth efficient method in the mobile communication system compared with present DSB(Double Sideband) modulation scheme. Using the othogonality between inphase PN code and Hilbert transformed quadrature PN code, we propose phase estimation structure that enables coherent demodulation in the reverse link basestation receiver Several system characteristics, bit error rate and phase error variance, are simulated and compared with balanced QPSK DS/CDMA system. To verify system performance, SSB/BPSK-DS/CDMA test board is implemented using FPGA chips.