• Journal of the Korea Institute of Information and Communication Engineering
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• v.2 no.2
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• pp.259-266
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• 1998

406MHz and INMARSAT-E EPIRB facility transmits the distress alerts by the relay of the polar-satellites and INTELSAT, but may cause the probability of delayed transmission because of the orbital period and not compliance with the implementation of GMDSS rules for small ships in A1 area.. Digital Selective Calling forms a critical part of the terrestrial elements of the GMDSS system and ensures the reliability and the efficiency in the system. In this paper, we suggests that new DSC EPIRB in the VHF band to overcome this defect for small ships in A1 area, and analyze the ITU-R recommendations and technical characteristics, design and implement the algorithm of calling sequences, frequency synthesizer for the RF signal and FSK moulation signals.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.10
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• pp.1186-1189
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• 2016

A distributed uplink power control algorithm based on flocking model is proposed to improve the energy efficiency of mobiles station (MS) in cellular networks. As each bird in a flock matches its velocity with the average velocity of the adjacent birds, each MS in a cell matches its uplink rate with the average uplink rate of the co-channel MSs in adjacent cells by controlling its transmission power. Results show that the proposed algorithm effectively reduces the power consumption in the MS, while maintaining a low outage probability, which eventually improves the energy efficiency of the MS.

• The KIPS Transactions:PartC
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• v.9C no.6
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• pp.945-952
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• 2002

For a successful inter-system handoff, several important issues must be handled and additional new features must be considered. This paper focuses on the cellular structure of small cells which are required for the high density of population and a handoff scheme designed between two heterogenous networks. Incase of inter-system handoff (ISHO), the time required to complete the handoff can vary and depends on the structure of networks. And also the transmission of additional signals can increase the probability of failure for ISHO. Here we propose the sub-boundary cell base station (Sub-BBS) to alleviate the role of the BBS. The Sub-BBS is adjacent to BBS in the same regional mobile network. 쪼en the mobile terminal enters Sub-BBS, the network starts finding a new route and after entering BBS, it initiates the transformation process. The proposed scheme significantly reduces the ISHO failure rate compared to the existing one which is the most recent and known as efficient.

• Proceedings of the Korean Information Science Society Conference
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• 2005.07a
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• pp.463-465
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• 2005

본 논문에서는 802.l1e MAC의 EDCA 모드를 기반으로 한 무선랜 환경에서 realtime data인 voice traffic의 QoS를 향상하기 위한 방안을 연구하였다. 동적으로 채널의 상태를 보고, 네트워크 상태를 예측하여 채널 경쟁에 참여할지를 결정하는 방안으로, 경쟁이 치열할 때 voice traffic에 차별화된 가중치를 더 줄 수 있어 전반적인 voice traffic의 성능 향상에 기여한다. 본 연구에서 SU(slot utilization)을 계산하여 PT(Probability of Transmission)을 구할 때, 기존의 DCC 알고리즘을 그대로 802.11e에 적용하게 되면 4개의 AC에 똑같은 알고리즘이 적용되어 802.11e의 핵심인 차별화된 QoS를 지원하는데 무리가 있다. 기존 DCC 알고리즘에서 재시도 회수만 고려해 구하는 것을 802.11e 구조에 맞추어 4개의 AC별로 차별화하여 전송확률(PT)를 구할 수 있게 하였다. 뿐만 아니라, 재시도 회수를 고려하여 재시도 회수가 않은 packet에는 PT값이 높게 나을 수 있게 하고, 최대 가능한 재시도 회수에 도달할 때에는 상위 AC 영역의 값이 나오게 하여 AC의 upgrade가 되는 효과를 가져오게 하였다. 이 때 각 AC의 lower bound와 upper bound를 정하고, 이 때 802.11e의 최대 재시도 회수 parameter와의 상관관계를 정의하여 하위 AC가 상위 AC의 영역을 침범하지 못하도록 정의하고 있다. 추가적으로 SU의 값을 구할 때에도 현재의 SU값 대신 누적된 평균 SU값을 사용해 PT값을 구하여, utilization, latency, Packet loss등 전반적인 부분의 성능개선을 확인할 수 있다.

• The Korean Journal of Physiology and Pharmacology
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• v.10 no.2
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• pp.59-64
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• 2006

The effects of $Zn^{2+}$ on spontaneous glutamate and GABA release were tested in mechanically dissociated rat CA3 pyramidal neurons which retained functional presynaptic nerve terminals. The spontaneous miniature excitatory and inhibitory postsynaptic currents (mEPSCs and mIPSCs, respectively) were pharmacologically isolated and recorded using whole-cell patch clamp technique under voltage-clamp conditions. $Zn^{2+}$ at a lower concentration $(30{\mu}M)$ increased GABAergic mIPSC frequency without affecting mIPSC amplitude, but it decreased both mIPSC frequency and amplitude at higher concentrations $({\ge}300{\mu}M)$. In contrast, $Zn^{2+}$ (3 to $100{\mu}M$) did not affect glutamatergic mEPSCs, although it slightly decreased both mIPSC frequency and amplitude at $300{\mu}M$ concentration. Facilitatory effect of $Zn^{2+}$ on GABAergic mIPSC frequency was occluded either in $Ca^{2+}$-free external solution or in the presence of $100{\mu}M$ 4-aminopyridine, a non-selective $K^{+}$ channel blocker. The results suggest that $Zn^{2+}$ at lower concentrations depolarizes GABAergic nerve terminals by blocking $K^{+}$ channels and increases the probability of spontaneous GABA release. This $Zn^{2+}$-mediated modulation of spontaneous GABAergic transmission is likely to play an important role in the regulation of neuronal excitability within the hippocampal CA3 area.

• Journal of information and communication convergence engineering
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• v.2 no.1
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• pp.9-14
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• 2004

In this paper the modeling of the RLP layer in CDMA2000 is presented, which uses the NAK based ARQ scheme for Random Error Channels. The RLP performs a partial link recovery through limited number of RLP frame transmission in case of frame error. In case when the RLP fails due to excessive frame error, the control is passed on to the higher (TCP) layer. The TCP layer provides the complete end-to-end recovery. Thus the reliable performance at the TCP/RLP is essential to maintain the required Quality of Service in the DS-CDMA wireless links. The modeling is done for the performance analysis of the system in terms of the throughput and the mean extra delays, which are calculated analytically and are compared with the results generated by the simulations. This paper studies the effect of the random errors over different types of RLP frame formats and also the performance of the NAK based ARQ mechanism used under these conditions. The simulation provides with the over all characteristics of the throughput and the mean extra delay in terms of realistic environment parameters like Eb/No and probability of packet error (PE), based on the channel conditions.

• Journal of Information Processing Systems
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• v.13 no.4
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• pp.677-688
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• 2017

In order to solve the undetected probability of multiple targets in ultra-wideband (UWB) through-the-wall radar imaging (TWRI), a time-delay and amplitude modified back projection (BP) algorithm is proposed. The refraction point is found by Fermat's principle in the presence of a wall, and the time-delay is correctly compensated. On this basis, transmission loss of the electromagnetic wave, the absorption loss of the refraction wave, and the diffusion loss of the spherical wave are analyzed in detail. Amplitude compensation is deduced and tested on a model with a single-layer wall. The simulating results by finite difference time domain (FDTD) show that it is effective in increasing the scattering intensity of the targets behind the wall. Compensation for the diffusion loss in the spherical wave also plays a main role. Additionally, the two-layer wall model is simulated. Then, the calculating time and the imaging quality are compared between a single-layer wall model and a two-layer wall model. The results illustrate the performance of the time-delay and amplitude-modified BP algorithm with multiple targets and multiple-layer walls of UWB TWRI.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.10
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• pp.4825-4847
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• 2016

In this paper, we focus on the per-flow throughput analysis of IEEE 802.11 multi-hop ad hoc networks. The importance of an accurate saturation throughput model lies in establishing the theoretical foundation for effective protocol performance improvements. We argue that the challenge in modeling the per-flow throughput in IEEE 802.11 multi-hop ad hoc networks lies in the analysis of the freezing process and probability of collisions. We first classify collisions occurring in the whole transmission process into instantaneous collisions and persistent collisions. Then we present a four-dimensional Markov chain model based on the notion of the fixed length channel slot to model the Binary Exponential Backoff (BEB) algorithm performed by a tagged node. We further adopt a continuous time Markov model to analyze the freezing process. Through an iterative way, we derive the per-flow throughput of the network. Finally, we validate the accuracy of our model by comparing the analytical results with that obtained by simulations.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.10
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• pp.4957-4976
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• 2016

This paper investigates the error performance of the amplify-and-forward (AF) relaying systems in the context of full-duplex (FD) communication. In addition to the inherent self-interference (SI) due to simultaneous transmission and reception, coexistent FD terminals may cause crosstalk. In this paper, we utilize the information exchange via the crosstalk channel to construct a particular distributed space-time code (DSTC). The residual SI is also considered. Closed-form pairwise error probability (PEP) is first derived. Then we obtain the upper bound of PEP in high transmit power region to provide more insights of diversity and coding gain. The proposed DSTC scheme can attain full cooperative diversity if the variance of SI is not a function of the transmit power. The coding gain can be improved by lengthening the frame and proper power control. Feasibility and efficiency of the proposed DSTC are verified in numerical simulations.

• Journal of Information Processing Systems
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• v.15 no.3
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• pp.604-615
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• 2019

Single-user spectrum sensing is susceptible to multipath effects, shadow effects, hidden terminals and other unfavorable factors, leading to misjudgment of perceived results. In order to increase the detection accuracy and reduce spectrum sensing cost, we propose an adaptive cooperative sensing strategy based on an estimated signal-to-noise ratio (SNR). Which can adaptive select different sensing strategy during the local sensing phase. When the estimated SNR is higher than the selection threshold, adaptive double threshold energy detector (ED) is implemented, otherwise cyclostationary feature detector is performed. Due to the fact that only a better sensing strategy is implemented in a period, the detection accuracy is improved under the condition of low SNR with low complexity. The local sensing node transmits the perceived results through the control channel to the fusion center (FC), and uses voting rule to make the hard decision. Thus the transmission bandwidth is effectively saved. Simulation results show that the proposed scheme can effectively improve the system detection probability, shorten the average sensing time, and has better robustness without largely increasing the costs of sensing system.