• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.2 s.332
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• pp.23-38
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• 2005

The state of channel between two or more wireless terminals is changed frequently due to noise or multiple environmental conditions in wireless network. In this paper, we analyze packet transmission time and queue length in a time-varying channel of packet based Wireless Networks. To reflect the feature of the time-varying channel, we model the channel as two-state Markov model and three-state Markov model Which are transformed to SFG(Signal Flow Graph) model, and then the distribution of the packet transmission can be modeled as Gaussian distribution. If the packet is arrived with Poisson distribution, then the packet transmission system is modeled as M/G/1. The average transmission time and the average queue length are analyzed in the time-varying channel, and are verified with some simulations.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.6
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• pp.1318-1323
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• 2013

We consider the design of opportunistic spectrum access schemes where secondary users can opportunistically access unused spectrum in non-slotted primary systems. Two non-slotted spectrum sensing and access schemes for secondary users are considered. We present experimental results that demonstrate the performance of the considered schemes.

• Journal of KIISE:Information Networking
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• v.36 no.3
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• pp.243-250
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• 2009

Channel diversity is exploited to increase multiuser diversity gains in IEEE 802.11 WLANs. To this end, we propose an opportunistic channel switching method and evaluate this with different number of stations, number of channels, switching latency, and the average channel condition of stations.

• Proceedings of the IEEK Conference
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• 2003.07a
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• pp.27-30
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• 2003

무선 통신 서비스에 대한 수요가 급격히 증가하면서 높은 데이터 전송율을 갖는 무선 통신에 대한 연구가 활발히 진행되고 있다. UWB는 (Ultra Wide Band) 이러한 문제점을 해결할 수 있는 통신 방법 중의 하나로 이 논문에서는 현재 IEEE 802.15.TG3a 표준화 위원회에서 제시하고 있는 채널 모델에 대해서 알아보고, 제시된 채널 모델에 LS (Least Square) 방법을 적용하여 채널의 임펄스 응답을 (Channel Impulse Response) 추정한다. 채널 추정의 성능 지표로 Preamble의 크기에 따른 MSE와 (Mean Square Error) 각각의 채널에 대한 비트 에러율을 사용하여 모의 실험을 본 논문에서 다루는 추정 기법의 성능을 분석한다.

• Information and Communications Magazine
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• v.12 no.5
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• pp.85-93
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• 1995

이동통신 서비스에 대한 수요가 크게 증가하므로 무선접속방식에 있어서 채널용량의 분석이 매우 중요한 요소로 부각되고 있다. 그러나 이동통신채널은 환경에 따라 매우 다르므로 용량을 정확하게 분석하기 어렵다. 이 논문에서는 PCS 환경에서 채널용량에 관계되는 요소들을 정량적으로 분석하고 이들을 사용하여 전형적인 CDMA와 TDMA 방식에 대한 채널용량을 분석하였다. 제시한 채널모델은 가능한 모델중에 하나가 될 수 있고, 제안된 채널 용량 분석방법중 요구되는 $E_b/N_a$ 값의 계산방식은 이동통신 시스팀에 있어 각 요소가 성능에 미치는 영향을 정량적으로 분석하는데 도움이 된다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.10B
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• pp.964-972
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• 2009

Wireless mesh network (WMN) is emerging a future core technology to resolve many problems derived from exist wireless networks by employing multi-interface and multi-channel. Ability to utilize multiple channels in WMNs substantially increases the effective bandwidth available to wireless network nodes. However, minimum interference channel assignment algorithms are required to use the effective bandwidth in multi-channel environments. This paper proposes a cluster-based minimum interference channel assignment (MI-CA) algorithm to improve the performance of WMN. The MI-CA algorithm is consists of Inter-Cluster and Intra-Cluster Intrchannel assignment between clusters and in the internal clusters, respectively. The Inter-Cluster channel assignment assigns a barebone channel to cluster heads and border nodes based on minimum spanning tree (MST) and the Intra-Cluster channel assignment minimizes channel interference by reassigning ortasgonal channels between cluster mespann. Our simheation results show that MI-CA can improve the performance of WMNs by minimizing channel interference.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.7B
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• pp.1167-1177
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• 2000

본 논문에서는 접속노드와 무선채널로 구성되는 무선 ATM(Asynchronous Transfer Mode) 접속망의 셀 손실율과 호손율간의 관계를 도출하였다. 이를 위해 우선 ATM 접속망의 트래픽 모델을 셀 레벨, 버스트셀 레벨 및 호접속레벨로 구부하여 분석하였고, 무선접속노드의 CLR(Cell Loss RAtio) 성능을 나타낼 수 있는 수식을 VBR(Variable Bit Rate) 및 램덤 트래픽으로 구분하여 제시하였으며 무선채널에 대해서는 랜덤에러 및 버스트 에러환경으로 구분하여 CLR 성능을 나타낼 수 있는 수식을 유도하였다. 그리고 접속노드와 무선채널의 CLR을 나타내는 수식을 이용하여 무선 ATM 접속망의 CLR 성능을 나타내는 수식을 도출한 후 접속망의 트래픽 성능평가를 위해 VBR, CBR 및 랜덤 트래픽 형태별로 CLR과 호손율간의 관계를 분석하였다. 즉 이용도와 CLR간의 관계로부터 셀 레벨의 접속망 CLR 목표치가 정해지면 이용도 및 접속 회선수를 구할 수 있으며 이를 호 접속레벨의 Erlang-B 관계식과 관련시켜서 CLR과 호손율간의 관계를 제시하였다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.1
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• pp.37-44
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• 2016

It is important that using of efficient radio resource because of deficiency spectrum problem, so that related to this problem many researches are have proceeded. To solve this problem, Cognitive Radio(CR) was suggested. The channels are allocated to the secondary users when the primary users don't use the channels, and unfairness of secondary users can be serious problem and channel quality of multichannel can be different due to the different traffic pattern of primary users. In this paper, we propose MAC prtocol both of the user's fairness and channel quality in CR networks. Simulation results show the comparison with CR MAC protocols.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.6
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• pp.1032-1037
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• 2006

The channel is one of the precious and limited resources in wireless networks. There are many researches on the channel management. Recently, the optimization problem of guard channels has been an important issue. In this paper, we propose an intelligent channel management technique based on the neural networks. An SRN channel allocation model is developed to generate the learning data for the neural networks and the performance analysis of system. In the proposed technique, the neural network is trained to generate optimal guard channel number g, using backpropagation supervised learning algorithm. The optimal g is computed using the neural network and compared to the g computed by the SRM model. The numerical results show that the difference between the value of 8 by backpropagation and that value by SRM model is ignorable.

• Journal of Korea Society of Industrial Information Systems
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• v.20 no.5
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• pp.25-35
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• 2015

Handoff is a critical issue for seamless roaming in IEEE 802.11-based wireless networks. In order to provide real-time services, handoff mechanism must be provided. However, the IEEE 802.11 standard handoff is not appropriate to provide the services, because it is based on the full-scanning approach which spends too much time searching Access Point (AP). In this paper, we propose a new scheme, which can reduce the scanning latency. A station performs full-scanning operation for finding APs when it enters wireless networks for the first time. The station sends the scanned channel information to AP. AP maintains the neighbor channel table based on the information received from stations. A station performs the partial-scanning by using the table. Therefore, the proposed scheme can reduce the scanning latency.