• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제11권1호
• /
• pp.61-77
• /
• 2017

The most challenging issues in the multi-channel MAC of the IEEE 1609.4 standard is how to handle the dynamic vehicular traffic condition with a high mobility, dynamic topology, and a trajectory change. Therefore, dynamic channel coordination schemes between CCH and SCH are required to provide the proper bandwidth for CCH/SCH intervals and to improve the quality of service (QoS). In this paper, we use a Markov model to optimize the interval based on the dynamic vehicular traffic condition with high mobility nodes in the multi-channel MAC of the IEEE 1609.4 standard. We evaluate the performance of the three-dimensional Markov chain based on the Poisson distribution for the node distribution and velocity. We also evaluate the additive white Gaussian noise (AWGN) effect for the multi-channel MAC coordination scheme of the IEEE 1609.4 standard. The result of simulation proves that the performance of the dynamic channel coordination scheme is affected by the high node mobility and the AWGN. In this research, we evaluate the model analytically for the average delay on CCHs and SCHs and also the saturated throughput on SCHs.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제6권1호
• /
• pp.361-378
• /
• 2012

Most of the current frequency hopping (FH) based dynamic spectrum access (DSA) methods concern a reactive channel access scheme with synchronous inter-channel spectrum sensing, i.e., FH is reactively triggered by the primary user (PU)'s return reported by spectrum sensing, and the PU channel to be switched to is assumed precisely just sensed or ready to be sensed, as if the inter-channel spectrum sensing moments are synchronous. However, the inter-channel spectrum sensing moments are more likely to be asynchronous, which risks PU suffering more interference. Moreover, the spectrum sensing is usually erroneous, which renders the problem more complex. To address this problem, we propose a proactive FH based DSA method against both erroneous spectrum sensing and asynchronous inter-channel spectrum sensing (moments). We term it as proactive DSA. The optimal FH sequence is obtained by dynamic programming. The complexity is also analyzed. Finally, the simulation results confirm the effectiveness of the proposed method.

• 대한임베디드공학회논문지
• /
• 제19권1호
• /
• pp.65-71
• /
• 2024

An indirect visual SLAM takes raw image data and exploits geometric information such as key-points and line edges. Due to various environmental changes, SLAM performance may decrease. The main problem is caused by dynamic objects especially in highly crowded environments. In this paper, we propose a robust feature-based visual SLAM, building on ORB-SLAM, via multi-channel dynamic objects estimation. An optical flow and deep learning-based object detection algorithm each estimate different types of dynamic object information. Proposed method incorporates two dynamic object information and creates multi-channel dynamic masks. In this method, information on actually moving dynamic objects and potential dynamic objects can be obtained. Finally, dynamic objects included in the masks are removed in feature extraction part. As a results, proposed method can obtain more precise camera poses. The superiority of our ORB-SLAM was verified to compared with conventional ORB-SLAM by the experiment using KITTI odometry dataset.

• 한국컴퓨터정보학회논문지
• /
• 제16권2호
• /
• pp.207-215
• /
• 2011

디지털 방송이 본격화되고 디지털 텔레비젼의 보급이 일반화되면서 시청자가 선택할 수 있는 채널의 수와 프로그램의 수는 기존 텔레비젼 환경과 비교하여 시청자가 이용할 수 있는 프로그램 리소스들이 큰 폭으로 증가되고 있다. 이러한 변화로 수백 개의 채널에서 시청자가자신이 선호하는 프로그램 채널을 찾기 위해서 리모컨이나 방송 편성표를 통해 검색하는 것은 많은 시간과 노력이 필요하다. 따라서, 본 논문에서는 up-down 채널 리모컨를 이용해 선호하는 프로그램 채널을 선택하는 시청자들을 위해, 현재 시청하는 채널을 기준으로 선호 프로그램 채널을 동적으로 배치함으로써 채널의 탐색 거리를 줄이는 방법을 제안한다. 그리고, 실험을 통해 그 성능을 평가한다.

• 한국통신학회논문지
• /
• 제32권6B호
• /
• pp.358-366
• /
• 2007

최근 FCC(Federal Communications Commission)에서는 통신 채널의 부족을 극복하기 위해 기존의 허가된 사용자의 무선 주파수에 대한 비 허가 사용자의 사용을 고려하고 있다. 이에 채널을 실시간으로 감지하고 선택하는 CR의 개념이 도입되어 IEEE 802.22 WRAN(Wireless Regional Area Networks) 워킹 그룹에서 CR(Cognitive Radio)의 기술개발을 진행 중에 있다. CR의 기술을 사용함에 있어서 채널을 선택하는 기준에 따라 네트워크의 통신 효율에 상당한 영향을 미치기 때문에 최적의 채널을 선택하는 방법이 중요하다. 따라서 본 논문에서는 효율적인 통신을 위해 무선인지 기술 기반의 정책에 따른 동적 채널 선택 구조(Policy-based Dynamic Channel Selection Architecture for Cognitive Radio Network)를 제안한다. 제안하는 동적 주파수 선택 방법에는 가중치 채널 선택 방법(weighted channel selection)과 순차적 채널 선택 방법(sequential channel selection)곡 혼합 채널 선택 방법(combined channel selection)의 세 가지 방법이 있으며 제안하는 방법을 사용함으로써 최적의 채널 리스트를 구성해 줄 수 있을 뿐만 아니라 동적으로 채널을 할당해 줄 수 있다.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제10권2호
• /
• pp.608-627
• /
• 2016

Wireless mesh networks (WMNs) based on IEEE 802.11s have emerged as one of the prominent technologies in multi-hop communications. However, the deployment of WMNs suffers from serious interference problem which severely limits the system capacity. Using multiple radios for each mesh router over multiple channels, the interference can be reduced and improve system capacity. Nevertheless, interference cannot be completely eliminated due to the limited number of available channels. An effective approach to mitigate interference is to apply dynamic channel switching (DCS) in WMNs. Conventional DCS schemes trigger channel switching if interference is detected or exceeds a predefined threshold which might cause unnecessary channel switching and long protocol overheads. In this paper, a P-learning based dynamic switching algorithm known as learning automaton (LA)-based DCS algorithm is proposed. Initially, an optimal channel for communicating node pairs is determined through the learning process. Then, a novel switching metric is introduced in our LA-based DCS algorithm to avoid unnecessary initialization of channel switching. Hence, the proposed LA-based DCS algorithm enables each pair of communicating mesh nodes to communicate over the least loaded channels and consequently improve network performance.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2009년도 제33회 추계학술대회논문집
• /
• pp.459-468
• /
• 2009

Analysis of the uncertainty to have engineering solution of gas-dynamic and hydrodynamic problems is based on the comparison the prospective engineering solution with experimental result. In this paper, the mathematical model to estimate heat flux along gas-dynamic channel wall and the solution sequence are shown. Statistical information and generalizing experimental characteristics about gas- and hydro-dynamic channels were applied to the mathematical model. As the results, it is possible to draw a conclusion that models of the integrated approach, using the averaged statistical data of generalizing characteristics for a turbulent flow, without consideration of the turbulent mechanism (characteristic pulsations), can predict a nominal operating regime for gas-dynamic and hydrodynamic systems. The probable deviation of operating regime for newly designed the gas-dynamic channel can achieve 20% from a regime predicted on a basis 1-D or 3-D modelling irrespective of a kind of used models.

• Journal of applied mathematics & informatics
• /
• 제32권1_2호
• /
• pp.129-136
• /
• 2014

One of the fundamental issues in the design of dynamic spectrum access policy is the modeling of the dynamic behavior of channel occupancy by primary users. Under a Markovian modeling of channel occupancy, a periodic sensing and greedy access policy is known as one of the simple and practical dynamic spectrum access policies in cognitive radio networks. In this paper, the primary occupancy of each channel is modeled as a discrete-time alternating renewal process with generally distributed on- and off-periods. A periodic sensing and greedy access policy is constructed based on the general channel occupancy model. Simulation results show that the proposed policy has better throughput than the policies using channel models with exponentially distributed on- or off-periods.

• Journal of Communications and Networks
• /
• 제15권2호
• /
• pp.222-227
• /
• 2013

This paper presents an analytical framework for dynamic spectrum allocation in cognitive radio networks. We propose a distributed queuing based Markovian model each for single channel and multiple channels access for a contending user. Knowledge about spectrum mobility is one of the most challenging problems in both these setups. To solve this, we consider probabilistic channel availability in case of licensed channel detection for single channel allocation, while variable data rates are considered using channel aggregation technique in the multiple channel access model. These models are designed for a centralized architecture to enable dynamic spectrum allocation and are compared on the basis of access latency and service duration.

• 대한기계학회논문집B
• /
• 제27권7호
• /
• pp.853-858
• /
• 2003

The suitable estimation of the filter width in the dynamic eddy viscosity model were investigated in high Reynolds number channel flow. In this study, the improvement on matters by optimizing the test filter shape was attempted through the numerical experiment. The way that select optimum test filter width is recommended. Some test filters, one is based on a discrete representation of the top-hat filter and another are based on a high-order filtering operation, are evaluated in simulations of the turbulent channel flow at Reynolds number 1020, based on friction velocity and channel half width. It appears that the estimation of test filter width practically can decrease the dissipative nature of dynamic eddy viscosity model with explicit test filter. It shows that the value of the filter width ratio used in the dynamic procedure must match the properties of the test filter actually used in the calculation.