• Journal of Information Processing Systems
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• 제2권2호
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• pp.107-113
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• 2006

It is essential to guarantee a handoff dropping probability below a predetermined threshold for wireless mobile networks. Previous studies have proposed admission control policies for integrated voice/data traffic in wireless mobile networks. However, since QoS has been considered only in terms of CDP (Call Dropping Probability), the result has been a serious CBP (Call Blocking Probability) unfairness problem between voice and data traffic. In this paper, we suggest a new admission control policy that treats integrated voice and data traffic fairly while maintaining the CDP constraint. For underprivileged data traffic, which requires more bandwidth units than voice traffic, the packet is placed in a queue when there are no available resources in the base station, instead of being immediately rejected. Furthermore, we have adapted the biased coin method concept to adjust unfairness in terms of CBP. We analyzed the system model of a cell using both a two-dimensional continuous-time Markov chain and the Gauss-Seidel method. Numerical results demonstrate that our CAC (Call Admission Control) scheme successfully achieves CBP fairness for voice and data traffic.

• 로봇학회논문지
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• 제6권2호
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• pp.97-107
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• 2011

This paper describes efficient flight control algorithms for building a reconfigurable ad-hoc wireless sensor networks between nodes on the ground and airborne nodes mounted on autonomous vehicles to increase the operational range of an aerial robot or the communication connectivity. Two autonomous flight control algorithms based on adaptive gradient climbing approach are developed to steer the aerial vehicles to reach optimal locations for the maximum communication throughputs in the airborne sensor networks. The first autonomous vehicle control algorithm is presented for seeking the source of a scalar signal by directly using the extremum-seeking based forward surge control approach with no position information of the aerial vehicle. The second flight control algorithm is developed with the angular rate command by integrating an adaptive gradient climbing technique which uses an on-line gradient estimator to identify the derivative of a performance cost function. They incorporate the network performance into the feedback path to mitigate interference and noise. A communication propagation model is used to predict the link quality of the communication connectivity between distributed nodes. Simulation study is conducted to evaluate the effectiveness of the proposed reconfigurable airborne wireless networking control algorithms.

• Journal of Communications and Networks
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• 제17권2호
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• pp.203-209
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• 2015

Although mobile applications are an essential characteristic of wireless sensor networks, most existing media access control (MAC) protocols focus primarily on static networks. In these protocols, fixed periodic neighbor discovery and schedule updating are used to connect and synchronize neighbors to provide successful data transmission; however, they cannot adapt to mobile speed variation and degrade the network performance dramatically. In this paper, we propose a mobile-supporting mechanism for MAC protocols, in which the decision to update the neighbors of a mobile node is made adaptively according to the mobile speed. Analysis and simulation results demonstrate that the mechanism efficiently avoids the disconnection of amobile node from its neighbors and achieves a better performance as compared with fixed periodic neighbor discovery.

• 대한전자공학회논문지TC
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• 제47권10호
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• pp.27-35
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• 2010

무선 패킷 망에서 무선 자원과 무선 단말의 전력을 얼마나 효율적으로 사용할 수 있는가 하는 것은 무선 패킷 망 보급을 위한 기본 해결 과제이다. 이에 단말의 전력 소모를 줄이면서 무선 망 용량 (capacity)을 증가시키는 기법으로 전송 파워 조절 기법이 주목받고 있다. 무선 패킷 망에 전송 파워 조절 기법을 적용할 때 전송 파워의 세기에 따라 공평한 전송성능을 보장하지 못하고 기아상태에 이르는 전송 불공평성 문제가 지금까지 깊이 연구되지 않고 있다. 이에 본 연구에서는 전송 파워의 세기에 따른 성능 불공평성을 경쟁자 수의 차이에 의한 불공평한 매체 접근 기회에 있음을 분석을 통해 보이고 불공평성을 해결하기 위한 간단한 물리-맥 (PHY-MAC) 계층 간 접근법을 제안한다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2003년도 하계종합학술대회 논문집 I
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• pp.569-572
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• 2003

The broadband wireless access industry, which provides high-tate network connections to stationary sites, has matured to the point at which it now has a standard for second-generation wireless metropolitan area networks. IEEE Standard 802.16, with its WirelessMAN air interface, set the stage for widespread and effective deployments worldwide. This paper presents an implementation of media access control that can be applied to BWA (Broadband Wireless Access) system. Medium access control (MAC) is a key issue in multi-access networks where a common channel is shared by many users. The designed MAC prototype roughly consists of MAC Hardware and MAC Software. The MAC Hardware part includes timing process, MAC transmission control, MAC reception control, and CRC/HCS process. The MAC Software part includes control of MAC signaling, network interface, and Physical (PHY) control. The designed MAC protocol will be integrated with the PHY of BWA in future and we can test overall system performance of MAC and PHY.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2003년도 ICCAS
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• pp.2405-2407
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• 2003

We propose a feedback-based congestion control algorithm for the wireless TCP network. In this paper, we present a new TCP protocol to control the congestion window size. In particular, the asymptotic analysis of the wireless TCP is presented. Through simulations, our algorithm shows an improvement of TCP’s performance in wireless networks.

• 한국정보통신학회논문지
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• 제11권9호
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• pp.1679-1686
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• 2007

클러스터링은 ad hoc네트워크에서 확장성 개선과 네트워크 수명 연장뿐만 아니라 클러스터 내 멤버 관리기능과 링크용량을 개선해주는 토폴로지 제어 기법이다. 본 논문에서는 단말의 이동성과 네트워크의 이종성을 고려하여 multi-radio무선 메쉬 네트워크를 위한 클러스터링 알고리즘을 설계하였다. 수학적 분석을 통하여 제안 알고리즘은 시간 t내에 종료되며, 메시지 제어 처리를 위한 복잡도는 각 노드 당 O(1)임을 알 수 있었다. 이는 본 제안 알고리즘을 적용함으로써 무선 메쉬 네트워크의 안정성, 연결성, 확장성과 에너지 효율성이 향상됨을 알 수 있었다.

• Journal of information and communication convergence engineering
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• 제5권2호
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• pp.93-97
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• 2007

In this paper, centralized access control and slot allocation algorithm is proposed for wireless networks. The proposed algorithm is characterized by the contention-based reservation. In order to reduce the collision probability of reservation request, the base station calculates and broadcasts the transmission probability of reservation requests, and the wireless terminal transmits its reservation request with the received transmission probability. The scheduler allocates the uplink data slots based on the successful reservation requests. Simulation results show that the proposed algorithms can provide high channel utilization, and furthermore, maintains constant delay performance in the heavy traffic environment.

• 한국멀티미디어학회논문지
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• 제9권12호
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• pp.1636-1648
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• 2006

In this paper, we propose a new optimization approach to the rate control problem in a wired-cum-wireless network. A primal-dual interior-point(PDIP) algorithm is used to find the solution of the rate optimization problem. We show a comparison between the dual-based(DB) algorithm and PDIP algorithm for solving the rate control problem in the wired-cum-wireless network. The PDIP algorithm performs much better than the DB algorithm. The PDIP can be considered as an attractive method to solve the rate control problem in network. We also present a numerical example and simulation to illustrate our conclusions.

• ETRI Journal
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• 제31권1호
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• pp.83-85
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• 2009

Compared with unicast, multicast over wireless ad-hoc networks do not support reliability due to their inability to exchange request-to-send/clear-to-send (RTS/CTS) and ACK packets with multiple recipients. Although several media access control (MAC) layer protocols have been proposed to provide reliable multicast, these introduce additional overhead, which degrades system performance. A novel MAC protocol for reliable wireless multicast is proposed in this paper. By adapting orthogonal frequency division multiple access characteristics in CTS and ACK packets, the protocol achieves reliability over wireless multicast with minimized overhead.