• 한국통신학회논문지
• /
• 제34권10B호
• /
• pp.964-972
• /
• 2009

무선 메쉬 네트워크(Wireless Mesh Network, WMN)는 다중 인터페이스와 다중 채널을 지원함으로써 기존의 무선 네트워크에서 발생되는 여러 문제점을 해결할 수 있는 핵심적인 미래기술로 대두되고 있다. WMN에서 다중 채널의 사용은 무선 네트워크 노드들이 사용하는 대역폭을 본질적으로 증가시켜준다. 그러나 이러한 대역폭을 충분히 사용하기 위해서는 다중 채널 환경에서 발생할 수 있는 채널 간 간섭을 최소화하는 채널 할당 기법이 요구된다. 본 논문에서는 WMN의 성능 향상을 위하여 클러스터링 기반의 최소 간섭 채널 할당(Minimum Interference Channel Assignment, MI-CA) 알고리즘을 제안한다. MI-CA 알고리즘은 클러스터 간의 Inter-Cluster 채널 할당과 클러스터 내부의 Intra-Cluster 채널 할당으로 구성된다. Inter-Cluster 채널 할당에서는 전체 WMN을 위한 베어본 채널을 MST(Minimum Spanning Tree) 기반으로 클러스터 헤더와 보더 노드에 할당하고, Intra-Cluster 채널 할당에서는 클러스터 멤버들 간에 직교채널을 재 할당함으로써 간섭을 최소화 한다. 시뮬레이션 결과 본 논문에서 제안한 MI-CA 알고리즘이 채널 간섭을 최소화함으로써 WMNs의 성능을 향상시킬 수 있음을 입증하였다.

• 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.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제6권9호
• /
• pp.2266-2284
• /
• 2012

Recent studies have indicated that a significant improvement in wireless video throughput can be achieved by Cross Layer Design with Side-information (CLDS) protocols. In this paper, we derive the operational rate of a CLDS protocol operating over a realistic wireless channel. Then, a Rate-Distortion (R-D) empirical model for above-capacity Scalable Video Coding (SVC) is deduced to estimate the loss of video quality incurred under inaccurate rate estimation scenarios. Finally, we develop a novel Unequal Error Protection (UEP) scheme which leverages the characteristics of LDPC codes to reduce the distortion of video quality in case of typically-observed burst wireless errors. The efficacy of the proposed rate adaptation architecture over conventional protocols is demonstrated by realistic video simulations using actual IEEE 802.11b wireless traces.

• Journal of Biosystems Engineering
• /
• 제17권1호
• /
• pp.45-54
• /
• 1992

A wireless control system was designed and constructed to control the rice transplanter of walking type with remote control. VHF(very high freqency) was sent from wireless transmitter to wireless reciever by usig 6 channels to control main clutch, steering clutch, plant lever and throttle lever within 200 meter distance between remote control and rice transplanter. The rice transplanter with wireless control system showed good performance for accuracy of travel speed, traveling mobility and turning diameter in the concrete, paddy and dry field. It is concluded that the developed wireless control system could be adapted to control not only conventional rice transplanters but also most of the agricultural machine by changing some parts of the control system.

• 산업기술연구
• /
• 제27권A호
• /
• pp.131-139
• /
• 2007

The recent advance in wireless network technologies has enabled the streaming media service on the mobile devices such as PDAs and cellular phones. Since the wireless network has low bandwidth channels and mobile devices are actually composed of limited hardware specifications, the transcoding technology is needed to adapt streaming media to given mobile devices. Futhermore owing to the diversity of bandwidth in the wireless network by reason of mobile users' movements and environments, it is difficult to provide stable QoS. In this paper, the autonomic multimedia transcoding system is proposed in order for users to provide network adaptive QoS. Our proposed system is based on the estimation of available bandwidth in wireless network for seamless multimedia streaming service. The proposed system is designed and implemented for various mobile clients. In experiments, we evaluate its seamless multimedia streaming and the adaptation transcoding bit rate according to the changes of bandwidth in wireless network.

• 한국통신학회논문지
• /
• 제25권3A호
• /
• pp.325-333
• /
• 2000

The proposed RPSS(Reference Picture Segment Selection) mode is the RPS mode in picture segment of the ISD mode. The RPS mode has the weakness that it has to change the whole reference picture even if transmission error occurs only in the small part of picture. If the RPS mode is applied only to an error-occurred part and a conventional coding scheme is applied to an error-free part, the higher coding efficiency can be obtained. Simulation results show that there is the optimal number of segment which provides that best performance with given environment such as the BER(Bit Error Rate) of wireless channels, the characteristics of imput sequence, what kind of RPSS mode is used, etc. To apply the channel-adoptive RPSS mode later, the scheme which can change the number of segment without INTRA refresh and spatial error propagation is proposed in this paper.

• 한국인터넷방송통신학회논문지
• /
• 제8권3호
• /
• pp.25-33
• /
• 2008

In this paper, the transmit power minimization for Poisson distributed wireless ad-hoc relay networks in Rayleigh fading channels is considered. We investigate two power allocation methods one is a minimum power allocation (MPA) strategy and the other is an equal outage power allocation (EOPA) strategy. We analyze the total transmit power of two allocation methods under the given end-to-end outage probability constraint. Our results show that the MPA achieves more power saving than EOPA, and the power saving is more significant as the number of relay nodes increases.

• 산업공학
• /
• 제14권3호
• /
• pp.227-235
• /
• 2001

There is a rapidly growing demand for wireless telecommunication. However, the number of usable channel is very limited. Therefore, the problem of channel assignment becomes more and more important to use channels as efficiently as possible. The objective of this paper is to develop an evolution program (EP) to find an efficient dynamic channel assignment method for minimum interference among the channels within reasonable time. The series of specific channel number is used as a representation of chromosome. The only changed chromosomes by crossover and mutation are evaluated in each generation to save computation time and memory for the progress of improved EP. We can easily differentiate the fitness value of each chromosome using proposed evaluation function. We also control the weighting factor of the mutation rate and the used number of elitist chromosomes for the speed of convergence to the optimal solution.

• 대한전자공학회:학술대회논문집
• /
• 대한전자공학회 1998년도 하계종합학술대회논문집
• /
• pp.30-33
• /
• 1998

In this paper, 60 GHz indoor broadband wireless channels are measured with various configurations in a typical coffice environment. Mesurements are taken at nine positions of the room and the base-station antenna is placed either at the center or at an edge of the measurement room, and the remote-station antenna is either sharp beam or broad beam type. The rms delay spread(RDS) and normalized received power (NRP) are estimated from the measurements. Bit error rate simulations are performed using impulse responses for two measurement positions with QPSK/DQPSK OFDM modulation. Using sharp beam antenna results in superior performances than using broad beam antenna in terms of both bit error rates (BER) and NRP penalty. Also, placing the bese-station antenna at the center is superior to placing it at an edge in terms of BER and NRP.

• 한국정보통신학회:학술대회논문집
• /
• 한국해양정보통신학회 2008년도 추계종합학술대회 B
• /
• pp.49-52
• /
• 2008

In this letter, we derive a tight closed form formula for an ergodic rapacity of a multiple-input multiple-output (MIMO) for the application of wireless communications. The derived expression is a simple close-form formula to determine the ergodic capacity of MIMO systems. Assuming the channels are independent and identically distributed (i.i.d.) Rayleigh flat-fading between antenna pairs, the ergodic capacity can be expressed in a closed form as the finite sum of exponential integrals.