• 한국인터넷방송통신학회논문지
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• 제11권3호
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• pp.17-22
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• 2011

본 논문에서는 멀티 홉 군통신 시스템에서 발생할 수 있는 동일채널 간섭 (CCI : Co-Channel Interference) 제거 성능을 분석하였다. 간섭 제거 기법으로 먼저 Zero Forcing (ZF)과 Minimum Mean Square Error (MMSE) 기법을 적용하여 간섭을 제거한 후, 연속 간섭 제거 (SIC : Successive Interference Cancellation) 알고리즘을 이용하여 추가적인 다이버시티 이득을 얻고 간섭 제거 성능을 향상시킨다. 무선 채널은 레일레이 (Rayleigh) 페이딩 채널을 고려하여 모의 실험을 하였으며, 시스템 성능은 비트 오류 확률 (Bit Error Probability) 측면에서 분석되었다. 모의실험 결과로부터, 멀티 홉 무선 네트워크 환경에서 MMSE가 ZF보다 BER 성능을 현저하게 향상시킴을 확인하였으며, 각각 기법에 연속 간섭 제거 알고리즘을 적용한 경우, 그 성능이 더욱 좋아지는 것을 알 수 있었다. 따라서 MMSE-SIC 방식은 멀티 홉 군통신 시스템에서 보다 신뢰성 있는 신호의 전송을 제공할 수 있다.

• 정보처리학회논문지:컴퓨터 및 통신 시스템
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• 제8권11호
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• pp.263-270
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• 2019

최근 주목받는 기술인 차량 클라우드 컴퓨팅은 운전자들에게 다양한 차량 응용 어플리케이션을 위한 클라우드 서비스를 제공해 줄 수 있다. 차량 클라우드는 각각의 차량들이 보유한 리소스를 서로 공유하는 차량들의 집합이다. 차량 클라우드를 형성하기 위해 차량들은 차량 대 차량(Vehicle-to-Vehicle) 통신을 통해 서로 협력해야 한다. 차량 클라우드 형성을 위해 협력하는 차량들은 각각의 속도와 이동 방향 및 현재 위치가 다르므로 차량 클라우드는 다중 홉에 걸쳐 형성되어야 한다. 다중 홉 통신을 이용한 차량 클라우드 형성은 간헐적인 무선 연결성과 제한된 리소스를 보유한 차량의 수가 적은 환경으로 인해 차량 클라우드의 형성이 어렵다. 따라서, 다중 홉 통신 방식을 이용한 차량 클라우드 형성은 차량 간 통신의 안정성을 높여 클라우드의 형성 및 서비스 효율을 높이고, 서비스 지연시간 및 차량 간 교환 패킷의 수 등에서 개선 방안이 필요하다. 본 논문은 요청 차량과 가용 리소스를 제공하는 제공 차량들 간의 연결 시간을 고려하여 클라우드 형성 및 서비스 효율을 높이고 서비스 지연과 전송 패킷의 수를 줄이는 다중 홉 클라우드 형성 방안을 제안한다. 제안 방안은 차량들 사이의 연결 시간을 기반으로 홉과 홉을 연결하기 위한 중간 차량을 선택하여 다중 홉 차량 클라우드 형성의 실패율을 감소시킨다. 다양한 환경에서 수행된 시뮬레이션은 제안 방안이 기존의 방안보다 향상된 성능을 보이는지 검증한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권1호
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• pp.193-214
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• 2017

In this paper, we study the problem of network utility maximization in a CSMA based multi-hop wireless network. Existing work in this aspect typically adopted continuous time Markov model for performance modelling, which fails to consider the channel conflict impact in actual CSMA networks. To maximize the utility of a CSMA based wireless network with channel conflict, in this paper, we first model its weighted network capacity (i.e., network capacity weighted by link queue length) and then propose a distributed link scheduling algorithm, called CSMA based Maximal-Weight Scheduling (C-MWS), to maximize the weighted network capacity. We derive the upper and lower bounds of network utility based on C-MWS. The derived bounds can help us to tune the C-MWS parameters for C-MWS to work in a distributed wireless network. Simulation results show that the joint optimization based on C-MWS can achieve near-optimal network utility when appropriate algorithm parameters are chosen and also show that the derived utility upper bound is very tight.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제4권1호
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• pp.62-77
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• 2010

Emerging applications with high data rates will need to transport bulk data reliably in wireless sensor networks. ARQ (Automatic Repeat request) or Forward Error Correction (FEC) code schemes can be used to provide reliable transmission in a sensor network. However, the naive ARQ approach drops the whole frame, even though there is a bit error in the frame and the FEC at the bit level scheme may require a highly complex method to adjust the amount of FEC redundancy. We propose a bulk data transmission scheme based on erasure-resilient code in this paper to overcome these inefficiencies. The sender fragments bulk data into many small blocks, encodes the blocks with LT codes and packages several such blocks into a frame. The receiver only drops the corrupted blocks (compared to the entire frame) and the original data can be reconstructed if sufficient error-free blocks are received. An incidental benefit is that the frame error rate (FER) becomes irrelevant to frame size (error recovery). A frame can therefore be sufficiently large to provide high utilization of the wireless channel bandwidth without sacrificing the effectiveness of error recovery. The scheme has been implemented as a new data link layer in TinyOS, and evaluated through experiments in a testbed of Zigbex motes. Results show single hop transmission throughput can be improved by at least 20% under typical wireless channel conditions. It also reduces the transmission time of a reasonable range of size files by more than 30%, compared to a frame ARQ scheme. The total number of bytes sent by all nodes in the multi-hop communication is reduced by more than 60% compared to the frame ARQ scheme.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권10호
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• pp.4738-4753
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• 2018

Efficient rendezvous node selection and routing algorithm (RNSRA) for wireless sensor networks with mobile sink that visits rendezvous node to gather data from sensor nodes is proposed. In order to plan an optimal moving tour for mobile sink and avoid energy hole problem, we develop the RNSRA to find optimal rendezvous nodes (RN) for the mobile sink to visit. The RNSRA can select the set of RNs to act as store points for the mobile sink, and search for the optimal multi-hop path between source nodes and rendezvous node, so that the rendezvous node could gather information from sensor nodes periodically. Fitness function with several factors is calculated to find suitable RNs from sensor nodes, and the artificial bee colony optimization algorithm (ABC) is used to optimize the selection of optimal multi-hop path, in order to forward data to the nearest RN. Therefore the energy consumption of sensor nodes is minimized and balanced. Our method is validated by extensive simulations and illustrates the novel capability for maintaining the network robustness against sink moving problem, the results show that the RNSRA could reduce energy consumption by 6% and increase network lifetime by 5% as comparing with several existing algorithms.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권9호
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• pp.3335-3356
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• 2015

In this paper, we analyze the connectivity of cognitive radio ad-hoc networks in a log-normal shadow fading environment. Considering secondary user and primary user's locations and primary user's active state are randomly distributed according to a homogeneous Poisson process and taking into account the spectrum sensing efficiency of secondary user, we derive mathematical models to investigate the connectivity of cognitive radio ad-hoc networks in three aspects and compare with the connectivity of ad-hoc networks. First, from the viewpoint of a secondary user, we study the communication probability of that secondary user. Second, we examine the possibility that two secondary users can establish a direct communication link between them. Finally, we extend to the case of finding the probability that two arbitrary secondary users can communicate via multi-hop path. We verify the correctness of our analytical approach by comparing with simulations. The numerical results show that in cognitive radio ad-hoc networks, high fading variance helps to remarkably improve connectivity behavior in the same condition of secondary user's density and primary user's average active rate. Furthermore, the impact of shadowing on wireless connection probability dominates that of primary user's average active rate. Finally, the spectrum sensing efficiency of secondary user significantly impacts the connectivity features. The analysis in this paper provides an efficient way for system designers to characterize and optimize the connectivity of cognitive radio ad-hoc networks in practical wireless environment.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권12호
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• pp.5785-5804
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• 2019

The information of localization is a fundamental requirement in wireless sensor network (WSN). The method of distance vector-hop (DV-Hop), a range-free localization algorithm, can locate the ordinary nodes by utilizing the connectivity and multi-hop transmission. However, the error of the estimated distance between the beacon nodes and ordinary nodes is too large. In order to enhance the positioning precision of DV-Hop, fast triangle flip bat algorithm, which is based on curve strategy and rank transformation (FTBA-TCR) is proposed. The rank is introduced to directly select individuals in the population of each generation, which arranges all individuals according to their merits and a threshold is set to get the better solution. To test the algorithm performance, the CEC2013 test suite is used to check out the algorithm's performance. Meanwhile, there are four other algorithms are compared with the proposed algorithm. The results show that our algorithm is greater than other algorithms. And this algorithm is used to enhance the performance of DV-Hop algorithm. The results show that the proposed algorithm receives the lower average localization error and the best performance by comparing with the other algorithms.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권11호
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• pp.3775-3788
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• 2014

With the increasing number of the wireless and mobile networks, the way that people use the Internet has changed substantively. Wireless multimedia services, such as wireless video streaming, mobile video game, and mobile voice over IP, will become the main applications of the future wireless Internet. To accommodate the growing volume of wireless data traffic and multimedia services, cognitive radio (CR) and Information-Centric Network (ICN) have been proposed to maximize the utilization of wireless spectrum and improve the network performance. Although CR and ICN have high potential significance for the future wireless Internet, few studies have been conducted on collaborative operations of CR and ICN. Due to the lack of infrastructure support in multi-hop ad hoc CR networks, the problem is more challenging for video streaming services. In this paper, we propose a Cross-layer Video Streaming Mechanism (CLISM) for Cognitive Radio Ad Hoc Information Centric Networks (CRAH-ICNs). The CLISM included two distributed schemes which are designed for the forwarding nodes and receiving nodes in CRAH-ICNs. With the cross-layer approach, the CLISM is able to self-adapt the variation of the link conditions without the central network controller. Experimental results demonstrate that the proposed CLISM efficiently adjust video transmission policy under various network conditions.

• 대한전자공학회논문지TC
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• 제44권1호
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• pp.106-112
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• 2007

본 논문에서는 다중-홉(multi-hop) 무선통신시스템에서 보조 및 관리단말을 추가로 갖는 시공간 협동 다이버시티 중계 시스템을 제안한다. 한 협동그룹에 1개 이상의 중계단말을 추가하여, 프레임 에러여부 및 채널정보 등의 상태정보만을 공유한다. 상태가 좋은 수신신호를 가지는 단말을 선택하며, 선택된 각 중계단말은 같은 시공간 부호로 다중안테나 송신다이버시티 중계전송을 한다. 그리고 협동그룹 내에 중계단말 간의 교신 프로토콜을 제안한다. 이 방식에 대해, 수신신호 대 송신신호 비($E_r/E_s$)를 측정하여 성능개선 됨을 증명하였으며, 플랫 페이딩(flat-fading) 채널에서의 시뮬레이션은 기존의 협동다이버시티에 비해 혁신적인 성능향상을 보인다.

• 한국통신학회논문지
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• 제32권1A호
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• pp.109-114
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• 2007

본 논문에서는 다중-홉(multi-hop) 무선통신시스템에서 보조 및 관리단말을 추가로 갖는 시공간 협동 다이버시티 중계 시스템을 제안한다. 한 협동그룹에 1개 이상의 중계단말을 추가하여, 프레임 에러여부 및 채널정보 등의 상태정보만을 공유한다. 상태가 좋은 수신신호를 가지는 단말을 선택하여, 선택된 각 중계단말은 같은 시공간 부호로 다중안테나 송신다이버시티 중계전송을 한다. 그리고 협동그룹 내에 중계단말 간의 교신 프로토콜을 제안한다. 이 방식에 대해, 수신신호 대 송신신호 비($E_r/E_s$)를 측정하여 성능개선 됨을 증명하였으며, 플랫 페이딩 (flat-fading) 채널에서의 시뮬레이션은 기존의 협동다이버시티에 비해 혁신적인 성능향상을 보인다.