• Journal of Communications and Networks
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• 제18권2호
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• pp.238-245
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• 2016

A sequence number checking technique is proposed to improve the performance of TCP connections in mobile ad hoc networks. While a TCP connection is initialized, a routing protocol takes the responsibility for checking the hop count between a source and destination pair. If the hop count is greater than a predefined value, the routing protocol decides to use a proxy node. The responsibility of a proxy node is to check the correctness of data packets and inform the missing packets by sending an acknowledgement from a proxy node to the source node. By doing so, the source node is able to retransmit any missing packet in advance without waiting until an end-to-end acknowledgement is received from the destination. Simulation results show that the proposed mechanism is able to increase throughput up to 55% in static network and decrease routing overhead up to 95%in mobile network.

• 한국통신학회논문지
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• 제34권1B호
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• pp.1-9
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• 2009

본 논문에서는 IETF NetLMM WG에서 표준화되고 있는 Proxy-MIPv6을 기반으로, 빠르고 효율적인 핸드오프를 지원하는 망 기반의 이동성 지원 방안을 제안하였다. 제안된 방식은 Mobile Access Gateway (MAG)간의 dynamic virtual hierarchy 망 구조를 활용함으로써 망의 확장성과 안정성을 제공하고, Policy Store(PS) 기반의 빠른 인증 및 프로파일 획득 기법을 활용함으로써 빠르고 효율적인 핸드오프를 제공할 수 있다. 또한, 제안된 방식과 기존의 PMIPv6의 성능 분석 및 토의를 통하여 제안된 방식의 우수성을 알 수 있다.

• Journal of Communications and Networks
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• 제9권3호
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• pp.296-311
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• 2007

Mobile multi-robot teams are useful in many critical applications such as search and rescue. Explicit communication among robots in such mobile multi-robot teams is useful for the coordination of such teams as well as exchanging data. Since many applications for mobile robots involve scenarios in which communication infrastructure may be damaged or unavailable, mobile robot teams frequently need to communicate with each other via ad hoc networking. In such scenarios, low-overhead and energy-efficient routing protocols for delivering messages among robots are a key requirement. Two important primitives for communication are essential for enabling a wide variety of mobile robot applications. First, unicast communication (between two robots) needs to be provided to enable coordination and data exchange. Second, in many applications, group communication is required for flexible control, organization, and management of the mobile robots. Multicast provides a bandwidth-efficient communication method between a source and a group of robots. In this paper, we first propose and evaluate two unicast routing protocols tailored for use in ad hoc networks formed by mobile multi-robot teams: Mobile robot distance vector (MRDV) and mobile robot source routing (MRSR). Both protocols exploit the unique mobility characteristics of mobile robot networks to perform efficient routing. Our simulation study show that both MRDV and MRSR incur lower overhead while operating in mobile robot networks when compared to traditional mobile ad hoc network routing protocols such as DSR and AODV. We then propose and evaluate an efficient multicast protocol mobile robot mesh multicast (MRMM) for deployment in mobile robot networks. MRMM exploits the fact that mobile robots know what velocity they are instructed to move at and for what distance in building a long lifetime sparse mesh for group communication that is more efficient. Our results show that MRMM provides an efficient group communication mechanism that can potentially be used in many mobile robot application scenarios.

• 한국통신학회논문지
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• 제34권9A호
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• pp.664-672
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• 2009

본 논문에서는 원형 등간격 어레이를 갖는 이동 릴레이를 위한 셀 탐색과 입사각 동시 추정기법을 제안한다. 제안된 셀 탐색과 입사각의 동시 추정기법은 인접 기지국에서 이동 릴레이로 수신되는 신호간에 심볼 타이밍 옵셋이 존재하는 경우에도 강건한 특성을 갖고, 셀 탐색과 입사각을 각각 독립적으로 추정하는 경우에 비하여 계산량과 수행시간을 감소시킬 수 있다. 제안된 동시 추정기법의 성능을 Mobile WiMAX 환경 하에서 모의실험을 통하여 검증한다.

• 한국통신학회논문지
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• 제29권5A호
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• pp.537-544
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• 2004

In this paper, we p개pose DS-CDM-SQAM(Superposed Quadrature Amplitude Modulation) which is characterized by its smooth phase transition and small envelope fluctuation, and improves the power efficiency as compared to DS-CDM-QPSK of satellited-based DMB system(ITR-R BO.1130-4 System E) in a nonlinearly amplified channel. Computer simulation results show that the proposed DS-CDM-SQAM improves Eb/No by 1.7㏈ to maintain BER=1${\times}$$10^{-3}$ in nonlinearly amplified multipath mobile radio environments. Therefore, the proposed DS-CDM-SQAM system significantly improves the power efficiency in nonlinear land mobile satellite DMB environments.

• 한국통신학회논문지
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• 제29권4A호
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• pp.384-389
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• 2004

본 논문에서는 comb 방식의 파일럿 패턴을 가지는 MIMO OFDM 시스템에서의 채널 추정 기법에 대하여 논의한다. 또한, 시변 채널 환경에서 채널 측정의 정확도를 높이기 위한 효율적인 채널 추정 기법을 제안한다. 시뮬레이션을 통해 제안한 채널 추정 기법이 채널이 변하는 상황에서 성능의 감소 없이 채별의 변화를 추정함을 알 수 있었다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제3권2호
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• pp.147-162
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• 2009

In this paper, we propose a Cooperative Transmission Strategy using Entropy-based Relay Selection in Mobile Ad-hoc Wireless Sensor Networks(MAWSN) with Rayleigh Fading Environments. The main features and contributions of the proposed cooperative transmission strategy are as follows. First, entropy-based relay selection is used to improve data transmission reliability from a source node to a destination node. Second, we present a theoretical analysis model for the proposed cooperative transmission strategy with the outage probability of the end-to-end performance. The performance of our protocol is evaluated using analysis and simulation.

• Journal of Communications and Networks
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• 제16권2호
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• pp.155-161
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• 2014

Mobility can lead to continual loss of data and service interruptions during communications in multi-hop cognitive radio networks. Mobility of primary users (PUs) or cognitive users (CUs) requires adjustment of multi-hop communications among CUs to avoid any interference to PUs. To provide durable and reliable data routing that ensures continuous network service, we propose mobility-aware cognitive routing (MCR) for multi-hop cognitive radio networks. MCR examines the risk level of each node against interference regions and selects the most reliable path for data delivery using a Markov predictor. Through simulation, we verify that the proposed scheme can avoid route destruction preemptively and achieve reliable data delivery.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권6호
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• pp.1828-1847
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• 2014

Coordinated multi-point (CoMP) transmission has been regarded as a potential technology for LTE-Advanced. In frequency division duplexing systems, channel quantization is applied for reporting channel state information (CSI). Considering the dynamic number of cooperation base stations (BSs), asymmetry feature of CoMP channels and high searching complexity, simply increasing the size of the codebook used in traditional multiple antenna systems to quantize the global CSI of CoMP systems directly is infeasible. Per-cell codebook based channel quantization to quantize local CSI for each BS separately is an effective method. In this paper, the theoretical upper bounds of system throughput are derived for two codeword selection schemes, independent codeword selection (ICS) and joint codeword selection (JCS), respectively. The feedback overhead and selection complexity of these two schemes are analyzed. In the simulation, the system throughput of ICS and JCS is compared. Both analysis and simulation results show that JCS has a better tradeoff between system throughput and feedback overhead. The ICS has obvious advantage in complexity, but it needs additional phase information (PI) feedback for obtaining the approximate system throughput with JCS. Under the same number of feedback bits constraint, allocating the number of bits for channel direction information (CDI) and PI quantization can increase the system throughput, but ICS is still inferior to JCS. Based on theoretical analysis and simulation results, some recommendations are given with regard to the application of each scheme respectively.

• Journal of Communications and Networks
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• 제7권3호
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• pp.367-376
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• 2005

The smooth handoff supported by the route optimization extension to the mobile IP standard protocol should support a packet buffering mechanism at the base station (BS), in order to reduce the degradation in TCP performance caused by packet losses within mobile network environments. The purpose of packet buffering at the BS is to recover the packets dropped during intersubnetwork handoff by forwarding the packets buffered at the previous BS to the new BS. However, when the mobile host moves to a congested BS within a new foreign subnetwork, the buffered packets forwarded by the previous BS are likely to be dropped. This subsequently causes global synchronization to occur, resulting in the degradation of the wireless link in the congested BS, due to the increased congestion caused by the forwarded burst packets. Thus, in this paper, we propose an implicit priority forwarding (IPF) packet buffering scheme as a solution to this problem within mobile IP based networks. In the proposed IPF method, the previous BS implicitly marks the priority packets being used for inter-subnetwork handoff. Moreover, the proposed modified random early detection (M-RED) buffer at the new congested BS guarantees some degree of reliability to the priority packets. The simulation results show that the proposed IPF packet buffering scheme increases the wireless link utilization and, thus, it enhances the TCP throughput performance in the context of various intersubnetwork handoff cases.