• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.3
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• pp.477-493
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• 2011

The IEEE 802.16 mobile multi-hop relay (MMR) task group 'j' (TGj) has introduced the multi-hop relaying concept in the IEEE 802.16 Wireless MAN, wherein a relay station (RS) is employed to improve network coverage and capacity. Several RSs can be deployed between a base station and mobile stations, and configured to form a tree-like multi-hop topology. In such architecture, we consider the problem of a path selection through which the mobile station in and outside the coverage can communicate with the base station. In this paper, we propose a new path selection algorithm that ensures more efficient distribution of resources such as bandwidth among the relaying nodes for improving the overall performance of the network. Performance of our proposed scheme is compared with the path selection algorithms based on loss rate and the shortest path algorithm. Based on the simulation results using ns-2, we show our proposal significantly improves the performance on throughput, latency and bandwidth consumption.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.7
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• pp.24-31
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• 2009

Resource reservation scheme is an effective method to guarantee QoS for handoff calls in the next generation multimedia mobile communication systems, but it causes negative impacts on blocking probability of new calls. In this paper, to optimize the tradeoff between dropping probability of handoff calls and blocking probability of new calls, relay station based handoff prioritization control algorithm is proposed. In this algorithm, the relay station participates in handoff procedure and enables mobile stations to have guaranteed prompt service after handoff by providing highly efficient data transmission. In this paper, Markov chain models of the proposed handoff prioritization schemes are developed, and dropping probability of handoff packets and blocking probability of new packets are derived. By numerical analysis, the proposed algorithm has been proved to outperform conventional handoff prioritization schemes in terms of dropping probability of handoff packets and blocking Probability of new packets.

• Journal of Communications and Networks
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• v.11 no.5
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• pp.464-472
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• 2009

In this paper, we propose a packet scheduling algorithm for cellular relay networks by considering relay selection, variation of channel quality, and packet delay. In the networks, mobile users are equipped with not only cellular but also user relaying radio interfaces, where base station exploits adaptive high speed downlink channel. Our proposed algorithm selects a user with good cellular channel condition as a relay station for other users with bad cellular channel condition but can get access to relay link with good quality. This can achieve flexible packet scheduling by adjusting transmission rates of cellular link. Packets are scheduled for transmission depending on scheduling indexes which are calculated based on user's achieved transmission rate, packet utility, and proportional fairness of their throughput. The performance results obtained by using computer simulation show that the proposed scheduling algorithm is able to achieve high network capacity, low packet loss, and good fairness in terms of received throughput of mobile users.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.8C
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• pp.689-695
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• 2007

Wireline relay stations(RS's) are connected to cellular base stations(BS's) via radio-over-fiber(RoF) to enhance system capacity and to reduce shadow areas. Unlike wireless multi-hop systems, BS-to-RS signaling is transmitted out-of-band, thus reducing the effect of interference caused by frequency reuse. In this paper, antenna arrays used in addition to the wireline RS's are considered to evaluate the transmission capacity gain and performance variations according to the may structures. In particular, RS locations to maximize the gain, may distribution patterns for a given number of antenna elements, performance enhancement for a varying number of elements are experimentally determined to suggest a proper utilization of antenna ways in conjunction with wireline RS's.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.11A
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• pp.853-860
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• 2011

In this paper, we proposed a transmission scheme for a full-duplex relay system that minimizes outage probability. A relay system with the full-duplex relay can mitigate resource inefficiency of a half-duplex relay system. However, the mobile station suffers from the interference because the base station and the relay station transmits signal simultaneously to the mobile station. First, we suggest a layered broadcasting for full-duplex relaying. Second, we derive an optimal power allocation for the layered broadcasting in terms of the outage probability minimization. The proposed algorithm shows better performance than a half-duplex relaying system with and without the diversity, and a conventional full-duplex relaying system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.2C
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• pp.196-205
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• 2012

In this paper, we investigate MSAP-TMFT in TICN systems that will be future NCW-based tactical networks. Although MSAP-TMFT implements the WiBro technology, we propose to design a NRC(NAT Relay Cell) that functions as a relay station and at the same time as a base station in combat environments. NRCs support extension of communication distance, increased data rate, efficient radio resource management, and survavibility of combat networks. From simulation results, we show that NRCs improve the efficacy of radio resource management and system throughput compared to the legacy systems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.9A
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• pp.758-766
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• 2011

Cooperative communications are adopted as a promising solution to achieve high data rate over large areas in the future 40 wireless system and the relay station (RS) is the key concept in cooperative communications. However, most existing works in this area focus only on optimal RS selections. In addition, there are only few works consider another crucial issue: how many relay stations we need to place. Only when the number of relay stations is defined, the relay station selection can be performed well. In this paper we derive a formula which describes the impact of varying number of RS on end-to-end link throughput assuming a clustering scheme which is based on Voronoi tessellation. In addition to mathematical analysis on the feasibility of the formula, we also examine its performance through a set of simulations under the Erceg path loss model. Simulation results verify that the link throughput gain of our proposed scheme is promising.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.9A
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• pp.664-672
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• 2009

In this paper, joint methods of cell searching and Direction-of-Arrival (DoA) estimation for a mobile relay station with a uniform circular array are proposed. The proposed joint estimation method for the mobile relay station is robust even when there exist symbol timing offsets between the signals received from adjacent base stations. Also, the proposed joint estimation method can reduce computational complexity and processing time, compared with the case where cell searching and DoA estimation are performed separately. Performances of the proposed method are evaluated by computer simulation under Mobile WiMAX environment.

• Journal of Communications and Networks
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• v.17 no.1
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• pp.84-92
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• 2015

Multi-hop relay networks have been widely considered as a promising solution to extend the coverage area and to reduce the deployment cost by deploying the relay stations (RSs) in mobile communication systems. Suitable deployment for the RSs is one of the most important features of the demand nodes (DNs) to obtain a high data transmission rate in such systems. Considering a tradeoff among the network throughput, the deployment budget, and the overall coverage of the systems, efficient RS deployment schemes and corresponding algorithms must be developed and designed. A novel cluster-based RS deployment scheme is proposed in this paper to select the appropriate deployment locations for the relay stations from the candidate positions. To make an ideal cluster distribution, the distances between the DNs are calculated when deploying the RSs. We take into account the traffic demands and adopt a uniform cluster concept to reduce the data transmission distances of the DNs. On the basis of the different candidate positions, the proposed scheme makes an adaptive decision for selecting the deployment sites of the RSs. A better network throughput and coverage ratio can be obtained by balancing the network load among the clusters. Simulation results show that the proposed scheme outperforms the previously known schemes in terms of the network throughput and the coverage ratio. Additionally, a suitable deployment budget can be implemented in multi-hop relay networks.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.9B
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• pp.876-882
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• 2009

In this paper, we propose a sub-cell coverage control algorithm for enhancement of the cell throughput in OFDMA based relay systems. Relay station (RS) is exploited for improved quality of the received signal in cellular communication systems, especially in shadow areas. However, since a RS requires additional radio resource consumption for the link between the base station (BS) and the RS, we have to carefully control the coverage areas if a mobile station (MS) is serviced via the BS or the RS considering the cell throughput. We consider radio resource reuse as well for the sub-cell coverage configuration by applying various reuse patterns between RSs. We also consider a time varying system by adaptively changing the threshold for coverage depending on the MSs' traffic in the cell. We initially determine the sub-cell coverage of the system depending on the ratio of received signal-interference-noise-ratio (SINR) of the MS from the BS and RSs, respectively. Then, the "sub-cell coverage threshold" varies based on the "effective transmitted bits per sub-channel" with time. Simulation result shows that the proposed "time varying coverage control algorithm" leads to throughput improvement compared to the fixed sub-cell coverage configuration.