• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.12 no.3
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• pp.87-95
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• 2013

In this paper, the outage probability of efficient partial relay selection(EPRS) using only one-hop channel information in multi-hop systems is analyzed in Rayleigh fading channels. In particular, we derive an exact and closed-form expression for the outage probability of decode-and-forward relaying based EPRS. In order to prove the usefulness of EPRS in multi-hop systems, we also analyze the correlation between the end-to-end signal-to-noise ratio(SNR) and the SNR for each hop at an arbitrary relaying path. Furthermore, through numerical investigation, we compare the outage performances for EPRS and the best relay selection using all channel information.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.5C
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• pp.487-494
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• 2010

This paper presents an OFDM-based dual-hop multi-relay system with best relay selection maximizing the mutual information. For the system either with decode-and-forward (DF) relays or with amplify-and-forward (AF) relays, we derive a lower-bound on the outage probability and the diversity order achievable in frequency selective fading channels and provide the outage capacity from simulation. Performance evaluation shows that both DF and AF provide the same diversity order as in the lower-bound but DF of which the outage probability is much closer to the lower-bound provides a better outage capacity than AF. It is also observed that the SNR gain of DF over AF gets larger as either the number of resolvable multipaths or the number of relay candidates increases, which makes DF relaying more favorable to the OFDM-based multi-relay system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.9
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• pp.798-809
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• 2013

In this paper, we propose robust relay and destination filter design methods for the multi-user peer-to-peer amplify-and-forward relaying systems while taking imperfect channel knowledge into consideration. Specifically, the relay and destination filter sets are developed to minimize the sum mean-squared-error (MSE). We first present a robust joint optimum relay and destination filter calculation method with an iterative algorithm. Motivated by the need to reduce computational complexity of the iterative scheme, we then formulate a simplified sum MSE minimization problem using the relay filter decomposability, which lead to two robust sub-optimum non-iterative design methods. Finally, we propose robust modified destination filter design methods which require only local channel state information between relay node and a specific destination node. The analysis and simulation results verify that, compared with the optimum iterative method, the proposed non-iterative schemes suffer a marginal loss in performance while enjoying significantly improved implementation efficiencies. Also it is confirmed that the proposed robust filter design methods provide desired robustness in the presence of channel uncertainty.

• KIPS Transactions on Computer and Communication Systems
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• v.5 no.5
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• pp.103-108
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• 2016

In this paper, we propose a resource allocation scheme that guarantees transmission rate for each mobile stations by mitigating interference between a base station-to-mobile station link and a relay station-to-mobile station link. Specifically, we dynamically adjust the boundary between access zone and relay zone using signal to interference plus noise ratio. Moreover, we cluster the mobile stations under sever interference and manage the channel quality of these mobile stations by allocating additional radio resource. Our simulation results show that the proposed scheme can improve the efficiency of radio resources and ensure fairness among mobile stations.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.2
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• pp.566-578
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• 2018

In this paper, we design a segment training based individual channel estimation (STICE) scheme for the classical two-way relay network (TWRN) with multi-pair sources (MPS) and amplify-and-forward (AF). We adopt the linear minimum mean square error (LMMSE) channel estimator to minimize the mean square error (MSE) without channel estimation error, where the optimal power allocation strategy from the relay for different sources is obtained. Then the MSE gains are given with different source pairs among the proposed power allocation scheme and the existing power allocation schemes. Numerical results show that the proposed method outperforms the existing ones.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.6
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• pp.1238-1240
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• 2009

In the wireless sensor network, cooperative transmission is an effective technique to combat multi-path fading and reduce transmitted power. Relay selection and power allocation are important technical issues to determine the performance of cooperative transmission. In this paper, we proposed a new multi-relay selection and power allocation algorithm to increase network lifetime. The proposed relay selection scheme minimizes the transmitted power and increase the network lifetime by considering residual power as well as channel conditions. Simulation results show that proposed algorithm obtains much longer network lifetime than the conventional algorithm.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2010.07a
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• pp.9-11
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• 2010

Multiple-input multiple-output (MIMO) systems assisted by multi-relays with single antenna are considered. Signal transmission consists of two hops. In the first hop, the source node broadcasts the vector symbols to all relays, then all relays forward the received signals multiplied by each power gain to the destination simultaneously. Unlike the case of full cooperation between relays such as single relay with multiple antennas, in our case there is no closed form solution for optimal relay power gain with respect to minimum mean square error (MMSE). Thus we propose an alternative approach in which we use an approximation of the cost function based on rank-one matrix decomposition. As a cost function, we choose the trace of MSE matrix. We give several simulation results to validate that our proposed method obtains a negligible performance loss compared to optimal solution obtained by exhaustive search.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.4 no.3
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• pp.258-272
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• 2010

The low-rate (LR) UWB is a promising technology for the ubiquitous sensor network (USN) due to its extremely low power consumption and simple transceiver implementation. However the limited communication range is a bottleneck for its widespread use. This paper deals with a new frame structure of class 4 active RFID multi-hop relay system based on ISO/IEC 18000-7 standard integrating with IEEE 802.15.4a LR-UWB PHY layer specification, which sets up a connection to USN. As a result of the vital importance of the coverage and throughput in the application of USN, further we analyze the performance of the proposed system considered both impulse radio UWB (IR-UWB) and chirp spread spectrum (CSS). Our simulation results show that the coverage and throughput are remarkably increased.

• Journal of Information Processing Systems
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• v.6 no.3
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• pp.403-412
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• 2010

Multi-Relay Networks should accommodate mobile users of various speeds. The cellular system should meet the minimum residency time requirements for handover calls while considering an efficient use of available channels. In this paper, we design speed-sensitive handover under dynamic hierarchical cellular systems, in which mobile users are classified according to the mean speed of mobile users and each class has its cellular layer. In order to meet the minimum residency time, the cell size of each cellular layer is dynamically determined depending on the distributions of mean speeds of mobile users. Since the speed-dependent non-preferred cell can provide a secondary resource, overflow and take-back schemes are adopted in the system. We develop analytical models to study the performance of the proposed system, and show that the optimal cell size improves the blocking probability.

• Electronics and Telecommunications Trends
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• v.23 no.3
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• pp.40-52
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• 2008

무선이동통신 시스템에서 셀 용량과 셀 영역을 확장하기 위한 기술로 Mobile Multi-hop Relay 기술에 대한 연구와 표준화 작업이 한창 진행되고 있다. 특히 고속으로 이동인터넷서비스를 제공할 수 있는 WiBro(Mobile WiMAX)에 적용할 수 있는 멀티홉기술이 IEEE 802.16j에서 표준화 작업이 진행되고 있다. 본 고에서는 IEEE 802.16j에서 추진되고 있는 멀티홉릴레이 기술에 대한 동향과 이에 소요되는 핵심기술에 대해서 소개하고자 한다.