• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.5
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• pp.874-887
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• 2011

Compared to nomadic and fixed relay stations, vehicle-mounted mobile relay stations show different characteristics caused by the time-variant topology, due to their mobility. Especially, a relay mounted in a vehicle is differentiated from nomadic or fixed relay by the restricted distance between the relay and associated mobile station and the variable density of relay deployment in a cell. In this paper, we identify the characteristics of vehicle-mounted mobile relay stations and provide some parameters that highly influence the performance of vehicle-mounted relay. Through simulation, we measure the effect of relay density, zone ratio, relay transmission power, and frame transmission mode on the performance of vehicle-mounted relay. The results show that the performance of vehicle-mounted relay is highly susceptible to the above vehicle-mounted relay-specific parameters.

• Journal of Internet Computing and Services
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• v.11 no.3
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• pp.43-51
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• 2010

In this paper, we evaluate the system throughput and the method of optimal wireless resource allocation for the access zone (AZ) and relay zone (RZ) in downlink when the cell coverage is extended using the non-transparent Relay Station (RS) in a 2-hop cellular relay system based on IEEE802.16j, which uses the OFDMA-TDD structure. For the analyses, we first introduce the MAC (Media Access Control) frame structure in the non-transparent mode, then we investigate the interfering elements in both AZ and RZ for the network devices such as the Mobile Station (MS) and RS. Through computer simulation, we analyze the cell coverage extension and system throughput in terms of the distance between Base Station (BS) and RS, then we present the amount of the optimal allocation of wireless resource for the AZ and RZ in downlink using our results.

• Journal of Communications and Networks
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• v.15 no.2
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• pp.191-197
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• 2013

In this paper, a mobile relay station (MRS) for vehicles with a beamforming antenna is considered to increase the reliability of the transmission link, particularly for the MRS at the cell boundary. A cell searching and direction-of-arrival estimation method for an MRS with a uniform linear array is proposed for OFDM-based cellular systems in a multipath environment, even with the existence of the symbol timing offsets and carrier frequency offsets. The performance of the proposed method is evaluated by computer simulation using the standard profile of IEEE 802.16e.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.15 no.5
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• pp.1944-1956
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• 2021

This paper considers a cellular two-way relay network with one base station (BS), one relay station (RS), and two users. The two users are far from the BS and no direct links exist, and the two users exchange messages with the BS via the RS. A non-orthogonal multiple access (NOMA) and network coding (NC)-based decode-and-forward (DF) two-way relaying (TWR) scheme TWR-NOMA-NC is proposed, which is able to reduce the number of channel-uses to three from four in conventional time-division multiple access (TDMA) based TWR approaches. The achievable sum-rate performance of the proposed approach is analyzed, and a closed-form expression for the sum-rate upper bound is derived. Numerical results show that the analytical sum-rate upper bound is tight, and the proposed TWR-NOMA-NC scheme significantly outperforms the TDMA-based TWR and NOMA-based one-way relaying counterparts.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.3
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• pp.1311-1324
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• 2019

In the traditional cellular network communication, the cellular user and the base station exchange information through the uplink channel and downlink channel. Meanwhile, device-to-device (D2D) users access the cellular network by reusing the channel resources of the cellular users. However, when cellular user channel conditions are poor, not only D2D user cannot reuse its channel resources to access the network, but also cellular user's communication needs cannot be met. To solve this problem, we introduced a novelty D2D communication mechanism in the downlink, which D2D transmitter users as half-duplex (HD) relays to assist the downlink transmission of cellular users with reusing corresponding spectrum. The optimization goal of the system is to make the cellular users in the bad channel state meet the minimum transmission rate requirement and at the same time maximize the throughput of the D2D users. In addition, i for the purpose of improving the efficiency of relay transmission, we use two-antenna architecture of D2D relay to enable receive and transmit signals at the same time. Then we optimized power of base station and D2D relay separately with consideration of backhaul interference caused by two-antenna architectures. The simulation results show that the proposed HD relay strategyis superior to existing HD and full-duplex (FD) models in the aspects of system throughput and power efficiency.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.6
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• pp.98-104
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• 2012

We consider the optimum power allocation problem for downlink system throughput maximization in a 2 time slotted relay interference channel. Base station (BS) transmits power to Mobile Station (MS) and Relay Station (RS) in time slot 1 (orthogonal channel). In time slot 2, BS and RS transmit power to each MS, while causing cochannel interference to each other. The obtained optimum power allocation scheme allows simultaneous transmissions of BS and RS when the interference level in time slot 2 is low. However, when the interference level is high, RS shuts down its power. Numerical results are provided to support our analysis.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.1
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• pp.58-67
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• 2013

In this paper, a mobile relay station(MRS) for vehicles with a beamforming antenna is considered to increase the reliability of a transmission link, especially for the MRS at cell boundary. Cell searching and direction-of-arrival(DoA) estimation methods for an MRS with a uniform linear array(ULA) are proposed for a multipath environment in OFDM-based cellular systems. Performances of the proposed methods(Method1 and Method2) are evaluated by computer simulation with the standard profile of IEEE 802.16e.

• ETRI Journal
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• v.33 no.4
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• pp.558-568
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• 2011

In this paper, we propose an efficient macrodiversity handover (MDHO) technique for time-division-based interference-limited IEEE 802.16j multihop wireless relay networks. In the proposed MDHO, when the diversity set members of the mobile station (MS) are a base station (BS) and relay station (RS), the MS receives the signal transmitted by the BS in the first phase. During the second phase, it also receives the simultaneous transmissions of the BS and RS. Furthermore, when the diversity set members are two RSs or two BSs, the MS receives only the simultaneous transmissions of the diversity set members. The superiority of the proposed MDHO is validated using analytical and simulation results. The performance analysis metrics are the average downlink (DL) carrier to interference and noise ratio (CINR), the average DL spectral efficiency, and the average service outage probability. Evaluation results show that the proposed MDHO significantly outperforms the conventional MDHO. The CINR gain achieved using the proposed MDHO is 4.71 dB compared to the conventional MDHO.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.11 s.353
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• pp.141-148
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• 2006

This paper deals with the performance improvement by eliminating loop interference signal and inserting adaptive equalizer for phase compensation in OFDMA based Wibro relay station. The Wibro relay station is used for the extension of communication service area and for throughput improvement of base station. The loop interference is important factor of performance determination of relay station when transmitter and receiver is very closely located. In order to design interference canceller, we generated base-band OFDMA signal and then transmitted the signal along with pilot tones alined with two different combinations for training mode. And then, we generated received fading signal due to the loop interference added noise to the received signal. In the receiver, the transmitted signal is recovered by elimination of the interference signal with channel estimate and compensating phase by adaptive equalizer. The performance improvement was verified by computer simulation which show channel estimation, constellation of signal and BER characteristics according to the variation of SNR ratio.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2013.10a
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• pp.54-56
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• 2013

A subcarrier allocation scheme for base station (BS), relay station (RS) and mobile station (MS) can affect the performance of orthogonal frequency division multiple access (OFDMA) relay systems. In this paper, we propose a subcarrier allocation scheme with inter-cell interference and network coding in OFDMA relay systems. In the network coding zone, we consider an environment where RS can transmit a frame to BS and MS simultaneously. We divide an OFDMA frame into downlink zone, uplink zone, and network coding zone. The proposed scheme allocates subcarriers to BS, RS, and MS for each zone with consideration of inter-cell interference in OFDMA relay systems. We evaluate the performance of the proposed subcarrier allocation scheme through simulation.