• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.1
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• pp.70-76
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• 2011

LTE Re1-10 aims at peak. data rates of 1Gbits/s for the downlink and 500 Mbits/s for the uplink, which can be accomplished by not only wide spectrum but also advanced MIMO techniques such as precoded MIMO and cooperative relays. Considering some relays can have more direct signal paths than mobile stations do, LoS components are examined to build more efficient codebooks for Rician channels. The proposed codebooks perform better than the existing LTE codebooks as the criterium of LoS, K-factor increases. Conserving the advantages and max-min chordal distance of the existing LTE codebooks, the proposed ones also maximize the minimum chordal distances between codewords over Rician fading channels. Link-level simulation with LTE system parameters confirm the performance improvements as the value of K increases.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.11
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• pp.1311-1317
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• 2010

In this paper, for a uplink space division multiple access system named cooperative spatial multiplexing(CSM), radio resource management(RRM) algorithms are proposed based on sharing uplink channel information among a serving base station(BS) and interfering BSs in a uplink coordinated wireless communication system. A constrained maximum transmit power algorithm is proposed for mobile station(MS) to limit uplink inter-cell interference(ICI). And joint scheduling algorithm among coordinated BSs is proposed to enhance uplink capacity through ICI mitigation by using channel information from interfering BSs. It is shown that the proposed RRM algorithm provides a considerable uplink capacity enhancement by effective ICI mitigation only with moderate complexity.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.6
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• pp.1379-1397
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• 2013

We consider a system where a licensed radio spectrum is shared by multiple primary users(PUs) and secondary users(SUs). As the spectrum of interest is licensed to primary network, power and channel allocation must be carried out within the cognitive radio network so that no excessive interference is caused to PUs. For this system, we study the joint beamforming and power allocation problem via game theory in this paper. The problem is formulated as a non-cooperative beamforming and power allocation game, subject to the interference constraints of PUs as well as the peak transmission power constraints of SUs. We design a joint beamforming and power allocation algorithm for maximizing the total throughput of SUs, which is implemented by alternating iteration of minimum mean square error based decision feedback beamforming and a best response based iterative power allocation algorithm. Simulation results show that the algorithm has better performance than an existing algorithm and can converge to a locally optimal sum utility.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.7 s.98
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• pp.709-719
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• 2005

The forward link of the 3 G CDMA system may become limited under the increasing of the number of users. The conventional channelization code, Walsh code, has not enough sizes for much possible non, therefore, the quasi orthogonal function(QOF), which process optimal cross-correlation with Walsh code, is considered. In this paper, we investigate quasi orthogonal function on Jacket matrices, which can lead lower correlations values and better performance in 3 G CDMA system. Moreover, to simple the detector and improve the BER performance, a novel detection for QOF CDMA system is proposed. Finally, the simple recursive generation of the bent sequences for QOF mask function is discussed.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.7
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• pp.45-52
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• 2008

In typical cellular systems using frequency reuse scheme, the terminal suffers a performance degradation due to the intercell interference signals from adjacent cells as the terminal moves toward the cell boundary. In this paper, a signal transmission and reception scheme which achieve spatial multiplexing and beamforming gain from a distributed MIMO (multiple-input multiple-output) channel using multiple-antenna terminal is proposed for the spectral efficiency enhancement in a multi-cell downlink environment, when geographically separated base stations cooperatively transmit signals. In particular, we analyze the effective signal-to-interference ratio and spectral efficiency of the proposed scheme for different frequency reuse patterns and for varying numbers of receive antennas, and compare with the performance of the MRC (maximal ratio combining) reception scheme in typical cellular systems. We evaluate the amount of transmission efficiency of the scheme by comparing the performance near the cell boundary where the strong intercell interference is experienced.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.10
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• pp.2113-2120
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• 2011

In this paper, so as to improve spectral efficiency for cell-boundary users, we introduce a coordinated multi-point (CoMP) system, which is one of inter-cell cooperative transmission strategies studied in 3GPP long-term evolution-advanced (LTE-A) systems, and develop a system-level simulator to evaluate performance. To identify performance improvement of the system with inter-cell cooperative transmission, we select a 3GPP LTE system as a reference, which shows the highest performance among the existing mobile communication systems, and conduct a performance comparison. System-level simulation is performed based on widely-used OPNET tool. We implement modules including central unit (CU), CoMP eNodeB (CeNB), user equipment (UE), and multiple-input multiple-output (MIMO) channel model, while designing the inter-cell cooperative transmission system. Under WINNER wireless channel model and international telecommunication union (ITU) network model environments, we then evaluate the performance of edge users who belong to the lower 5% in terms of spectral efficiency. It is finally shown that throughput of the proposed CoMP system gets improved up to 2.5 times compared to that of the 3GPP LTE reference system.

• Journal of Communications and Networks
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• v.11 no.2
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• pp.196-206
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• 2009

Over the last five years, relaying or multihop techniques have been intensively researched as means for potentially improving link performance of wireless networks. However, the data rates of relays are often limited because they cannot transmit and receive on the same frequency simultaneously. This limitation has come to the attention of researchers, and recently a number of relay techniques have been proposed specifically to improve the data efficiency of relaying protocols. This paper surveys transmission protocols that employ first single relays, then multiple relays and finally multiple antenna relays. A common feature of these techniques is that novel signal processing techniques are required in the relay network to support increased data rates. This paper presents results and discussion that highlight the advantages of these approaches.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.3
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• pp.956-970
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• 2015

In this paper, we study the design of network coding for the generalized transmit scheme in multiple input multiple output Y channel, where K users wish to exchange specified and shared information with each other within two slots. Signal space alignment at each user and the relay is carefully constructed to ensure that the signals from the same user pair are grouped together. The cross-pair interference can be canceled during both multiple accessing channel phase and broadcasting channel phase. The proposed signal processing scheme achieves the degrees of freedom of ${\eta}(K)=K^2$ with fewer user antennas.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2009.11a
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• pp.379-382
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• 2009

본 논문에서는 폐회로 다중 안테나 송수신 (closed-loop multiple-input multiple-output) 기법을 사용하는 적응형 협동 다중 홉 중계 시스템을 제안한다. 중계기와 기지국 사이의 이동성이 낮기 때문에, 폐회로 다중 안테나 송수신 기법은 개회로 다중 안테나 송수신 기법보다 높은 다이버시티 이득을 얻을 수 있다. 이 때, 한 개 이상의 중계 터미널들은 기지국으로 전송을 공유하고 프리코딩 가중치벡터를 피드백하기 위해 하나의 협동 그룹에 포함되어야 한다. 피드백 비트의 증가로 인한 전송량 감소를 최소화 하기 위해 코드북 기반의 최대비 전송 기법을 사용하여 비트백 비트수를 제한한다. 기지국은 협동 중계 그룹 중에서 채널 상태가 가장 좋은 중계기를 선택하고, 프리코딩을 위한 인덱스 값을 중계기에 피드백한다. 이러한 중계 시스템을 위해 피드백 형태와 선택 프로토콜 시나리오를 제안하고, 모의실험을 통해 중계기 선택에 따른 성능을 확인한다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2013.06a
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• pp.214-216
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• 2013

최근, 협력통신은 MIMO시스템을 대신하여 신뢰성 있는 통신을 위하여 많은 연구가 진행되고 있다. 기존 통신에 비하여 신뢰성 있는 통신은 가능하지만 중계기에 의한 협력시간은 시간 슬롯(slot)을 낭비시킨다. 그 결과 전송률이 감소되어 최대 전송률을 이룰 수 없다. 또한 전송률이 감소되는 동시에 전송속도도 감소되는 단점을 가지고 있다. 이 논문에서는 협력통신에서 감소된 전송률의 단점을 보완하고자 전송률을 증가시키는 기법을 제안하여, 초고속 통신을 가능하게 하는 기법을 제안한다. 또한 제안된 전송기법에 따른 복조기법을 제안하여 효율적으로 신호를 복조하는 기법을 제안한다. 모의실험을 통하여 제안한 기술의 성능평가를 한다.