• ETRI Journal
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• 제34권5호
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• pp.763-766
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• 2012

This letter proposes an iterative multimode precoding scheme with limited feedback for nonreciprocal MIMO interference channels. Based on analysis of game theory, we model the iterative multimode precoding as a noncooperative game with a finite set of strategies. Numerical results are presented to verify the sum rate performance of the proposed scheme.

• 한국통신학회논문지
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• 제33권11A호
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• pp.1043-1052
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• 2008

본 논문에서는 간섭 제한적인 환경의 OFDM 시스템에서 시공간 부호화 기술과 순환지연 다이버시티 기술의 성능을 비교한다. 통신 시스템은 다이버시티 기술을 보통 자신의 성능을 향상시키기 위하여 사용하지만 시스템이 간섭 제한적인 환경에서 동작된다면 다른 사용자에게 미치는 영향도 함께 고려해야 한다. 다른 사용자와의 간섭을 고려하지 않을 때 시공간 부호화 기술은 순환지연 다이버시티 기술보다 우수한 성능을 보이지만 다른 사용자에게 미치는 영향을 함께 고려할 때는 순환지연 다이버시티를 사용하는 것이 더 우수한 성능을 보일 수 있다.

• ETRI Journal
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• 제39권6호
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• pp.803-812
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• 2017

A decode-and-forward system with an energy-harvesting relay is analyzed for the case when an arbitrary number of independent interference signals affect the communication at both the relay and the destination nodes. The scenario in which the relay harvests energy from both the source and interference signals using a time switching scheme is analyzed. The analysis is performed for the interference-limited Nakagami-m fading environment, assuming a realistic nonlinearity for the electronic devices. The closed-form outage probability expression for the system with a nonlinear energy harvester is derived. An asymptotic expression valid for the case of a simpler linear harvesting model is also provided. The derived analytical results are corroborated by an independent simulation model. The impacts of the saturation threshold power, the energy-harvesting ratio, and the number and power of the interference signals on the system performance are analyzed.

• IEIE Transactions on Smart Processing and Computing
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• 제3권5호
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• pp.285-297
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• 2014

This paper presents the results of an investigation into bi-directional communication in spectrum sharing-based cognitive radio (Bi-CR) systems. A Bi-CR system can increase the spectral efficiency significantly by sharing the spectrum and through the bi-directional use of spatial resources for two-way communication. On the other hand, the primary user experiences more interference from the secondary users in a Bi-CR system. Satisfying the interference constraint by simply reducing the transmission power results in performance degradation for secondary users. In addition, secondary users also experience self-interference from echo channels due to full duplexing. These imperfections may weaken the potential benefits of the Bi-CR system. Therefore, a new way to overcome these defects in the Bi-CR system is needed. To address this need, this paper proposes some novel power allocation schemes for the Bi-CR system. This contribution is based on two major analytic environments, i.e., noise-limited and interference-limited environments, for providing useful analysis. This paper first proposes an optimal power allocation (OPA) scheme in a noise-limited environment and then analyzes the achievable sum rates. This OPA scheme has an effect in the noise-limited environment. In addition, a power allocation scheme for the Bi-CR system in an interference-limited environment was also investigated. The numerical results showed that the proposed schemes can achieve the full duplexing gain available from the bi-directional use of spatial resources.

• 한국방송∙미디어공학회:학술대회논문집
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• 한국방송공학회 2011년도 하계학술대회
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• pp.137-140
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• 2011

A precoding strategy is one of the representative interference management techniques in cognitive radio (CR) network which is a typical interference-limited environment. The interference minimization approach to precoding is an appropriate scheme to mitigate the interference efficiently while it may cause the capacity loss of the desired channel. The precoding scheme for the maximal capacity of the desired channel improves the capacity of the desired channel while it increases the interference power and finally causes the capacity loss of the interfered users. Therefore, we propose a precoding scheme which satisfies these two conflicting goals and manages the interference signal in such an interference-limited environment. The proposed scheme consists of two steps. First, the precoder nulls out the largest singular value of the interference channel to mitigate the dominant interference signal based on the interference minimization approach. Second, the transmitter calculates the sum capacities per mode and selects a mode to maximize the sum capacity. In the second step, each mode consists of the right singular vectors corresponding to the singular values except the largest singular value eliminated in the first step. Simulation results show that the proposed precoding scheme not only efficiently mitigate the interference signal, but also has the best performance in terms of the sum capacity in a MIMO-based CR network.

• 한국통신학회논문지
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• 제36권5C호
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• pp.276-285
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• 2011

본 논문에서는 한정된 자원에 여러 개의 연결이 혼재해 있는 상황에서 협력적으로 제한적인 피드백을 사용하여 성능을 개선시킬 수 있는 방법을 제안한다. 제안하는 방법은, 코드북에 있는 각 프리코더의 성능 우선순위에 따라 가중치를 부여하여 각 연결로부터 피드백 받은 가중치 데이터로부터 가중치의 합이 가장 높은 프리코더를 선택하는 방식이다. 시뮬레이션 결과 기존의 비협력적 방식에 비해 전송도 뿐만 아니라 시스템의 안정성에 관여되는 프리코더 선택의 수렴 정도 또한 향상됨을 알 수 있다.

• Journal of Communications and Networks
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• 제18권3호
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• pp.351-363
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• 2016

This paper investigates the performance of interference-limited two-way transmission protocols in the Rayleigh fading channels. New lower bound of outage probability and approximate expression of bit error rate (BER) for three-phase two-way relaying (3P-TWR) protocol are derived in closed-form. These expressions are valid for arbitrary signal-to-noise ratio values, numbers of co-channel interferers and amajority of modulation formats employed in the practical system. Then a comparative study is developed for the performance of three two-way transmission protocols, i.e., direct transmission (DT) protocol, two-phase two-way relaying (2P-TWR) protocol and 3P-TWR protocol based on the asymptotic expressions of outage probability and BER. On the basis of the theoretical results, the thresholds on the strength (variance) of direct channel and target rate for the relative performance of different protocols are obtained and the effect of interferences at the terminal and relay on the relative performance is analyzed. The results present key insights on how to choose proper two-way transmission protocol with the knowledge of fading channels, required date rate and modulation format to optimize the system performance in the practical interference-limited scenarios. Simulation results are presented to validate the theoretical analysis.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권4호
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• pp.692-710
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• 2013

Conventional interference alignment (IA) for a MIMO interference channel (IFC) requires global and perfect channel state information at transmitter (CSIT) to achieve the optimal degrees of freedom (DoF), which prohibits practical implementation. In order to alleviate the global CSIT requirement caused by the coupled relation among all of IA equations, we propose an IA scheme with a single feedback link of each receiver in a limited feedback environment for a three-user MIMO IFC. The main feature of the proposed scheme is that one of users takes out a fraction of its maximum number of data streams to decouple IA equations for three-user MIMO IFC, which results in a single link feedback structure at each receiver. While for the conventional IA each receiver has to feed back to all transmitters for transmitting the maximum number of data streams. With the assumption of a random codebook, we analyze the upper bound of the average throughput loss caused by quantized channel knowledge as a function of feedback bits. Analytic results show that the proposed scheme outperforms the conventional IA scheme in term of the feedback overhead and the sum rate as well.

• 전기전자학회논문지
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• 제25권3호
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• pp.420-424
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• 2021

5G통신의 핵심 기술인 거대다중안테나 시스템은 송신단에서 많은 양의 채널정보가 필요하기 때문에 제한된 채널 피드백을 사용하는 주파수 분할 이중 시스템에서 구현이 어려운 문제점이 있었다. 이러한 문제점을 해결하기 위해 장시간 변하지 않는 채널 상관도 정보를 이용하여 단말 그룹 간 간섭을 제거함으로써 채널정보 요구량을 비약적으로 감소시키는 Joint Spatial Division and Multiplexing(JSDM)기법이 제안되었고, 최근에는 그룹 간 잔여 간섭을 허용함으로써 성능을 더욱 향상시키는 정규화된 JSDM기법이 제안된 바 있다. 하지만 기존 JSDM관련 연구들은 주로 그룹 간 간섭제거에 초점을 두고 설계되었기 때문에, 그룹내 간섭 제거 단계에서 제한적인 피드백을 가정한 보다 실제적인 환경에서 성능분석이 이루어지지 못하였다. 본 논문에서는 JSDM기법과 정규화된 JSDM기법을 제한된 피드백 환경에서 그룹 수와 그룹 내 사용자 수에 따른 성능을 분석하고 시뮬레이션 결과를 통해 정규화된 JSDM기법이 제한된 피드백 환경에서 기존 JSDM대비 더욱 두드러지는 이득을 보임을 입증한다.

• Journal of Communications and Networks
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• 제18권6호
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• pp.913-925
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• 2016

In-band wireless full-duplex is a promising technology that enables a wireless node to transmit and receive at the same time on the same frequency band. Due to the complexity of self-interference cancellation techniques, only base stations (BSs) are expected to be full-duplex capable while user terminals remain as legacy half-duplex nodes in the near future. In this case, two different nodes share a single subchannel, one for uplink and the other for downlink, which causes inter-node interference between them. In this paper, we investigate the joint problem of subchannel assignment and power allocation in a single-cell full-duplex orthogonal frequency division multiple access (OFDMA) network considering the inter-node interference. Specifically, we consider two different scenarios: i) The BS knows full channel state information (CSI), and ii) the BS obtains limited CSI through channel feedbacks from nodes. In the full CSI scenario, we design sequential resource allocation algorithms which assign subchannels first to uplink nodes and then to downlink nodes or vice versa. In the limited CSI scenario, we identify the overhead for channel measurement and feedback in full-duplex networks. Then we propose a novel resource allocation scheme where downlink nodes estimate inter-node interference with low complexity. Through simulation, we evaluate our approaches for full and limited CSIs under various scenarios and identify full-duplex gains in various practical scenarios.