• 한국통신학회논문지
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• 제27권2A호
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• pp.99-108
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• 2002

본 논문에서는 불완전한 채널 정보가 시공간 블록 부호의 M-QAM 심볼에러율의 성능에 미치는 영향을 분석한다. 시공간 블록 부호를 복호하기 위해서는 채널 정보가 반드시 필요하므로 불완전한 채널 정보는 시공간 블록 부호의 성능을 저하시키는 원인이 된다. 본 논문에서는 채널 불일치 오차를 발생시키는 주된 원인을 채널 추정의 부정확성으로 인한 오차와 채널의 변화로 인한 오차로 모델링하고 이를 통해 채널 불일치 오차를 분석한다. 그리고 M-QAM 심볼에러율을 채널 불일치 오차 항이 들어간 채널당 평균 신호대 간섭비의 함수로 유도한다. 실험 결과 신호대 잡음비 20dB에서 허용할 수 있는 채널 추정 오차는 $10^{-3}$이고 채널 변화 정도는 f$_{d}$ T$_{B}$=0.001이다.다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권8호
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• pp.2626-2646
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• 2014

This study presents a power and Physical Resource Blocks (PRBs) joint allocation algorithm to coordinate uplink (UL) interference in the device-to-device (D2D) underlaying Long Term Evolution-Advanced (LTE-A) networks. The objective is to find a mechanism to mitigate the UL interference between the two subsystems and maximize the weighted sum throughput as well. This optimization problem is formulated as a mixed integer nonlinear programming (MINLP) which is further decomposed into PRBs assignment and transmission power allocation. Specifically, the scenario of applying imperfect channel state information (CSI) is also taken into account in our study. Analysis reveals that the proposed PRBs allocation strategy is energy efficient and it suppresses the interference not only suffered by the LTE-A system but also to the D2D users. In another side, a low-complexity technique is proposed to obtain the optimal power allocation which resides in one of at most three feasible power vectors. Simulations show that the optimal power allocation combined with the proposed PRBs assignment achieves a higher weighted sum throughput as compared to traditional algorithms even when imperfect CSI is utilized.

• 한국통신학회논문지
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• 제32권3C호
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• pp.189-194
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• 2007

본 논문에서는 시간 동기 추정을 위한 잡음 예측이 불완전한 경우에 직교분할 주파수 다중화 (OFDM) 시스템의 시간 동기 확률을 다중 경로 레일레이 페이딩 채널 환경에서 분석한다. 시간 동기 방식은 반복되는 CAZAC 시퀀스에 대한 상관기 구조를 가지며, 심벌간 간섭을 줄이기 위한 pre-advancement 기법을 적용한다. 시스템의 성능 평가 척도로서, 다중 경로 레일레이 채널 환경에서 유도된 동기 검파 확률을 분석한다.

• 한국전자파학회논문지
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• 제13권3호
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• pp.269-278
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• 2002

본 논문에서는 비동기 Rayleigh 페이딩 채널에서 MUD 과정에서 발생하는 시간 지연을 최소화 하면서 서비스 별로 다르게 요구되는 QoS 요구를 충족시킬수 이는 부분 SSPIC I. II형 다중 사용자 검파 기법을 제안하고 성능을 분석하였다. 결과에 의하면 제안한 부분 SSPIC I, II형 기법 모두 SIC 단에서 발생되는 시간 지연을 효과적으로 단축할 수 있으며, 부분SSPIC I형 기법은 성능 및 용량 면에서 기존 SICPIC 기법보다 향상되었고, 부분 SSPIC II형 기법은 유사한 성능을 나타내었다. 따라서, 본 논문에서 제안한 부분 SSPIC I, II형 다중 사용자 검파 기법은 기존SICPIC 다중 사용자 검파 기법의 단점인 간섭 제거 과정에서 발생되는 시간 지연을 효과적으로 단축시킬 수 있고, 간섭 제거 기법을 적용하지 않은 기존의 CDMA 수신기와 비교하여 과도한 시스템의 복잡도 및 시간 지연의 증가 없이 효과적으로 시스템의 성능을 개선 할 수 있다.

• Journal of Communications and Networks
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• 제18권5호
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• pp.762-772
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• 2016

This paper studies the problem of precoding and post-coding design for multicell multiuser downlink transmissions in the absence of perfect channel state information (CSI). Using statistical information of imperfect CSI, an iterative multiuser multicell transceiver design is formulated by minimizing the mean squared error (MSE) cost function of signal and leakage interference under per-base station power constraint (PBPC). The convergence of the iterative precoding and postcoding algorithm is verified by analytical and empirical results. The proposed precoding and postcoding algorithm offers a low computational complexity and robustness against CSI imperfection.

• 한국정보기술학회 영문논문지
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• 제9권2호
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• pp.1-14
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• 2019

This paper considers a multiple-input multiple-output (MIMO) power line communication (PLC) network where interference alignment (IA) technique is used to mitigate the interference that arises in multi-user networks. IA as a precoding technique requires perfect channel state information (CSI) to achieve maximum multiplexing gain. Due to the common-mode reception at the receiver ports, we assume imperfect CSI for the IA precoding design. Here, the CSI is quantized and sent via feedback to the transmit ports. For different levels of CSI quantization, we evaluate the performance of various IA algorithms via Monte Carlo simulations. Simulation results reveal the superior performance of the proposed scheme due to common-mode reception in IA MIMO PLC networks. It is shown that for a quantization level of 5 bits, the CM reception improves the sum-rate by up to 70%.

• Journal of Communications and Networks
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• 제18권2호
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• pp.210-217
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• 2016

In this paper, we propose a low complexity multiple-input multiple-output (MIMO) detection algorithm with adaptive interference mitigation in downlink multiuser MIMO (DL MU-MIMO) systems with quantization error of the channel state information (CSI) feedback. In DL MU-MIMO systems using the imperfect precoding matrix caused by quantization error of the CSI feedback, the station receives the desired signal as well as the residual interference signal. Therefore, a complexMIMO detection algorithm with interference mitigation is required for mitigating the residual interference. To reduce the computational complexity, we propose a MIMO detection algorithm with adaptive interference mitigation. The proposed algorithm adaptively mitigates the residual interference by using the maximum likelihood detection (MLD) error criterion (MEC). We derive a theoretical MEC by using the MLD error condition and a practical MEC by approximating the theoretical MEC. In conclusion, the proposed algorithm adaptively performs interference mitigation when satisfying the practical MEC. Simulation results show that the proposed algorithm reduces the computational complexity and has the same performance, compared to the generalized sphere decoder, which always performs interference mitigation.

• 한국통신학회논문지
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• 제35권9C호
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• pp.735-742
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• 2010

본 논문에서는 다수의 송신 안테나와 수신 안테나를 갖는 RF 중계기를 위한 적응 간섭제거 알고리즘을 제안한다. 중계기에서 다수의 안테나를 사용하는 경우 송신 안테나와 수신 안테나간의 불완전한 격리로 인해 간섭이 발생하고, 궤환 간섭 경로는 MIMO (multi-input multi-output) 채널로 모델링된다. 이런 궤환 간섭을 제거하기 위해 적응 신호처리 기법에 기반하여 LMS (least mean square) 간섭제거 알고리즘과 RLS (recursive least squares) 간섭제거 알고리즘을 유도한다. 모의 실험을 통해 제안된 간섭 제거 알고리즘의 수렴 특성 및 정상 상태에서의 간섭 제거 성능을 비교한다.

• 한국통신학회논문지
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• 제22권8호
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• pp.1632-1642
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• 1997

In this paper, we studied the effects of the power control imperfection on the system performances of a microcellular DS/CDMA system. The maximum user capacity, defined as the maximum number of users can be serviced simultaneouly, meeting a given voice quality, is first considered. Then the performence degradation due to the control error is analyzed. The frequency selective Raician channel model is used to characterize a microcellular mobile communication environment. The DS/CDMA system under consideration uses BPSK modulation and convolutional coding/Viterbe decoding with soft decision for forward error correction. It is shown that the user capacity falls linearly down with the increase of the power control error(in terms of the standard deviation in dB) and the interference from users outside the third tier cells have a minor effect on the performance. And the performance of DS/CDMA with the imperfect power control model is made to be less than 50% of that with perfect power control moded.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제15권6호
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• pp.2204-2224
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• 2021

This paper studies secure wireless transmission from a multi-antenna transmitter to a single-antenna intended receiver overheard by multiple eavesdroppers with considering the imperfect channel state information (CSI) of wiretap channel. To enhance security of communication link, the artificial noise (AN) is generated at transmitter. We first design the robust joint optimal beamforming of secret signal and AN to minimize transmit power with constraints of security quality of service (QoS), i.e., minimum allowable signal-to-interference-and-noise ratio (SINR) at receiver and maximum tolerable SINR at eavesdroppers. The formulated design problem is shown to be nonconvex and we transfer it into linear matrix inequalities (LMIs). The semidefinite relaxation (SDR) technique is used and the approximated method is proved to solve the original problem exactly. To verify the robustness and tightness of proposed beamforming, we also provide a method to calculate the worst-case SINR at eavesdroppers for a designed transmit scheme using semidefinite programming (SDP). Additionally, the secrecy rate maximization is explored for fixed total transmit power. To tackle the nonconvexity of original formulation, we develop an iterative approach employing sequential parametric convex approximation (SPCA). The simulation results illustrate that the proposed robust transmit schemes can effectively improve the transmit performance.