• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권6호
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• pp.1926-1945
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• 2014

In this paper, we propose a distributed signal subspace interference alignment algorithm for single beam K-user ($3K{\geq}$) MIMO interference channel based on sum rate maximization and game theory. A framework of game theory is provided to study relationship between interference signal subspace and altruistic-egoistic bayesian game cost function. We demonstrate that the asymptotic interference alignment under proposed scheme can be realized through a numerical algorithm using local channel state information at transmitters and receivers. Simulation results show that the proposed scheme can achieve the total degrees of freedom that is equivalent to the Cadambe-Jafar interference alignment algorithms with perfect channel state information. Furthermore, proposed scheme can effectively minimize leakage interference in desired signal subspace at each receiver and obtain a moderate average sum rate performance compared with several existing interference alignment schemes.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권9호
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• pp.4295-4316
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• 2018

In this paper, the performance of non-orthogonal multiple access (NOMA) dual-hop (DH) amplify-and-forward (AF) relaying networks is investigated, where Nakagami-m fading channel is considered. In order to cover more details, in our analysis, the transceiver hardware impairments at source, relay and destination nodes are comprehensively considered. To characterize the effects of hardware impairments brought in NOMA DH AF relaying networks, the analytical closed-form expressions for the exact outage probability and approximate ergodic sum rate are derived. In addition, the asymptotic analysis of the outage probability and ergodic sum rate at high signal-to-noise ratio (SNR) regime are carried out in order to further reveal the insights of the parameters for hardware impairments on the network performance. Simulation results indicate the performance of asymptotic ergodic sum rate are limited by levels of distortion noise.

• 한국통신학회논문지
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• 제40권7호
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• pp.1257-1265
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• 2015

본 논문은 투영 행렬을 이용한 높은 채널 용량을 획득할 수 있는 사용자 선택 기법을 제안한다. 기존의 Frobenius norm기반의 사용자 선택 기법이 다수의 사용자를 선택할수록 정확도가 감소하는 점을 투영 행렬의 근사화 형태를 이용하여 개선하였다. Flop count를 이용한 제안 기준의 계산복잡도를 분석하였고, 모의 실험을 통하여 안테나 구성에 따른 획득 가능한 채널 용량에 대해서 비교하였다. 모의 실험 결과를 통해 제안한 사용자 선택 기법이 더 높은 채널 용량을 획득하는 것을 확인하였다.

• 한국통신학회논문지
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• 제36권4A호
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• pp.318-324
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• 2011

본 논문에서는 두 셀 대칭적 간섭 채널 환경에서 세 가지 방식의 협력적 불규칙 빔형성 방법을 분석한다. 먼저, 기지국 선택을 통한 간단한 형태의 부분 협력 빔형성 방법은 연계적 인코딩을 적용한 불규칙 빔형성 방법과 동일한 평균 합 전송률을 갖는다는 것을 증명한다. 또한, 전송 모드 선택 방법을 적용하는 경우에 시스템의 사용자가 많을 때에 부가적인 합 전송율의 이득이 발생하는 것을 증명하였다. 모의 실험 결과를 통해서 성능에 대한 분석이 유효함과 정확성을 확인하였다.

• 한국통신학회논문지
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• 제37A권9호
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• pp.753-761
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• 2012

이 논문에서 우리는 Tomlinson-Harashima precoding (THP)를 이용한 다중 입력 단일 출력 다중 사용자 하향링크 시스템을 위한 전력할당 기법에 대해 알아본다. Zero-forcing THP 시스템의 sum rate를 최대화하기 위해 우리는 이전 방법과는 달리 mutual information 방법을 적용하였다. 나아가서, 모듈로 오퍼레이션을 사용하는 유저에 적절한 전력 레벨을 할당하기 위해 간단한 전력 할당 알고리즘을 제안한다. 실험 결과는 제안된 기법이 기존의 water-filling 기법보다 성능이 우수하고, 시스템의 최적의 성능을 내는 기법과 성능은 유사하면서 보다 작은 복잡도로 이루는 것을 보여준다.

• 한국환경과학회지
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• 제17권10호
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• pp.1069-1073
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• 2008

Indoor air quality can be affected by indoor sources, ventilation, decay and outdoor levels. Although technologies exist to measure these factors, direct measurements are often difficult. The purpose of this study was to develop an alternative method to characterize indoor environmental factors by multiple indoor and outdoor measurements. Using a mass balance model and regression analysis, penetration factor (ventilation rate divided by the sum of ventilation rate and deposition constant) and source strength factor (source strength divided by the sum of ventilation rate and deposition constant) were calculated using multiple indoor and outdoor measurements. Subsequently, the ventilation rate and $NO_2$ generation rate were estimated. Mean of ventilation rate was 1.41 ACH in houses, assuming a residential N02 deposition constant of 0.94 $hr^{-1}$. Mean generation rate of $NO_2$ was 16.5 ppbv/hr. According to house characterization, inside smoking and family number were higher $NO_2$ generation rates, and apartment was higher than single-family house. In conclusion, indoor environmental factors were effectively characterized by this method using multiple indoor and outdoor measurements.

• Journal of Communications and Networks
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• 제14권2호
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• pp.151-161
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• 2012

This paper considers a two-user Gaussian interference channel with energy harvesting transmitters. Different than conventional battery powered wireless nodes, energy harvesting transmitters have to adapt transmission to availability of energy at a particular instant. In this setting, the optimal power allocation problem to maximize the sum throughput with a given deadline is formulated. The convergence of the proposed iterative coordinate descent method for the problem is proved and the short-term throughput maximizing offline power allocation policy is found. Examples for interference regions with known sum capacities are given with directional water-filling interpretations. Next, stochastic data arrivals are addressed. Finally, online and/or distributed near-optimal policies are proposed. Performance of the proposed algorithms are demonstrated through simulations.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권4호
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• pp.1594-1617
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• 2018

In this paper, we consider a spectrum access scenario which consists of two groups of users, namely Primary Users (PUs) and Secondary Users (SUs) in Cooperative Cognitive Radio Networks (CCRNs). SUs cooperatively relay PUs messages based on Amplify-and-Forward (AF) and Decode-and-Forward (DF) cooperative techniques, in exchange for accessing some of the spectrum for their secondary communications. From the literatures, we found that the Conventional Distributed Algorithm (CDA) and Pragmatic Distributed Algorithm (PDA) aim to maximize the PU sum-rate resulting in a lower sum-rate for the SU. In this contribution, we have investigated a suit of distributed matching algorithms. More specifically, we investigated SU-based CDA (CDA-SU) and SU-based PDA (PDA-SU) that maximize the SU sum-rate. We have also proposed the All User-based PDA (PDA-ALL), for maximizing the sum-rates of both PU and SU groups. A comparative study of CDA, PDA, CDA-SU, PDA-SU and PDA-ALL is conducted, and the strength of each scheme is highlighted. Different schemes may be suitable for different applications. All schemes are investigated under the idealistic scenario involving perfect coding and perfect modulation, as well as under practical scenario involving actual coding and actual modulation. Explicitly, our practical scenario considers the adaptive coded modulation based DF schemes for transmission flexibility and efficiency. More specifically, we have considered the Self-Concatenated Convolutional Code (SECCC), which exhibits low complexity, since it invokes only a single encoder and a single decoder. Furthermore, puncturing has been employed for enhancing the bandwidth efficiency of SECCC. As another enhancement, physical layer security has been applied to our system by introducing a unique Advanced Encryption Standard (AES) based puncturing to our SECCC scheme.

• 한국통신학회논문지
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• 제36권4A호
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• pp.414-422
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• 2011

모바일 WiMAX 표준 IEEE 802.16e의 블록길이 2,304 비트, 부호율 1/2을 지원하는 LDPC(low-density parity-check) 복호기를 설계하였다. 설계된 LDPC 복호기는 최소-합(min-sum) 알고리듬과 layered 복호를 기반으로 $96{\times}96$ 크기의 부행렬을 병렬로 처리하는 부분병렬 구조를 갖는다. 최소-합 알고리듬의 특징을 이용하여 메모리 용량을 감소시킬 수 있는 새로운 방법을 고안하여 적용함으로써 검사노드 메모리 용량을 기존의 방법보다 46% 감소시켰다. Verilog HDL로 설계된 LDPC 복호기를 $0.18{\mu}m$ CMOS 셀 라이브러리로 합성한 결과 174,181개의 게이트와 52,992 비프의 메모리로 구현되었으며, Eb/No=2.1dB의 AWGN 채널에 대해 평균 비트 오율 (BER)는 $4.34{\times}10^{-5}$이고, 100 MHz@1.8-V로 동작하여 약 417 Mbps의 성능을 갖는다.

• Journal of Positioning, Navigation, and Timing
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• 제7권2호
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• pp.53-59
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• 2018

This paper proposes a pseudo-random beamforming technique for time-synchronized mobile base stations (BSs) for multi-cell downlink networks which have mobility. The base stations equipped with multi-antennas and mobile stations (MSs) are time-synchronized based on global positioning system (GPS) signals and generate a number of transmit beamforming matrix candidates according to the predetermined pseudo-random pattern. In addition, MSs generate receive beamforming vectors that correspond to the beam index number based on the minimum mean square error (MMSE) using transmit beamforming vectors that make up a number of transmit beamforming matrices and wireless channel matrices from BSs estimated via the reference signals (RS). Afterward, values of received signal-to-interference-plus-noise ratio (SINR) with regard to all transmit beamforming vectors are calculated, and the resulting values are then feedbacked to the BS of the same cells along with the beam index number. Each of the BSs calculates each of the sum-rates of the transmit beamforming matrix candidates based on the feedback information and then transmits the calculated results to the BS coordinator. After this, optimum transmit beamforming matrices, which can maximize a sum-rate of the entire cells, are selected at the BS coordinator and informed to the BSs. Finally, data signals are transmitted using them. The simulation results verified that a sum-rate of the entire cells was improved as the number of transmit beamforming matrix candidates increased. It was also found that if the received SINR values and beam index numbers are feedbacked opportunistically from each of the MSs to the BSs, not only nearly the same performance in sum-rate with that of applying existing feedback techniques could be achieved but also an amount of feedback was significantly reduced.