• 한국통신학회논문지
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• 제39A권7호
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• pp.398-400
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• 2014

In this letter, we propose a cross-layer technique jointly considering modulation coding schemes (MCSs) of medium access control (MAC) layer, source significance information (SSI) and error concealment unit of application (APP) layer, and channel quality information (CQI) of physical (PHY) layer. We demonstrate the improved video quality by the proposed technique when H.264 videos are streamed over Rayleigh fading wireless channels.

• 전자공학회논문지
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• 제49권12호
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• pp.10-19
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• 2012

본 논문에서는 AMC(Adaptive Modulation and Coding) 기법을 적용한 릴레이 프로토콜을 제안한다. AMC 기법은 다양한 변조와 코딩 기법을 통해, 통신 시스템의 전송률과 신뢰도를 향상시킬 수 있다. 본 논문에서는 AMC 기법을 적용한 릴레이 프로토콜의 성능을 분석하고, AMC 기법이 적용된 릴레이 프로토콜이 AMC 기법이 적용되지 않은 기존의 기법과 비교하여 낮은 SNR(Signal to Noise Ratio) 레벨에서 더 좋은 평균 전송률을 제공할 수 있음을 확인하였다. 비적응적 MCS(Modulation and Coding Scheme) 릴레이 프로토콜과 적응적 MCS 릴레이 프로토콜의 성능을 증명하기 위해 LTE-A(Long Term Evolution-Advanced) 파라미터와 함께 몬테카를로 시뮬레이션을 수행하였다. 모의실험 결과, 적응적 MCS가 적용된 시스템에서 AF(Amplify-and-Forward), DF(Decode-and-Forward) 및 DMF(DeModulate-and-Forward) 프로토콜 중 DMF 프로토콜이 낮은 SNR 값에서 가장 좋은 성능을 보이고, 더 좋은 평균 전송률을 제공하는 것을 확인하였다.

• 인터넷정보학회논문지
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• 제4권5호
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• pp.1-9
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• 2003

본 논문에서는 CDMA 시스템에서 적응 변조 및 부호화 (AMC) 기법의 성능을 향상시키기 위한 방안으로서 기지국과 단말기 간에 개루프 및 폐루프 전송 다이버시티를 적용하였다. 이는 전송 다이버시티를 적용하여 수신 단의 신호 대 잡음비 (SNR)를 개선함으로써, 보다 높은 전송률을 지원하는 변조 및 부호화 레벨이 선택될 확률을 증가시키고 이에 따른 평균 전송률의 이득을 얻고자 하는 것이다. 개루프 전송 다이버시티로는 시공간 블록 부호화 기반 전송 다이버시티 (STTD) 기법을, 폐루프 전송 다이버시티로는 선택적 전송 다이버시티 (STD) 기법을 적용하였다. 모의 실험 결과, AMC 기법과 전송 다이버시티를 결합함으로써 기존 시스템에 비하여 향상된 전송률을 얻을 수 있었다. 단일 경로 레일리 페이딩 채널 환경에서 두 개의 전송 안테나를 사용한 AMC-STTD는 9dB신호 대 잡음비에 대하여 기존의 AMC 기법보다 약 250kbps의 전송률 이득을 보였다. 또한 두 개의 전송 안테나를 사용한 AMC-STD의 경우는 역시 9dB 신호 대 잡음비에서 약 420kbps의 전송률 이득이 얻어짐을 확인하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 심포지엄 논문집 정보 및 제어부문
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• pp.163-165
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• 2008

In this paper we compare performance of exponential effective SINR mapping (EESM) with traditional actual value interface (AVI) approach for various modulation and coding schemes (MCS) in terms of coded bit error rate (BER) or block error rate (BLER) using different transmission schemes. This paper provides explanation and comparison of the two algorithms for single input single output (SISO), and single input multi-output (SIMO, 1X2) in OFDM systems. We calibrate the value of beta ($\beta$) in EESM using large number of channel realizations, here $\beta$ is a calibration constant. This paper also presents importance of beta value in EESM and how it improves the performance of OFDM wireless systems. We propose different modulation and coding schemes. Here we consider Standford university interim (SUI) channel models. Furthermore this paper also shows the detail observation of the two algorithms. Finally the conclusion review given for short summary.

• Journal of Information Processing Systems
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• 제16권5호
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• pp.1048-1063
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• 2020

In this study, we propose a reinforcement learning agent to control the data transmission rates of nodes in carrier sensing multiple access with collision avoidance (CSMA/CA)-based wireless networks. We design a reinforcement learning (RL) agent, based on Q-learning. The agent learns the environment using the timeout events of packets, which are locally available in data sending nodes. The agent selects actions to control the data transmission rates of nodes that adjust the modulation and coding scheme (MCS) levels of the data packets to utilize the available bandwidth in dynamically changing channel conditions effectively. We use the ns3-gym framework to simulate RL and investigate the effects of the parameters of Q-learning on the performance of the RL agent. The simulation results indicate that the proposed RL agent adequately adjusts the MCS levels according to the changes in the network, and achieves a high throughput comparable to those of the existing data transmission rate adaptation schemes such as Minstrel.

• Journal of Computing Science and Engineering
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• 제7권3호
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• pp.168-176
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• 2013

Long-term evolution (LTE) is emerging as a major candidate for 4G cellular networks to satisfy the increasing demands for mobile broadband services, particularly multimedia delivery. Multiple-input multiple-output (MIMO) technology combined with orthogonal frequency division multiple access and more efficient modulation/coding schemes (MCS) are key physical layer technologies in LTE networks. However, in order to fully utilize the benefits of the advances in physical layer technologies, the MIMO configuration and MCS need to be dynamically adjusted to derive the promised gains of 4G at the application level. This paper provides a performance evaluation of video traffic with variations in the physical layer transmission parameters to suit the varying channel conditions. A quantitative analysis is provided using the perceived video quality as a video quality measure (evaluated using no-reference blocking and blurring metrics), as well as transmission delay. Experiments are performed to measure the performance with changes in modulation and code rates in poor and good channel conditions. We discuss how an adaptive scheme can optimize the performance over a varying channel.

• Journal of Communications and Networks
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• 제18권3호
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• pp.420-428
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• 2016

In this paper, we investigate the scheduling and power allocation for coordinated multi-point transmission in downlink long term evolution advanced (LTE-A) systems, where orthogonal frequency division multiple-access is used. The proposed scheme jointly optimizes user selection, power allocation, and modulation and coding scheme (MCS) selection to maximize the weighted sum throughput with fairness consideration. Considering practical constraints in LTE-A systems, the MCSs for the resource blocks assigned to the same user need to be the same. Since the optimization problem is a combinatorial and non-convex one with high complexity, a low-complexity algorithm is proposed by separating the user selection and power allocation into two subproblems. To further simplify the optimization problem for power allocation, the instantaneous signal-to-interference-plus-noise ratio (SINR) and the average SINR are adopted to allocate power in a single cell and multiple coordinated cells, respectively. Simulation results show that the proposed scheme can improve the average system throughput and the cell-edge user throughput significantly compared with the existing schemes with limited feedback.

• Journal of Communications and Networks
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• 제15권6호
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• pp.589-600
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• 2013

In this paper, we propose a new feedback scheme called mode selection-based feedback by scheduling probability prediction (SPP-MF) for channel state feedback in OFDMA downlink system. We design the scheme such that it determines the more desirable feedback mode among selective feedback by scheduling probability prediction (SPP-SF) mode and bitmap feedback by scheduling probability prediction (SPP-BF) mode, by calculating and comparing the throughputs of the two modes. In both feedback modes, each user first calculates the scheduling probability of each subchannel (i.e., the probability that a user wins the scheduling competition for a subchannel) and then forms a feedback message based on the scheduling probability. Specifically, in the SPP-SF mode, each user reports the modulation and coding scheme (MCS) levels and indices of its best S subchannels in terms of the scheduling probability. In the SPP-BF mode, each user determines its scheduling probability threshold. Then, it forms a bitmap for the subchannels according to the scheduling probability threshold and sends the bitmap along with the threshold. Numerical results reveal that the proposed SPP-MF scheme achieves significant performance gain over the existing feedback schemes.