• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 추계종합학술대회 논문집(1)
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• pp.245-248
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• 2000

In this paper, we present the performance of a multi-code parallel combinatory CDMA system using bi-orthogonal modulation under multipath fading channel. In general, the dynamic range of the amplitude of the transmit signal is very large in conventional multi-code CDMA systems, resulting in severe nonlinear distortion due to high power amplifier and thus significant BER performance degradation. Since the number of simultaneously multiplexed code channels in the proposed system is reduced, the proposed system exhibits reduction of peak-to-average power ratio (PAPR) of the transmit signal amplitude with significant BER improvement. We verify the performance of the proposed system by computer simulations under the Vehicular B multipath fading channel model by ARIB.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권9호
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• pp.2191-2201
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• 2012

Traffic classification seeks to assign packet flows to an appropriate quality of service (QoS) class based on flow statistics without the need to examine packet payloads. Classification proceeds in two steps. Classification rules are first built by analyzing traffic traces, and then the classification rules are evaluated using test data. In this paper, we use self-organizing map and K-means clustering as unsupervised machine learning methods to identify the inherent classes in traffic traces. Three clusters were discovered, corresponding to transactional, bulk data transfer, and interactive applications. The K-nearest neighbor classifier was found to be highly accurate for the traffic data and significantly better compared to a minimum mean distance classifier.

• 전기전자학회논문지
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• 제22권4호
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• pp.1019-1024
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• 2018

In this paper, we suggest a combined cost function to find out the optimal operation of an envelope tracking system, and evaluated its performance with Quadrature Amplitude Modulation (QAM) waveform, with which envelope tracking coefficients for the peak drain efficiency and the bandwidth of power amplifiers are determined. Based on the classical envelope tracking theory, the operation of the supply modulator, which is a key part of the envelope tracking process, is modeled and analyzed mathematically. Then characteristics of the modulator by setting envelope shaping function as a cubic polynomial and sweeping the coefficients of this function was analyzed. By sweeping the coefficients, efficiency and bandwidth at each condition with 64-QAM signal was used to obtain optimal point of the supply modulator. Compared to the conventional shaping functions, the optimized function showed the bandwidth reduction by 12.7 percent point while the efficiency was maintained.

• 한국항행학회논문지
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• 제10권1호
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• pp.20-25
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• 2006

현재 OFDM(Orthogonal Frequency Division Multiplexing)은 다중경로 채널 환경에서 고속 통신에 적합한 방식으로 각광을 받고 있으나, 몇 가지 단점을 지니고 있다. 단일 반송파 방식에 비해 PAR(Peak-to-Average power Ratio)이 높다는 점은 그러한 단점 가운데 하나이다. 신호의 PAR이 높을 경우 고출력 증폭기를 통과하면서 비선형 왜곡이 발생할 수 있고, 이를 방지하기 위해서는 고출력 증폭기의 선형 구간을 비효율적으로 증가시켜야 하는 문제가 발생한다. 본 논문에서는 OFDM의 PAR 감소 기법중 하나의 OFDM 심벌을 나타내는 다수의 신호를 발생(Mapping)시킨 후, 그 중 가장 낮은 PAR을 갖는 신호를 선택해서 전송하는 SLM(Selected Mapping) 기법에 대한 성능을 분석한다.