• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권4호
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• pp.1292-1306
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• 2014

This paper proposes a space-polarization division multiple access (SPDMA) system that has limited feedback channels. The system simultaneously serves data streams to multiple mobile users through dual-polarized antenna arrays, by using pre-determined sets of precoding vectors that are orthogonal in both space and polarization domains. To this end, a codebook whose elements are sets of the precoding vectors is systematically designed based on the discrete Fourier transform (DFT) matrix and considering the power imbalance of polarized channels. Throughput of the SPDMA system is evaluated and compared to that of space division multiple access (SDMA) system, according to the various parameters including cross polarization discrimination (XPD). The results show that the throughput of SPDMA system outperforms that of SDMA in the environments of high XPD with many mobile users.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2008년도 하계학술대회 논문집
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• pp.91-93
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• 2008

In this paper, novel phase angle following algorithm for the single phase grid-connected inverter is proposed. Gird-connected inverter needs phase angle detection for synchronization grid voltage with the inverter output. In case of single phase grid-connected inverter, zero crossing detection and virtual 2-phase PLL using digital all pass filter or digital low pass filter are used conventionally. But these methods have a weakness for harmonics, noises and ripples. The proposed method of PLL achieve DFT(Discrete Fourier Transform) using Goertzel algorithm. It can extract fundamental voltage of grid. As a results, it can obtain phase angle using digital all pass filter without effect of harmonics, noises and ripples. Simulation results are presented to demonstrate the effectiveness of the proposed algorithm.

• 한국전자파학회논문지
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• 제29권3호
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• pp.192-199
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• 2018

본 논문은 기존 DFT-s-SSB(Discrete Fourier Transform spread Single Sideband) OFDM(Orthogonal Frequency Division Multiplexing) 시스템이 가지는 문제점을 해결하는 개선된 DFT-s-SSB OFDM 시스템을 제안한다. 기존 DFT-s-SSB 시스템은 SSB 변조를 적용하기 위하여 PAM(Pulse Amplitude Modulation) 변조를 사용한다. 때문에 변조레벨이 높아질수록 BER(Bit Error Rate) 성능열화가 심각해진다. 그리고 오직 LSB(Lower Sideband) 스펙트럼을 통해서만 송신이 가능하며 LSB와 USB(Upper Sideband) 스펙트럼을 동시에 사용하여 송신하는 경우, 간섭이 발생하고 스펙트럼 복구가 올바르게 이루어지지 않는다. 제안하는 시스템은 이러한 문제를 해결하기 위해 2/3 convolution coding을 적용하여 BER 성능을 개선하고 DFT 크기를 조절하고 USB 스펙트럼을 선택하는 방법을 제시하여 남은 스펙트럼 자원을 이용할 수 있도록 한다. 또한 다중사용자를 지원하는 환경 혹은 제한적인 대역폭을 갖는 환경에서 이 시스템을 이용하는 경우 스펙트럼을 절반만 사용하기 때문에 남은 스펙트럼 자원을 이용할 수 있고 스펙트럼 효율을 향상시킬 수 있다.

• 대한전기학회논문지:전력기술부문A
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• 제54권6호
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• pp.293-305
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• 2005

This paper describes an improved Prony method in its speed, accuracy and reliability by efficiently determining the optimal sampling interval with use of DFT (discrete Fourier transformation). In the Prony method the computation time is dominated by the size of the linear prediction matrix, which is given by the number of data times the modeling order The size of the matrix in a general Prony method becomes large because of large number of data and so does the computation time. It is found that the Prony method produces satisfactory results when SNR is greater than three. The maximum sampling interval resulting minimum computation time is determined using the fact that the spectrum in DFT is inversely proportional to sampling interval. Also the process of computing the modes is made efficient by applying Hessenberg method to the companion matrix with complex shift and computing selectively only the dominant modes of interest. The proposed method is tested against the 2003 KEPCO system and found to be efficient and reliable. The proposed method may play a key role in monitoring in real time low frequency oscillations of power systems .

• 대한전자공학회논문지
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• 제26권10호
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• pp.1617-1623
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• 1989

The introduction of the fast Fourier transform(FFT),an efficient computational algorithm for the discrete Fourier transform(DFT) by Cooley and Tukey(1965), has brought to the limelight various other discrete transforms. Some of the analog functions from which these transforms have been derived date back to the early 1920's, for example, Walsh functions (Walsh, 1923) and Hadamard Transform(Enomoto et al, 1965). Fast algorithms developed for the forward transform are equally applicable, exept for minor changes, to the inverse transform. In this paper, we present a simple pipelined Hadamard matrix(HM) which is used to develop a fast algorithm for the Hadamard Processor (HP). The Fast Hadamard Transform(FHT) can be derived using matrix partitioning techniques. The HP system is incorporated through a modular design which permits tailoring to meet a wide range of video data link applications. Emphasis has been placed on a low cost, a low power design suitable for airbone system and video codec.

• Journal of applied mathematics & informatics
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• 제22권1_2호
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• pp.159-167
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• 2006

The transform domain characterization of cyclic codes over finite fields using Discrete Fourier Transform(DFT) over an appropriate extension field is well known. In this paper, we extend this transform domain characterization for cyclic codes over $F_p + uF_p +... + u^{k-l}F_p$. We give a way to characterize cyclic codes over $F_p + uF_p +... + u^{k-l}F_p$ by Mattson-Solomon polynomials and multiple defining sets.

• 전력전자학회논문지
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• 제17권2호
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• pp.93-98
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• 2012

A precise measurement of the grid voltage is one of the essential techniques, which is required to connect a renewable energy to the grid. In general, when a filter is used to eliminate unnecessary harmonics and noises, a signal is distorted by phase delay, amplitude attenuation, and other distortions. And the response characteristic of a controller is directly affected by bandwidth of cut-off frequency of the filter. To alleviate this problems, we propose an effective algorithm based on DFT(Discrete Fourier Transform) instead of approaching the filter application. The proposed algorithm ensures high precise measurement of the grid voltage because it can extract the fundamental and harmonics from the raw signal without any distortions. The high performance of the proposed algorithm is verified by PSIM simulation and experiments of Grid-Connected VSI.

• ETRI Journal
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• 제46권3호
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• pp.392-403
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• 2024

Even though generalized frequency division multiplexing is an alternative waveform method expected to replace the orthogonal frequency division multiplexing in the future, its implementation must alleviate channel effects. Least-squares (LS), a low-complexity channel estimation technique, could be improved by using the discrete Fourier transform (DFT) without increasing complexity. Unlike the usage of the LS method, the DFT-based method requires the receiver to know the channel impulse response (CIR) length, which is unknown. This study introduces a simple, yet effective, CIR length estimator by utilizing LS estimation. As the cyclic prefix (CP) length is commonly set to be longer than the CIR length, it is possible to search through the first samples if CP is larger than a threshold set using the remaining samples. An adaptive scale is also designed to lower the error probability of the estimation, and a simple signal-to-interference-noise ratio estimation is also proposed by utilizing a sparse preamble to support the use of the scale. A software simulation is used to show the ability of the proposed system to estimate the CIR length. Due to shorter CIR length of rural area, the performance is slightly poorer compared to urban environment. Nevertheless, satisfactory performance is shown for both environments.

• 전자공학회논문지B
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• 제30B권9호
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• pp.18-26
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• 1993

This paper presents a multiplier free technique for the complex DFT by rotations and additions based on the complex approximation of the ring of algebraic integers. Speeding-up the computation time and reducing the dynamic range growth has been achieved by the elimination of multiplication. Moreover the DFT of no twiddle factor quantization errors is possible. Numerical examples are given to prove the algorithm and the applicable size of the DFT is 16 has been concluded.

• 전기학회논문지
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• 제61권4호
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• pp.542-548
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• 2012

This study presents a new method of system modeling by using the Discrete Fourier Transform for the position control system of DC Motor. And the proposed method is similar to the method of System Identification by analysis of correlation of the measured input-output data. The measured output signals are transformed to the frequency domain using DFT. The Fourier Spectrum of the transformed signals is used for knowing to the feature of having an important effect on the system. And transfer function of the second order system is estimated by the dominant parameter which is computed in the magnitude and the phase of Fourier spectrum of the transformed signals. In addition, the output signal includes the unique feature of system. So, although the basic parameter of the system is unknown for us, the proposed method has an advantage to system modeling. And the controller is easily designed by the estimated transfer function. Thus, in this paper, the proposed method is applied to the system modeling for the position control system of DC Motor and the PD-controller is designed by the estimated model. And the efficiency and the reliability of the proposed method are verified by the experimental result.