• KSII Transactions on Internet and Information Systems (TIIS)
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• 제14권11호
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• pp.4355-4371
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• 2020

Phase retrieval, recovering a signal from phaseless measurements, is generally considered to be an NP-hard problem. This paper adopts an amplitude-based nonconvex optimization cost function to develop a new stochastic gradient algorithm, named stochastic reweighted phase retrieval (SRPR). SRPR is a stochastic gradient iteration algorithm, which runs in two stages: First, we use a truncated sample stochastic variance reduction algorithm to initialize the objective function. The second stage is the gradient refinement stage, which uses continuous updating of the amplitude-based stochastic weighted gradient algorithm to improve the initial estimate. Because of the stochastic method, each iteration of the two stages of SRPR involves only one equation. Therefore, SRPR is simple, scalable, and fast. Compared with the state-of-the-art phase retrieval algorithm, simulation results show that SRPR has a faster convergence speed and fewer magnitude-only measurements required to reconstruct the signal, under the real- or complex- cases.

• 한국군사과학기술학회지
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• 제10권2호
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• pp.160-169
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• 2007

In this paper, we have described and simulated the effect analysis and correction of phase errors in the SAR rawdata induced by satellite attitude errors such as drift, jitter. This simulation is based on the FSA(Frequency Scaling Algorithm) for high resolution image formation of the Spotlight SAR. Phase errors produce the degradation of SAR image quality such as loss of resolution, geometric distortion, loss of contrast, spurious targets, and decrease in SNR. To resolve this problem, this paper presents method for correction of phase errors using the PGA(Phase Gradient Algorithm) in connection with the FSA. Several results of the phase errors correction are presented for Spotlight SAR rawdata.

• 한국음향학회:학술대회논문집
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• 한국음향학회 1987년도 학술발표회 논문집
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• pp.79-81
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• 1987

In this paper we propose a fast adaptive least squares algorithm for linear phase FIR filters. The algorithm requires 10m multiplications per data point where m is the filter order. Both linear phase cases with constant phase delay and constant group delay are examined. Simulation results demonstrate that the proeposed algorithm is superior to the LMS gradient algorithm and the averaging scheme used for the modified fast Kalman algorithm.

• 전자공학회논문지B
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• 제31B권9호
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• pp.27-35
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• 1994

It is known that a unified phase I-phase II semi-infinite optimization algorithm with a steerign parameter performs better than the original unified phase I-phase II algorithm. In this paper, the effect of the steering parameter is analized and a new algorithm is presented based on the facts that when the point x is far away from the feasible region, reaching to the feasible region is more important than minimizing the cost functio and that when the point x is near the region, it is more efficient to try to reach the feasible region and to minimize the cost function concurrently. It is also important to consider the relationship between the feasible direction and the gradient of the cost function. Even though changing the steering parameter does not change the rate of convergence of the algorithm, it is shown from examples that given new algorithm is more efficient than the previous ones.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1994년도 Proceedings of the Korea Automatic Control Conference, 9th (KACC) ; Taejeon, Korea; 17-20 Oct. 1994
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• pp.483-487
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• 1994

In this paper, we analize the effect of a steering water used in a unified phase I-phase II semi-infinite constrained optimization algorithm and present a new algorithm based on the facts that when the point x is far away from the feasible region where all the constraints are satisfied, reaching to the feasible region is more important than minimizing the cost function and that when the point x is near the region, it is more efficient to try to reach the feasible region and to minimize the cost function concurrently. Also, the angle between the search direction vector and the gradient of the cost function is considered when the steering parameter value is computed. Even though changing the steering parameter does not change the rate of convergence of the algorithm, we show through some examples that the proposed algorithm performs better than the other algorithms.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제18권7호
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• pp.2027-2046
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• 2024

Reconfigurable Intelligent Surface (RIS) is an innovative technique to precisely control the phase of incident signals with the help of low-cost passive reflective elements. It shows excellent potential in the sixth generation of mobile communication systems, which not only extends wireless coverage but also boosts channel capacity. Considering that multipath propagation and a high number of antennas are involved in RIS in assisted mega multiple-input multiple-output (MIMO) systems, it suffers from severe channel fading and multipath effects, which in turn lead to signal instability and degradation of transmission performance. To overcome this obstacle, this essay suggests an improved gradient optimization algorithm to dynamically and optimally adjust the phase of the reflective elements to counteract channel fading and multipath effects as a strategy. In order to overcome the optimization problem of falling into local minima, this paper proposes an adaptive learning rate algorithm based on Adagrad improvement, which searches for the global optimal solution more efficiently and improves the robustness of the optimization algorithm. The suggested technique helps to enhance the estimate of channel efficiency of RIS-assisted large MIMO systems, according to simulation results.

• 전자공학회논문지B
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• 제31B권7호
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• pp.179-189
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• 1994

A two-phase neural network finds exact feasible solutions for a constrained optimization programming problem. The time-varying programming neural network is a modified steepest-gradient algorithm which solves time-varying optimization problems. In this paper, we propose a time-varying two-phase optimization neural network which incorporates the merits of the two-phase neural network and the time-varying neural network. The proposed algorithm is applied to system identification and function approximation using a multi-layer perceptron. Particularly training of a multi-layer perceptrion is regarded as a time-varying optimization problem. Our algorithm can also be applied to the case where the weights are constrained. Simulation results prove the proposed algorithm is efficient for solving various optimization problems.

• 한국군사과학기술학회지
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• 제17권5호
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• pp.680-687
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• 2014

PGA(phase gradient autofocus) has been widely used to remove motion induced phase errors in the ISAR(inverse synthetic aperture radar) imaging. The critical process for the processing time and image quality is windowing stage in PGA. In this paper, the new method to determine window size based on polynomial least square approximation is proposed. Moreover, dominant range bins are selected for efficient phase error estimation, which improve image quality and speed up convergence. The simulation results show that the proposed algorithm provides high quality ISAR images while computational efficiency of inherent PGA is retained.

• 한국통신학회논문지
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• 제25권7A호
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• pp.978-985
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• 2000

블라인드 등화기는 학습신호를 이용하지 않고 저송된 데이터의 알려진 특성을 이용해 신호를 복원하며 일반적으로 가장 많이 이용되는 알고리즘은 구현이 간단한 Steepest Gradient Descent 계열의 알고리즘으로서 CMA나 Sato 알고리즘이 여기에 속한다. 본 논문에선, CMA 및 Normalized CMA (NCMA)의 장점과 이중모드 위상복원 알고리즘의 장점을 결합하는 이중모드 NCMA 알고리즘을 제안하고 QAM 시스템에 적용한 컴퓨터 시뮬레이션을 수행하여 제안한 알고리즘이 CMA와 이중모드 CMA 보다 더 빠른 수렴속도와 더 적은 정상상태 잔류에서 특성을 가짐을 확인하다.

• 한국광학회지
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• 제35권3호
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• pp.107-114
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• 2024

본 연구에서는 다채널 결맞음 빔결합 시스템에서 공분산 행렬 적응 진화 전략(covariance-matrix-adaptation-evolution-strategy, CMA-ES) 알고리즘의 구현 가능성을 실험적으로 확인하였다. 파장이 635 nm인 결맞음 광원과 함께 공간 광 변조기를 다채널 위상 변조기 배열로 활용하는 다채널 결맞음 빔결합 시스템을 구성하고, 확률적 병렬 경사 하강(stochastic parallel gradient descent, SPGD) 및 CMA-ES 알고리즘을 결맞음 빔결합 시스템에 적용하여 획득한 두 알고리즘의 동작 특성을 비교하였다. 사각 구조인 16채널 및 벌집 구조인 19채널 결맞음 빔결합 시스템에서 두 알고리즘의 동작 특성을 평가한 결과 두 알고리즘의 동작 특성은 주어진 조건에서 평균적으로 유사하였으나, CMA-ES 알고리즘이 SPGD 알고리즘에 비해 초기 위상값 설정에 따른 동작 특성 변동이 상대적으로 작아 보다 안정적으로 동작할 수 있음을 확인하였다. 본 연구는 저자가 아는 범위 내에서 CMA-ES 위상제어 알고리즘을 다채널 결맞음 빔결합 시스템에 적용한 최초의 원리증명 시연이며, 향후 CMA-ES 위상제어 알고리즘에 기반한 다채널 결맞음 시스템에서 채널 수 증가 혹은 외부 위상잡음 효과 등을 실험적으로 연구할 때 유용하게 활용될 수 있을 것으로 기대된다.