• 한국음향학회지
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• 제39권6호
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• pp.585-591
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• 2020

적응형 전송 기법은 수중 음향 채널의 상태에 따라 전송 파라미터를 변경하여 전송 및 성능을 향상 시키는 효율적인 방법이다. 본 논문에서는 적응형 전송 기법에서 전송 모드를 결정하기 위한 네 가지 모드와 이의 모드를 검출하기 위한 세 가지 임계값 검출 알고리즘을 제안한다. 송신기에서 정보비트의 크기를 자유롭게 설정하기 위하여 컴볼루션 부호를 사용하였으며, 수신기에서는 성능을 향상시키기 위하여 BCJR 복호 기반 터보등화기법을 적용하였다. 또한 수중 실험을 통해 각 모드에서 성능을 만족하는 임계값 간의 관계를 분석하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권3호
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• pp.1700-1721
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• 2017

The problem of blocking artifacts is very common in block-based image and video compression, especially at very low bit rates. In this paper, we propose a post-processing method for JPEG-coded image deblocking via sparse representation and adaptive residual threshold. This method includes three steps. First, we obtain the dictionary by online dictionary learning and the compressed images. The dictionary is then modified by the histogram of oriented gradient (HOG) feature descriptor and K-means cluster. Second, an adaptive residual threshold for orthogonal matching pursuit (OMP) is proposed and used for sparse coding by combining blind image blocking assessment. At last, to take advantage of human visual system (HVS), the edge regions of the obtained deblocked image can be further modified by the edge regions of the compressed image. The experimental results show that our proposed method can keep the image more texture and edge information while reducing the image blocking artifacts.

• 한국군사과학기술학회지
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• 제20권2호
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• pp.187-196
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• 2017

The size of raw data has dramatically increased due to the recent trend of Synthetic Aperture Radar(SAR) development plans for high resolution and high definition image acquisition. The large raw data has an impact on satellite operability due to the limitations of storage and transmission capacity. To improve the SAR operability, the SAR raw data shall be compressed before transmission to the ground station. The Block Adaptive Quantization (BAQ) algorithm is one of the data compression algorithm and has been used for a long time in the spaceborne SAR system. In this paper, an optimization method of BAQ threshold table is introduced using real SAR raw data to prevent the degradation of signal quality caused by data compression. In this manner, a new variation estimation strategy and a new threshold method for block type decision are introduced.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 1999년도 추계종합학술대회 논문집
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• pp.495-498
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• 1999

In this paper, we propose the adaptive Odd/Even Multi-shell Median Filter(adaptive O/E MMF) to improve the defect that Modified Multi-shell Median Filter(MMMF) can not recover missing lines of vertical and cross direction. This filter uses odd/even multi-shells and new proposed threshold strategy The performance of the proposed filter is evaluated over image 'airfield 'by using MATLAB. As the proposed threshold strategy eliminate the number of redundant replacement, it suppresses impulse noise and recovers missing lines.

• 한국통신학회논문지
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• 제22권4호
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• pp.748-760
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• 1997

The handoff failure probability has to be enhanced efficiently to enhance the performance of PCS system. In this paper a new scheme called velocity adaptive handoff algorithm for reducing handoff failure probability and maintaining the carried traffic constantly in PCS systems, by assigning low handoff threshold value for high mobility calls, and assigning high handoff threshold value for low mobility calls, is presented. The performance of evaluation of this new scheme is carried out in terms of tranffic characteristics. Also velocity estimation algorithm for this new scheme is presented. According to the result, the handoff failure probability of velocity adaptive handoff algorithm is enhanced about 60%.

• 한국음향학회지
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• 제18권7호
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• pp.45-55
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• 1999

본 논문에서는 그레인 잡음을 제거하기 위해서 웨이브렛 변환(wavelet transform)에 근간을 둔 웨이브렛 적응 필터(WLMS adaptive filter : Wavelet domain Least Mean Square adaptive filter)를 사용하였다. 보통 그레인 잡음은 고온의 환경에서 금속의 결정구조가 변화함에 따라 발생된다. 웨이브렛 평면에서의 적응 필터링은 필터의 입력신호를 직교 변환하여 입력으로 이용함으로써 수렴 속도를 향상시킬 수 있는 장점을 가지고 있다. 적응 필터의 기준 입력 신호는 원시 입력 신호를 지연시킨 신호를 이용하였으며, 적응 필터의 출력은 다시 CA-CFAR(Cell Average - Constant False Alarm Rate) 임계 추정기(threshold estimator)를 거쳐 자동적으로 원하는 신호부분만 나타내도록 하였다. 우선 신호의 통계적 특성을 알기 위하여 run 테스트를 수행하여 기준 입력 신호가 비정상성(nonstationarity)을 나타냄을 보였고, 웨이브렛 적응필터가 시평면 적응필터보다 수렴속도면에서 우수함을 보였으며, 각 적응 필터의 출력신호에 대해서 신호대 잡음비를 통해 성능평가를 하였다. 시평면 적응 필터링 후에는 신호대 잡음비가 2-3㏈ 향상을 보였고, 반면 웨이브렛 적응 필터링후에는 신호대 잡음비가 4-6㏈ 향상을 보였다.

• Journal of Positioning, Navigation, and Timing
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• 제7권1호
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• pp.25-35
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• 2018

This paper describes the measurement of pulse positioning (input time) to calculate a time of arrival (TOA) that takes from transmitting a signal from the target of multilateration (MLAT) system to receiving the signal at the receiver. In this regard, this paper analyzes performances of simple threshold method and level adjust system (LAS) method, which is one of the adaptive threshold detector (ATD) methods, among many methods to calculate pulse positioning of signal received at the receiver. To this end, Cramer-rao lower bound (CRLB) with regard to pulse positioning, which was measured when signals transmitted from a transponder mounted at the target were received at the receiver, was induced and then deviation sizes with regard to pulse positioning, which was measured with simple threshold and LAS methods through MATLAB simulations, were compared. Next, problems occurring according to a difference in amplitude of signals inputted to each receiver are described when pulse positioning is measured at multiple receivers located at a different distance from the target as is the case in the MLAT system. Furthermore, LAS method to resolve the problems is explained. Lastly, this study analyzes whether a pulse positioning error occurring due to the signal noise satisfies the requirement (6 nsec. or lower) recommended for the MLAT system when using these two methods.

• International Journal of Internet, Broadcasting and Communication
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• 제11권1호
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• pp.39-46
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• 2019

This paper proposes an adaptive threshold watershed algorithm, which is the method used for image segmentation and boundary detection, which extends the region on the basis of regional minimum point. First, apply adaptive thresholds to determine regional minimum points. Second, it extends the region by applying adaptive thresholds based on determined regional minimum points. Traditional watershed algorithms create over-segmentation, resulting in the disadvantages of breaking boundaries between regions. These segmentation results mainly from the boundary of the object, creating an inaccurate region. To solve these problems, this paper applies an improved watershed algorithm applied with adaptive threshold in regional minimum point search and region expansion in order to reduce over-segmentation and breaking the boundary of region. This resulted in over-segmentation suppression and the result of having the boundary of precisely divided regions. The experimental results show that the proposed algorithm can apply adaptive thresholds to reduce the number of segmented regions and see that the segmented boundary parts are correct.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권7호
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• pp.3095-3111
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• 2018

Spectrum sensing (SS) is one of the fundamental tasks for cognitive radio. In SS, decisions can be made via comparing the test statistics with a threshold. Conventional adaptive algorithms for SS usually adjust their thresholds according to the radio environment. This paper concentrates on the issue of adaptive SS whose threshold is adjusted based on the Markovian behavior of primary user (PU). Moreover, Bayesian cost is adopted as the performance metric to achieve a trade-off between false alarm and missed detection probabilities. Two novel adaptive algorithms, including Markov Bayesian energy detection (MBED) algorithm and IMBED (improved MBED) algorithm, are proposed. Both algorithms model the behavior of PU as a two-state Markov process, with which their thresholds are adaptively adjusted according to the detection results at previous slots. Compared with the existing Bayesian energy detection (BED) algorithm, MBED algorithm can achieve lower Bayesian cost, especially in high signal-to-noise ratio (SNR) regime. Furthermore, it has the advantage of low computational complexity. IMBED algorithm is proposed to alleviate the side effects of detection errors at previous slots. It can reduce Bayesian cost more significantly and in a wider SNR region. Simulation results are provided to illustrate the effectiveness and efficiencies of both algorithms.

• Journal of Communications and Networks
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• 제12권1호
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• pp.74-85
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• 2010

For the purpose of compromising hosts, attackers including infected hosts initially perform a portscan using IP addresses in order to find vulnerable hosts. Considerable research related to portscan detection has been done and many algorithms have been proposed and implemented in the network intrusion detection system (NIDS). In order to distinguish portscanners from remote hosts, most portscan detection algorithms use a fixed threshold that is manually managed by the network manager. Because the threshold is a constant, even though the network environment or the characteristics of traffic can change, many false positives and false negatives are generated by NIDS. This reduces the efficiency of NIDS and imposes a high processing burden on a network management system (NMS). In this paper, in order to address this problem, we propose an automatic portscan detection system using an fast increase slow decrease (FISD) scheme, that will automatically and adaptively set the threshold based on statistical data for traffic during prior time periods. In particular, we focus on reducing false positives rather than false negatives, while the threshold is adaptively set within a range between minimum and maximum values. We also propose a new portscan detection algorithm, rate of increase in the number of failed connection request (RINF), which is much more suitable for our system and shows better performance than other existing algorithms. In terms of the implementation, we compare our scheme with other two simple threshold estimation methods for an adaptive threshold setting scheme. Also, we compare our detection algorithm with other three existing approaches for portscan detection using a real traffic trace. In summary, we show that FISD results in less false positives than other schemes and RINF can fast and accurately detect portscanners. We also show that the proposed system, including our scheme and algorithm, provides good performance in terms of the rate of false positives.