Maximum Cross-correlation Value Research Articles

Series Arc Fault Detection in Photovoltaic Systems Based on Signal-to-Noise Ratio Characteristics Using Cross-Correlation Function

Series arc fault (SAF) is one of the most important causes for failure of photovoltaic (PV) systems. Conventional protections could not detect SAF at initial moments. In this paper, a new method is presented for detection of SAF. The method is based on extracting SAF signatures from high frequency contents of the normalized dc terminal voltage. Inverter switching signatures in the signal have a periodic nature, which are rejected by subtracting the resized data-windows based on the lag relevant to maximum cross-correlation value. The utilized criterion is defined as ratio of power of the low frequency components to power of the arc signal (or signal-to-noise ratio). A set of possible scenarios, whether in practice or simulation, is considered to evaluate the performance of the method. They include different arc lengths, different fault locations in the PV system, various partial shadings, different switching frequencies for the inverter, and different types of environmental noise.

상호 상관을 이용한 부가정보가 필요 없는 Selected Mapping 수신방법 제안

직교 주파수 분할 다중 반송파(OFDM) 방식은 다양한 장점이 있지만 최대 전력 대 평균 전력비율(PAPR)이 커서 증폭기의 비선형 왜곡에 취약하다는 단점이 존재한다. 이러한 단점을 해결하고 데이터의 손실도 방지하기 위하여 선택사상 기법이 제안되었다. 그러나 선택사상 기법은 송신단에서 위상 변형에 사용된 위상 시퀀스를 수신단에서도 알아야 되기 때문에 부가 정보를 추가하여 전송해야 한다. 이에 따라 데이터 전송효율 손실이 발생한다. 본 논문에서는 부가 정보가 필요 없는 상호 상관을 이용한 새로운 선택사상 기법의 수신기를 제안한다. 수신단이 알고 있는 송신단에서 전송할 파일럿 신호와 위상시퀀스 곱을 수신된 파일럿 신호와 상호 상관을 취하여 상호 상관 값이 가장 큰 위상시퀀스로 부가정보를 검출한다. 모의실험을 통하여 본 수신기는 기존의 방식보다 개선된 비트오류율(BER) 및 부가정보 오류확률(SIER) 성능을 보인다는 것을 확인하였다. Orthogonal frequency division multiplexing(OFDM) systems have many advantages. However, OFDM systems are much affected by a nonlinear distortion because those systems have a high peak to average power ratio(PAPR) value. A selected mapping technology was suggested to reduce a PAPR value. The technology does not have data loss but receivers need side information to know modified phase sequence. Therefore, side information causes decreased a transmission efficiency. In this paper, we suggest a blind SLM receiver using a cross correlation technology. This receiver does not require side information. The proposed blind SLM receiver calculates sums of cross-correlation between transmitted pilot signals multiplied by each phase sequence and received pilot signals. So, this receiver detects side information which has a maximum sum cross-correlation value. We compared our proposed SLM receiver to a conventional blind SLM receiver through bit error rate(BER) and side information error rate(SIER) performances. Simulation results show that the proposed SLM receiver has improved BER and SIER performances than the conventional SLM receiver.

An approach for estimating the magnetization direction of magnetic anomalies

An approach for estimating the magnetization direction of magnetic anomalies in the presence of remanent magnetization through correlation between normalized source strength (NSS) and reduced-to-the-pole (RTP) is proposed. The observation region was divided into several calculation areas and the RTP field was transformed using different assumed values of the magnetization directions. Following this, the cross-correlation between NSS and RTP field was calculated, and it was found that the correct magnetization direction was that corresponding to the maximum cross-correlation value. The approach was tested on both simulated and real magnetic data. The results showed that the approach was effective in a variety of situations and considerably reduced the effect of remanent magnetization. Thus, the method using NSS and RTP is more effective compared to other methods such as using the total magnitude anomaly and RTP.

Evaluation of repeatability and reproducibility of continuous friction measuring equipment (CFME) using cross-correlation

Lack of sufficient friction between tyre and pavement is known to be one of the contributing factors in vehicle crashes. The application of new technologies can be used to determine the low friction areas or vulnerable accident sites at both the project and network levels. Continuous friction devices are one of the newest systems currently used in European countries that have recently been introduced to the United States. Continuous friction measuring devices are designed to measure the friction under conditions similar to those produced by an anti-lock braking system. Although continuous friction measuring equipment (CFME) provides valuable information about surface friction, processing of the relatively large amount of data produced is time-consuming. Traditional methods such as comparing the average friction provide a quick and simple data analysis method; however, they neglect other important characteristics such as friction spatial variation and low friction spots. This study proposes a methodology based on cross-correlation to compare CFME measurements. The data used in the study were collected during the annual rodeo that took place at the Virginia Smart Road. Two GripTester and one Dynatest 6875H Highway Friction Tester were used for data collection. Cross-correlation was used to synchronise the measurements. Repeatability and reproducibility of the measurements were evaluated based on the maximum cross-correlation value.

The Quick Method for Image Registration Combined with Information Entropy and Cross-Correlation Matrix

The current image registration technique based on gray-level information has shortcomings on time and amount of computation brought by the whole image registration, this paper proposes a quick registration method, which makes a combination of image information entropy and cross-correlation matrix: First, segmenting the target image into blocks and calculating to get the maximum entropy image block, then using it as a template to calculate the cross-correlation matrix with floating image; Second, making the point where the maximum cross-correlation value ​​is as the upper left corner, grasping a same-size block with template on floating image; Finally, obtaining registration parameters through calculation for these two blocks to achieve the purpose of registration. Experimental results show that this method has less computational complexity with the similar registration results, and takes less time. It’s effective and feasible.

Accurate Analysis of Double-Weight Codes with an Arbitrary Maximum Cross-Correlation Value for Two-Chip-Power Optical CDMA

Due to power restriction of some laser sources, the use of same power (per bit duration) in optical codes in incoherent optical code-division multiple-access multimedia networks with variable quality-of-services was previously studied. In those studies, the performance of double-weight codes with the maximum cross-correlation function λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> = 1 was exactly analyzed, but an approximation was only applied to the codes with λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> > 1 due to mathematical complexity. In this paper, an exact analytical model of double-weight codes with an arbitrary λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ≥ 1 is formulated and validated with computer simulation. This general, more accurate performance model is also useful for power-sensitive applications, such as in-service monitoring and fiber-fault surveillance in optical networks and sensor-identification in fiber-sensor systems using optical codes for address or user identification.

Performance Estimation of STCDMA on Various Channels for Effective Meta Data

Wavelet theory has emerged as a new mathematical tool and the important area of application of wavelets in communication: multiple accesses. Among the multiple access applications one of the most notable work is wavelet packet-based multiple access communication. The two new multiple access systems are Scale-Time-Code Division Multiple Access (STCDMA) and Scale-Code Division Multiple Access (SCDMA). In a STCDMA system, the channel is partitioned into different scales, and each scale into different time slots. This system uses Direct-Sequence (DS) Code-Division Multiple Access (CDMA) in each time slot to identify multiple users. These systems are analysed over a synchronous Additive White Gaussian Noise (AWGN) by using a conventional detector and a multiuser detector. Kasami sequences are optimal since the maximum cross correlation value achieves the Welch Lower Bound. The main purpose of using Kasami sequences is that, it decreases the multiple access interference. This paper deals with STCDMA over synchronous AWGN, Rayleigh channel and for different modulation schemes by using a multiuser detector. The main aim of multiuser detector is to mitigate the multiple access interference (MAI) and to improve the performance of STCDMA.

Study of Power Control on Double-Weight Codes With an Arbitrary Maximum Cross-Correlation Value in Variable-QoS Optical CDMA

In this paper, the use of power and weight control in multimedia, variable quality-of-services (QoS) incoherent optical code-division multiple-access (O-CDMA) systems in on-off keying is studied. An adjustable-power and variable-weight incoherent O-CDMA architecture is presented and the general performance model of 1-D and 2-D double-weight optical codes with an arbitrary maximum cross-correlation value λ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> is formulated as functions of code weight and chip power. Our results show that the performance of double-weight codes can be fine-tuned by varying both code weight and power, and they play different roles in the QoS differentiation. From the numerical examples, we show that λ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> =2 double-weight codes can perform as good as their λ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> =1 counterparts and, at the same time, have the advantage of supporting more possible subscribers. This general analytical model is important for power-sensitive applications, such as in-service monitoring and fiber-fault surveillance in optical networks and sensor-identification in fiber-sensor systems with the use of optical codes.

Computerized method for estimation of the location of a lung tumor on EPID cine images without implanted markers in stereotactic body radiotherapy

The purpose of this study was to develop a computerized method for estimation of the location of a lung tumor in cine images on an electronic portal imaging device (EPID) without implanted markers during stereotactic body radiotherapy (SBRT). Each tumor region was segmented in the first EPID cine image, i.e., reference portal image, based on a multiple-gray level thresholding technique and a region growing technique, and then the image including the tumor region was cropped as a ‘tumor template’ image. The tumor location was determined as the position in which the tumor template image took the maximum cross-correlation value within each consecutive portal image, which was acquired in cine mode on the EPID in treatment. EPID images with 512 × 384 pixels (pixel size: 0.56 mm) were acquired at a sampling rate of 0.5 frame s−1 by using energies of 4, 6 or 10 MV on linear accelerators. We applied our proposed method to EPID cine images (226 frames) of 12 clinical cases (ages: 51–83, mean: 72) with a non-small cell lung cancer. As a result, the average location error between tumor points obtained by our method and the manual method was 1.47 ± 0.60 mm. This preliminary study suggests that our method based on the tumor template matching technique might be feasible for tracking the location of a lung tumor without implanted markers in SBRT.

Design and Analysis of 2-D Codes With the Maximum Cross-Correlation Value of Two for Optical CDMA

In this paper, a new family of two-dimensional (2-D) optical codes with the maximum cross-correlation value of two is constructed and analyzed for optical code-division multiple access. Our 2-D codes employ wavelength hopping, controlled by the permutations of ¿synchronized¿ prime sequences, onto the pulses of a time-spreading optical orthogonal code (OOC). The new construction supports larger code cardinality (for more subscribers) and heavier code weight (for better code performance) without increasing the code length or number of wavelengths. Under certain conditions, our analysis shows that the new codes can perform better than our multiple-wavelength OOCs, which have cross-correlation values of at most one.

Multiple-Wavelength Optical Orthogonal Codes Under Prime-Sequence Permutations for Optical CDMA

A new family of two-dimensional (2-D) wavelength-hopping time-spreading codes, which employs wavelength hopping algebraically under prime-sequence permutations on top of time-spreading optical orthogonal codes, is studied and analyzed. Different from other 2-D codes, our new codes allow the number of wavelengths and code length to be chosen independently and, at the same time, the code cardinality is a quadratic function of the number of wavelengths without sacrificing the maximum cross-correlation value (i.e., still at most one). They are particularly suitable for high bit-rate optical code-division multiple-access systems with broadband mode-locked lasers, in which the number of time slots is very limited, and system capacity can only be grown by increasing the number of wavelengths, rather than code length. Finally, a novel wavelength-aware detector for wavelength-hopping time-spreading codes is discussed and shown to provide improved code performance.

Generalised Sarwate bounds on the aperiodic correlation of sequences over complex roots of unity

General aperiodic correlation bounds named generalised Sarwate bounds are derived, for sequence sets over complex roots of unity with zero or low correlation zone (ZCZ/LCZ), with respect to family size, sequence length, maximum autocorrelation sidelobe, maximum cross-correlation value and the zero or low correlation zone. It is shown that the existing aperiodic binary sequence bounds, such as Sarwate bounds, Welch bounds, Levenshtein bounds, Tang–Fan bounds and Peng–Fan bounds, are only special cases of the presented generalised Sarwate bounds. In addition, the new bounds are also, in general, stronger than the existing aperiodic binary sequence bounds, as well as Boztas aperiodic correlation bounds for normal complex roots-of-unity sequences.

High resolution 21 cm mapping of the Ursa Major Galactic cirrus: Power spectra of the high-latitude HI gas

We present a power spectrum analysis of interferometric 21 cm observations of the Ursa Major high-latitude cirrus, obtained with the Dominion Radio Astrophysical Observatory (DRAO) of Penticton (Canada). These high-resolution data reveal the intricate structure of the diffuse Galactic Hi, at angular scales from 1 arcmin to 3 degrees. A filtering method based on a wavelet decomposition was used to enhance the signal-to-noise ratio of the data. The power spectra of the integrated emission and of the centroid velocity fields were used to deduce the three-dimensional (3D) spectral index of the density and velocity fields of the Hi cirrus. The spectral index is similar for the 3D density and velocity fields with a value of . Using the Leiden/Dwingeloo observations, this analysis was extended to the whole North Celestial Loop (which includes the Ursa Major cirrus), showing that the scaling laws prevail from 0.1 to 25 pc. The centroid velocity and integrated emission fields show moderate correlation, with a maximum cross-correlation value of 0.44.

Generalised Sarwate bounds on periodic autocorrelations and cross-correlations of binary sequences

A general periodic correlation bound named generalised Sarwate bound for binary zero or low correlation zone (ZCZ/LCZ) sequence set with respect to family size, sequence length, maximum autocorrelation sidelobe, maximum cross-correlation value and the zero or low correlation zone, are derived. It is shown that all the previous periodic sequence bounds, such as Sarwate bound, Welch bound and Tang-Fan bound, are only special cases of the generalised Sarwate bound.

Signal set design with constrained amplitude spectrum and specified time-bandwidth product

A new method for designing signals with a given time-bandwidth product, such that all the signals in the set have a flat amplitude spectrum and have low cross-correlation function values is introduced. It is shown that these signals lie on a signal parameter space ellipse. For a given duration and bandwidth, it is possible to trade off the cardinality of the set for better cross-correlation properties between remaining members of the set. Proof that the cross-correlation between these signals is bounded from above by a factor proportional to the square-root of inverse distance between these signals along one of the axes of the ellipse is given. It is also shown that the cross-correlation between two signals that are furthest apart is bounded by the square-root of inverse time-bandwidth product of the signals in the set. An example design is then given and a comparison of this signal set to some well-known signal sets illustrates that it performs better when the metric is maximum cross-correlation value. The proposed signal set also has the advantage that it can be designed for any time-bandwidth product instead of discrete values.