Sharif Digital Repository

In this paper, we investigate PN-sequences with ideal autocorrelation property and the consequences of this property on the number of +1s and -1s and run structure of sequences. We begin by discussing and surveying about the length of PN-sequences with ideal autocorrelation property. From our discussion and survey we introduce circulant matrix representation of PN-sequence. Through circulant matrix representation we obtain system of non-linear equations that lead to ideal autocorrelation property. Rewriting PN-sequence and its autocorrelation property in {0,1} leads to a definition based on Hamming weight and Hamming distance and hence we can easily prove some results on the PN-sequences... 

Multistage process surveillance is considered to effectively improve the product reliability in manufacturing or service operations. To this end, the process output is commonly inspected under specific conditions and the values of the reliability-related quality characteristic are measured. However, in some cases, the observations from the process output are autocorrelated. This brings about the situation where the use of existing monitoring schemes is futile. Therefore, a class of survival analysis regression models called the proportional hazards (PH) model has been modified to justify the effect of cascade property in line with the autocorrelation issue. Subsequently, three monitoring... 

Pitch detection is the process of determining the period of the vocal cords closure or in another word the time duration of one glottal closed, open and returning phase. Dyadic wavelets transform (DyWT) and modified higher order moment, which is based on the autocorrelation function, are two pitch detection methods. DyWT is an accurate pitch detection method, however it has less accuracy compared to modified higher order moment. On the other hand modified higher order moment has high computational complexity and is time consuming. In this paper, we propose a pitch detection method based on DyWT which has use modified higher order moment. Modified higher order moment is applied only in some... 

It is proved that the out-of-phase autocorrelation of a well-known class of multiplexed sequences for cryptographic and spread spectrum applications is necessarily high for relatively small values of the phase shifts. Related design criteria for the multiplexer generator including the use of full positive difference sets are proposed. By generalizing the classical occupancy problem, higher order statistical weaknesses of multiplexed sequences are also established. © 2002 Elsevier Science (USA)  

Distinguishing reflected waveforms from two separated targets which are very close to each other is an important challenge in radar signal processing. Pulse compression is a technique used for accounting for this problem. There are several methods for compressing such as phase coding waveform and the goal of this paper is finding these optimal codes. In this paper, by combining several contents, a new optimum method based on Genetic Algorithm is suggested. This method has low computational operation and its speed is faster than the other ordinary algorithms. This method is belonged to local or partial search methods and has following advantages: 1. It uses branch-and-bound strategy; 2. It's... 

Pitch detection is the process of determining the period of the vocal cords closure or in another word the time duration of one glottal closed, open and returning phase. Dyadic wavelets transform (DyWT) and modified higher order moment, are two pitch detection methods. DyWT is an accurate pitch detection method, however it has less accuracy compared to modified higher order moment. On the other hand modified higher order moment has high computational complexity and is time consuming. The DyWT pitch period detection is based on a two pass dyadic wavelet transform over a signal. Modified higher order moment is based on autocorrelation function (ACF) and in this method the speech signal has... 

In this paper, an approach based on the U statistic is first proposed to eliminate the effect of between-profile autocorrelation of error terms in Phase-II monitoring of general linear profiles. Then, a control chart based on the adjusted parameter estimates is designed to monitor the parameters of the model. The performance of the proposed method is compared with the ones of some existing methods in terms of average run length for weak, moderate, and strong autocorrelation coefficients under different shift scenarios. The results show that the proposed method provides significantly better results than the competing methods to detect shifts in the regression parameters, while the competing... 

Recently, many researchers and practitioners have shown interest on profile monitoring as a relatively new subarea of statistical process control. One main reason for this interest, and perhaps a key factor for the contributions of many researchers to this field, is the various applications of profile monitoring in real life. Although one can easily encounter many univariate applications of profile monitoring in service and manufacturing environments, there exist situations where quality of a product or process needs to be modeled in multivariate terms. In this paper, we investigate monitoring of multivariate simple linear profiles in phase II when independence assumption of observations... 

Autocorrelation receiver (AcR) is usually used as the general receiver for transmitted reference (TR) communication systems on a quite intuitive basis. In this paper, we apply the principle of statistical invariance to obtain the optimum TR receiver on a decision-theoretic basis, and it is shown that the autocorrelation receiver is optimal only in a special case. Performance of the optimum receiver and the suboptimum AcR for some important modulation schemes is also evaluated. The results imply that allocating a part of the transmitted energy and bandwidth to reference pulses would not help improve the performance of the system and the optimal performance might be achieved via much simpler... 

In this paper, the authors analyze conditions under which they can be certain on the intensity addition of a given device, such as tapped-delay lines, used in digital incoherent all-optical communication systems. A general expression for phase-induced intensity noise that is applicable to all types of semiconductor lasers is derived by defining an optical self-SNR expression that can be used to analyze and measure phase-induced intensity noise. The result shows that in order to have a minimal phase-induced intensity noise in most digital optical incoherent systems, a large optical self-SNR, e.g., 20 dB or more, is needed. This in turn is shown to place a limit on the maximum rate of... 

Knowing the time of change would narrow the search to find and identify the variables disturbing a process. The knowledge of the change point can greatly aid practitioners in detecting and removing the special cause(s). Count processes with an autocorrelation structure are commonly observed in real-world applications and can often be modeled by the first-order integer-valued autoregressive (INAR) model. The most widely used marginal distribution for count processes is Poisson. In this study, change-point estimators are proposed for the parameters of correlated Poisson count processes. To do this, Newton's method is first used to approximate the parameters of the process. Then, maximum... 

In an electronic warfare environment, an electronic support system receives signals emitted by different radars. One of the key tasks in an electronic support system is detection of Pulse Repetition Interval Modulation for these signals. In this paper we present a new robust and yet simple method for detection of complex PRI Modulation. Simulation results show that the proposed method is more robust against noise (spurious and missing pulses) and unwanted jitter than previous methods  

In this article, a transformation method using the principal component analysis approach is first applied to remove the existing autocorrelation within each profile in Phase I monitoring of autocorrelated simple linear profiles. This easy-to-use approach is independent of the autocorrelation coefficient. Moreover, since it is a model-free method, it can be used for Phase I monitoring procedures. Then, five control schemes are proposed to monitor the parameters of the profile with uncorrelated error terms. The performances of the proposed control charts are evaluated and are compared through simulation experiments based on different values of autocorrelation coefficient as well as different... 

In this paper an efficient method is proposed for blind detection of multiuser spread spectrum signal and pseudo noise (PN) length estimation in downlink scenario. This method is based on fluctuating observation of second order statistic (SOS) estimator of received signal; estimating length of spreading code with no need to primary information based on observing second order peaks of correlation estimator is presented. In low SNR, the fading multipath phenomenon especially in length of small codes leads to problem in detecting place of correlation estimator peaks. In this paper besides expanding blind estimation to multiuser environment, by using searching method in updating the length of... 

Autocorrelation receiver (AcR) is usually used as the general receiver for transmitted reference (TR) communication systems on a quite intuitive basis. In this paper, we apply the principle of statistical invariance to obtain the optimum TR receiver on a decision-theoretic basis, and it is shown that the autocorrelation receiver is optimal only in a special case. Performance of the optimum receiver and the suboptimum AcR for some important modulation schemes is also evaluated. The results imply that allocating a part of the transmitted energy and bandwidth to reference pulses would not help improve the performance of the system and the optimal performance might be achieved via much simpler... 

Thermal stability of the topological color code in the presence of a thermal bath is studied. We study the Lindblad evolution of the observables in the weak-coupling limit of the Born-Markov approximation. The autocorrelation functions of the observables are used as a figure of merit for the thermal stability. We show that all of the observables autocorrelation functions decay exponentially in time. By finding a lower bound of the decay rate, which is a constant independent of the system size, we show that the topological color code is unstable against thermal fluctuations from the bath at finite temperature, even though it is stable at T=0 against local quantum perturbations  

This paper will design non-linear frequency modulation (NLFM) signal for Chebyshev, Kaiser, Taylor, and raised-cosine power spectral densities (PSDs). Then, the variation of peak sidelobe level with regard to mainlobe width for these four different window functions are analyzed. It has been demonstrated that reduction of sidelobe level in NLFM signal can lead to increase in mainlobe width of autocorrelation function. Furthermore, the results of power spectral density obtained from the simulation and the desired PSD are compared. Finally, error percentage between simulated PSD and desired PSD for different peak sidelobe level are illustrated. The stationary phase concept is the possible... 

This paper develops a new evolutionary algorithm for generating low autocorrelation binary sequences. These sequences are of interest in pulse compression technique. The proposed algorithm is fast enough to yield optimum or near optimum codes. The generated sequences were compared to the best literature and were seen that its results are better than the others. This suggested method could change 11 rows of the previous best known PSLs table, whereas the previous literature could change only one record. These records were combined with the best results reported in the papers to produce a new best minimal-PSL binary sequence table for bit lengths 71 through 100. ©2008 IEEE