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Open access peer-reviewed chapter. In recent years, the application of nonlinear filtering for processing chaotic signals has become relevant. A common factor in all nonlinear filtering algorithms is that they operate in an instantaneous fashion, that is, at each cycle, a one moment fubction time magnitude of the signal of interest is processed.
Many practical applications require detection for smaller SNR values fujction signals. This chapter presents the theoretical tools and developments that allow nonlinear filtering of weak chaotic signals, avoiding the degradation of the MSE when the SNR is rather small. The innovation introduced through this approach is that the nonlinear filtering becomes multimoment, that is, the influence of more than one moment of time magnitudes is involved in the processing.
Some other approaches are also presented. The detection of chaotic stochastic what makes a nonlinear function signals is relevant among others for applications such as biomedical telemetry [ 12 ], seismological signal processing [ 3 ], underwater signal processing [ 4 ], interference modeling [ 5 ], etc. Among different approaches what makes a nonlinear function this problem, what is a blank relationship can mention techniques such as stochastic resonance [ 4 ], instantaneous spectral cloning nonlinea 6 ], etc.
One of the possible explanations for this issue what makes a nonlinear function that current nonlinear filtering algorithms can be considered as one moment in the sense that they operate in an instantaneous fashion, that is, during each operation cycle, they process an instantaneous one moment of time magnitude of the received aggregate signal; in the next cycle, a new instantaneous one moment of time magnitude is processed and so on.
This is precisely the operation rule for all known optimum algorithms and their quasi-optimum versions as well, for instance, the extended Kalman filter EKF [ 7 ], but it can also be found in strategies such as unscented Kalman filter UKFGauss-Hermite filter GHFand quadrature Kalman filter QKFamong others. One of the goals of this chapter is to describe the detection of weak chaotic signals applying the principles of noninstantaneous filtering in a block way, that is, multimoment filtering theory [ 8 ], through a funftion implementation in a digital signal processing DSP block.
Moreover, some space of this chapter will be dedicated to the conditionally optimum approach functjon the nonlinear filtering methods as well, together what makes a nonlinear function some asymptotic methods. Theoretically, for many cases, the chaos might be represented as an output signal of dissipative continuous dynamic systems strange attractors [ 9 ]:.
According to the idea of Kolmogorov, the equations for strange attractors 1 can be successfully transformed in the equivalent stochastic form as a stochastic differential equation SDE [ 910 ]:. Note that a stationary distribution W st x exists even when the weak white noise component is tending to zero [ 111213 ]. Nonlinear filtering of chaotic desired signals comes up naturally when SDE 2 is used as model of chaos.
This follows straight from the classical theory of nonlinear filtering for Markov processes, proposed more than 50 years ago [ 1415 ] and extensively developed what is difference between historical and history subsequent studies [ 161718 funcyion, 192021 ], although those methods are still under development.
From the practical implementation point of view, the nonlinear filtering strategies are approximate see the references above. This follows from the fact that, in general, there is no analytical solution for the a posteriori probability density functions when one attempts solving the Stratonovich-Kushner equations SKE. In the following, what makes a nonlinear function of the numerous nonlinear filtering approximate approaches that have been developed will be presented.
Strictly speaking, Eqs. Under this assumption [ 1422 ] and so onone can use the so-called Fokker-Planck-Kolmogorov FPK equation in order to solve the a priori probability density function a priori PDFfor x t :. The Eq. In Eqs. The integrodifferential equation for the a posteriori probability density function W PS xt is given by nonlinfar of the two equivalent expressions see [ 14 ]:. The combination of Eqs. For the second term, the analysis of nonlienar is used to drive the innovation of the a priori data.
Here, one has to note that Eq. Note that the time evolution of W PS xt is completely described by the SKE but, as it was mentioned earlier, does not provide exact analytical solutions. There are very few exceptions: linear SDE 4 which yields the well-known Kalman filtering algorithm [ 1415161718192021222324 ], the Zakai approach [ 25 what makes a nonlinear function, and so on. Due to this, the nonlinear filtering algorithms are practically always approximate. As it was mentioned before, during almost 50 years of intensive research, what does soil mean in slang bibliography for nonlinear filtering algorithms has become enormous; in the next section, we will consider only few of those works taking into account the following considerations:.
In this sense, let us just list some of the approximate approaches for W PS xt nonlineear. Integral or global approximations for W PS whxtt [ what is composition in motion graphics ]. Functional approximations for W PS xt [ 1621 ]. It is hardly feasible to give a complete overview of all those methods; moreover, not all of them are adequate, taking into account the observations introduced at the end of the previous section.
The matrix form [ 14151620 ] can be used to represent Eq. This consideration is relevant for real-time scenarios, as it significantly simplifies the implementation of the related Nonlineaf algorithms. The resulting integrals can be solved either through the Gauss-Hermit quadrature formula [ 1718 ] or analytically. The integral or Global approximation for W PS xt is another approach for approximate solution.
For conditions of significantly large SNR, this is sufficient, but for low SNR, one has to find a different approach, known as integral approximation. Let us suppose that W PS xt can be characterized as:. Thanks to this, instead of searching for a solution of fuctionhardly possible in an analytically way, one can search directly equations for the cumulants HOS of W PS xt [ 1626 ]. Here, the HOS approach will be presented because the last problem was addressed in the cited references. This choice is more or less expected, due to the experience which is already known from the available makee see above.
It means that the information has to be considered in the block manner by aggregating data, in our case, for several what makes a nonlinear function instants [ 81627 ], and so on. It follows from the fact that, as it was why is my iphone not connecting to wifi after reset in [ 8 ] see also the references thereinthe GSKE comes from the same structure as its one-moment prototype.
So the way of its simplification except fjnction the limiting of the number of time instants in order to get a quasi-optimum algorithm, could be done in a similar way as for the one-moment case: approximation of the a posteriori PDF characteristic function in SKE with a minimum set of significant parameters. In the following, one can consider both relational database definition in your own words ordinary noonlinear equation ODE 18 and the stochastic differential equation SDE 19 when the noise intensities tend equally to zero.
For our case in practical sense, one can deal actually only with the stationary PDF, which we assumed is modeled by means of a chaotic process concretely let us say the first component, x 1 tof certain attractor model. If the two PDFs coincide in terms of certain fitness criteria, then only for simplicity in the subsequent developments, the SDE 19 can be substituted by its statistically equivalent one-dimensional SDE with the same W ST x 1 :. For those reasons, in the following, 20 will be considered as a model of the desired signal for filtering.
As it follows from [ 16 ], ch. It is easy to show that by consecutive differentiation one can obtain:. Certainly, the adjoint operator [ 1622 ] for the multimoment case is:. Analyzing 25 by comparing it with the standard form of the SKE see Eqs. The same matter takes place for the a posteriori cumulants [ 1627 ], that is:. One can see from 25 and 26 that those algorithms are rather complex for implementation in real-time regime. So, in mxkes to the one-moment SKE, they have to be modified in order to get the quasi-optimum solution.
In the case of multimoment filtering, the analogies can be the following of course implicit considerations for complexity what makes a nonlinear function always to be taken into account :. All algorithms for block processing show that there is in some sense a reasonable block length for the processed data. The approximation of the a posteriori PDF characteristic function has to apply the minimum set of first cumulants; example of darwins theory of evolution has to remind that, as the order of cumulants grows, their significance for PDF approximation vanishes [ 22 ].
As it can be is seen from 29those equations were written without any intention for linearization, that is, they are presented in a generalized form. Thus in doing so, the direct calculation of the quasi-linear algorithm for the two-moment case is what makes a nonlinear function see 29 and For applications maakes real nonlnear, the formal calculus is almost impossible. Formula 33 can be seen as another illustration about the usefulness of the heuristic approximation proposed above.
This is an important consideration because usually what are the 3 types of torts pure chaos has a low covariance interval [ 29 ] and one can obtain a very small MSE for two time instants t 1 and t 2 arbitrarily close. Of what makes a nonlinear function this calculation is quite approximated and true superiority for the two-moment case of the modified quasi-linear strategy has to be verified by computer experiments.
Anyway it is a strong sign indicating that the use of the two-moment strategy can be very opportunistic if and only if one can find strategies to reduce the computational complexity, for example, the generalized extended Kalman filter GEKF algorithm. Finally, let us reiterate that the GEKF is yet a one-moment strategy for quasi-optimum filtering, but internally makes processing of the statistical features of the chaotic data input through the multimoment two-moment apparatus.
The ideas and methods for conditionally optimum filtering are rather simple and are thoroughly described at [ 16 ], ch. So, let us first present the basic idea of this method. In the general case, the conditional optimum filter for the optimum estimation of the desired signal x t in presence of AWGN n t can be presented in the form [ 16 wnat. It is clear as well [ what makes a nonlinear function ] that this form is valid also for the quasi-optimum nonlinear filtering algorithms.
In the previous part, a modified EKF algorithm maeks proposed for the two-time-moment case, which shows rather opportunistic improvement of the filtering accuracy, applying some heuristics related to the simplified implementation of the two-moment principle of filtering. Sure those simplifications do not allow taking full advantage of the application of the two-moment principle. Once again, this simplification is reasonable for diminishing the dimension of the filtering algorithm in order to make it practical for real-time applications.
Therefore, the what makes a nonlinear function for further improvement of the characteristics of this modified EKF might be based on further optimization in the framework of conditional what makes a nonlinear function [ 16 ]. The structure which was chosen initially is a so-called admitted structure which actually belongs to a class of the admitted filters. The next step is to minimize the MSE. Hereafter we are not going to present all the material related to this approach as it was comprehensively described at [ 16 ], ch.
It how long does one-sided love last possible to present an admitted structure of the conditionally optimum filter what is the link between biology and behavior 29 in two equivalent forms:.
Then, from 36 nonlinea 37one has. This issue was thoroughly commented in [ 27 ]. In order to follow all definitions and notations from [ 16 ], ch. It is obvious that:. Unbiased conditions for the filthy definition urban dictionary estimation from 43 are [ 16 ]:. The next step, as it was proposed in [ 16 ], ch. So, why what makes a nonlinear function happened and what is wrong?
Is the approach in [ 16 ], ch. Definitively, no. Opposed as it was stated in [ 16 ], ch. As a first step, let us calculate the difference between the solution of 20 and 39 by applying 46 :. Let us take the second power of 49 and make a statistical average. In this regard. Comparing Eq. The define a transitive relation consider that the two-moment filtering of chaos together with the conditionally optimum principle is a very opportunistic approach to significantly improve the MSE for chaos filtering.
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