Maximum likelihood recursive least squares estimation for multivariate equation-error ARMA systems

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Abstract

This paper focuses on the parameter estimation problems of multivariate equation-error systems. A recursive generalized extended least squares algorithm is presented as a comparison. Based on the maximum likelihood principle and the coupling identification concept, the multivariate equation-error system is decomposed into several regressive identification models, each of which has only a parameter vector, and a coupled subsystem maximum likelihood recursive least squares identification algorithm is developed for estimating the parameter vectors of these submodels. The simulation example shows that the proposed algorithm is effective and has high estimation accuracy.

Introduction

For a long time, system identification and model parameter estimation have been applied in control and signal processing [1], [2], [3]. Most control laws are designed based on the mathematical models [4], [5], [6]. Parameter estimation is used in system and signal modeling [7], [8], [9]. Due to the complex structures, input and output variables, uncertain interference signals and high dimension of multivariate systems, they have become a hot issue [10], [11], [12]. For multivariate systems, Wang et al. provided a hierarchical extended stochastic gradient algorithm for nonlinear multi-input multi-output Hammerstein systems [13]; Ma et al. presented a decomposition-based recursive generalized least squares algorithm for multivariate pseudo-linear autoregressive systems [14].

The parameter estimation methods have wide applications in many areas and play an important role in system identification [15], [16] and signal processing [17], [18], [19]. Different from the least squares [20], [21], [22] and the stochastic gradient methods [23], [24], [25], the maximum likelihood identification method needs to construct a likelihood function with respect to the observed data and the unknown parameters, and the parameter estimation can be obtained by maximizing the likelihood function [26], [27]. Chen et al. derived a filtering based maximum likelihood multi-innovation extended gradient algorithm for controlled autoregressive autoregressive moving average systems based on the maximum likelihood principle [28]. Li et al. proposed a maximum likelihood least squares based iterative algorithm for identifying the parameters of bilinear systems with colored noises [29]. Wang et al. extended the maximum likelihood estimation to multivariable controlled autoregressive moving average like systems in colored noise environment and proposed a recursive maximum likelihood identification identification algorithm [30].

The coupling identification concept is useful for simplifying the parameter estimation of the coupled parameter multivariable systems and can be applied other areas [31], [32], [33]. It is based on the coupled relationship of the parameter estimates between the subsystems of a multivariable system [31]. Recently, a coupled least squares algorithm has been proposed for multiple linear regression systems [32]. Huang et al. derived the coupled stochastic gradient parameter estimation algorithms by using the auxiliary model identification idea and the coupling identification concept [34].

This paper studies the parameter estimation for the multivariate equation-error systems. The main contributions of this paper are as follows.

  • The system is decomposed into several subsystems, each of which has only a parameter vector.

  • Based on the maximum likelihood principle and the coupling identification concept, a coupled subsystem maximum likelihood recursive least squares identification algorithm is derived.

  • The average value of the parameter estimates of these subsystems is taken to improve the accuracy of parameter estimation. Moreover, a recursive generalized extended least squares algorithm is derived as a comparison.

Briefly, the rest of this paper is organized as follows. Section 2 gives the identification model of a multivariate equation-error system. Section 3 presents a coupled subsystem maximum likelihood recursive least squares algorithm for the multivariate equation-error system. As a comparison, a recursive generalized extended least squares algorithm is given in Section 4. The numerical example is provided in Section 5 to show the effectiveness of the proposed algorithm. Finally, Section 6 offers some concluding remarks.

Section snippets

System description

Let us introduce some notation. The symbol Im is an m × m identity matrix; 1n is an n-dimensional column vector whose elements are 1; the superscript T denotes the matrix transpose; z represents unit forward shift operator: zx(t)=x(t+1) and z1x(t)=x(t1).

Consider the following multivariate equation-error system: A(z)y(t)=Φs(t)θs+D(z)C(z)v(t),where y(t):=[y1(t),y2(t),,ym(t)]TRm is the system output vector, Φs(t)Rm×n is the measured information matrix consisting of the input-output data, θsRn

The coupled subsystem maximum likelihood recursive least squares algorithm

In order to distinguish the estimation of θ in each subsystem, we mark θj as θ in the jth subsystem. For a given data set of measurements ϕjL:=[ϕj(1),ϕj(2),,ϕj(L)] and yjL:=[yj(1),yj(2),,yj(L)]. Assume that Lj(yjL|ϕjL,θj) (j=1,2,,m) is the likelihood function. The maximum likelihood estimate is obtained by maximizing the likelihood function, θ^ML=argmaxθjLj(yjL|ϕjL,θj),j=1,2,,m.The likelihood function Lj(yjL|ϕjL,θj) can be expressed as Lj(yjL|ϕjL,θj)=p(yjL|ϕjL,θj)=p[yj(L)|yj,L1,ϕj,L1,θj]p[

The recursive generalized extended least squares algorithm

As a comparison, we simply derive the recursive generalized extended least squares algorithm for the multivariate equation-error system. From Eq. (1), we can get the following equation for the multivariate equation-error system y(t)+i=1naaiy(ti)=Φs(t)θsi=1ncciw(ti)+i=1nddiv(ti)+v(t).Transform the above equation into the following identification model y(t)=φ(t)θ+v(t),where ϑ:=[θsT,aT]TRn+na,θ:=[ϑT,cT,dT]TRn0,ϕ(t):=[Φs(t),y(t1),y(t2),,y(tna)]Rm×(n+na),ψ(t):=[w(t1),w(t2),,w(t

Example

Consider the following multivariate equation-error model: A(z)y(t)=Φs(t)θs+D(z)C(z)v(t),y(t)=[y1(t)y2(t)],Φs(t)=[Φs1(t)Φs2(t)],v(t)=[v1(t)v2(t)],A(z)=1+0.23z1+0.90z2,C(z)=1+0.62z1,D(z)=10.36z1,θs=[0.850.60].

The parameter vectors to be identified are a=[0.23,0.90]T,c=0.62,d=0.36,θ=[θsT,aT,c,d]T=[0.85,0.60,0.23,0.90,0.62,0.36]T.

In simulation, y(t)=[y1(t)y2(t)]R2 is the output vector, Φs(t) is a 2 × 2 matrix sequence, v(t)=[v1(t)v2(t)]R2 is a white noise vector with zero mean, σ12 and σ2

Conclusions

The coupled subsystem maximum likelihood recursive least squares estimation algorithm is presented for multivariate equation-error systems by using the maximum likelihood principle and the coupling identification concept. The proposed algorithm is compared with the existing recursive generalized extended least squares algorithm. The simulation results indicate that the coupled subsystem maximum likelihood recursive least squares estimation algorithm is effective and has high estimation

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    This work was supported by the Jiangsu Province Industry University Prospective Joint Research Project (BY2015019-29), the Fundamental Research Funds for the Central Universities (JUSRP51733B), the Graduate Education Innovation Program of Jiangsu Province (No. KYCX17\_1458), the Taishan Scholar Project Fund of Shandong Province of China (No. ts20130939), the 111 Project (B12018) and the National First-Class Discipline Program of Light Industry Technology and Engineering (LITE2018-026).

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