Constrained-least-squares FIR multiband filter design (2024)

Constrained-least-squares FIR multiband filter design

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Syntax

b = fircls(n,f,amp,up,lo)

fircls(n,f,amp,up,lo,"design_flag")

Description

example

b = fircls(n,f,amp,up,lo) generates a length n + 1 linear phase FIR filter. The frequency-magnitude characteristics of this filter match those given by vectors f and amp. up and lo are vectors with the same length as amp. They define the upper and lower bounds for the frequency response in each band.

fircls(n,f,amp,up,lo,"design_flag") enables you to specify visual display options for the filter design.

Examples

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Constrained Least-Squares Lowpass Filter

Open Live Script

Design a 150th-order lowpass filter with a normalized cutoff frequency of 0.4π rad/sample. Specify a maximum absolute error of 0.02 in the passband and 0.01 in the stopband. Display the design error and magnitude responses of the filter. The bound violations denote the iterations of the procedure as the design converges.

n = 150;f = [0 0.4 1];a = [1 0];up = [1.02 0.01];lo = [0.98 -0.01];b = fircls(n,f,a,up,lo,"both");
 Bound Violation = 0.0788344298966 Bound Violation = 0.0096137744998 Bound Violation = 0.0005681345753 Bound Violation = 0.0000051519942 Bound Violation = 0.0000000348656 Bound Violation = 0.0000000006231 

Constrained-least-squares FIR multiband filter design (1)

Input Arguments

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nFilter order
real positive scalar

Filter order, specified as a real positive scalar.

Note

The fircls function always uses an even filter order for configurations with a passband at the Nyquist frequency (that is, highpass and bandstop filters). This is because for odd orders, the frequency response at the Nyquist frequency is necessarily 0. If you specify an odd-valued n, fircls increments it by 1.

fNormalized frequency points
real-valued vector

Normalized frequency points, specified as a real-valued vector. The transition frequencies are in the range [0, 1], where 1 corresponds to the Nyquist frequency. The first point of f must be 0 and the last point must be 1. The frequencies must be in increasing order.

ampPiecewise-constant desired amplitude
real-valued vector

Piecewise-constant desired amplitude of the frequency response, specified as a real-valued vector. The length of amp is equal to the number of bands in the response, length(f)-1.

upUpper bounds
real-valued vector

Upper bounds for the frequency response in each band, specified as a real-valued vector with the same length as amp.

loLower bounds
real-valued vector

Lower bounds for the frequency response in each band, specified as a real-valued vector with the same length as amp.

Note

Normally, the lower value in the stopband is specified as negative. By setting lo equal to 0 in the stopbands, a nonnegative frequency response amplitude is obtained. Such filters are spectrally factored to obtain minimum phase filters.

"design_flag"Filter design display
"trace" | "plots" | "both"

Filter design display, specified as one of these:

  • "trace" — View a textual display of the design error at each iteration step.

  • "plots" — View a collection of plots showing the full-band magnitude response of the filter and a zoomed view of the magnitude response in each sub-band. All plots are updated at each iteration step. The O's on the plot are the estimated extrema of the new iteration and the X's are the estimated extrema of the previous iteration, where the extrema are the peaks (maxima and minima) of the filter ripples. Only ripples that have a corresponding O and X are made equal.

  • "both" — View both a textual display and plots.

Output Arguments

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b — Filter coefficients
row vector

Filter coefficients, returned as a row vector of length n + 1.

Algorithms

The fircls function uses an iterative least-squares algorithm to obtain an equiripple response. The algorithm is a multiple exchange algorithm that uses Lagrange multipliers and Kuhn-Tucker conditions on each iteration.

References

[1] Selesnick, I. W., M. Lang, and C. S.Burrus. “Constrained Least Square Design of FIR Filters withoutSpecified Transition Bands.” Proceedings of the1995 International Conference on Acoustics, Speech, and Signal Processing. Vol.2, 1995, pp. 1260–1263.

[2] Selesnick, I. W., M. Lang, and C. S. Burrus.“Constrained Least Square Design of FIR Filters without SpecifiedTransition Bands.” IEEE® Transactions on SignalProcessing. Vol. 44, Number 8, 1996, pp. 1879–1892.

Extended Capabilities

Version History

Introduced before R2006a

See Also

Apps

  • Filter Analyzer | Filter Designer

Functions

  • fircls1 | firls | firpm

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Constrained-least-squares FIR multiband filter design (2)

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Constrained-least-squares FIR multiband filter design (2024)

FAQs

Constrained-least-squares FIR multiband filter design? ›

The Constrained Least Squares (CLS) FIR filter

FIR filter
In signal processing, a finite impulse response (FIR) filter is a filter whose impulse response (or response to any finite length input) is of finite duration, because it settles to zero in finite time.
https://en.wikipedia.org › wiki › Finite_impulse_response
design functions implement a technique that enables you to design FIR filters without explicitly defining the transition bands
transition bands
The transition band, also called the skirt, is a range of frequencies that allows a transition between a passband and a stopband of a signal processing filter. The transition band is defined by a passband and a stopband cutoff frequency or corner frequency.
https://en.wikipedia.org › wiki › Transition_band
for the magnitude response
. The ability to omit the specification of transition bands is useful in several situations.

What is constrained least square filter? ›

the constrained least squares filter seeks to find the minimum of. subject to the constraint. The solution to this problem is given by the following equation: where H(u,v) is the degradation function and. is the complex conjugate of the degradation function.

What is least square method of FIR filter design? ›

firls designs a linear-phase FIR filter that minimizes the weighted integrated squared error between an ideal piecewise linear function and the magnitude response of the filter over a set of desired frequency bands. Reference [2] describes the theoretical approach behind firls .

What are the disadvantages of FIR filter? ›

The primary disadvantage of FIR filters is that they often require a much higher filter order than IIR filters to achieve a given level of performance. Correspondingly, the delay of these filters is often much greater than for an equal performance IIR filter.

What are the design techniques of FIR filters? ›

(i) A desired or ideal response is chosen, usually in the frequency domain. (ii) An allowed class of filters is chosen (e.g. the length N for a FIR filters). (iii) A measure of the quality of approximation is chosen. (iv) A method or algorithm is selected to find the best filter transfer function.

What is constrained total least squares? ›

Abstract: The Total Least Squares (TLS) method is a generalized least square technique to solve an overdetermined system of equations Ax\simeqb . The TLS solution differs from the usual Least Square (LS) in that it tries to compensate for arbitrary noise present in both A and b .

What is the difference between Kalman filter and least squares? ›

This is unintuitive, given the derivation of the different algorithms; least-squares is based on minimizing the measurement residuals (i.e., the difference between the actual and predicted measurements) whereas the Kalman filter is derived based on minimizing the mean-square error of the solution.

Which window is best for FIR filter design? ›

FIR filter designed using different window functions provides Good main lobe width and smaller side lobe width but, among the above window Kaiser window is provide good side lobe than another window. Paper presents the following window functions which are being used for designing a FIR filter.

What is the least square method used for? ›

The least squares method is a statistical procedure to find the best fit for a set of data points. The method works by minimizing the sum of the offsets or residuals of points from the plotted curve. Least squares regression is used to predict the behavior of dependent variables.

What is optimal method FIR filter? ›

In the optimal method, the objective is to determine the filter coefficients, h(n), such that the value of the maximum weighted error, is minimized in the pass band and stop band, i.e. over the pass band and stop band. The most dominant of the optimum solution generation algorithms is the Parks-McClellan algorithm.

Why are FIR filters better than IIR? ›

Stability: As FIRs do not use previous output values to compute their present output, i.e. they have no feedback, they can never become unstable for any type of input signal, which is gives them a distinct advantage over IIR filters.

Can FIR filter be unstable? ›

In contrast, FIR filters are always stable because the FIR filters do not have poles. You can determine if pole-zero pairs are close enough to cancel out each other effectively. Try deleting close pairs and then check the resulting frequency response.

Is FIR filter always linear? ›

FIR filters are usually designed to be linear-phase (but they don't have to be.) A FIR filter is linear-phase if (and only if) its coefficients are symmetrical around the center coefficient, that is, the first coefficient is the same as the last; the second is the same as the next-to-last, etc.

Why is a rectangular window mostly preferred in FIR filter design? ›

The rectangular window clearly has the narrowest main lobe, and thus, for a given length, it should yield the sharpest transitions of H(ei) at a discontinuity of Ha(ei).

What are the four types of linear phase FIR filters? ›

Types of Linear Phase FIR Filters
TypeClassification
IEven-order, symmetric
IIOdd-order, symmetric
IIIEven-order, antisymmetric
IVOdd-order, antisymmetric

What is the formula for FIR filter? ›

An FIR filter is a special case of Equation (1), where a0=1 a 0 = 1 and ak=0 a k = 0 for k=1,...,N−1 k = 1 , . . . , N − 1 . Stability and linear-phase response are the two most important advantages of an FIR filter over an IIR filter. A linear-phase frequency response corresponds to a constant delay.

What is constrained Kalman filter? ›

Norm-Constrained Kalman Filtering. Given a state that evolves through linear dynamics and given linear measurements, the optimal estimate in a mean-square error (MSE) sense is obtained using the Kalman filter algorithm. A norm constrained estimate can be obtained by normalization of the Kalman (unconstrained) estimate.

What is a filter constraint? ›

Filter constraints represent all non-relational constraints that are used to filter records by any set of restrictions. Filter constraints are defined within a DDOs OnConstrain method and are specified within this method by using the Constrain command. Object oCustomer_DD Is A Customer_DataDictionary.

What do you mean by constrained minimization? ›

Objective: Minimize the equation: f(x,y)=5−(x−2)2−2(y−1)2. Under constraint: x+4y=3. Theory: Constrained minimization (constrained optimization) is the process of optimizing an objective function with respect to some variables in the presence of constraints on those variables.

What is meant by least mean square filter? ›

The idea behind LMS filters is to use steepest descent to find filter weights which minimize a cost function. We start by defining the cost function as. where is the error at the current sample n and. denotes the expected value. This cost function ( ) is the mean square error, and it is minimized by the LMS.

References

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