Accelerating the pace of engineering and science

# normlms

Construct normalized least mean square (LMS) adaptive algorithm object

## Syntax

alg = normlms(stepsize)
alg = normlms(stepsize,bias)

## Description

The normlms function creates an adaptive algorithm object that you can use with the lineareq function or dfe function to create an equalizer object. You can then use the equalizer object with the equalize function to equalize a signal. To learn more about the process for equalizing a signal, see Adaptive Algorithms.

alg = normlms(stepsize) constructs an adaptive algorithm object based on the normalized least mean square (LMS) algorithm with a step size of stepsize and a bias parameter of zero.

alg = normlms(stepsize,bias) sets the bias parameter of the normalized LMS algorithm. bias must be between 0 and 1. The algorithm uses the bias parameter to overcome difficulties when the algorithm's input signal is small.

### Properties

The table below describes the properties of the normalized LMS adaptive algorithm object. To learn how to view or change the values of an adaptive algorithm object, see Access Properties of an Adaptive Algorithm.

PropertyDescription
AlgTypeFixed value, 'Normalized LMS'
StepSizeLMS step size parameter, a nonnegative real number
LeakageFactorLMS leakage factor, a real number between 0 and 1. A value of 1 corresponds to a conventional weight update algorithm, while a value of 0 corresponds to a memoryless update algorithm.
BiasNormalized LMS bias parameter, a nonnegative real number

## Examples

For an example that uses this function, see Delays from Equalization.

expand all

### Algorithms

Referring to the schematics presented in Equalizer Structure, define w as the vector of all weights wi and define u as the vector of all inputs ui. Based on the current set of weights, w, this adaptive algorithm creates the new set of weights given by

$\left(\text{LeakageFactor}\right)w+\frac{\left(\text{StepSize}\right){u}^{*}e}{{u}^{H}u+\text{Bias}}$

where the * operator denotes the complex conjugate and H denotes the Hermitian transpose.

## References

[1] Farhang-Boroujeny, B., Adaptive Filters: Theory and Applications, Chichester, England, John Wiley & Sons, 1998.