15th Triennial World Congress of the International Federation of Automatic Control
  Barcelona, 21–26 July 2002 
ASYMPTOTICALLY OPTIMAL SMOOTHING OF AVERAGED LMS FOR REGRESSION PARAMETER TRACKING
Alexander V. Nazin** and Lennart Ljung*
** Division of Automatic Control, Linköping University,
SE-58183 Linköping, Sweden. E-mail: ljung@isy.liu.se
** Institute of Control Sciences, Profsoyuznaya str., 65, 117997
Moscow, Russia. E-mail: nazine@ipu.rssi.ru

The sequence of estimates formed by the LMS algorithm for a standard linear regression estimation problem is considered. In this paper it is first shown that smoothing the LMS estimates using a matrix updating will lead to smoothed estimates with optimal tracking properties, also in the case the true parameters are slowly changing as a random walk. The choice of smoothing matrix should be tailored to the properties of the random walk. Second, it is shown that the same accuracy can be obtained also for a modified algorithm, SLAMS, which is based on averages and requires much less computations.
Keywords: Regression; Parameter estimation; Random walk; Recursive algorithms; Tracking; Smoothing; Mean-square error; Asymptotic properties
Session slot T-Tu-A02: Time-Varying System Estimation and Tracking/Area code 3a : Modelling, Identification and Signal Processing