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Open Access Research Article

Fast Subspace Tracking Algorithm Based on the Constrained Projection Approximation

Amir Valizadeh12* and Mahmood Karimi1

Author Affiliations

1 Electrical Engineering Department, Shiraz University, 713485 1151 Shiraz, Iran

2 Engineering Research Center, 134457 5411 Tehran, Iran

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EURASIP Journal on Advances in Signal Processing 2009, 2009:576972  doi:10.1155/2009/576972

The electronic version of this article is the complete one and can be found online at: http://asp.eurasipjournals.com/content/2009/1/576972

Received:19 May 2008
Revisions received:4 November 2008
Accepted:28 January 2009
Published:1 March 2009

© 2009 The Author(s).

This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


We present a new algorithm for tracking the signal subspace recursively. It is based on an interpretation of the signal subspace as the solution of a constrained minimization task. This algorithm, referred to as the constrained projection approximation subspace tracking (CPAST) algorithm, guarantees the orthonormality of the estimated signal subspace basis at each iteration. Thus, the proposed algorithm avoids orthonormalization process after each update for postprocessing algorithms which need an orthonormal basis for the signal subspace. To reduce the computational complexity, the fast CPAST algorithm is introduced which has complexity. In addition, for tracking the signal sources with abrupt change in their parameters, an alternative implementation of the algorithm with truncated window is proposed. Furthermore, a signal subspace rank estimator is employed to track the number of sources. Various simulation results show good performance of the proposed algorithms.

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