Time domain implementations of the coherent signal-subspace transformations

The authors propose CST (coherent signal-subspace transformation) preprocessors as time domain equivalents of the frequency domain based preprocessing in the coherent signal-subspace method for wideband direction finding in a possible multipath environment using general arrays. The preprocessor consisted of multichannel filters following the sensor array and were able to render real-time capability. The authors introduce two approaches to implementing the focusing in the time domain, based on the principles of Taylor series expansion and least squared error. The time domain preprocessor is realized by a multichannel digital FIR (finite impulse response) filter, thus rendering real-time application. For diagonal transformations, the problem reduces to implementing different delays at each sensor by suitable tapped delay lines. Various tapped delay line filters are proposed, and an error analysis is detailed.