The signal subspace analysis technique, usually applied to signals corrupted by noise, is theme of some papers since the beginning of the 80s decade. This new technique has presented important features, as robustness and precision, and became widely employed in digital signal processing. However, the main problem associated to this new method is the high computational cost. This characteristic has restricted the use of signal subspace analysis to some off-line systems. A possible way to overcome this burden was to track the signal and noise subspace behavior in the time-domain. The main objective of these methods is to allow the signal subspace analysis technique application to real time systems, sometimes at the expense of limiting analysis precision or scope. This work proposes a new subspace tracking procedure. The goal is to describe a new algorithm with good performance (precision-speed), allowing some real time systems applications. A new analysis and characterization of almost circulant systems is introduced by reinterpreting the circulating matrix decomposition scheme. The set of contributions is applied to a new analogue modulation communication signals automatic recognition structure.