ICA with Overcomplete Bases
Aapo Hyvärinen, Juha Karhunen, Erkki Oja · 2001
The ICA problem becomes much more complicated if there are more independent components than observed mixtures. Basic ICA methods cannot be used as such. In most practical applications, it may be more useful to use the basic ICA model as an approximation of the overcomplete basis model, because the estimation of the basic model can be performed with reliable and efficient algorithms.