Why do we say that signal subspace and noise subspace are orthogonal in e.g. MUSIC algorithm? precisely, Suppose we have 2 sources (signals) which are WSS, in WGN in a uniform linear array. After computing the covariance matrix of received data "Y=AS+N", and decomposing R (covariance matrix) into 2 subspaces, we say that these 2 subspaces are orthogonal. Why?
