In this paper, we propose a sequential bi-iteration singular value decompos
ition (Bi-SVD) noise-subspace-tracking algorithm for adaptive singular valu
e decomposition of the cross-covariance matrix in the recursive instrumenta
l variable (RIV) methods of system identification. This algorithm can be us
ed for the RIV subspace processing of signals in unknown, correlated Gaussi
an noise, The algorithm is based on the pseudo-inverse lemma and standard m
atrix-vector multiplication. The application and performance of the algorit
hm are demonstrated by tracking the noise subspace of the cross-covariance
matrix between two data vectors and finding recursively the total least-squ
ares solution of the over-determined instrumental-variable normal equations
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