On adaptive IIR filters and parallel adaptive identifiers with adaptive error filtering

Presently, for provable global stability and unbiasedness in the presence of zero-mean, colored output measurement noise, adaptive infinite impulse response (IIR) filters (or adaptive output error identifiers) require a restrictive SPR condition on the transfer function dividing the error smoothing coefficient polynomial by the unknown desired denominator. This paper considers two attempts to bypass this restriction by incorporating error smoothing coefficient adaption. This paper clearly identifies the possible stall/failure mechanism of one of these candidate algorithms and proves the global stability of the other, but notes the equation error type source of the second´s biased-ness in the presence of output measurement noise.