Hyperspherical parametrization for unit-norm based adaptive IIR filtering

The bias problem associated with equation error based adaptive infinite impulse response (IIR) filtering can be surmounted by imposing a unit-norm constraint on the autoregressive (AR) coefficients. We propose a hyperspherical parameterization to convert the unit-norm-constrained optimization into an unconstrained optimization. We show that the hyperspherical parameterization does not introduce any additional minima to the equation error surface.