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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.

• IIR filters
• Adaptive IIR filtering
• Hyperspherical parametrization
• Adaptive infinite impulse response filtering
• Unit-norm constraint
• Autoregressive AR coefficients
• AR coefficients
• Unit-norm-constrained optimization
• Unconstrained optimization
• Equation error surface
• Equation error minimisation