Patent ID: 7412469

Claim:
A training method for a power amplifier pre-distorter formed by a Finite Impulse Response (FIR) filter structure comprising an individual look-up table for each filter tap, each look-up table representing a discretized polynomial in a variable representing input signal amplitude, and means for selecting, from each filter tap look-up table, a filter coefficient that depends on the amplitude of a corresponding complex signal value to be multiplied by the filter tap, said training method comprising the steps of: storing measured unamplified input signal samples and corresponding power amplifier output signal feedback samples; determining look-up table filter coefficients for each filter tap by separate independent iterative procedures using said stored samples, wherein said iterative procedures are least mean square based, said step of determining comprising: calculating a refined filter coefficient estimate T qi (b) corresponding to a filter tap with a delay q and a signal amplitude bin b from a previous filter coefficient estimate T qi−1 (b) in accordance with the equation: T q ⁢ ⁢ i ⁡ ( b ) = T q ⁢ ⁢ i - 1 ⁡ ( b ) + μ q · 1 N b · ∑  x k - q  ∈ M b ⁢ x k - y k  x k - q  2 · x k - q * where: μ q is a predetermined constant associated with filter tap q; N b is the number of stored input signal samples that have an amplitude that falls within a predetermined window M b around the center amplitude of bin b; x k−q is a stored input signal sample that has a delay q; y k is a power amplifier output signal feedback sample corresponding to power amplifier input signal sample x k ; and, * denotes complex conjugation.