A variable step-size diffusion affine projection algorithm

We propose a combination method for a diffusion affine projection algorithm. There are two steps to estimate unknown optimal weight in Adapt-then-combine strategy of diffusion adaptive filtering. In an adaptation step, variable step-size affine projection algorithm works to get an improvement of convergence rate and small steady-state error. In a diffusion step, the proposed combination method is applied to achieve small steady-state errors without additional communicational complexity. The cooperative strategy using information across the network achieves fast convergence rate, small steady-state error and robustness against outliers compared to a non-cooperative way. The proposed algorithm is motivated from the optimal combination rule and it has a physical meaning of weighting on how close the estimates reach in steady state.