  We propose a novel digital backpropagation (DBP) technique that combines
perturbation theory, subband processing, and splitting ratio optimization. We
obtain 0.23 dB, 0.47 dB, or 0.91 dB gains w.r.t. dispersion compensation with
only 74, 161, or 681 real multiplications/2D-symbol, improving significantly on
existing DBP techniques.
