A Method Performed by a Sphere Decoder Based Turbo Equalizer

A sphere decoder based turbo equalizer is described. A method comprises assorting in a first vector Quadrature Amplitude Modulation, QAM, symbols on a particular tree level based on first distance properties, assorting in a second vector QAM symbols on the particular tree level based on second distance properties, selecting the QAM symbol with the minimum second distance property in the second vector, wherein said selecting comprises labeling the selected QAM symbol as protected, identifying the selected QAM symbol in the first vector assorted by distance properties, pruning the first vector by eliminating all QAM symbols having a larger first distance property compared to the selected QAM symbol, wherein said pruning is restricted to QAM symbols not being labeled as protected, and repeating the steps d-e selecting the QAM symbol with the next minimum second distance property.