On the efficiency of the sequential detector for solving soft-output detection problems

Combining tree search detection with iterative detection-decoding allows achieving near-capacity performance in multiple antenna systems. In this contribution we show that the list sequential detector employing a Schnorr-Euchner enumeration strategy visits the minimum amount of tree nodes necessary to find a given number of hypotheses on the transmit signal which maximize the a posterior probability. It it thus the tree search scheme with lowest complexity for solving the soft output detection task optimally for a given list size.