  In this paper two complexity efficient soft sphere-decoder modifications are
proposed for computing the max-log LLR values in iterative MIMO systems, which
avoid the costly, typically needed, full enumeration and sorting (FES)
procedure during the tree traversal without compromising the max-log
performance. It is shown that despite the resulting increase in the number of
expanded nodes, they can be more computationally efficient than the typical
soft sphere decoders by avoiding the unnecessary complexity of FES.
