  We present novel soft-input soft-output (SISO) multiple-input multiple-output
(MIMO) detectors based on the Chase detection principle [1] in the context of
iterative and decoding (IDD). The proposed detector complexity is linear in the
signal modulation constellation size and the number of spatial streams. Two
variants of the SISO detector are developed, referred to as SISO B-Chase and
SISO L-Chase. An efficient method is presented that uses the decoder output to
modulate the signal constellation decision boundaries inside the detector
leading to the SISO detector architecture. The performance of these detectors
significantly improves with just a few number of IDD iterations. The effect of
transmit and receive antenna correlation is simulated. For the high-correlation
case, the superiority of SISO B-Chase over the SISO L-Chase is demonstrated.
