  Classical ML decoders of MIMO systems like the sphere decoder, the
Schnorr-Euchner algorithm, the Fano and the stack decoders suffer of high
complexity for high number of antennas and large constellation sizes. We
propose in this paper a novel sequential algorithm which combines the stack
algorithm search strategy and the sphere decoder search region. The proposed
decoder that we call the Spherical-Bound-Stack decoder (SB-Stack) can then be
used to resolve lattice and large size constellations decoding with a reduced
complexity compared to the classical ML decoders.
  The SB-Stack decoder will be further extended to support soft-output
detection over linear channels. It will be shown that the soft SB-Stack decoder
outperforms other MIMO soft decoders in term of performance and complexity.
