  In multiple-input multiple-output (MIMO) fading channels maximum likelihood
(ML) detection is desirable to achieve high performance, but its complexity
grows exponentially with the spectral efficiency. The current state of the art
in MIMO detection is list decoding and lattice decoding. This paper proposes a
new class of lattice detectors that combines some of the principles of both
list and lattice decoding, thus resulting in an efficient parallelizable
implementation and near optimal soft-ouput ML performance. The novel detector
is called layered orthogonal lattice detector (LORD), because it adopts a new
lattice formulation and relies on a channel orthogonalization process. It
should be noted that the algorithm achieves optimal hard-output ML performance
in case of two transmit antennas. For two transmit antennas max-log bit
soft-output information can be generated and for greater than two antennas
approximate max-log detection is achieved. Simulation results show that LORD,
in MIMO system employing orthogonal frequency division multiplexing (OFDM) and
bit interleaved coded modulation (BICM) is able to achieve very high
signal-to-noise ratio (SNR) gains compared to practical soft-output detectors
such as minimum-mean square error (MMSE), in either linear or nonlinear
iterative scheme. Besides, the performance comparison with hard-output decoded
algebraic space time codes shows the fundamental importance of soft-output
generation capability for practical wireless applications.
