Patent ID: 7245666

Claim:
A method for determining soft metrics in a multiple input, multiple output communication system, wherein a number B*M t of bits are transmitted in a channel period as M t symbols in a signaling constellation via a number M t of transmit antennas to a number M r of receive antennas, the method comprising: (a) receiving through the communication channel a signal represented by an M r -dimensional vector r, wherein each component of the vector r corresponds to a signal received by a respective one of the receive antennas; (b) computing an M t -dimensional vector x sub representing a sub-optimal reconstruction of the transmitted set of symbols; (c) for each component x sub,k of the vector x sub , selecting a corresponding plurality of constellation points to be searched, the plurality of constellation points making up a set X k of nearest neighbor constellation points, wherein fewer than all of the constellation points in the signaling constellation are included in the set X k ; (d) for a combination of constellation points formed by selecting one of the plurality of nearest neighbor constellation points from the set X k for each of the transmit antennas k, computing a residual error d using the received signal r and the constellation points in the combination; and (e) computing from the residual error d a metric L(k,j) for a transmitted bit b j sent by a transmit antenna k.