A soft symbol decoder for use in a multiple input multiple output (MIMO)
and OFDM (orthogonal frequency division multiplexing) system. The decoder
generates soft symbol values for a digital signal that represents a
number of source bits. The source bits are transmitted as symbols in
corresponding to points in a signaling constellation. Soft metrics are
determined by searching for all possible multi-dimensional symbols that
could have been transmitted. The method includes transmitting a sample of
the multi-dimensional symbol using K transmit antennas. The
multi-dimensional symbol is represent-able as a complex, K-dimensional
vector x. Each vector component of vector x represents a signal
transmitted with one of the K transmit antennas. After transmission
through a communication channel, a sample corresponding to the
transmitted sample is received. The received sample is represented by a
complex, N-dimensional vector y, where N is the number of receive
antennas in the MIMO system. After the sample is received, a soft metric
L(b.sub.i) is determined for each bit b.sub.i encoded by x according to
the equation:.function..sigma..times..times..times..times. ##EQU00001##
and x.sub.j represents all possible values for x. In addition, a reduced
complexity method is used for providing soft metric values in the MIMO
system. This exemplary aspect reduces the complexity of the above
computations from 2.sup.BK to 2.sup.B(K-1), where B is the number of bits
transmitted per symbol per antenna.