Abstract
We present a hybrid soft detector that has a good
performance/complexity trade-off for a multiple-input
multiple-output (MIMO) wireless communication system with known
channel information. The new soft detector combines the merits of
a simple unstructured least-squares (LS)-based soft detector and
a list sphere decoder (LSD)-based soft detector for data bit
detection. The former is computationally much more efficient than
the latter at the cost of poorer performance. The poor
performance of the former occurs mainly when the channel matrix
is ill-conditioned. Whenever this happens, we use the LSD-based
soft detector in the hybrid soft detector; otherwise, we use the
LS-based one. Moreover, we provide a tight radius for a sphere
decoder, a hard detector, via using the output of an LS-based
hard detector. These two hard detectors are needed to determine
if LS or LSD should be used in the hybrid soft detector. As an
application example, we consider doubling the maximum data rate
of the IEEE 802.11a conformable wireless local area networks by a
MIMO system with two transmit and two receive antennas. For this
application, the new soft detector is about 10 times faster than
the LSD-based one and is about 10 times slower than the LS-based
one. Yet the packet error rate due to using the new soft detector
is quite close to that of using the LSD-based one.