ABSTRACT
Code division multiple access (CDMA) and multiple-input multiple-
output (MIMO) communication systems are two different, but
fundamentally very similar communication techniques. In CDMA a
number of users simultaneously transmit information symbols, with
each user being identified by a spreading code (Viterbi, 1995; Verdu`,
1998). In MIMO, on the other hand, a data stream is separated
into a parallel set of streams, which are then transmitted through
separate antennas (Foschini, 1996; Telatar, 1999). The key point
here is that the multiuser data, in a CDMA system, as well as
the parallel data streams, in a MIMO system, are transmitted in
the same frequency band. Hence, the system capacity increases
with the number of users/transmit antennas. Joint detection has
to be carried out at the receiver to harness this potential capacity
of the multiuser/MIMO systems. Suboptimum receivers, such as
decorrelating and minimum mean square error (MMSE) detectors,
can only realize a fraction of the capacity (Verdu`, 1998). The
full channel capacity can only be harnessed through the optimum
detector that jointly detects data streams (Verdu`, 1996). The
optimum detector, unfortunately, has a complexity that grows
exponentially with the number data streams.
