Adaptive Space-Time Multiuser Detection in Synchronous CDMA
Generally speaking, space-time processing involves the
exploitation of spatial diversity using multiple transmit and/or receive
antennas and, perhaps, some form of coding. In previous sections we have focused
on systems that employ one transmit antenna and multiple receive antennas.
Recently, however, much of the work in this area has focused on transmit
diversity schemes that use multiple transmit antennas. They include delay
schemes [444, 572, 573] in which copies of the same
symbol are transmitted through multiple antennas at different times, the
space-time trellis coding algorithm in [477], and the simple space-time block
coding (STBC) scheme developed in [12], which has been adopted in
third-generation (3G) wideband CDMA (WCDMA) standards [294, 479]. A generalization of this simple
space-time block coding concept is developed in [475, 476]. It has been shown that these
techniques can significantly increase capacity [122, 478].
In this section we discuss adaptive receiver structures for
synchronous CDMA systems with multiple transmit antennas and multiple receive
antennas. Specifically, we focus on three configurations: (1) one transmit
antenna, two receive antennas; (2) two transmit antennas, one receive antenna;
and (3) two transmit antennas, two receive antennas. It is assumed that the
orthogonal space-time block code [12] is employed in systems with two
transmit antennas. For each of these configurations, we discuss two possible
linear receiver structures and compare their performance in terms of diversity
gain and signal separation capability. We also describe blind adaptive receiver
structures for such multiple-antenna CDMA systems. The methods discussed in this
section are generalized in the next section to mutipath CDMA systems. The
materials discussed in this and the following sections first appeared in [415].
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