Space-time processing for increased capacity of wireless CDMA
Spatial and temporal processing are combined to increase the capacity of CDMA-based wireless communications systems. Degrees of freedom provided by space-time processing are exploited to combat both fading and co-channel interference (the near-far effect). The following methods are formulated and studied: (1) space-time diversity, (2) cascade optimum spatial-diversity (RAKE) temporal, (3) cascade optimum spatial-optimum temporal, and (4) joint domain optimum processing. It is shown that, due to its interference cancellation capability, optimum combining provides significantly better performance than diversity processing. In particular, in a typical CDMA scenario with two antennas, the joint domain optimum combining system provides at least a 30% increase in capacity over diversity processing. Optimum combining may also be applied to compensate for imperfect power control of the signals received at the base station.