On Maximizing Symmetric Capacity via Signal Design in CDMA Systems

The maximization through signal design of the symmetric capacity of CDMA systems with optimal and minimum mean-square error decision feedback (MMSE-DF) decoding is considered. In particular, lower bounds on maximum symmetric capacity (and the signal set that achieves them) are derived for the two decoders. A common sufficient condition is obtained for both decoders under which the signal design is optimal in that the lower bounds coincide with an upper bound on the maximum achievable symmetric capacity.