Optimization for crosstalk suppression with noncoordinating users

A joint transmitter/receiver optimization problem for multiuser communications in a symmetric crosstalk environment based on the minimum mean squared error (MMSE) criterion is addressed. It is assumed that each user employs an identical transmit pulse shaping filter and sees identical direct and crosstalk channel responses. All the channels are assumed to be bandlimited with identical support that, in general, extends beyond the basic Nyquist zone [-(1/2T), 1/2T], corresponding to the common symbol period T. Necessary conditions for the optimum transmitter and receiver are derived and several useful insights generated. In particular, the performance advantage obtained by exploitation of the cyclostationary nature of the interference is demonstrated, corroborating earlier results. An algorithmic procedure to solve for the jointly optimal transmit-receive pair is outlined and used for numerical evaluation of the system performance as a function of several parameters of interest such as system bandwidth, the number of users and the number of points at which the transmitter is nonzero in the set (f: f₀+k/T) where T is the symbol period, and f₀ ∈[-(1/2T),1/2T]