Joint transmitter/receiver optimization in synchronous multiuser communications over multipath channels

Increasingly evident in recent work, it appears that transmitter optimization in addition to receiver optimization contributes significantly to efficient interference suppression in multiple access and multipath channels. The system design in this paper is based on the joint optimization of the transmitter and the receiver in a synchronous multiuser channel characterized with multipath propagation. Joint optimization is represented by a linear transformation of transmitted signals in the transmitter and a linear transformation of received signals at each receiving site that minimize the effect of multiple access and multipath interference. The minimum mean squared error between the true bit value and its estimate at the output of the receiver is taken as the cost function, subject to the average transmit power constraint. It is shown that joint transmitter-receiver optimization outperforms significantly transmitter optimization and conventional receiver based techniques, matched filter and RAKE receivers. The crucial assumption is that the transmitter knows multipath characteristics of all channels and that channel dynamics are sufficiently slow so that multipath profiles remain essentially constant over a block of preceded bits.