TRANSMITTER PRECEDING IN SYNCHRONOUS MULTIUSER COMMUNICATIONS

In this paper a synchronous multiuser system operating in an additive white Gaussian noise channel, with or without multipath fading, is con sidered. It is shown that when either a conventional single user recei ver or the RAKE receiver is employed, both multiple access and intersy mbol interference can be eliminated by means of a suitable transmitter preceding scheme, Transmitter preceding represents a linear transform ation of transmitted signals, such that the mean squared errors at all receivers are minimized. Preceding, with both conventional single use r receiver and with the RAKE receiver, results in near-far resistant p erformance and outperforms considerably the respective schemes without preceding. The crucial assumption, in the multipath case, is that the transmitter knows the multipath characteristics of all channels and t hat channel dynamics are sufficiently slow so that multipath profiles remain essentially constant over the block of preceded bits.