  In this correspondence, we propose a space domain index modulation (IM)
scheme for the downlink of multiuser multiple-input multiple-output (MU-MIMO)
systems. Instead of the most common approach where spatial bits select active
receiver antennas, in the presented scheme the spatial information is mapped
onto the transmitter side. This allows IM to better exploit large dimensional
antenna settings which are typically easier to deploy at the base station. In
order to mitigate inter-user interference and allow single user detection, a
precoder is adopted at the BS. Furthermore two alternative enhanced signal
construction methods are proposed for minimizing the transmitted power or
enable an implementation with a reduced number of RF chains. Simulation results
for different scenarios show that the proposed approach can be an attractive
alternative to conventional precoded MU-MIMO.
