Constructive Multiuser Interference in Symbol Level Precoding for the MISO Downlink Channel

This paper investigates the problem of interference among the simultaneous
multiuser
transmissions in the downlink of multiple-antenna systems. Using symbol-level precoding, a new approach to exploit the multiuser interference is discussed. The concept of exploiting the interference between
spatial multiuser transmissions by jointly utilizing data information
(DI)
and channel state information (CSI), in order to design symbol-level precoders,
is proposed. To this end, the interference between data streams
is transformed under certain conditions into useful signal that can improve the signal to interference
noise ratio (SINR) of the downlink transmissions. We propose a maximum ratio
transmission (MRT) based algorithm that jointly exploits DI and CSI to glean the benefits from constructive multiuser interference. Subsequently, a relation between the constructive interference downlink transmission and physical
layer multicasting is established. In this context, novel constructive interference precoding techniques that tackle the transmit power minimization (min-power) with
individual SINR constraints at each user's receivers is proposed. Furthermore, fairness through maximizing the weighted minimum SINR (max-min SINR) of the users is addressed by finding the link between the min power and max min SINR problems. Moreover, heuristic precoding techniques are proposed
to tackle the weighted sum rate problem.
Finally, extensive numerical results
show that the proposed schemes outperform other state of the art techniques.