Joint Linear and Nonlinear Precoding in MIMO Systems

Multiuser MIMO vector perturbation precoding facilitates multiple representations of the transmit symbols in order to improve transmit power normalisation of the transmitted signal. All the receiver needs to do is to apply a modulo operation to undo the perturbation. However existing system with multiuser MIMO support, such as LTE, employ linear precoding. This means that these legacy users will not be able to operate together with new users with vector perturbation capabilities, reducing the system throughput and flexibility in resource allocation. In this paper we present a novel precoding technique which allows the joint precoding of legacy and new users. The precoding ensures that no perturbations are made to linearly precoded users, while minimising the power normalisation using a modified sphere encoder. We also show that the diversity order of the joint precoding scheme is the difference between the number of transmit antennas and the number of legacy users, regardless of the number of new users.