Selection Criteria of Multiple Users
In the last chapter, different selection schemes have been introduced to choose a single user among multiple users to access the MIMO channel at a time. In some cases, as multiple users are able to access the MIMO channels at the same time, the selection of multiple users has to be considered. By viewing multiuser MIMO as virtual antennas in a single user MIMO system, various antenna selection techniques have been studied to determine the subset of multiple antennas that transmit or receive signals [86, 87, 88]. For example, a mutual information-based criterion is proposed in  to select the antenna subset that maximizes the mutual information. In addition, a geometrical-based criterion is developed with an LR-based linear detector to minimum the error probability in . Note that those schemes can also be adopted to select multiple users in multiuser MIMO systems.