Selection Criteria of Single User
A rich spatial diversity gain can be obtained by employing various MIMO detectors (e.g., ML and LR-based detectors) to MIMO systems. Considering that multiple users are able to access the MIMO channel from different locations and under different channel conditions, it is possible to exploit another diversity gain, where the performance can be maximized by choosing the user of the best channel at a time. The resulting diversity gain is regarded as the multiuser diversity gain  in multiuser MIMO systems , where the multiuser MIMO user selection [41, 42] becomes an effective way to increase this diversity. In this chapter, for multiuser MIMO systems, we introduce the user selection criteria to select a single user from multiple users at a time, where different selection schemes are developed for different MIMO detection methods to be employed.