LSF CSI are regenerated at each realization). It is observed that there exist $K^*_{\text{RUS}}$ and $K^*_{\text{LUS}}$ which maximize the system sum rate for $K$-RUS and $K$-LUS, respectively. Moreover, we have $K^*_{\text{RUS}}<M$ and $K^*_{\text{LUS}}<M$ for the simulation parameters considered. In Fig. \[fig3\] we also show the approximate sum rates given by and , which are very tight. Therefore, it is reasonable to design user selection schemes based on them.

In order to provide intuitive insights into how $K^*_{\text{RUS}}$ and $K^*_{\text{LUS}}$ are affected by $P$ and $N$, we evaluated $K^*_{\text{RUS}}$ and $K^*_{\text{LUS}}$ with no transmit correlation and perfect CSI estimation (i.e., $\rho=0, \delta=0$) in Fig. \[fig4\] (a) and (b), respectively. It is observed that both $K^*_{\text{RUS}}$ and $K^*_{\text{LUS}}$ increase with the transmit power $P$. On the other hand, when we increase $N$, $K^*_{\text{LUS}}$ increases and $K^*_{\text{RUS}}$ remains unchanged. This can be easily explained from the perspective of multiuser diversity gain. In particular, $K^*_{\text{LUS}}$ is related to $N$ because we select UEs according to LSF in $K^*$-LUS. By contrast, $K^*_{\text{RUS}}$ is independent of $N$ because random selection is adopted in $K^*$-RUS. Moreover, Fig. \[fig4\] (c) and Fig. \[fig4\] (d) provide the sum rates of $K^*$-RUS and $K^*$-LUS. As expected, we can see that 