Multiuser separation and performance analysis of millimeter wave   channels with linear precoding
  In the conventional multiuser MIMO systems, user selection and scheduling has previously been used as an effective way to increase the sum rate performance of the system. However, the recent concepts of the massive MIMO systems (at centimeter wavelength frequencies) have shown that with higher spatial resolution of antenna arrays different users in the dense scenarios can be spatially separated. This in turn significantly reduces the signal processing efforts required for multiuser selection algorithms. On the other hand, recent measurements at millimeter wave frequencies show that multipath components only arrive from few angular directions leading to high spatial correlation between the paths and co-located users. This paper focus at the investigation of spatial separation among the users at the millimeter wave frequencies with fully digital linear zero-forcing transmit precoding considering various channel propagation parameters. Our analysis results convincingly give a proof that multiuser selection algorithms are still important for millimeter wave communication systems. Results also show that increased number of antenna elements does not give a major benefit to sum rate improvements as compared to the selection of correct number of users to be selected/scheduled. 
Waqas Ahmad, Geamel Alyami and Ivica Kostanic
cs.IT math.IT