Low-Complexity Downlink User Selection for Massive MIMO Systems

Abstract

In this paper we propose a pair of low-complexity user selection schemes with\nzero-forcing precoding for multiuser massive MIMO downlink systems, in which\nthe base station is equipped with a large-scale antenna array. First, we derive\napproximations of the ergodic sum rates of the systems invoking the\nconventional random user selection (RUS) and the location-dependant user\nselection (LUS). Then, the optimal number of simultaneously served user\nequipments (UEs), $K^*$, is investigated to maximize the sum rate\napproximations. Upon exploiting $K^*$, we develop two user selection schemes,\nnamely $K^*$-RUS and $K^*$-LUS, where $K^*$ UEs are selected either randomly or\nbased on their locations. Both of the proposed schemes are independent of the\ninstantaneous channel state information of small-scale fading, therefore\nenjoying the same extremely-low computational complexity as that of the\nconventional RUS scheme. Moreover, both of our proposed schemes achieve\nsignificant sum rate improvement over the conventional RUS. In addition, it is\nworth noting that like the conventional RUS, the $K^*$-RUS achieves good\nfairness among UEs.\n