Massive MIMO enabled joint unicast transmission to IoT devices and mobile terminals

We investigate the viability of downlink (DL) unicast transmission from a base station (BS) with massive number of antennas jointly to support machine-centric communication among the internet-of-things (IoT) devices and human-centric communication among the mobile terminals. Specifically, we derive a new expression for the DL sum spectral efficiency (SE) for the IoT devices with maximum ratio precoding when channel estimates are acquired via the proposed distance-dependent grouping based hybrid pilot assignment strategy. We also derive a new DL sum SE expression for IoT devices based on non-orthogonal pilot assignment. We show that under statistical channel inversion based power control at the BS, the proposed strategy yields the highest sum SE and can serve the largest number of IoT devices when compared against orthogonal, non-orthogonal and distance-independent grouping based hybrid strategies. Furthermore, we also analyse the DL sum SE of mobile terminals in the presence of IoT devices when every mobile is given an orthogonal pilot and prove that the sum SE is independent of the pilot assignment strategy employed by the IoT devices. We also obtain the max–min rate for the IoT devices and prove that it is independent of the pilot assignment strategy used by the devices.