  Supporting Ultra-Reliable Low-Latency Communication (URLLC) in the Internet
of Things (IoT) era is challenging due to stringent constraints on latency and
reliability combined with the simple circuitry of IoT nodes. Diversity is
usually required for sustaining the reliability levels of URLLC, but there is
an additional delay associated to auxiliary procedures to be considered,
specially when communication includes low-cost IoT devices. Herein, we analyze
Selection Combining (SC) and Switch and Stay Combining (SSC) diversity schemes
as plausible solutions for enabling ultra-reliable low-latency downlink
communications to low-cost IoT devices. We demonstrate the necessity of
considering the time spent in auxiliary procedures, which has not been
traditionally taken into account, while we show its impact on the reliability
performance. We show there is an optimum number of receive antennas, which
suggests that under certain conditions it might be required to turn off some of
them, specially under the SC operation. We highlight the superiority of SSC
with respect to SC as long the associated Signal-to-Noise Ratio threshold is
properly selected. We propose using a fixed threshold relying only on long-term
channel fading statistics, which leads to near-optimum results.
