Link-Adaptation for Downlink MIMO URLLC Transmissions

We analyze link-adaptation for downlink ultra-reliable and low-latency communication (URLLC) in a flashlight effect scenario where uncoordinated beamforming at an interferer changes between the time when interference power is measured and the time of payload transmission. Backoffs are optimized to guarantee the success of transmission with target reliability. We present the receiving antenna selection method to guarantee the ultra-high reliability to URLLC user. The statistical distribution of ratio of interference powers is derived in closed form, and devise backoff methods guaranteeing reliability of transmissions against the flashlight effect. In an interference limited case, we find that strict reliability guarantees reduce expected transmission rate to a small fraction of that of best effort service. When increasing the number of transmit antennas, most of the array gain is compromised by the increasing backoff needed to guarantee reliability. Furthermore, it is observed from the theoretical results that having a large number of antennas at the base stations is not hardening the channels, rather it is softening them in the context of URLLC transmission.