Pre-scheduled Resources for Retransmissions in Ultra-Reliable and Low Latency Communications

The fifth generation (5G) cellular network demands new solutions to meet, in an efficient way, the stringent targets for ultra-reliable and low latency communication (URLLC), such as 1-10-5 reliability within 1 ms. In a wireless system, the control signaling of the scheduling process is also a source of errors and delays. Semi-persistent scheduling (SPS) is an option to reduce the signaling, leading to lower latency and improved transmission reliability. However, conventional SPS still applies grant signaling to schedule the retransmission. In this work it is proposed an alternative scheme in which a group of users shares a pre-scheduled resource for retransmission. The benefit is that it provides a retransmission opportunity without needing a scheduling control information. Besides that, if the pre-scheduled resource can not be reallocated, the sharing mechanism avoids excessive capacity loss. It is demonstrated through a simple analytical model that, for right grouping sizes and initial transmission error rates, the target error probability e.g. 10(-5) can be achieved. It is also shown that the suggested scheme can provide improved resource efficiency compared to a single conservative transmission which also avoids re-scheduling.