Pipelined Multi-User IR-HARQ for Improved Latency Performance and Energy Efficiency in URLLC

The need to meet stringent latency requirements in ultra-reliable low-latency communications (URLLC) led to the exploration of configured grant (CG) leveraged techniques in order to remove the need of scheduling requests, and accelerate uplink access time. The CG can be paired with an IR-HARQ scheme, improving the finite block length performance, but leads to inefficient resource usage. This inefficiency can be mitigated by setting the CG to a group of UEs. In this paper, two new IR-HARQ GCG schemes are proposed. The first scheme eliminates feedback latency overhead, as UEs transmit serially through the entire group bandwidth. The second scheme is a fusion between the first scheme and MU-HARQ. This scheme is able to balance MU-HARQ latency reduction and the first scheme feedback latency protection. Results show that this second scheme is able to outperform the one-shot with equal transmission power, both in latency and energy, for a wide interval of feedback latency values.