Side-Link Assisted Hybrid Automatic Repeat Request for Ultra-Reliable Low Latency Communications

One of the key use cases of fifth generation of mobile radio (5G) is to deliver ultra-reliable low latency communication (URLLC). Besides antenna- and frequency diversity techniques, hybrid automatic repeat request (HARQ) is a powerful tool to increase reliability. However, due to the low latency requirement, only a very small number of retransmissions can be carried out. In this paper, we consider the help of additional supporting user equipment (sUE) devices. The sUE listens to the transmitter user equipment (tUE) and relays the retransmitted data in case the transmission fails between the tUE and the base station. The proposed approach improves reliability since the sUE offers an additional source of antenna diversity, and it can provide benefits because of better path gain conditions compared to the tUE. Hence, the number of required transmissions will be significantly reduced thanks to the side-link assistance. In this way, the complete setup can be considered as a distributed smart antenna system. The simulation results show that the considered sidelink-assisted framework achieves a significant reduction of the latency compared to the scenario relying on direct-link-only.