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

One of the key use cases of 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, as well as improved path gain conditions. Hence the number of required retransmissions will be significantly reduced where the complete setup is considered as smart antenna system. The simulation results show that the considered sidelink-assisted framework achieves a significant reduction of the latency comparing to the scenario relying on direct link only.