Improving link robustness in 5G ultra-dense small cells by hybrid ARQ

A new 5^th generation (5G) radio access technology is expected to cope with an estimated factor of ~x1000 growth in mobile data traffic in the upcoming years. Such system will be optimized for a massive uncoordinated deployment of small cells, where autonomous operation of the individual nodes may bring unpredictable and fast varying link quality. In this paper, Hybrid Automatic Repeat Request (HARQ) is studied as a solution to cope with such unpredictability. An operational mode of HARQ for our 5G system definition is proposed, and its performance is evaluated for two different scheduling options. Simulation results confirm the capability of HARQ of improving the final throughput and solving outage problems, with limited impact on the end delay.