Link-Level Investigations of Hybrid-ARQ schemes for 5G URLLC Scenarios

Ultra Reliable Low Latency Communication (URLLC) is one of the most relevant services emerging in future fifth generation (5G) wireless systems. In this work we address Hybrid Automatic Repeat reQuest (HARQ) schemes, whose purpose is enhancing URLLC reliability, if latency constraint allows for retransmissions. In particular, we focus on performance comparison between Incremental Redundancy (IR) and two flavours of Chase Combining (CC), where bit-mapping is applied before or after symbol demodulation. Our studies are supported by link level-simulations of Low-Density Parity-Check (LDPC) codes specified for 5G data transmission. We compare the performance of the three HARQ schemes and their sensitivity with respect to the relevant link parameters. We assess then the URLLC reliability in a realistic system scenario, without abstraction of the encoding and decoding steps typically assumed in the literature with system-level simulators.