Frequency-Hopping Enhanced Repetition Scheme for URLLC in Multi-Connectivity Networks Over Slow Fading Channels
Qingjiao Song, Fu‐Chun Zheng, Chunguo Li · IEEE Internet of Things Journal · 2025
Frequency-hopping enhanced repetition (FHER) scheme, which provides time diversity and frequency diversity, has been considered a promising approach to meet the ultra-high reliability requirement of ultra-reliable and low latency communications (URLLC) in Grant-free (GF) random access networks. However, the effects of slow fading may significantly reduce the diversity gains offered by an FHER scheme, and such effects so far have not been considered in most studies. Moreover, practical designs for FHER patterns tailored to URLLC remain underexplored. In this paper, we employ a multi-connectivity (MC) scheme to overcome the effects of slow fading and enhance reliability through space diversity. We then propose a novel FHER pattern design to meet both low latency and high reliability requirements. To support more UEs with a limited number of subchannels, we further propose an FHER pattern assignment scheme that allows pattern reuse by distant UEs while mitigating the effects of slow fading. The performance of the proposed scheme is then analyzed and approximated in closed-form expressions under both selection combining (SC) and maximum ratio combining (MRC). Simulation results show that the proposed scheme significantly increases the number of successfully served UEs compared to the K-repetition schemes. Furthermore, the simulation results closely match the analytical results under SC, while the MRC-based analysis provides a tight reliability approximation when the number of associated base stations (BSs) is small (as it is in practice).