Aalborg Universitet Efficient Resource Configuration for Grant-Free Ultra-Reliable Low Latency

Achieving efficient ultra-reliable low-latency communications (URLLC) in the uplink with strict requirements such as 99.999% reliability in 1 ms is extremely challenging . Grant-free transmission is a promising access method as the error prone scheduling phase and its associated delays are avoided. For aperiodic traffic, sharing of grant-free resources is used to improve resource utilization. However, interand intra-cell interference caused by simultaneous transmiss ions from multiple users can drastically reduce the supported URLLC load in the network. In this paper, a resource configuration scheme for uplink grant-free URLLC is proposed. Our solution includes different modulation and coding scheme (MCS) opti ons associated with sub-bands allocations and power control se ttings. A simple MCS selection scheme is used to assign higher MCSs and reduced sub-bands to user equipments with high coupling gains, thus reducing the impact from overlapping transmissions. Our grant-free system design includes hybrid automatic repeat request retransmissions along with a mini-slot structure and linear receiver with interference rejection capability for multipacket reception. The performance of the proposed solutionis evaluated in a multi-cell urban scenario. System level resu lts reveal an up to 90% gain on the achievable URLLC load with respect to a single-MCS reference configuration, when a 2 antennas receiver is used. The usage of a 4 antenna receiver further boosts the achievable load by a factor of 7.