## 2 Related Work  
The 5G NR standard introduces the use of grant-free scheduling (also referred to as Configured Grant [7]). With grant-free scheduling, the network pre-configures the radio resources and assigns them to UEs without waiting for UEs to request resources. UEs can utilize the pre-assigned resources as soon as they have data to transmit. This is in contrast to grant-based scheduling, where UEs must request access to radio resources through the transmission of Scheduling Requests (SR). The BS assigns the radio resources to the UEs and notifies them using grant messages. UEs must wait to receive these grant messages before transmitting any data. Grant-free scheduling eliminates all delays introduced by the handshaking present in grant-based scheduling. Grant-free scheduling also improves the energy consumption of the UEs, reduces their complexity, and decreases the signaling overhead compared with grant-based scheduling ([8; 9]). Grant-free scheduling can assign dedicated or shared resources to the UEs. The BS decides whether resources are dedicated to specific UEs, or are shared by a group of UEs [10]. Reserving resources to dedicated UEs is an interesting approach when we can plan ahead what is the demand for resources. This is for example the case of periodic traffic. However, reserving resources to dedicated users can be highly inefficient if the traffic demand is uncertain or aperiodic, and it is not possible to anticipate when these resources will be needed. In this case, it is possible to share radio resources by a group of UEs. This option ensures a more efficient utilization of resources, and the possibility to satisfy URLLC communication requirements. However, users must contend for the resources, and collisions can happen if two or more UEs simultaneously contend for the same resources. 5G NR introduces the possibility of transmitting \(K\) replicas of the same packet in consecutive slots to combat collisions and thus increase the probability of a correct reception [11; 12]. The study in [13] analyzes the performance of the \(K\) replicas scheme. The authors propose transmitting the first copy of a packet using dedicated resources, and the following replicas using shared resources. The proposal also exploits shared diversity and advanced receiver processing techniques to reduce the impact of packet collisions. The proposal achieves adequate reliability levels and reduces the number of reserved (shared) radio resources, compared to a configuration that reserves resources to dedicated UEs. The study in [14] also transmits the first copy of a packet using dedicated resources. However, it does not consider the transmission of \(K\) replicas of a packet. Instead, the authors propose to retransmit the original packet in a shared resource only if the first transmission is not successful. This requires a handshaking between the UEs and the BS to exchange acknowledgement messages. This handshaking increases the latency, and can compromise the capability to adequately support URLLC applications with stringent latency requirements. In [15], the authors study the optimum number of replicas (\(K\)) necessary to achieve a target reliability level within a deterministic latency deadline. The study focuses upon aperiodic traffic and the case in which a group of UEs share resources. The authors show that randomly choosing the resource for each replica increases the probability of correctly delivering a packet. However, the study focuses on reliability levels up to 1-10\({}^{-5}\) while some critical Industry 4.0 applications require higher reliability levels. Previous studies have shown that transmitting \(K\)-repetitions of a packet increases the reception rate. However, this can be done at the expense of an inefficient use of the radio resources due to packet collisions or the unnecessary reservation of resources when the first replicas are correctly delivered.