# Resource-Efficient Multicast URLLC Service in 5G Systems
## 5 Conclusions  
In this paper, we studied the new mechanisms introduced in 3 GPP specifications that enabled multicast in 5G systems. We analyzed how to efficiently configure these mechanisms and how to adapt transmission parameter selection algorithms (i.e., precoder selection, RB allocation, and MCS selection) to provide reliable delivery of an mURLLC stream with low channel resource consumption. Based on the extensive simulation results, we provide the following recommendations (see Table 2 for details).  
1. The performance and complexity of various precoder selection algorithms significantly depend on the number of antennas at the gNB. For the M-MIMO case, orthogonal subspace construction algorithms (e.g., SBFC, QR) provide the lowest resource consumption with low complexity;
2. The usage of the FS EDF scheduler notably reduces the channel resource consumption only for low multicast group size and a low number of antennas at the gNB. In other cases, the non-FS EDF scheduler provides almost the same resource consumption and up to 40% lower computational complexity;
3. If the latency budget allows HARQ retransmissions, they shall be enabled because, in contrast to traditional broadband multicast traffic, they allow reducing resource consumption up to three times for mURLLC;
4. In the case of two transmissions, the usage of two different target BLERs for MCS selection significantly reduces resource consumption compared with the widely used approach of selecting the same MCS for the initial transmission and retransmission;
5. Out of three considered feedback schemes, the NACK-only scheme provides the lowest resource consumption for mURLLC;
6. In the case of mURLLC, optimization of the sounding period allows a notable reduction in resource consumption only in low-mobility scenarios.  
Summing up, by implementing the recommendations above, the network operator can provide mURLLC service with much lower channel resource consumption compared with the baseline solutions proposed for broadband multicast or unicast URLLC traffic and, therefore, significantly increase the network capacity in terms of the number of concurrent mURLLC flows or their aggregated load.  
One of the promising directions for future research is to adaptively select the best sounding period for each multicast group member.  
Conceptualization, A.K. and E.K.; Formal analysis, E.K. and R.Y.; Investigation, I.L. and R.Y.; Methodology, A.K. and R.Y.; Software, I.L. and R.Y.; Validation, A.K., I.L., R.Y. and E.K.; Writing--original draft, A.K., I.L., R.Y. and E.K. All authors have read and agreed to the published version of the manuscript.  
The research was carried out at HSE University and supported by the Russian Science Foundation (Grant No 21-79-10158, [[https://rscf.nu/en/project/21-79-10158/](https://rscf.nu/en/project/21-79-10158/)]([https://rscf.nu/en/project/21-79-10158/](https://rscf.nu/en/project/21-79-10158/)) (accessed on 10 April 2024)).  
Figure 8: Scenario with different \(T_{SRS}\) and UE mobility: (**a**) downlink resource consumption, (**b**) overall resource consumption.  
Conflicts of Interest: The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.