UAV Beamwidth Design for Ultra-Reliable and Low-Latency Communications with NOMA

In this paper, we investigate the non-orthogonal multiple access (NOMA) based unmanned aerial vehicle (UAV) assisted ultra-reliable and low-latency communications (URLLC) without the presence of base station. To achieve URLLC, we minimize the block error probability by appropriately reducing the beamwidth. Since the user grouping approach can reduce the coverage of user-free area to achieve the beamwidth reduction by only covering the users in each group, we propose two user grouping algorithms for UAV-assisted NOMA transmission. The first one is the improved K-means algorithm. It needs to set the number of groups in advance and has good performance in solving the problem considered in this paper. The second one is an extended affinity propagation (AP) clustering algorithm. This algorithm is easier to implement than the first one because it does not need to pre-define the number of groups, but the performance is inferior to the first algorithm. After user grouping, we introduce a location-based beamwidth design for each group to further minimize the beamwidth and solve the optimization problem. Numerical results show that the performance of the proposed user grouping algorithms with the location-based beamwidth design schemes are superior to the benchmark schemes under the URLLC constraints.