Minimization of Power Consumption for NOMA-Assisted UAV Uplink Networks with Imperfect SIC Receiver

Unmanned Aerial Vehicle (UAV) communication networks can move in three-dimensional (3D) space, which can lead to a higher Line of Sight (LoS) probability for wireless communication channels between network nodes. Non-Orthogonal Multiple Access (NOMA) techniques are one of the proposed methods to overcome emerging challenges and meet requirements in the fifth (5G) and sixth (6G) generations of cellular systems. Due to the utilisation of an imperfect Successive Interference Cancellation (SIC) receiver, the performance of the NOMA scheme is vulnerable to error propagation. This paper aims to minimise the power consumption of the NOMA-UAV uplink network, which has limited energy resources. In addition, the impact of Channel State Information (CSI) on resource allocation methods is analysed. The hybrid multiple access schemes are introduced to minimise the sum power in the NOMA-UAV uplink network, subject to minimum data rate and available resource constraints. The frequency sub-bands and transmission power are jointly optimised to decrease the impact of error propagation in the SIC receiver via three hybrid multiple access models, including (i) a hybrid NOMA and OMA scheme with user grouping on multi-NOMA sub-bands, (ii) a hybrid NOMA and OMA scheme with one NOMA sub-band, and (iii) a multi-NOMA sub-bands scheme. The iterative Sequential Quadratic Programming (SQP) algorithm is employed to solve the optimisation problems. The numerical results show the effectiveness of the proposed hybrid schemes in terms of power consumption compared to the conventional NOMA scheme as benchmarks, where the improvement ratio is more than 20%. The hybrid schemes outperform the NOMA schemes reported in other papers, where the performance was compared relative to the OMA scheme. The high diversity of available resources in the hybrid multiple access schemes contributed to achieving the best performance in terms of sum power, which negatively affects the time cost performance. Considering an imperfect SIC receiver, available resources in the NOMA-UAV uplink network are optimised at the ground base station to decrease the transmission power of the UAV communication system, which enhances the energy efficiency of UAVs.