Optimized Power Allocation for Uplink Rate Splitting Multiple Access Over OFDMA for Urban Air Mobility

Abstract

Urban Air Mobility (UAM) is expected to rely on terrestrial cellular infrastructure for cost-effective connectivity. However, uplink (UL) transmissions from aerial user equipment (AUE) may cause severe interference due to favorable airto-ground propagation toward multiple base stations (BSs). Motivated by this challenge, this paper studies an UL orthogonal frequency-division multiple access (OFDMA) coexistence scenario in which the AUE and terrestrial user equipment (TUE) share the same sub-channels under coordinated reception among multiple BSs. An UL rate-splitting transmission strategy is studied, in which the AUE’s signal on each sub-channel is divided into a common stream, decoded by all BSs in the coordination set, and a private stream, decoded by one selected BS, while one TUE is multiplexed on the same sub-channel. Under transmitpower constraints, we formulate a weighted sum-rate (WSR) maximization problem over all sub-channels and develop an iterative solution based on successive convex approximation (SCA). To avoid the combinatorial complexity of joint BS selection, the decoding BS for the private stream on each subchannel is chosen according to the strongest AUE-BS channel gain. Simulation results based on 3rd generation partnership project (3GPP) channel models show that the proposed scheme achieves consistent WSR gains over benchmark non-orthogonal multiple access (NOMA) and OFDMA schemes in the considered aerial-terrestrial coexistence setting.