Optimizing Transmission Rate in NOMA via Block Diagonalization Beamforming and Power Allocation In this paper, we propose a new transmission scheme, relying on user clustering, transmit beamforming and power allocation, for nonorthogonal multiple access (NOMA) in a downlink cellular framework. Assuming that channel state information is available at the base station, the users are first partitioned into small clusters based on a weighted multiobjective optimization, so that each cluster may be served by a single beamforming vector. The complete set of beamforming vectors is jointly designed to remove intercluster interference by taking advantage of block diagonalization along with maximum ratio transmission. Subsequently, the NOMA power allocation factors for the users in each cluster are determined by solving an optimization problem, where the aim is to maximize the transmission sum rate subject to power and SINR constraints. The performance of the proposed NOMA scheme is validated by means of numerical analysis. Compared to the benchmark approaches, the results show significant improvements in terms of spectral efficiency and interference cancellation.

Novel EnergyEfficiency Enhancement Schemes for Asynchronous NonOrthogonal Multiple Access Nonorthogonal multiple access (NOMA) has been extensively studied in 5G New Radio (NR) for massive multimedia transmissions in scenarios such as massive MachineType Communication (mMTC). Existing researches normally assume synchronous usermultiplexing, which may introduce additional signaling overhead as well as large power consumption. However, the users in mMTC may not have strict synchronization due to signaling reduction and energy efficiency (EE) concern. To this end, two enhanced NOMA schemes are proposed to promote EE of asynchronous NOMA. Specifically, discontinuous transmission and rate splitting are respectively introduced to provide chances for successive interference cancellation receiving, which promotes the received SINR. Numerical simulations validate the advantages of the proposed schemes with respect to EE.