  This letter studies how to use spatial beams pre-configured in a legacy
spatial division multiple access (SDMA) network as bandwidth resources via the
implementation of non-orthogonal multiple access (NOMA). Two different beam
management schemes, namely beam selection and beam aggregation, are developed
to improve the overall system throughput without consuming extra spectrum or
changing the performance of the legacy network. Analytical and simulation
results are presented to show that the two schemes realize different tradeoffs
between system performance and complexity.
