Finite-Alphabet Beamformed NOMA for Multiuser MISO Broadcast Visible Light Communications

In this paper, we consider an optimal finite-alphabet non-orthogonal multiple access (NOMA) design for a multiuser multi-input single-output (MISO) visible light communication (VLC) broadcast system when channel state information is available at the transmitter. By utilizing the cooperation of multiuser interference, an optimal multidimensional additively uniquely decomposable constellation group (AUDCG) is designed to maximize the received worst-case minimum Euclidean distance of all users subject to a normalized average optical power within the orthants of a real-valued space. This optimal AUDCG is proved to be commonly used pulse amplitude (PAM) with an optimal beamformer, which is the optimal solution to a linear max-min programming problem. In addition, our optimal AUDCG admits fast demodulation of the sum signal from a noisy received signal as well as fast decoding individual signal from the estimated sum signal. Computer simulations indicate that our proposed finite-alphabet NOMA design has significantly better error performance than currently available zero-forcing (ZF), minimum mean square error (MMSE) and time-division orthogonal access (TDMA) transmission schemes for multiuser MISO VLC broadcast systems.