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In this letter, we study a multiuser multi-input single-output (MU-MISO) visible light communication (VLC) broadcast system under the peak-power constraint and dimming control. The space-time modem is designed to maximize the worst-case minimum Euclidean distance of received signals for all users. We prove that the optimal space-time constellation for our considered scenario can be realized by sending identical signals, which is optimal in terms of the SISO intensity channel with peak- and average-power constraints, across all transmitters. Simulation results indicate that our proposed scheme has better bit-error ratio (BER) performance compared with the precoding design and joint detection (PDJD) method and minimum mean-squared error (MMSE) precoder design.

For high-rate peak-limited intensity-modulated optical systems, the two-dimensional time-disjoint signal space (TDSS) is proposed. Based on the TDSS, the optimal hexagonal constellations (OHCs) are proposed analytically under a peak optical power constraint. Both analytical and simulation results show that our proposed OHCs based on the TDSS have the asymptotical peak optical power gain of 0.753 dB over the baseline schemes at no extra bandwidth cost.