## Abstract

Massive multi-color visible light communications (mMC-VLC) sufficiently utilizing space and color domain resources is proposed to satisfy high-spectral-efficiency, high-speed, and high-density-coverage requirements of next-generation indoor data connections. However, the gap between the number of LEDs and photodiodes (PDs) and the high correlation among different channels limit the multiplexing of mMC-VLC. Also, the mobility of the receiver is the bottleneck of mMC-VLC. So, adaptive spatial-layout selection (ASLS) is proposed to settle the above problems, which selects $ N $ sets $ n $-color LEDs from the transmitter to form an approximate optimal closed-circle layout adapting to the receiver position. First, the optimal parameter problems to minimize the ill condition of the activated system under layout constraints of the closed circle and linear types are formulated for a fixed receiver position. Second, to achieve adaptivity, the fitting curves of the optimal layout parameter and $ {D_v} $ under both constraints are researched; $ {D_v} $ is the vertical distance between the transmitter and receiver planes. Finally, the closest layout-selected principle (CLSP) is proposed to solve the problem of the LEDs perhaps not perfectly forming the optimal parameter layout for mMC-VLC. The bit-error ratio (BER) performances and application scopes of ASLS under both layout constraints are compared to determine that the constraint layout is a closed circle; meanwhile the available maximal $ N $ corresponding to the receiver position is obtained. The optimal parameter of ASLS is linearly related to the receiver position and not related to $ N $. The ASLS always achieves better BER performance than optical multi-stream spatial modulation.

© 2019 Optical Society of America

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