Channel Adaptive Spatial Modulation for Indoor VLC system with Random Direction Mobility

Multi-input multi-output techniques can obtain a considerable potential in wide bandwidth and high-speed transmission of visible light communication system. In this work, considering the mobility of the user, we propose the adaptive spatial modulation (ASM) scheme and channel adaptive spatial modulation (CASM) scheme to reduce inter-channel interference and improve the bit error rate (BER) performance. In both schemes, the modulation constellation size is adaptively selected based on the distribution of indoor signal-to-noise ratio and optimize the transmit rate while adapting the modulation size to meet the BER requirement. Unlike the ASM scheme, the CASM scheme activates the LED transmitter with best channel gain through feedback. The corresponding closed-form expressions of probability density function and cumulative distribution function are obtained. Numerical results show that the developed ASM frameworks can improve the average spectral efficiency and provide low BER.