Research On Modulation Algorithms Of Indoor Visible Light Communication

Visible light communication is a new technology that can solve the problem of the scarcity of spectrum resources, and eliminate the electromagnetic interferance. Indoor visible light communication can light the room simultaneously, thus it can realise energy conservation, electric circuit reduction and information safety in a room with no light penetration. Therefore, indoor visible light communication has a promising future.Firstly, this paper introduces white LED and its feature, and discusses the modulation of visible light communication. On-off keying is the most simple and robust modulation, based on which this paper introduces the realization of hardware. Pulse modulation includes pulse amplitude, position and width modulation. They can increase the transmission speed with pulse’s diversity. On the basis of indoor MIMO visible light communication system, this paper also introduces the algorithms of demodulation and compares the BER performance.The channel model is highly correlated in indoor visible light communication, which results low reliability. The comparison of the three MIMO techniques shows that spatial modualtion outperforms reprtition coding and spatial multiplexing. On the basis of the combination of spatial modulation and pulse amplitude modulation, this paper proposes an enhanced SM. Instead of activating only one antenna, the proposed algorithm activates two, and using power imbalance in highly correlated channels. The simulation is done in a 4 × 4 channel, and the proposed algorithm shows better BER performance.In order to make the brightness of a room controllable, algorithms of dimming control, such as pulse width modulation and free slot time activation, is necessary in the case that there is restriction for the amplitude of the pulse. It can be concluded by comparing the BER performance between PPM-average and VMPPM in SISO channel that VMPPM performs more stably. Then, this paper proposes a new algorithm with combining VMPPM with PAM which can reach any brightness proportion in a certain range by maintaining a constant reliability. Further, the two algorithms are applied in indoor MIMO system, and it proves that PPM-average gives a better BER performance.