| Visible Light Communications(VLC) is one of the hottest fields in the communications research at home and abroad, it uses Light Emitting Diode(LED) that quickly switches on and off to transmit data signals. LED is able to meet the requirement of daily indoor and outdoor lighting as well as wireless communications. Compared to conventional radio communications, VLC that use the visible light as an information carrier, thus reducing the equipment’s complexity and having no electromagnetic interference.In this paper, we present a low complexity spatial modulation(SM) scheme that possesses the high spectral efficiency for indoor visible light communications system using LED lights. In SM, the white LEDs mixed by three kinds of LED chips(RGB LEDs) are fixed up at different spatial positions, each of which can be acted as an additional degree of freedom. The SM technique combined with multiple-input-multiple-output(SM-MIMO) system is able to address better functions in both spectral efficiency and error performance. In this scheme, only one transmitter is active during a symbol time while the others are idle. At the receiver, the optimal maximum likelihood(ML) criterion is responsible for detecting the original signals and then retrieving them. Firstly, through analyzing the distribution of illuminance of white LED, we give illuminance formula, and execute the simulation of distribution of illuminance to verify the feasibility of indoor lighting. Then, with the study of received optical power, we simulate the distribution of received optical power to verify the feasibility of indoor communications.Secondly, the simulation of signal to noise is analyzed. With the research of source of noise, we simulate the relationship between the signal to noise and the rate of data transmission, and identify the main and secondary sources of noise.Finally, the simulation of reliability and validity is analyzed. The number of white LEDs and photo detectors(PD) and the parameters of them are investigated. Then the analytical and simulation results have been given out. It illustrates that selecting right parameters and configuring the number of them properly can improve the whole performance of communications system. And MIMO link blocking scheme is presented to improve the performance of communication system. |
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