Research On Spatial Modulation For Visible Light Communications

Visible light communication(VLC) is a burgeoning technology that uses the visible spectrum for high-speed short-range communications. Intensity modulation/direct detection(IM/DD) is predominantly used for VLC in which commercial white light-emitting diodes(LED) serve as transmitters, neglecting frequency and phase of signals. Therefore the correlation of optical channel is much larger than that of radio frequency channel which limits the application of traditional multiple- input multiple-output(MIMO) technology in VLC. Aiming at this question, the research of antenna sele ction and power allocation in op tical spatial modulation(OSM) system is presented on the basis of analysis of the correlation of optical MIMO channel in this paper.1. Analysis model of optical multiple- input multiple-output(OMIMO) channel correlation is established in the first instance according to the illumination request and typical indoor application of VLC. The influence of channel factors on channel correlation is analyzed. Study indicates that the correlation between the channel paths is worse due to the decrease of the distance between transmitter units, receiver units, and the increase of half-power angle, height and offset of transceivers. According to the mutual influence of signal-to-noise rate(SNR) and channel correlation, optimal channel parameters are obtained in specific scenes for optimal bit error rate(BER) performance. Furthermore, the influence of spatial inter-symbol interference(SISI) due to channel correlation on channel capacity and SNR is analyzed. The relationship between the channel capacity and the transceiver distance, the number of LEDs and PDs is also obtained.2. Aiming at the high correlation of optical channel, an antenna selection method is put forward via maximizing the minimal distance involved for generalized space shift keying(GSSK). In addition, an adaptive generalized spatial modulation(AGSM) jointly optimizing the antenna combinations and modulation levels based on channel state information is presented for higher BER performance for GSM. Simulation results validate the validity of antenna group selection and modulation level selection. A simplified optimization algorithm utilizing Q R decomposition to confine searching space is also proposed for lower computational complexity.3. In order to enhance the channel differentiability of OSM and make the receiver obtain enough SNR, an optimal power allocation strategy for OSM is presented. Based on the fact that the SER of OSM is a convex function of power allocation factor, the optimal allocation factor is derived minimizing the SER analytically. Simulation results show that a significant SER performance improvement is obtained by using proper transmit power allocation for the best tradeoff between spatial domain SER and signal domain SER.4. A novel space shift keying modulation technique combined color modulation according as the spectral response characteristic of photo-electricity detector is proposed. Transmitters radiate light with different color, i.e. different wavelength but same power and the receiver detects the color and position of LED jointly by the spectral response characteristic of PD. The optimal color allocation method is presented for better BER performance of space shift keying according to the closed-form of pair-error-probability.