Research On Key Technologies Of Lighting LED Based Indoor High Speed Visible Light Communication

With the increasing demand for mobile data transmission, the shortage of the radio frequency spectrum becomes more and more obvious. At the background of the rapid growth of light-emitting diode(LED) lighting industry,visible light communication(VLC) is considered as one of the most promising wireless communication methods in the future. In indoor lighting systems, as multiple LED lamps are adopted to provide uniform and overall illumination in common as well as each LED has the advantages of fast response speed and high optical power, VLC is suitable for the indoor high speed data transmission. The thesis mainly investigates the key technologies of high speed VLC system,including single-LED based VLC system, multi-chip-LED based VLC system and multi-LED based VLC system, under the indoor lighting scenario.The thesis studies the channel characteristics of VLC system. The pathloss of the optical wireless channel is analyzed, the system response and the nonlinear model of LED lamp are measured and discussed. Further, single-LED based orthogonal frequency-division multiplexing(OFDM) VLC system is investigated in the thesis. A phase error correction algorithm is proposed to solve the phase error caused by inaccurate channel estimation. Constellation predistorion algorithm is carried out to transform the non-Gaussian noise introduced by the LED lamp to Gaussian noise, resulting in a 1.3 d B power gain.The peak-to-average power ratio(PAPR) distribution is analyzed and the effect of input signal power back-off on the system performance is discussed. A bit and power allocation algorithm is designed to cope with the non-independent Gaussian noise. As high as 779.4 Mbps off-line data transmission based on phosphorescent LED and 2.49 Gbps off-line data transmission based on RGB LED are achieved.Multi-chip-LED based subcarrier-grouping OFDM(SCG-OFDM) system is presented in the thesis. All subcarriers of the OFDM signal are divided into several groups and each group is transmitted by one chip in the LED lamp,which means the signal's PAPR on each LED chip can be mitigated significantly.The system performance of the SCG-OFDM is analyzed in theory. The analysis results show that the SCG-OFDM can achieve higher reachable performance when the input signal power is relatively high. The results are validated by both simulations and experiments. As high as 834.56 Mbps off-line data transmission is achieved by using the SCG-OFDM system. Adaptive switching schemes for typical scenarios based on the SCG-OFDM are also proposed and analyzed to obtain better system robustness.A cubic receiver based non-imaging multi-input-multi-output(MIMO)VLC system is proposed and studied in the thesis. The problem of the high correlation of channel matrix in traditional non-MIMO system can be efficiently solved by adopting the cubic receiver. When the channel state information(CSI)unknown at the transmitter, a diversity transmission scheme with a maximum ratio combining(MRC) receiver can be utilized, or a multiplexing transmission scheme with a zero-forcing(ZF) receiver can be adopted. When the CSI known at the transmitter, the multiplexing transmission scheme with a pre-coding algorithm can be used and the MIMO channel can be equivalented as parallel Gaussian channel. System performances of all the schemes are analyzed and simulated. The features and the suitable application scenarios of all the schemes are also discussed.