Research On Modulation And Optimization Of Power Distribution For Indoor Visible Light Communication

In the fast-developing information era,the shortage of spectrum resources has become increasingly serious.Towards the radio frequency(RF)spectrum saturation crisis,visible light communication(VLC)technologies are deemed as an effective solution.So far,there are some crucial issues about VLC remain unsolved.1.Asymmetrically clipped optical-OFDM(ACO-OFDM)is one of the important modulation method for high-speed VLC.Most of the relevant research focus on improving the performance of the ACO-OFDM system,but pay little attention to the hardware implementation.2.The transmission of VLC signal relies on the lighting emitting diode(LED)with fixed position.The LED array with fixed position can cause deterioration of illumination and communication quality.To address the problems above,this thesis focus on following three aspects:First,the parameters including the power,the illuminance and the signal-to-noise ratio(SNR)in the multiple-input and multiple-output(MIMO)communication system were analyzed.An indoor VLC system was proposed to simulate the channel impulse response and the power distribution on the receiving plane.Simulation result shows receiving power decreases from the center to the corners of the room.And the relationship between the field of view(FOV)of receiver and the distribution of the receiving power was discussed.Second,the indoor high-speed VLC modulation method was discussed.Comparative study between on-off keying(OOK)modulation,quadrature amplitude modulation(QAM)and orthogonal frequency division multiplexing(OFDM)modulation was conducted.Besides,this thesis explored the ACO-OFDM system and fast Fourier transform(FFT)algorithm.The FFT module in traditional ACO-OFDM modulation system relies on IP core to fulfil its function,which shows weak portability and high risk.In pursuit of higher signal processing speed and the reliability of the system,this thesis applied the standard delay format(SDT)to design the FFT module and makes it applicable in practice.According to simulation,the proposed system outperformed the recursive FFT-based system with increase in terms of the data processing speed.Moreover,simulation towards the FFT-based ACOOFDM system has been conducted in order to observe its error rate characteristics.Third,to optimize the distribution of receiving power and illumination on the indoor VLC receiving place,this thesis designed a new LED array pattern that based on the division of areas.By adjusting the number of LED array in different areas to optimize the distribution of receiving power and illumination,simulation result shows that the reduction of the receiving power deviation is about 24.6 % under the proposed LED array pattern.An improved ant colony algorithm(ACA)is proposed to dynamically modify the power of transmitters for obtaining uniform received power& illumination distribution.Simulation result shows that the optimization performance of the improved ACA is not significantly influenced by the variation of LED array pattern.And the power deviation from peak is 14% under the new LED array configuration.The convergence speed of improved ACA increased by 39.5%.