Research And Implementation Of Indoor Visible Light Communication System Transmitter Based On DCO-OFDM

As inter-symbol interference(ISI) generated by multipath effects is one of the main factor affecting system performance of visible light communication(VLC) based on LED, Orthogonal Frequency Division Multiplexing(OFDM) technology is introduced into the system so as to combat multipath effects effectively. Current VLC systems are based on light intensity modulation, which means that modulated signal should be real and non-negative. However, OFDM signal is complex and bipolar, which cannot be utilized in VLC systems directly. Therefore, in this thesis, DCO-OFDM modulation technology is introduced on the basis of OFDM.Firstly, the concept and development of VLC systems are discussed, and then the characteristics of white LED are studied including light-emitting mechanism, modulation characteristics and so on. In addition, this thesis compares several modulation technologies adopted in transmitter and analyzes the advantages and disadvantages of each modulation technology. And then basic principles of DCO-OFDM modulation technology are introduced in detail.Secondly, development environment of FPGA is introduced, and transmitter modules of VLC system based on DCO-OFDM are studied and designed. Modulation modules of the transmitter are chosen to adopt DCO-OFDM modulation. Under the ISE-based development environment, Verilog HDL hardware description language is utilized to design each module including mapping module, IFFT module, adding cyclic prefix module and so on, and then functional simulations are conducted by simulation tools in ISE. Results of software simulation are also discussed.Finally, selection critera of LED is discussed and then the LED driver circuit and the filter amplifier circuit design are discussed to achieve system design and construction. The focus of this thesis is the design of transmitter modules based on DCO-OFDM modulation and driver circuits. Realization of this test system provides initial experiment results for further optimization.