| Along with the increasing congestion of radio band, the optical wireless communication (OWC) which has a higher available bandwidth, greater communication capacity, faster transmission rate and stronger anti-electromagnetic interference ability has become the research hotspot of the communication technology in recent years. The optical wireless communication possesses many advantages that other communication modes don’t have, for example, it has a wider communication bandwidth; it is easy to use digital baseband technology; its reception of small size can provide spatial diversity; it has a high confidentiality; it is green and flexible deployment. Therefore, it has an important research value and extensive application prospect.At present, the wireless optical communication technology is still far from mature, and its existing achievements are mostly in point-to-point communication system, simplified static channel characteristics in non-line of sight communication system and simple modulation coding and other aspects. It considers less for all kinds of actual complicated parameters of communication environment, and it doesn’t make any systematic research on the background noise in communication, and the receiver just adopts the receiving scheme of single detector, so it doesn’t have a good anti-multipath channel fading technology both from theory and practice.The study of this dissertation is supported by the National Natural Science Foundation of China, addressing key issues and technical challenges regarding OWC communication. The main work and innovations as follows:First, aiming at the characteristics of the visible light communication, it studies the mechanism of action that the molecular absorption and molecular scattering (Rayleigh scattering) the visible light received when it transmits in atmosphere; it comprehensively and quantitatively analyzes the influence of atmospheric absorption and scattering factors on the optical signal, and then studies the mechanism of the scattering transmission of the white LED pulse signal in the air; it puts forward the new VLC channel noise model under the synthetic action of background noise and electrical noise, and studies the VLC noise suppression theory that uses the optical filtering, low noise amplifier and digital signal processing and other control means to reduce the noise effect.Secondly, it mainly studies LDPC decoding algorithm that is applicable to the optical wireless communication system, designs and realizes RS (18,10) and LDPC (960,480) hardware Codec, sets up the experimental platform of ultraviolet communication, verifies the good performance of RS code and LDPC code in the optical wireless communication system on reducing the system bit error rate and improve the communication distance through simulation and a large number of experiment analysis. The experiments and simulation show that:the standard bit error rate is 10-6, the sending and receiving elevation angle is 10° to 10°, RS code can improve 42% of the communication distance and LDPC code can extend about 89%. Under the background that the elevation angel is 20° to 20°, RS can increase the communication distance about 42%, LDPC can increase 116.6% of the communication distance.Thirdly, because it is affected by the atmospheric environment and the channel characteristic of power limited, the communication distance of NLOS UV communication is limited. Because the current ultraviolet communication basically works a one-way broadcast transmission mode, combined with the wireless cooperative communication technology, it can achieve multi-user ultraviolet communication in local area through the arrangement of relay nodes. This aspect of study is very few, so this paper will study the feasibility of realizing multi-user communication system in the interference channel, build a system model and make a theoretical analysis on the key indicators in the system. Due to the power constraint of the ultraviolet communication system, the power allocation algorithm is still need to be studied in order to guarantee the normal communication between multi-users.Lastly, the wireless mobile communication technology and the atmospheric optical communication technology are being deeply integrated, and the latter pays more attention to the new structure of receiver and new technology of signal. processing under the heterogeneous application. For the multipath fading and low signal-to-noise ratio of the signal in the receiving end in the visible light communication system, the traditional receiver scheme has been unable to further enhance the system’s performance. Adopting the technology of multiple inputs and multiple outputs can significantly improve the system’s sensitivity and communication distance, and effectively enhance the communication ability. This paper studies MIMO and spatial diversity technology in the visible light communication system, puts forward the scheme of improving the system sensitivity and anti-multipath fading ability, builds the VLC MIMO communication system model and makes a theoretical analysis, and verifies that adopting space-time coding technology can improve the system’s performance through simulation.
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