| Indoor visible light communication as a new research field,compared with the traditional wireless communication technology,which has the advantages of green environmental protection,high transmission rate,and has been widely concerned by the major scientific research institutions.The optical receiving antenna plays an important role in the visible light communication system,which can increase the optical gain of the optical system and improve the signal-to-noise ratio of the visible light communication system.In this thesis,based on the background of indoor visible light communication,the basic theory of optical receiving antenna is analyzed.In order to sovle the problem of the low signal-to-noise ratio in the current system and the low optical gain in the large receiving field of view,the optical receiving antenna of visible light communication is studied.The main content of this thesis is as follows:1.Aiming at the problem of low received power in indoor visible light communication system,a Fresnel lens for indoor visible light communication system was designed by analyzing the parameters of Fresnel lens material,aperture,focal length ratio and the number of prism rings.Using 3D modeling software,optical software to modeling and simulation,the optical efficiency and field of view of the Fresnel lens were analyzed.The simulation results show that the optical efficiency of the Fresnel lens reaches 90%.At the same time,the designed Fresnel lens was processed and tested.The Fresnel lens was added to the front end of the visible light communication system,and the system signal-to-noise ratio was calculated based on the test results.The results show that the signal-to-noise ratio is increased by 13 dB compared with the non-receiving antenna.2.In order to improve the optical efficiency of the Fresnel lens,a compound Fresnel lens was designed by using the partition method.The inner ring is a traditional lens structure,and the outer ring is a double total reflection prism structure.The optical efficiency,the field of view,and uniformity of the Fresnel lens were analyzed.At the same time,the uneven distribution of energy in the spot affects the photodetector.The lens calculation method is improved and the structure is optimized to achieve even distribution of energy under large optical efficiency.The simulation results show that the optical efficiency reaches 91.1% and the uniformity is 1.78.3.For the problem that indoor visible light communication can not satisfy the high gain and large field of view,combined with Fresnel lens with large optical gain and large field of view of the hemispherical lens,a Fresnel lens-hemispherical lens combined optical antenna was designed.The radius of the hemispherical lens and the distance d between the Fresnel lens and the hemispherical lens were optimized.When the receiving field of view reaches 40°,the optical gain reaches 6.88.Using Matlab software for simulation experiments,the simulation environment is a 5m×5m×3m room with an field of view of 40°.Non-optical receiving antenna,a single Fresnel lens optical receiving antenna,and the combined optical receiving antenna as the receiving front end in turn were modeled and simulated.The results show that when the combined optical receiving antenna is added to the front end of the visible light communication system,the received power is the best among the three.And through simulation analysis,when the receiving field of view is 40°,the signal can be received at different locations in the room.In summary,this thesis studies the indoor optical communication optical receiving antenna,designs three optical receiving antennas,and verifies its feasibility through simulation.The proposed method has certain reference value. |
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