| Recent years, more and more rotor UAV has been used in aerial photography,electricity inspection and some other areas, and the image transmission system has increasingly become an important part of the work of the UAV.For rotor UAV load limited, often requiring long-distance operations, and other characteristics, combining with the requirements of image quality, this thesis presents a design of digital video transmission system which has the feature of small size, light weight, easy to carry and the low transmission delay.The rotor UAV image transmission system is divided into air-launched and ground receiving terminal side.This thesis studies the entire process of video signal acquisition, encoding compression, wireless transmission and decode. In the HDMI receiving portion, the ADV7611 receive chip is been used.Its volume is 50 percent smaller than competing chips, and it integrates audio and video capture capabilities.By reading the chip manual, mastering ADV7611 composition and function, this design with external controller sets up the chip via IIC bus.Being familiar with video compression technology, H.264 is selected as the image transmission system according to different coding standard features.Depth studying of H.264 code algorithm principle, hierarchical format and key technology, then the design selects high performance coding module using MCU encoder configuration, monitoring.Selecting Microhard DDL HD IP radio station, whose transmission distance is farther than 5 km.TS Over IP system protocol encapsulation make the TS stream become IP packets for transmission over a wireless network.The design complete the ground-side development, based on the.NET platform using C # language for map development,GDI+ graphics technology,and serial communication. Decoding the audio and video signal,the real player embedded within the ground control is made.Selecting STM32F405 processor as the system controller, each module is initialized and real-time control, such as: receiver configured,detecting the state of the encoder, setting the station IP address.At last,various system modules are integrated,and the Cadence can draw circuit schematic and PCB Fig.The design completed the small rotor UAV digital transmission systems by sub-module design and then achieved overall integration.Testing by the State Grid, the UAV carrying video transmission equipment has a good working condition. The system can operate very well at simulated high altitude and electromagnetic interference environment.Image transmission distance is more than 2 km, and the image delay is about 350 milliseconds, what has achieved the technical indicators. |
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