UAV image transmission system is an important part of UAV. It is a kind of wireless electronic transmission equipment that uses certain technology to transmit the video captured by the camera of UAV to the remote rear in real time. Therefore, UAV image transmission is also known as the "eyes" of UAV.

At present, the mainstream technology of UAV image transmission is as follows

1. OFDM Technology

In technology, the most widely used transmission technology in UAV is OFDM, which is a kind of multi carrier modulation. This technology is more suitable for high-speed data transmission. OFDM has many advantages, such as: it can also send a lot of data in narrow-band bandwidth, and can resist frequency selective fading or narrow-band interference, etc. However, OFDM has some disadvantages: (1) carrier frequency offset（ 2) It is sensitive to phase noise and carrier frequency offset（ 3) The peak to peak ratio is relatively high. Therefore, it is the perfect technology to solve these three defects and bottlenecks.

2. COFDM Technology

COFDM is coded OFDM. Before OFDM modulation, some channel codes (mainly error correction and interleaving) are added to improve the reliability of the system. The difference between COFDM and OFDM is that the error correction coding and protection interval are added before quadrature modulation, so that the signal can be transmitted more effectively. OFDM is mainly used in LTE (4G), WiFi and other application systems.

3. WiFi Technology

WiFi transmission is the most widely used technology of UAV image transmission with high cost performance. However, because WiFi has many limitations in technology and can not be modified, and many manufacturers use the scheme to build directly, its disadvantages are also very prominent: for example, the chip is designed in whatever format, which can not be modified, and the technology is relatively fixed; The real-time performance of interference management strategy is not strong; The channel utilization ratio is low and so on.

4. High definition and long distance digital image transmission technology of lightbridge

Lightbridge technology uses one-way image data transmission, which is similar to the data transmission form of a TV broadcasting tower located at a high place. The data transmission of Wi Fi image transmission requires that the sender and receiver first establish the communication handshake system, and then transmit each 512 byte data packet. After confirming that a packet is received completely, the next packet will be transmitted, which is the root cause of the delay of graph transmission.

5. Analog image transmission technology

Some UAVs without PTZ camera can reach a speed of more than 80 km / h, using analog signal transmission technology. There is almost no delay in analog image transmission, and another feature of analog image transmission is that when the limit distance is reached, there will be no sudden card screen or complete loss of the whole picture. Analog image transmission is also a one-way signal transmission technology, which is a bit similar to the analog TV broadcast signal transmission before the digital TV signal appeared. When the signal becomes weak, snowflake screen will appear to warn the pilot that he should adjust his flight direction or fly back to get closer to the return point.

It can be said that OFDM technology and WiFi technology are the mainstream of UAV image transmission, and COFDM technology is more advanced. In fact, in general, UAV long-distance transmission is actually the balance between distance and power consumption, which also involves many modulation technologies, such as using spread spectrum to improve anti-interference ability, channel source technology optimization and so on.