The composition of the UAV image transmission system
What is a UAV image transmission system?
If the flight control is the brain of the drone, then the image transmission system is the "eyes" of the drone, and we can overlook the beautiful world from a God's perspective through the drone. The UAV image transmission system uses appropriate video compression technology, signal processing technology, channel coding technology, and modulation and demodulation technology to wirelessly transmit the video captured by the camera mounted on the UAV to a long-distance receiver in real time. A kind of wireless electronic transmission equipment.
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If UAV image transmission systems are classified by equipment type, they can usually be divided into two categories: analog image transmission and digital image transmission. Since the video quality and stability transmitted by digital image transmission are much better than those of analog image transmission systems, Therefore, digital image transmission is usually used in industrial applications.
The image transmission of drones mainly uses three frequency bands: 1.2G, 2.4G, and 5.8G. 2.4G and WiFi belong to the same frequency band; 1.2G is a controlled frequency band. There is currently no 1.2G open amateur frequency band in our country, and it is only available for legal use by radio enthusiasts who have obtained qualification certificates; the country has divided the 5.8G frequency band into open amateur frequency bands. There are fewer devices working in 5.8G and there is less interference. High-frequency antennas can be more miniaturized. However, the higher the frequency, the higher the cost of electronic components. The requirements for precision of antennas are higher. The magnetic conductor is more sensitive than low frequency, and it is more difficult to produce high power than low frequency.
At present, the mainstream technologies for UAV image transmission include OFDM, WiFi, etc. OFDM (Orthogonal Frequency Division Multiplexing) is a type of multi-carrier modulation, which is more suitable for high-speed data transmission. It can also send out a large amount of data under narrow-band bandwidth, and can resist frequency-selective fading or narrow-band interference, etc. However, OFDM also has shortcomings, such as carrier frequency offset, which is very sensitive to phase noise and carrier frequency offset, and the average peak value is relatively high. WiFi image transmission is a cost-effective UAV image transmission technology. However, WiFi has many technical limitations. Many manufacturers build it directly with the solution. The format of the chip design cannot be modified. WiFi image transmission interference management strategy The real-time performance is not strong and the signal utilization rate is relatively low.
UAV image transmission system composition
The UAV image transmission system consists of four parts: the remote server, the aircraft, the store relay and the mobile phone video control terminal. For example, there are 2 high-power WiFi modules, which are embedded in the UAV relay and ground relay respectively. end.
The high-power WiFi module used in the drone has a transmission power of +28dBm and a transmission distance of up to 2 kilometers. The high-power WiFi module can not only transmit aerial camera video in real time, but also transmit control signals from ground mobile terminals, such as mobile phones, in real time.
Why can’t the WiFi signal of a wireless router travel so far?
Under the same frequency, drones can perform long-distance image transmission, but the WiFi signal of wireless routers has no signal at such a distance. A large part of the reason is that the power of wireless routers and mobile terminals such as mobile phones is limited. The country has relevant regulations that the transmit power of wireless routers cannot exceed 100mW (20dBm), and the antenna gain is generally 3dBi and 5dBi. Some products with outstanding wall penetration capabilities use 6dBi or 7dBi gain antennas. The signal strength improvement of the antenna gain is still very large. It is limited, so the WiFi signal of the wireless router can cover 200 meters without obstruction.
In addition, low-power mobile phones and computers in daily life also cause great limitations, causing the WiFi signal to be very good, but still unable to access the Internet or the network quality is very poor. This is like two people going into the mountains at the same time. After they are separated for a certain distance, the person with the louder voice can hear the person with the smaller voice, and the person with the smaller voice responds to the person with the louder voice, but the person with the louder voice can't hear anything. Naturally There will be no response.
In fact, mobile phones and other Internet access through WiFi need to go through a three-way handshake process before they can actually establish a connection to access the Internet. If the transmitting power of the WiFi signal end is very high and the mobile phone exceeds the maximum distance it can respond to the signal, it will cause a situation where the WiFi signal is strong and the information can be received, but the information cannot be sent out.
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In addition, drones fly in relatively open areas outdoors for image transmission, while router WiFi is generally used in complex environments with many obstacles. Therefore, it is considered good if the router’s WiFi signal can cover about 10 meters at home.