Currently, there are five main modulation techniques of UAV image transmission:
1. OFDM(Orthogonal Frequency Division Multiplexing)
Technically, currently, the most widely used transmission technology on unmanned aerial vehicles is orthogonal frequency modulation, which is a kind of multi-carrier modulation. This technology is more suitable for high-speed data transmission. Orthogonal frequency modulation has many advantages, such: A large amount of data can also be sent out under narrow band bandwidth, and can resist frequency selective fading or narrow band interference, etc.
2. COFDM
The difference between COFDM and orthogonal modulation is that before orthogonal modulation, error correction of coding and guard interval are added to make the signal transmit more effectively. It is mainly used in application systems such as LTE(4G) and WIFI. COFDM is currently the most widely used in DVB (Digital Video Broadcasting), including DVB-T,DVB-S,DVB-C, etc. COFDM is widely used in Europe, Southeast Asia, South America, and Australia.
3. WIFI
In addition to orthogonal frequency modulation, many manufacturers are also using WiFi technology, which may make people feel very low-end. In fact, this is not the case, and WiFi technology is also constantly improving. WiFi transmission is the most widely used technology for UAV image transmission with high cost performance, but because WiFi has many limitations in technology and cannot be modified, and many manufacturers use solutions to build directly, therefore, its disadvantages are also very prominent: for example, what format the chip is designed to be, which cannot be modified, and the technology is relatively solid; The real-time performance of interference management strategy is not strong; The channel utilization rate is relatively low, etc.
4. Digital modulation(Lightbridge 2)
Lightbridge technology uses one-way image data transmission, which is similar to the data transmission form of TV broadcasting tower located high. Lightbridge uses one-way broadcast data. Even if it flies far away, the image transmission delay remains stable at about 100-200 milliseconds.
When you reach the limit distance of Lightbridge image transmission, there will be warnings of stripes and weak signals on the screen. In most cases, even if the signal is interrupted, the reconnection speed is very fast, because reconnection does not need to re-establish the handshake mechanism like Wi-Fi. When the signal is insufficient or lost, the flier can check and get a reminder through remote control to stop the flight or make the plane hover in time. However, once the image transmission is interrupted, turning to the aircraft slowly to adjust the relative position of the antenna, or pulling up the height can improve the signal transmission. The probability of reconnection is very high, and the whole process is usually within 10 seconds.
5. Analog modulation
Some unmanned aerial vehicles without PTZ camera can reach a speed of more than 80 kilometers per hour, using analog signal transmission technology. There is almost no delay in analog graph transmission, and another feature of analog graph transmission is that when the limit distance is reached, the situation of card screen or completely losing the whole picture will not occur suddenly. Analog image transmission is also a one-way signal transmission technology, which is somewhat similar to the transmission of analog TV broadcasting signals before digital TV signals appear. When the signals become weaker, snowflake screens will appear, warning fliers should adjust their flight direction or fly back, which is closer to the return point. The power consumption of analog graph transmission is very large. If you want to reach the distance of Lightbridge over 2 kilometers, its transmission power has far exceeded the regulations of relevant departments.
It can be said that the two image transmission modes, namely, OFDM and WIFI technology, are the mainstream of UAV image transmission at present, and the more advanced one is COFDM Technology. In fact, in general, the long-distance transmission of unmanned aerial vehicles 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 and optimizing channel information source technology, etc.
