As a manufacturer of professional wireless communication video links, We bet you were frequently asked by users: how long range can your UAV COFDM Video Transmitter or UGV data links reach?
To answer this question,we also need information such as antenna installation height/terrain conditions/obstacles, etc. Wireless radio performance is only one factor. In fact, only through this comprehensive investigation can evaluate the actual distance of wireless communication. However such an assessment requires a lot of knowledge and experience skills.
This blog will provide some basic and principled methods to help you make some judgments about the communication distance.
Here are factors that affect the communication distance and effectiveness of Wireless Video Transmission System.
1. The specifications of the wireless video transmission product
● RF power: a bigger RF power of transmitter could reach a longer communication distance.
The higher RF power, the farther radio waves can travel. The relationship between the output power and the wireless communication distance is inversely proportional to the square, that is to say, the output power is doubled, and the communication distance is twice the root of the original. The output power is 4 times of the original, and the communication distance is 2 times of the original.
● Receiving Sensitivity: The lower receiving sensitivity, the better
Receiving sensitivity refers to the minimum level that wireless communication radios can receive and recognize. When the distance is longer and the signal strength becomes very weaker, the lower sensitivity radios have the advantage of capturing the signal, that is, it can work at a longer distance.
2. Radiation
The propagation of radio waves is an electromagnetic field phenomenon. It travels as a wave in electric and magnetic fields.
How are radio waves transmitted from an antenna?( Figure 1) Many books describe the radio emission of this antenna as looking like a "doughnut", as shown in the image below Figure(2):
The use of this method to describe the propagation of radio waves is still somewhat imperfect. For example, people still ask, "How big is the circle?" "What is outside the circle?”
Therefore, in order to give a more intuitive understanding of radio emission, we use a fluorescent lamp to simulate radio radiation as below figure (3).
Brightness is strong in the middle part and weak at both end, indicating the intensity distribution of light emitted from the lamp. This phenomenon can be compared to an antenna for wireless transmission, where the signal strength in the middle is high and the signal strength at both ends is low. That’s why the installation height of the antenna is an important factor affects the communication distance.
3.Environmental Factors
The radio energy "breaks free" from the antenna and travels into free space. There are static electric and magnetic fields in free space. Radio energy travels in the form of "waves" that "ripple" through a static field.
When radio energy propagates in the form of electric waves, it will encounter obstacles, and it will also produce phenomena similar to reflection or refraction like light, water waves, and air waves as Figure(4).
After a radio wave is reflected once, the phase of the wave will change completely. Peaks become troughs, and troughs become crests. Of course, there is also a coincidence that the reflected path is only half a wavelength farther than the direct path. Then there will be peaks superimposed on peaks, and troughs superimposed on troughs, and the signal will be strengthened to the greatest extent.
LOS (Line Of Sight) wireless communication has two propagation paths: direct and reflective. If there is an obstacle in the direction Of propagation, so that the direct path is blocked, the signal can only be reached by reflection, which is called non-line-of-sight propagation (NLOS). The effect of transmission is greatly reduced. There is another case, the height of the obstacle is not so high, the direct path can be reached. But that kind of reflection path of the "enhanced" signal is blocked, and the impact on transmission is also great.
At present, engineering uses the Fresnel zone to evaluate the impact of obstacles on line-of-sight communication. The Fresnel zone takes into account the direct and reflective areas. As long as there are no obstacles and no obstructions in this area, the approximate communication distance can be estimated.
Conclusion
Wireless mobile video transmitter works in place where both parties can see each other is not necessarily line-of-sight communication. Only when the terrain in the Fresnel zone is satisfied can the condition of line-of-sight transmission be achieved. What should we do if there are obstacles? In the case that the obstacle cannot be moved, we can raise the antenna according to the principle of the Fresnel zone.
Post time: Jun-20-2023
