Views:47 Author:Site Editor Publish Time: 2019-06-16 Origin:Site
People always asking what are the characteristics of wireless high-definition video transmission system? What is the resolution of the video? How long range is the transmission distance? How about the image definition and end to end transmitting latency?
The concept of "video transmission" has only been around for a few years. It is said that the term has been spread so fast in recent years because of DJI's fast developing. Video transmission is popular with the development of drones.
Wireless Video Links Working Process:
Payload connects with Tx. Tx sends video to Rx. Rx connects with GCS.
There are three important features associated with the development of drones: High Definition, real-time, and long-distance. These three characteristics are also the points where people always misunderstand. Today we will explain these three features in details.
The HD mentioned here is actually a little different from the concept in HD of TV. The HD standard of the TV industry is: HD(720P), Full HD(1080P), Ultra HD(4K). The HD standard of the TV industry is distinguished by resolution. By this way, Everyone pays less attention to the concept of "streaming".
Based on same full HD video, if the code stream rate is different, the picture clarity will be different. If the code stream rate is the same. But using different video compression methods, the quality of the picture will be also different.
Compression mentioned above, which is the way to compress video. The commonly used technology is H.264. H.265 is a relatively new technology.
Why does the video need to be compressed? Let's see the following equation: One second data of a 1080P60 video is 1920*1080*32*60=3,981,312,000bit about 4Gb/s. To transmit such large data even though via optical fiber it also needs some time. Not to mention using wireless transmission method with limited bandwidth. Therefore, the international organization has agreed on a standard and method, compressing the video and then transmitting it and decompressing it after receiving.
The compression efficiency of H.265 is twice that of H.264, and the video of same quality compressed with H.265, the code rate is much lower. So "high definition" we called , a more reasonable formulation should be the quality of image. If the resolution is sufficient, the more advanced compression coding technology, the higher code rate, the better image quality. To achieve clear video displayed on GCS, all IFLY wireless data links for drones adapts H.264+H.265's Algorithms built-in encoder and decoder in Tx and Rx.
"Real-time" is a concept that has been hyped by many manufacturers, and a large part of it is influenced by Israel's Amimo's "zero-latency uncompressed" program. The delay of this scheme is really short, but it is not zero delay. It is measured between 30ms~80ms, 5.8GHz frequency, bandwidth 40MHz, and it can be said to transmit 3Gb/s data.
"Real-time" is actually a relative concept. The satellite phone can establish communication in a few seconds. The speed of 1000km/h can approach 30m within 100ms, and the visual persistence time of the human eye is 100~400ms. Therefore, "zero delay" is the goal that all real-time systems pursue and cannot reach.
Short delay is one of IFLY Drones video transmitter’s advantage. Latency for short range is 15-30ms. For long range model the delay is 50ms.
Long distance is easy to understood, but the distance will generally add a "LOS" (eg: "Light bridge2 signal transmission distance of up to 5 km (LOS). LOS means the distance is measured in the open air without interference).
At present, the most popular video transmission system for UAV is 2.4G. 2.4Ghz is GSM band. It is freely to use in many countries. Other band such as 300-900Mhz, 1.3Ghz, 1.4Ghz, 2.3Ghz and 2.5Ghz are always need license to use. 2.4Ghz system has bad diffraction ability with short wavelength. If the drones fly environment is not LOS, 2.4G system is not a better choice. If you can get license, 800Mhz or lower band will be better.