We often do various unmanned system experiments, such as the need to wirelessly collect video images from the remote end, local to the remote end of a serial port control quantity, remote sensor data collection and so on. Sometimes you need TCP/IP network data, sometimes you need transparent data transmission through serial ports, sometimes you need to read various sensor data from remote DRONES/unmanned vehicles. Network port transmission is no doubt a more ideal choice, support TCP/IP protocol, high bandwidth (can transmit HD video data), of course, if the distance is far some very good.

There are also a lot of data transmission links on the market to choose from, but each has its own advantages and disadvantages: 1: RF data transmission usually has a bandwidth frequency of 400MHz to 1000MHz, which is cheap. The lower the bandwidth frequency, the farther the transmission distance is. Usually, it can reach 3000 meters or even farther under the condition of visibility. However, the bandwidth of data transmission is limited, usually ranging from a few KB/S to tens of KB/S. We are watching online movies and know that a 1080P online movie requires 200 to 400KB/S download rate for smooth viewing. This relatively low frequency radio frequency digital is not enough, but because the frequency is low, so the transmission distance, to keep out through or diffraction capability is strong, can transfer further, some switch control signal, or data link back very small sensor signal, right before the Internet of things, and industrial field data collection, data collection will be a lot of wisdom farm use this equipment. Small transmission bandwidth, low cost and long transmission distance are typical characteristics.

2: WIFI digital bandwidth frequency in the 2.4 GHZ or 5.8 GHZ, the frequency is very high, the transmission of data can be very much, but the frequency is too high, the barrier penetration performance or diffraction ability is poor, transmission distance is relatively, it is not so far away, but by point-to-point antenna, and relay WIFI LAN can also usually long transmission distances. The transmission rate can be as fast as 12MB/S with 100 mbit /S bandwidth. 1MB=1024KB, if a 1080 HD webcam has a bit rate of 300KB/S, theoretically 12X3=36, theoretically it can accommodate 36 1080P HD cameras. These are all theoretical values, but the actual situation should be greatly discounted. And take into account that the further you go, the more your transmission rate drops. High bandwidth, short distance of general module transmission.

3:4G /5G Data transmission 4G/5G module, the transmission bandwidth can be very high, but generally through the public network link, the transmission delay is difficult to be guaranteed, the cost of traffic is also a large expense. If you can use a dedicated base station, it might be a good choice.

The following are some basic theories of radio electromagnetic wave, and we can try to understand that the higher the frequency, the more data can be transmitted and the wider the transmission bandwidth: wave speed = wavelength * frequency (frequency is inversely proportional to wavelength), then:

  • The lower the frequency, the longer the wavelength, the stronger the diffraction ability, the stronger the penetration ability, the smaller the signal loss attenuation, the farther the transmission distance, to achieve a wide coverage of the signal.
  • The higher the frequency is, the shorter the wavelength is, the stronger the direct firing ability is, the stronger the penetration ability is, the greater the signal loss attenuation is, the shorter the transmission distance is, the stronger the lethality is, and the local signal coverage is realized.

Note: (Wave-particle duality: the shorter the wavelength, the greater the energy, the stronger the penetration ability)

When we are doing experiments, we often need to transmit some data back remotely: 1. Remote desktop, access to onboard computer data, start some ROS nodes and so on. 2, additional serial port transparent transmission of some sensor data interface. 3, can access some network port camera data, ground station QGC can be opened. 4, the distance should be as far as possible more than 1KM. 5, can be networking, data between each node can be interactive. 6, transmission bandwidth to be close to the possible wide.

The above are some problems I often meet. We have developed the following products according to our needs. Video link: www.bilibili.com/video/BV1yr…

Remote unmanned devices need some interactive interfaces and communication means to realize the monitoring and control of unmanned systems. We used some outdoor WIFI modules to do it before. The distance of general WIFI is usually relatively close, and the transmission bandwidth is unstable and delayed. For example, our operation of a drone may be hundreds of meters, even kilometers away. General low-cost WIFI modules certainly can not meet the requirements. There are also some networking cases 4G/5G development is more troublesome, some algorithms in the LAN is more appropriate.

After more than one year of research and development testing, we cooperated with Zhigong Electronics to develop a multi-interface high-bandwidth data transmission link. Based on TCP/IP protocol, strong interface versatility, transmission of images, video, data, bandwidth can bear. Ground saw test is more than 800 meters, about 2KM ground to air. The key is the high transmission bandwidth, control instructions, to hd video streaming can be smoothly transmitted.

Several features: 1, high bandwidth (peak wireless data transmission 12MB/S) 100 mbit /S bandwidth; 2. Long distance and the farthest distance is 4KM, with visible distance; 3, multi-interface, support 3 serial ports, 3 network ports; 4, based on TCP/IP general network LAN, can access webcam, flight control data transmission, RTK; 5. Data of ten ROS nodes can be networked; 6, light weight, mobile terminal more than 100 grams; 7, control signal, sensor data, video data can be transmitted at the same time; Generally speaking, it is very suitable for graph transmission, data transmission, networking some long-distance, high bandwidth data transmission occasions.

It can achieve: 1. Linkage between the video data of the pod and the data of the ground station. 2 network system based on WIFI, ROS multimachine networking, specific test case can see this article: mp.weixin.qq.com/s/DONRk7L0z…

Above is the module connection diagram, which can access flight control, webcam, on-board computer, RTK, some independent sensor data, etc.Preliminary test data are as follows: The bandwidth of a single ROS node peaks at 347KB.Multiple ROS nodes (5) bandwidth at 1.16MB transmission bandwidth is still no pressure.Multiple ports: three serial ports and three network ports. It can be used for sensor data, flight control data, webcam data, RTK data access.Serial ports: Each serial port is transparent and can send data to each other. It is also very easy to send data between serial ports, or from the aircraft to the ground station. Network port: Can access the network port device for data transmission or network.

Author: Amu Lab – Xiao Qi

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