[Summary]:Wireless image transmission technology can be understood: wireless image transmission technology. In recent years, frequent natural disasters, terrorist activities and various emergencies all over the world have seriously threatened people's lives, which has promoted the rapid development of rescue robots. For the successful completion of the task, the commander of the robot to be remote control and make judgments based on the image, which involves remote wireless images, sound, a variety of sensor information acquisition and control instructions, Robot has been widely used.
Remote wireless map relay technology of rescue robot can be divided into: mobile communication network (GPRS), 3G wireless system, 2.4GHz wireless network technology. The first two technologies are to use the public mobile network to transmit images, 2.4GHz wireless network technology is used for emergency emergencies of the special image transmission technology, they are mobile video image transmission system.
Ⅰ、GPRS mobile communication network
GPRS is a global group for mobile communications (global system for mobilecommunications, GSM) system of wireless packet technology, by the British BTCellnet company in 1993. GPRS network with 900MHz frequency band, the peak rate of 115.2Kbit / s, the average business rate can be 20 ~ 40Kbit / s. The main advantage of GPRS is always online and by traffic billing, no dial-up can access the Internet at any time, not affected by the distance, at any time to keep in touch with the network, resource utilization. But its disadvantage is the bandwidth is small, only suitable for low frame rate, low-quality video transmission, mainly for individual users.
It can realize the remote monitoring of mobile robots by GPRS network. However, because of the low transmission rate caused by various factors in the environment, it takes about 30 ~ 60s to transmit a 3KB JPG format image. GPRS network structure shown in image 1.
Third-generation wireless network (3G) supports the transmission of about 384Kbit / s outdoor, indoor 2Mbit / s bandwidth, has been able to achieve its wireless connectivity in the visual communication. The advantages of using 3G communication data transmission are: high spectral efficiency, low cost, fast login, high-speed transmission of information, non-line-of-sight transmission, high security and so on.
3G communication module effectively solves the problem of limited control distance and image transmission quality in wired or wireless remote monitoring of robot, which makes it possible to transmit large amount of data in real time, thus perfecting the powerful function of the system terminal.
In 2008, China's Second Artillery Engineering Institute for rescue robots in the rescue area for image acquisition problems, proposed a 3G-based remote monitoring system. The system uses 3G communication technology to command and real-time video transmission of rescue robot, and is equipped with GPS satellite navigation system for precise navigation. The robot control system mainly includes the terminal module, the 3G transmission network, the backstage monitoring system, is used to carry on the long-distance real-time monitoring to the robot scene environment, the position, the sensor and so on the index to create the favorable condition for the robot command control. The system is based on the 3G network for image transmission, a video transmission flow control module is added on the processor side, and the monitor side can solve the stability of the video transmission system under the 3G environment by receiving the buffer size change feedback. It solves the problem that the remote control distance of the rescue robot in the wired and wireless remote monitoring is short, the positioning is difficult and the data quantity of the transmission is small. The overall composition of remote monitoring system shown in image 2, with flow control video transmission system block diagram shown in image 3.
GPS is by the United States Department of defense of land, sea and air forces in the 20th century, 70 years jointly developed a new satellite navigation system, its full name is "navigationsatellite timing andranging / global positioning system", which means
"GPS satellite positioning system", referred to as "GPS". It can provide a full range of real-time three-dimensional navigation and precise positioning for land, sea and air users. It has the advantages of automation, high efficiency, all-weather and high precision. It is a modern aerospace, military, communication, meteorology, transportation, And other areas of indispensable technical means and methods. With the continuous improvement of global positioning technology, GPS as an auxiliary tool for image transmission also plays an extremely important role, together with the image transmission network to form a perfect whole, for mobile robots remote monitoring and positioning to provide accurate information.
Ⅲ、2.4GHz wireless network technology
2.4GHz ISM (industry science medicine) is the world's public use of the wireless band, because of its ultra-low radiation and the overall bandwidth is better than other ISM band is called a global green band. 2.4GHz ISM band image transmission equipment and antenna size is very small, very convenient to install. Frequency hopping and direct sequence spread spectrum 2 kinds of work:
◆ frequency hopping mode throughput rate is low, low transmission rate, but strong anti-interference ability and frequency hopping sequence can be reused with the site.
◆ Direct sequence spread spectrum mode has a high throughput rate but poor anti-jamming performance, and multiple systems with the site is limited. Although 2.4GHz channel transmission distance closer, less penetrating obstacle weaknesses, but 2.4GHz RF technology has a great market opportunity, it does not require a permit, so it is an open market, and because the frequency is high , So the interference signal is less, the image transmission effect is also good. And support two-way communication, send and receive signals from foreign objects obscured, from the angle or position restrictions.
In 2006, Dr. Timothy Kinkaid proposed a new type of wireless image transmission system for the problem of image instability caused by the unstable flight process. As shown in image 4, the system uses a 2.4GHz transmission frequency, power consumption of 50mW, video transmitter quality is 1.6g, the aircraft carrying the camera quality is about 3.3g, omni-directional antenna detection, 2.4GHz wireless communication system , Can be timely to detect the image information back to the ground control station. The image transmitted by this system is very stable, which reduces the influence of flight instability on image quality.
In addition, 1.2GHz, 5.8GHz wireless image transmission also has some applications (image 5), but because of its high requirements on the wireless environment, it can only be used in specific environments, such as 1.2GHz unmanned in the air Machine wireless image transmission, 5.8GHz in building top point-to-point wireless bridge image transmission.
At present, with the development of 3G technology and lower service costs, 3G wireless image technology will be in accordance with its strong advantage to occupy a large civilian market. Thus, the mobile robot wireless image transmission technology is not only used in the military, in civilian areas (especially radio) is also very popular.