The channel is the basis of wireless communication. The deeper the understanding of the channel, the higher the efficiency of coding and modulation, and the closer to the theoretical line of Shannon's theorem, and the multi-channel communication system makes the channel very complicated. More than 8 channels of MIMO technology have a very obvious effect on improving spectrum utilization, and will be the key technology for 5G scale applications. Currently, we plan to test 10 types of scenarios, and we will test more than 20 types of scenarios in the future, including shopping malls, airports, large stadiums, open large squares and beaches, and high-speed rails moving at speeds of 200 to 300 kilometers per hour. Channel.
Through the continuous breakthrough of 3G and 4G, China's overall strength has been greatly enhanced in 5G research. Recently, at the "3rd China Information and Communication Test Technology Conference" held in Shanghai, the reporter saw the industry's first officially launched MIMO parallel channel acquisition and channel simulation platform (currently implementing eight channels). With this platform, the industry can The understanding of 5G key technology MIMO has been raised to a new level. With the curiosity about the difficulty, role and purpose of the MIMO parallel channel acquisition platform and the next use plan, the reporter interviewed Yang Lan, director of the Shanghai Wireless Communication Research Center, which developed the platform.
Why do parallel eight-channel channel platforms?
The industry has formed a basic consensus on multi-channel technology (MIMO). Compared with the single-channel and dual-channel applications of large-scale applications in the past, 8-channel MIMO technology has a very obvious effect on improving spectrum utilization, and will be applied to 5G scale. Key technology.
The industry is also launching related equipment. For example, ZTE has launched a 64-antenna MIMO device and actively promoted the MIMO device to enter China Mobile's 4G+ network. Li Yue, president of China Mobile, also said at the World Mobile Congress Shanghai Exhibition at the end of June. In order to speed up the introduction of 5G technology such as 3D-MIMO in 4G networks; in April this year, Datang Telecom launched the 256-antenna array device to push MIMO technology to a new level. At the same time, however, the channel model of MIMO is built by single-channel simulation. The real channel situation when multi-channel is parallel has not been measured.
"Channel is the basis of wireless communication. The deeper the understanding of the channel, the higher the efficiency of coding and modulation, and the closer it is to the theoretical line of Shannon's theorem, and the multi-channel communication system makes the channel very complicated." Yang Wei said, "The 5G research has stipulated many new scenarios, including high-speed mobile high-speed rail, subway, large stadiums and crowded gathering places. These scenarios are complex and challenging, and MIMO is needed to support reliable communication. However, if the understanding of the multi-channel channel is only theoretically derived and there is no measured data, it cannot be truly commercialized. Because the terminal or base station equipment should be verified in the experiment, after the actual verification, our understanding of the multi-channel communication channel will be improved. At a new height, we can confidently push it into commercial use."
Four challenges in platform construction
Why did this parallel eight-channel channel test platform take two years before and after launch? Yang Lan told reporters that the platform was realized by integrating eight single channels. In the past two years, they mainly solved four challenges. .
One is the challenge of multi-channel calibration. Unlike a single channel, how to maintain the consistency of each channel in multiple channels is a common problem encountered in the industry. Even if the product is produced by the same company, the difference between the eight channels due to the small difference in hardware often leads to the difference of different channels. Only the channel difference generated by the hardware difference is removed in advance, and the obtained data will be the data of the spatial channel. So multi-channel calibration is the first challenge.
The second is the challenge of synchronizing the two channels of â€œreceivingâ€ and â€œtransmittingâ€. In the test, it is necessary to ensure that all signals are sent at the same time and are received at the receiving end. Because the distance between the antennas is on the order of centimeters, the time difference between the signals is within 100 picoseconds. Therefore, only when the synchronization accuracy is less than 100 picoseconds, the time when the same signal reaches different antennas can be distinguished, and the synchronization precision is very high. "We use the high-precision cuckoo clock system plus our own synchronization algorithm to achieve an accuracy of 30 picoseconds." Yang Wei said, "Using picoseconds in optical communication, as long as milliseconds in wireless communication." Level is fine."
The third is to test the challenges of data storage. The 8 channels have 8 transmitters and 8 receivers, and each transmitter has 8 receivers to form a matrix transceiver. In the actual measurement, 64 channels of data will be generated. Therefore, 64 channels of data are stored and the amount of computation is very large. "We use a ZERO COPY technology of the computer, which is zero-copy technology, which saves storage time. The data can be stored in real time without compression. This data stream technology ensures that the data measured on site can be stored completely and completely. "Yang Yang thinks this is very important. "It's like taking a complete picture of the data. It's like taking a high-resolution photo. The higher the accuracy of the photo, the more details you can see. The understanding of the channel will be The deeper."
The fourth is the challenge of matrix computing. Since the single-channel 1&TImes;1 becomes the 8-channel 8&TImes;8, the matrix data makes the amount of computation soar, so a parallel post-processing software is needed. "We developed together with Teacher Yin Xuefeng of Tongji University to extend the SAGE algorithm to parallel, from the original one to the other, so that the correlation between the channels and the related information hidden in the matrix can be extracted. This is more complicated than the original single-channel test, and it is more profound than the original understanding of multi-channel systems.â€ Yang Wei believes that because the details and analysis are more accurate, the industry can use these advantages of multi-channel and do more. accurate.
Complete multi-scenario testing and open shared data
At present, equipment manufacturers MIMO product prototypes have been launched, but there have been bottlenecks in channel modeling. Each manufacturer also uses different methods to verify its own technology, but no one has fully verified the products in a real environment. Yang Wei told reporters that he plans to open the measured data to the research community. On the one hand, he will give back the support of the entire research community. Second, he hopes that they will have more requirements and feedback on these data in order to serve them more. Because only the data has more requirements, the data is more valuable. And now there are only measurement data of different scenarios, but in the channel modeling and the impact of the channel on various devices and terminals, we must also promote with the more advantageous enterprises in China.
â€œThe very good thing is that there is already a prototype of the product, and then we have to go through the process of painful verification, iteration and correction. Our platform can make the original enterprise take time and effort to test in different scenarios, and then simplify the process of modifying the laboratory. "Yang Wei said, "because we will move the data of the various scenarios we have tested back to your lab, making the iteration and verification of the enterprise more efficient, and the problem is found in the test and then the device is withdrawn. The cost is very high, and the test plays an important role in the process of industrial maturity. Whoever solves the problem before the sale, the less trouble in the future, the greater the contribution to the industry."
According to reports, the current planning of 10 types of scenarios will be tested in more than 20 types of scenarios in the future, including shopping malls, airports, large stadiums, open large squares and beaches, and high-speed trains at speeds of 200 to 300 kilometers per hour. The channel in high speed movement. The impact of weather changes on the channel will be further measured, such as rainy days and sunny days. These data can allow researchers to get all kinds of outdoor data without leaving home, which is equivalent to having done field testing to achieve "outdoor testing indoors." â€œWe moved the real scene of the outdoor test back to the lab and played back the data, which is basically the same as walking around the site with your device and terminal.â€ Yang Wei said, â€œIf you find an error in the drive test. Researchers can continually replay to study the core causes of this error."
Promote the development of high frequency and more channels
The MIMO parallel channel acquisition and channel simulation platform now uses the frequency band below 6 GHz, which is also the main frequency band of China's 5G technology research and test. Yang Lan expressed the hope that the data and model of this platform test can be promoted to the 5G technology research and test.
In the future, this platform will expand to more channels and higher frequency bands. Yang Wei said that the next step is to expand the 8-channel test to 64 channels, but the work is still in progress and there is no mature solution. It is imperative that the industry use the data obtained by testing and analyze the data so that the work done before is recognized by the industry. Then analyze whether the data of these channels is enough to understand the multi-channel. "Perhaps there is not much difference between 64 and 8 roads, because the fineness of resolution has reached a certain level, and there is no new secret discovery, but this is also related to the scene. The next step is to improve our capabilities. Make a comparison." Yang Lan said.
Yang Wei said that in the next step, we also want to expand upward in the frequency band, reaching 28G or even more than 70 G, and finally can cover within 100G. At present, the 8-channel platform has been set up, and the high-frequency expansion is mainly to improve the software, time precision and data storage. "We are working hard in this direction, but if we go down, we need industry colleagues to give us ideas and help us improve our platform capabilities." With a scholar's attitude, Yang Lan issued such an invitation to the industry.
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