The Core Technology Behind 5G: Beamforming

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/ 2019-04-22 / Tech

Virtual reality, drones, autopilots, behind these cool hot technologies, you can see the 5G mobile communication system. The 3GPP organization transferred part of the 5G air interface standardization work from the research phase to the work phase.


5G base stations can support large-scale antenna arrays, and the number of configurable antennas can reach 1024. To take full advantage of the potential of these large-scale antenna arrays, 5G beamforming technology is absolutely essential! Today we will bring everyone together, close to the wings of this double-assisted 5G communication.


Principles of Beamforming Technology

The quality of the wireless signal will decay during spatial propagation. The attenuation phenomenon known as "path-loss" can have a huge impact on communication systems. Especially for 5G communication systems in the millimeter band, up to tens of dB of signal attenuation may cause the system to malfunction. In this case, beamforming technology can be used to effectively combat road damage.


Researchers have discovered for a long time: Multi-antenna communication can improve the transmission quality of wireless signals. Wireless signals propagate in space as if the ship is driving in water, the road loss is equivalent to the resistance of water to the ship; the antenna transmits wireless signals with a certain power, like the propeller overcomes the water resistance and pushes the ship. Forward.


5G system uses beamforming technology


The number of antennas in traditional base stations is small, and the quality of wireless signal transmission is limited. This is similar to the way of rowing or double-paddle boating, which is slow due to fewer paddles, fewer people, and less power. The 5G base station adopts a large-scale antenna array, decisively upgrades the solo row and the double paddle to the dragon boat, and the paddle is multi-person and the power is bursting! The beamforming technology effectively superimposes the signals by adjusting the phase of each antenna to generate a stronger signal gain. To overcome road damage,Thereby providing a strong guarantee for the transmission quality of 5G wireless signals. Like the dragon's drums, the dragon boat is closely matched with many paddles, making the dragon boat racing, the boat is like an arrow, is it a monkey sere?!


Beamforming technology produces directional beam

Beamforming technology produces directional beam


Interestingly, beamforming technology will focus on the energy of wireless signals To form a directional beam (Beam). Generally, the narrower the beam, the greater the signal gain. However, the side effect is that once the beam is directed away from the user, the user can not receive a high-quality wireless signal, which is a difference. Thousands of miles! Therefore, how to quickly align the beam to the user becomes the main content of the Beam Management technology in the 5G standard.


5G Beam Management Technology

Combined with the results of the newly released 5G standard in the research phase, as well as mobile communications Downlink (Downlink, the base station to the user's wireless transmission), let's look at the basic technical principles of beam management.


After beamforming, the 5G base station must use multiple different directional beams to fully cover the cell. As shown in the figure above, the base station uses 8 beams to cover it. The community of services.In the downlink process, the base station sequentially transmits wireless signals using different directional beams. This process is called beam sweeping. At the same time, the user measures the wireless signals (Beam measurements) transmitted by different beams and reports to the base station. Related information (Beam reporting); the base station determines the best beam alignment for the user based on the user report.


More complicated is that users also have antenna arrays. This means that we have to consider both the transmit beam and the receive beam in the beam alignment process. To this end, the 5G standard allows the user to transform different receive beams for the transmit beam and select the best receive beam therefrom, thereby producing a pair of optimal transmit-receive beams. The optimal beam pairs corresponding to users 1 and 2 in the above figure are (t4, r3) and (t6, r2), respectively.


At this point, you may find that the beam management process is very simple, but this is not the case. In fact, to ensure that you get enough signal gain, the beam generated by a large-scale antenna array usually needs to be narrow. Yes, the base station needs to use a large number of narrow beams to ensure that users in any direction in the cell can be effectively covered. In this case, the strategy of traversing all narrow beams to find the best transmit beam is time-consuming and laborious, and 5G expects The user experience does not match. To quickly align the beam, the 5G standard adopts a hierarchical scanning strategy, which is from wide to narrow scanning.



The first stage is a coarse scan, and the base station covers the entire whole with a small number of wide beams. The cell, and sequentially scans the directions of the wide beam alignment. As shown in the above figure, the base station uses the wide beams tA and tB at this stage, and only aligns the wide beam for the user, the alignment direction accuracy is not high, and the established wireless The quality of the communication connection is also limited.


The second stage is a fine scan, and the base station scans one by one using multiple narrow beams. In the first stage, the direction covered by the wide beam. For a single user, although the scanning beam is narrowed at this time, the range of scanning required is reduced, and the number of scanning is reduced accordingly. As shown in the above figure, On the basis of one-stage wide beam alignment, the base station only needs to continue to refine and scan four narrow beams related to each user, for example, scanning beam t1-t4 for user 1 and scanning beam t5-t8 for user 2. At this time, the base station Improves the accuracy of aligning the beam direction of each user,The quality of the established wireless communication connection is improved. Therefore, in the illustrated two-stage beam management process, the base station only needs to scan each user six times without having to scan all eight narrow beams.


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Beam estimation algorithm-assisted beam management process


In addition, the beam management process can be further optimized by the beam estimation algorithm. As an example above, the base station scans the entire cell using four moderately wide beams. If user 1 is just between beam t2 and t3, according to the traditional method,In order to improve the beam alignment accuracy, the base station needs to further refine the direction of scanning the user 1. To this end, Intel China Research Institute has developed an effective beam estimation algorithm: the base station can further estimate the user's optimal beam direction by combining user report information, improve the accuracy of existing beam scan results and correct the beam direction, thereby reducing or avoiding further refinement. scanning. With the beam estimation algorithm, the base station may only need to scan the beam of the moderate width for 4 times to achieve the effect achieved by the previous two levels of scanning 6 different width beams, thereby realizing fast beam management.


Finally, considering that the user may be in a mobile state, in order to better track the user (Beam tracking), hierarchical scanning It can be deployed at any time according to the needs of each user, and the optimal beam is continuously switched. The optimal beam changes with the user's position, providing seamless coverage for the user, ensuring that the communication is not interrupted or dropped.


Beam management greatly improves the accuracy of beam alignment, ensuring the quality of wireless communication connections, and the communication speed of 5G can begin to take off!


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