Analyzing the core technology behind 5G: beamforming

Virtual reality, drones, and autonomous driving, behind these cool and popular technologies, we can see the presence of 5G mobile communication systems. This spring, the 3GPP organization transferred the standardization of some 5G air interfaces from the research stage to the working stage. This means that after years of eager anticipation, the legendary 5G is really coming this time!

5G base stations can support large-scale antenna arrays, and the number of configurable antennas can even reach 1024. To fully tap the potential of these large-scale antenna arrays, 5G beamforming technology is absolutely essential! Today, we will take you to get closer to these wings that help 5G communications take off.

Beamforming Technology Principles

During the process of spatial propagation, the quality of wireless signals will attenuate. This attenuation phenomenon, called "path-loss," will have a huge impact on the communication system. Especially for 5G communication systems in the millimeter wave band, signal attenuation of up to tens of dB may cause the system to not work properly. In this case, beamforming technology can be very useful and effectively combat path loss.

Researchers have long discovered that multi-antenna communication can improve the transmission quality of wireless signals. The propagation of wireless signals in space is like a boat sailing in water, and the path loss is equivalent to the resistance of water to the boat; the antenna sends wireless signals at a certain power, just like the oars overcoming the water resistance to push the boat forward.

5G system uses beamforming technology

Traditional base stations have a small number of antennas, so the quality of wireless signal transmission is limited. This is similar to the way of sailing a boat with a single row or two oars. The boat speed is slow due to the small number of oars, small number of people, and small power. The 5G base station uses a large-scale antenna array, which decisively upgrades the single row and two oars to a dragon boat, with more oars and more people, and more power! Beamforming technology adjusts the phase of each antenna to effectively superimpose the signal and generate stronger signal gain to overcome path loss, thus providing a strong guarantee for the transmission quality of 5G wireless signals. Just like the drumbeat of the dragon head guides the many oars of the dragon boat to work closely together, the dragon boat races and the boat moves like an arrow. Isn't it amazing?!

Beamforming technology produces directional beams

Interestingly, beamforming technology focuses the energy of wireless signals to form a directional 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 will not receive high-quality wireless signals. Therefore, how to quickly align the beam with the user has become the main content of beam management technology in the 5G standard.

5G Beam Management Technology

Combining the results of the research phase of the newly released 5G standard and the downlink process of mobile communications (Downlink, i.e. wireless transmission from base stations to users), let’s take a look at the basic technical principles of beam management.

Principles of Beam Management Technology

After adopting beamforming technology, 5G base stations must use multiple beams with different directions to fully cover the cell. As shown in the figure above, the base station uses 8 beams to cover the cell it serves. During the downlink process, the base station uses beams with different directions to transmit wireless signals in turn. This process is called beam sweeping. At the same time, the user measures the wireless signals emitted by different beams (Beam measurement) and reports relevant information to the base station (Beam reporting). The base station determines the best transmission beam for the user based on the user's report (Beam determination).

To make matters more complicated, users also have antenna arrays. This means that we need to consider both the transmit beam and the receive beam in the process of beam alignment. To this end, the 5G standard allows users to transform the transmit beam into different receive beams and select the best receive beam from them, thereby generating a pair of best transmit-receive beams. In the figure above, the best beam pairs corresponding to users 1 and 2 are (t4, r3) and (t6, r2) respectively.

At this point, you may think that the beam management process is very simple, but it is not. In fact, in order to ensure sufficient signal gain in the end, the beams generated by large-scale antenna arrays usually need to be very narrow. The price to pay is that the base station needs to use a large number of narrow beams to ensure that users in any direction within the cell can be effectively covered. In this case, the strategy of traversing and scanning all narrow beams to find the best transmitting beam is time-consuming and laborious, which is inconsistent with the user experience expected by 5G. In order to quickly align the beam, the 5G standard adopts a hierarchical scanning strategy, that is, scanning from wide to narrow.

Beam management hierarchical scanning process

The first stage is a rough scan, where the base station uses a small number of wide beams to cover the entire cell and scans the directions in which each wide beam is pointed in turn. As shown in the figure above, the base station uses wide beams tA and tB in this stage and only points the wide beams to the user. The direction of the pointing is not accurate, and the quality of the wireless communication connection established is also limited.

The second stage is fine scanning, where the base station uses multiple narrow beams to scan the directions covered by the wide beam in the first stage one by one. For a single user, although the scanning beam is narrower at this time, the required scanning range has been reduced, and the number of scans is reduced accordingly. As shown in the figure above, based on the wide beam alignment in the first stage, the base station only needs to continue to refine the scanning of the four narrow beams related to each user, such as scanning beams t1-t4 for user 1 and scanning beams t5-t8 for user 2. At this time, the base station improves the accuracy of the beam direction aligned with each user, and the quality of the established wireless communication connection is improved. Therefore, in the two-level beam management process shown in the figure, the base station only needs to scan 6 times for each user, without scanning all 8 narrow beams.

Beam management process assisted by beam estimation algorithm

In addition, the beam management process can be further optimized through the beam estimation algorithm. Taking the above figure as an example, the base station uses 4 beams of moderate width to scan the entire cell. If user 1 is exactly between beams t2 and t3, according to the traditional method, the base station needs to further refine the direction of scanning user 1 in order to improve the beam alignment accuracy. To this end, Intel China Research Institute has developed an effective beam estimation algorithm: the base station can further estimate the user's best beam direction in combination with user report information, improve the accuracy of existing beam scanning results and correct the beam direction, thereby reducing or avoiding further refinement of scanning. With the help of the beam estimation algorithm, the base station may only need to scan 4 beams of moderate width to achieve the effect achieved by the previous two-level scanning of 6 beams of different widths, thereby realizing fast beam management.

***, considering that users may be in a mobile state, in order to better track users (Beam tracking), hierarchical scanning can be carried out at any time according to the needs of each user, and the *** beams are continuously switched. The *** beams will change with the user's location, providing users with seamless coverage and ensuring uninterrupted communication without disconnection.

Beam management greatly improves the accuracy of beam alignment, ensuring the quality of wireless communication connections. 5G communication speeds can begin to soar!