Base stations, in fact, have long been integrated into our lives like water and electricity, serving us all the time.However, this behind-the-scenes hero is not understood by most people.
After reading this issue, you will learn about the most important component of the base station, the advanced device version of RRU-AAU:
Why does ① need AAU?
What types of AAU does ② have?
③ What benefits can AAU bring to 5G networks?
一
Why do I need AAU?
RRU, that is, the remote RF unit, is one of the two cores of modern base stations (BBU and RRU), also known as the source of all evils of radiation.
With the development of wireless network, a base station should not only support a variety of systems such as 2G, 3G, 4G, but also take into account more than 900m, 1800m, 2100m, and so on. There are even 4G dedicated frequency bands such as 700m and 2600m.
Considering that a base station usually has three sectors, 15 RRU of each frequency band will be hung on the tower, and then connected to 3 multi-port antennas, a total of 18 devices, resulting in congestion on the tower.
Internationally, many operators lease towers according to the number of equipment hanging above, so how to reduce the number of equipment hanging on the tower under the premise of the same frequency band and capacity has become a strong demand.
Moreover, in the later stage of the development of 4G network, in order to support stronger MIMO and diversity reception capability, RRU needs to support more and more antenna ports, from two ports to 4 ports or even 8 ports.
It is natural to think that since the RRU needs to be installed at close range with the antenna and must be connected with a radio frequency cable, why not combine the pair into one module?
In this way, not only is there less equipment on the tower, the jumper between the RRU and the antenna is no longer needed, and there is no feeder loss!
In this context, the equipment that combines RRU and antenna, AAU (Active Antenna Unit, active antenna unit) arises at the historic moment.
The so-called active, because this kind of equipment with antenna needs power supply to send out the signal, after all, the RRU is installed in it. The traditional antenna does not need power supply, which is also called passive antenna.
With the advent of the 5G era, in order to support ultra-high download speed, the ordinary MIMO in the 4G era is upgraded to large-scale MIMO (Massive MIMO). The RRU needs to support 64 transmissions and be connected to an antenna array with 192 antenna elements.
In this way, both the RRU and the antenna have to support 64 ports and be connected by 64 jumpers. How can this fit? It's a little crazy, or it's a neat combination of the two.
In this way, the AAU began to sprout from the 4G era, to 5G, then became the standard. RRU has become increasingly marginalized in the 5G era.
二
有What types of AAU?
1. RRU and antenna loosely coupled AAU
Although AAU has many advantages, it also has some inflexibility, that is, the antenna and radio frequency are fully coupled, and the product architecture needs to be redesigned.
In the 4G era, a variety of RRU and antennas have been very mature, the scope of use of AAU is limited, equipment manufacturers are not willing to make great efforts to redesign brand-new integrated products, so there is a compromise design of antenna and RF loosely coupled AAU.
This kind of AAU uses a customized antenna, which directly installs the ready-made high-frequency RRU on the back of the antenna, and it is easy to replace the RRU if it is broken. Like the ordinary antenna, it can also use the radio frequency line to connect the low-band RRU, and its expansibility is very good.
Because the antenna can be seamlessly docked with the RRU, the antenna needs power, which is the source of the "active" in its name; at the same time, the port it uses to connect the RRU is called the "passive" port, which is a combination of active and passive.
This kind of AAU can barely be used in the 4G era, but it will be completely overwhelmed in the 5G era.
two。 Beautified AAU for deep overlay
This is a kind of AAU for deep coverage of densely populated areas such as downtown areas, with lower requirements for transmission power, but a high degree of beautification of the products. The loosely coupled AAU mentioned above is large in size, large in power, scary in appearance, and does not meet the demand.
Therefore, the AAU dedicated to this scenario generally supports only one or two band 2T2R, and there are no passive ports connected to other RRU, so the structure is simple, compact and beautiful.
3. The mainstream of the 5G era: AAU supporting Massive MIMO technology
In order to provide ultra-high download speed, Massive MIMO (large-scale multi-input and multi-output) has become the core technology such as 5G.
In the 4G era, mainstream RRU supports 4T4R, that is, downlink supports up to four data signals and 4x4 MIMO with mobile phone, while uplink supports four antennas to receive the same signal at the same time to enhance uplink coverage.
The 5G Massive MIMO AAU generally uses 192 antenna units to support 64 transmit and receive signals, while the downlink can stably support 24 data signals to be transmitted at the same time, and the uplink can also receive 12 stream signals at the same time.
In this way, even if 5G uses the same carrier bandwidth and subcarrier spacing as 4G, the downlink throughput of the cell can be improved by 5 times under the blessing of Massive MIMO.
It can be seen that the Massive MIMO has many RF channels, the antenna array is large, the complexity is increased, and the coupling between the two modules is closer, so they must be integrated into one hardware and supplemented by appropriate software algorithms to achieve good performance.
Therefore, in the 5G mainstream Sub6G band, AAU which supports Massive MIMO has become the absolute mainstream.
And the antennas in this kind of AAU generally can only support a single frequency band, and can not provide passive ports to external RRU of other low frequency bands, or the technical difficulty is too great.
For example, 3.5GHz products can only work in this specific band of bandwidth (100m), want the antenna to support 700MHz low frequency, external 700MHz RRU to expand coverage, it is impossible.
4. Once again merging AAUB and Antenna
As mentioned earlier, the mainstream band of 5G is 2.6GHz, which is 3.5GHz, which can provide a super large carrier bandwidth of 100m, and Massive MIMO technology is provided through AAU to support the high speed of 5G.
At the same time, low-frequency bands such as 700MHz are favored by operators because of their low frequency and narrow bandwidth, which can not support 5G high speed, but can provide good coverage.
However, the AAU of the higher frequency band Massive MIMO can not support the 700MHz band, so it needs an independent antenna. In this way, the equipment on the tower will be increased again, not to mention the increase in rent, there is probably no room for it at all.
As a result, some people in the industry have come up with the method of splicing high-frequency AAU and low-frequency antenna, no matter how its internal structure is, anyway, it is a big box from the outside, which saves space on the sky and the rent of the tower can be saved.
This kind of scheme is called Aspirp. A stands for the active module, that is, the high-frequency AAU;P which needs power supply represents the passive module, which is the low-frequency antenna wrapped in it.
As can be seen from the picture above, there is an obvious seam in the middle of this product, indicating that it is pieced together and traces, but makes no secret of its origin.
三
AAU carries the banner of 5G
5G is first deployed in urban hot spots, where there are generally high-rise buildings, which not only need to cover the ground, but also very important for vertical coverage of tall buildings.
Massive MIMO AAU's large-scale antenna array not only supports multi-stream transmission in the horizontal plane, but also distributes the beam flexibly on the vertical plane, which greatly enhances the coverage of high-rise buildings.
Due to the large number of transmission channels, it can form a very narrow beam, and the ability of space division multiplexing is stronger, so the same frequency and time resources are shared with multiple users. The industry can support up to 24 downlink data streams to be sent at the same time, and the cell capacity is 5 times higher than that of 4G 4x4 MIMO (4-stream).
The substantial increase in speed is the full meaning of the eMBB business at the beginning of the deployment of 5G, which makes users feel the pleasure brought by 5G intuitively.
It is AAU that carries the banner of 5G.
The author: mayfly collection
(disclaimer: this article only represents the author's point of view, not Sina's position. )