RRU, BBU, AAU

BBU, RRU

BBU and RRU are both devices of the mobile base station. The BBU is connected for uplink transmission, and the downlink is connected to the RRU. The RRU is connected to the antenna.RRU is equivalent to a transceiver, receiving and transmitting signals, BBU+RRU=BTS mobile transceiver station, BBU (BuildingBasebandUnite) indoor baseband processing unit.Complete the baseband processing functions of the Uu interface (coding, multiplexing, modulation and spread spectrum, etc.).

BBU (BuildingBasebandUnite) indoor baseband processing unit is used to complete the baseband processing functions of the Uu interface (coding, multiplexing, modulation and spread spectrum, etc.), the Iub interface function of the RNC, signaling processing, local and remote operation and maintenance functions, as well as the working status monitoring and alarm information reporting functions of the NodeB system.

The function of the RRU (Radio Frequency Remote Module) is that the transceiver module completes the conversion of the intermediate frequency signal to the radio frequency signal; then the radio frequency signal is transmitted through the antenna port through the power amplifier and filter module.

The Remote Radio Unit (RRU) is divided into 4 large modules: IF module, transceiver module, power amplifier and filter module.The digital intermediate frequency module is used for modulation and demodulation of optical transmission, digital up-conversion, A/D conversion, etc.

AAU

AAU appeared in 5G, in fact, because 5G introduced Massive MIMO technology, Massive MIMO, massive multiple input multiple output.
MIMO is a multiple-input multiple-output technology. This is actually easier to understand. You can imagine it as a highway. If you let more cars run on a highway, you need more lanes. Obviously, eight lanes are better than four lanes.The traffic flow is much higher.
The higher the order of MIMO, the more antennas are required, the more antennas, the more feeders, the more feeder interfaces on the RRU, and the more complex the process is.Come higher.In addition, the feeder itself has a certain attenuation, which will also affect part of the system performance.
In 5G, the RRU and the original passive antenna are integrated, forming the latest AAU (Active Antenna Processing Unit).

AAU also adds some BBU functions.

In the 5G era, not only is the RRU and the antenna integrated into an AAU, but the physical structure of the BBU has also evolved into a CU (centralized unit) and DU (distributed unit) due to the changed network framework of 5G.
Among them, the real-time part of the BBU has become a DU (distribution unit), while the non-real-time function of the BBU has evolved into a CU (centralized unit).It will carry some core network functions.
Part of the physical layer functions of the BBU are designed into the AAU. Therefore, compared with the RRU, the AAU is not only the function of the multi-integrated antenna part, but also has some additional functions of the physical layer of the BBU.

Of course there will still be RRU in 5G.
There are also some low-frequency parts in 5G, such as the 700Mhz that will be used by radio and television, and this low-frequency part is difficult to support large-scale antenna arrays because the wavelength is too large and the antenna array is too large.
Moreover, for some areas that do not require high system capacity, such as rural areas and mountainous areas, there is no need to use expensive AAUs.