Mobile communication system from the first generation mobile communication system
(1g) began to develop gradually. At present, it has developed to the fourth generation mobile communication system (4G), and the fifth generation mobile communication system (5g) has also begun to be standardized. It is expected to be commercially available in 2020.
This paper summarizes the base station architecture of 2G, 3G, 4G and 5g systems.
2G communication system adopts three-level network architecture, namely bts-bsc-core network. 2G core network includes CS domain and PS domain.
At first, 2G communication system mainly adopts integrated base station architecture. The architecture of the integrated base station is shown in the figure below. The antenna of the base station is located on the tower, and the rest is located in the machine room next to the base station. The antenna is connected with the indoor machine room through the feeder.
The integrated base station architecture needs to build a computer room under each tower, which has a long construction cost and cycle, and is not convenient for the expansion of network architecture.
Later, it developed into a distributed base station architecture. Distributed base station architecture divides BTS into RRU and BBU. RRU is mainly responsible for RF related modules, including four modules: if module, transceiver module, power amplifier and filter module. BBU is mainly responsible for baseband processing and protocol stack processing. The RRU is located on the tower, while the BBU is located in the indoor computer room. Each BBU can connect multiple (3-4) rrus. The BBU and RRU are connected by optical fiber.
When developing 3G network, in order to save the cost of network construction, 3G network architecture is basically consistent with 2G.
3G communication system also adopts three-level network architecture, namely NodeB – RNC core network. 3G core network includes CS domain and PS domain at the same time.
3G era mainly adopts distributed base station architecture. Similarly, the distributed base station architecture divides NodeB into BBU and RRU.
With the advent of 4G era, the base station architecture has undergone great changes. In order to reduce the end-to-end delay, 4G adopts a flat network architecture. The original three-level network architecture is “flattened” into two levels: eNodeB core network. Part of the functions of RNC are divided into eNodeB and part is moved to the core network. 4G core network only contains PS domain.
4G base station basically adopts the architecture of distributed base station. At the same time, the c-ran architecture proposed and promoted by China Mobile is gradually promoted. C-ran architecture further centralizes, cloud and virtualizes the functions of BBU. Each BBU can connect 10-100 rrus, further reducing the network deployment cycle and cost.
Different from the traditional distributed base station, c-ran breaks the fixed connection between the remote radio frequency unit and the baseband processing unit. Each remote radio frequency unit does not belong to any baseband processing unit entity. The signal processing of each far end RF unit is completed in a virtual baseband base station, and the processing capacity of the virtual base station is composed of some processors in the baseband pool allocated by real-time virtual technology.
In order to further improve the flexibility of 5g mobile communication system, 5g adopts a three-level network architecture, namely, a three-level du-cu-core network (5gc). Du and Cu constitute GNB, and each Cu can connect one or more Du. There are many function partition schemes between Cu and Du, which can adapt to different communication scenarios and different communication requirements.
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