5G Fronthaul / Midhaul / Backhaul
1. To understand what 5G fronthaul, midhaul and backhaul are, we first need to understand the logical architecture diagram of 5G mobile communication:
Mobile Phone-Access Network-Bearer Network-Core Network-Bearer Network-Access Network-Mobile Phone
Access network, in our wireless communication, generally refers to the wireless access network, which is also commonly referred to as RAN (Radio Access Network). The function of connecting all mobile phone terminals to the network is the wireless access network.
The familiar base station (BaseStation) belongs to the radio access network (RAN).
2. The composition of the base station:
A 4G base station usually includes BBU (mainly responsible for signal modulation), RRU (mainly responsible for RF processing), feeder (connecting RRU and antenna), and antenna (mainly responsible for conversion between guided waves on the cable and space waves in the air).
Baseband processing unit BBU: completes channel coding and decoding, modulation and demodulation of baseband signals, and protocol processing. It also needs to provide interface functions with upper-layer network elements.
RF processing unit RRU: It is an intermediate bridge between the antenna system and the baseband processing unit: When receiving signals, the RRU filters the RF signals from the antenna, amplifies them with low noise, converts them into optical signals, and transmits them to the BBU. The optical signal transmitted from the BBU is converted into a radio frequency signal and transmitted through an antenna.
Antenna system: It mainly receives and sends signals, and is an information energy converter between base station equipment and end users.
In 5G networks, the access network is no longer composed of BBUs, RRUs, and antennas. Instead, it is restructured into three functional entities: CU (Centralized Unit), DU (Distribute Unit) and AAU (Active Antenna Unit):
CU: The non-real-time part of the original BBU will be split and redefined as CU, which is responsible for processing non-real-time protocols and services.
AAU: Part of the physical layer processing function of the BBU is merged with the original RRU and passive antenna into an AAU.
DU: The remaining functions of the BBU are redefined as DUs, which are responsible for handling physical layer protocols and real-time services.
According to the standards proposed by 5G, CU, DU, and AAU can be separated or co-located, so there will be multiple network deployment forms:
3. The prequel, midpass, and backhaul are connections between different entities:
Fronthaul refers to the connection of the AAU to the DU
Middlethaul refers to the connection of the DU to the CU
Backhaul: above CU
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