Radio access network in 5G
Radio access network (RAN) hardware consists of antennas, radio units, and baseband units. RAN software includes network functions which is responsible for data transmission, QoS (quality of service), signal handover, and management and orchestration.
RAN Hardware
The RAN node hardware consists of the antennas, radio units, and baseband units.
Antenna
Data transmissions receive by RAN antennas from user equipment and then send it to the radio unit. There are various kind of RAN antenna available. MIMO antenna is one of the recent RAN antennas in RAN technology. The definition of MIMO is in its name that is multiple input and multiple output. MIMO antenna is capable to transmit and receive more than one data stream at the same time.
Remote Radio Unit (RRU)
The function of the radio unit is to receive signal from antenna and convert it to digital format which is required to understand by baseband unit. Radio unit can be at the bottom of the tower, or it may be adjacent to antenna. Placing radio unit with antenna will reduce signal loss due to lower cable length.
The Baseband Unit (BBU)
The function of baseband unit (BBU) is to receive data from radio unit and send it to core network and receive data from core network and sent it back to radio unit. BBU is physically connected via fiber optics cable to the core network. The management and orchestration functions are also implemented at BBU.
The location of the BBU can at tower or it can be located at central location. It may be located at cloud which is called C-RAN or centralized RAN architecture. The virtualization of RAN is coming into the picture in C-RAN architecture where a pool of BBU placed in data centre.
RAN Software
Software is disrupting in each domain and RAN is not excluded from it. Virtualization and disaggregation are the key enabler for software disruption and faster innovation. There are various flavor of RAN available in the market like vRAN(virtual RAN), C-RAN and Open RAN(O-RAN) etc.
Here network function is decoupled from hardware.
Further BBU is disaggregated into two-part central unit (CU) and a distributed unit (DU). Each of these functions are responsible for different BBU function. CU and DU can deployed together or separately.
Central unit (CU)
- CU functions are mentioned below.
- Information broadcasting
- Establishing and releasing connections to user equipment
- Data transfer
- executing quality of service functions
- Compressing and decompressing IP data streams etc.
CU can be further disaggregated based on software defined networking (SDN) principles.
The CU control plane (CU-CP)
The function of CU-CPs is
CU-CP operate the RRC (radio resource control) protocol
Control plane portion of the PDCP protocol (packet data convergence protocol)
CU user plane (CU-UP)
The function of CU-UPs is
the CU-UP operate SDAP protocol (service data adaptation protocol)
PDCP User plane part.
Distributed unit (DU)
The DU hosts the radio link control and medium access control (MAC) layers in along with some of the physical layer at a base station.
The management and orchestration (MANO)
ETSI defined MANO (management and orchestration) framework can be used in RAN as well. There are other organization working on MANO that can also be used in RAN. The function of orchestrator is provisioning of network function, lifecycle management and rollout required bulk upgrade.
MANO is also existed in O-RAN architecture as well. Here, it is called SMO (service management and orchestration). This SMO is present in open cloud (O-Cloud). O-Cloud consists of various physical RAN node which includes CU, DU, SMO, operating systems, and runtime environments etc.