# [Intern] 28/09/2022 What is 5G base station architecture?
###### tags: `BMW-Lab`, `Intern`

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**Goal:** To understand the 5G base station architecture.
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**References**
- [5G base station architecture](https://5g.systemsapproach.org/arch.html)
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## The difference between 4G and 5G network architecture
4G was introduced back in 2009 and is responsible for trends such as the Internet of Things (IoT) and the massive growth of smart phones. 4G has been so successful, we want more, and we want it even faster. As we move towards 5G, it’s worth comparing the difference with its predecessor, 4G. The similarities between 4G and 5G include the technologies used:
Unified IP
Seamless integration of broadband LAN/WAN/PAN and WLAN
Among the spectrums used by 5G is 4G LTE.


## Non-standalone base station
NSA enables operators to leverage the investments in their existing 4G network instead of deploying a new core for their 5G infrastructure. This makes 5G base station costs considerably less than SA architecture. Operators can lower their costs, find new 5G revenue streams and provide faster data speeds with:
5G Radio Access Network (RAN), which can be supporting by the existing Evolved Packet Core (EPC), lowering CAPEX and OPEX
Adopt the virtualisation of Control and User Plane Separation (CUPS), and software-defined networking (SDN)
NSA architecture includes new RAN, deployed alongside 4G or LTE radio with existing 4G Core or EPC. The increased data bandwidth is enabled by these two new radio frequency ranges:
Range 1: 450 MHz – 6000 MHz – overlaps with 4G LTE frequencies and termed as sub-6 GHz.
Range 2: 24 GHz – 52 GHz – main mmWave band
Standalone base station
5G network architecture is based on entirely new standards introduced by the 3rd Generation Partnership Project (3GPP). This is the organisation that sets international standards for all cellular communications. SA is the new core architecture as defined by 3GPP. It introduces critical changes:
Service-Based Architecture (SBA) – Interconnected Network Functions (NFs) deliver control plane functionality and common data repositories with authorisation to access each other's services
Separates different network functions
Better end-to-end high-speed and service assurance
5G SA involves a new radio. It’s comprised of:
Virtualised cloud-native architecture (CNA), which delivers new ways of developing, deploying and managing services
Its SBA uses edge technology architecture to deploy 5G software network functions
Non-Standalone vs. Standalone
How do the two directly compare?

## Coverage

Both are measured by Maximum Allowable Path Loss (MAPL), which denotes the upper limit of the path loss for a quality signal. Both NSA and SA are impacted by transmit power, antenna gain, frequency band, system characteristics, and receiver performance.
NSA: Uplink data can be transmitted by NR or dynamically selected Radio Access Technology (RAT) between NR and LTE, depending on the service provider.
SA: Uplink data can only be transferred through the uplink data channel of NR. This binds the uplink data coverage of SA to the NR Physical Uplink Share Channel (PUSCH) coverage.
If the uplink path switching is used by the NSA, then SA coverage will be smaller.

## Latency

In both SA and NSA, latency is measured by the idle-to-active procedure and handover interruption time. The idle-to-active procedure in NSA is larger than in SA. This is because SA user equipment (UE) connects to NR without additional signalling procedures.
NSA: Handover needs both LTE handover and NR cell change with or without SN change
SA: Handover only requires NR cell change

## Mobility

In a direct SA option to migration from legacy LTE, mobility scenarios are easier with NR deployed at a nation-wide scale.
SA: UE can manage LTE and NR connection on its own with either the LTE or NR network.

## Voice Service

VoNR is a voice solution based on IP Multimedia Subsystem (IMS) in SAs.
SA: If VoNR has not yet been deployed on a SA network, this feature may not be supported.
In that case, it will use Evolved Packet System (EPS) fallback and RAT fallback.

## 5G architecture diagram

With service-based architecture (SBA), network functions are divided by service. The key components of a 5G core network are seen here:


User Equipment (UE):  5G cellular devices, such as smartphones, connect via the 5G New Radio Access Network to the 5G core and then to the internet.
Radio Access Network (RAN): Coordinate network resources across wireless devices. 
Access and Mobility Management Function (AMF): The UE connection’s single-entry point for the UE connection. The AMF selects the SMF based on the UE’s service request.
User Plane Function (UPF): Carries the IP data traffic – user plane – between the UE and external networks.
Authentication Server Function (AUSF): Enables the AMF to authenticate the UE and access services.
Session Management Function (SMF): Responsible for managing Protocol Data Unit (PDU) allocating IP addresses, GRP-U tunnel management, and downlink notification management.
Network Exposure Function (NEF): Securely expose the services and capabilities to approved third parties.
Network Repository Function (NRF):  Serves as a central repository for Network Functions (NFs).
Policy Control Function (PCF): Supports the unified policy framework that governs network behaviour.
Unified Data Management (UDM): Supports advanced authorisation and enables operators to easily adapt to customer needs. 

## 5G base station components

The base stations in 4G LTE networks are called either evolved Node B or eNodeB. You’ll find that eNodeB is usually abbreviated as eNB in 5G network architecture diagrams, and gNodeB as gNB. It helps to keep mind that a base station called eNB is for 4G, and gNB is for 5G.
So eNodeB vs. gNobeB is essentially 4G vs 5G. eNodeB is the radio network node for LTE networks, while gNodeB is used for 5G NR. You’ll also see ng-eNB, which is next-generation eNodeB. This is the upgraded version of 4G LTE radio base station. It connects 4G LTE devices to the mobile network when a 5G CAN is used instead of a 4G Core network (EPC).
These nodes are installed at operators’ cell sites and can be seen as cell towers, or tall masts. Below illustrates how 5G NSAs and 5G SAs can be deployed.
5G NSA and 5G SA: your deployment options
With SA options, only one independent access network – either LTE or 5G NR – is connected to the EPC or 5GC. With NSA options, both LTE and 5G NR radio access technologies are used, with one of the access networks aiding the other in connecting to an EPC or a 5GC. Here are the options as laid out by 3GPP – note, option 1 is 4G, but serves as a reference point.