What is 5G base station architecture?

Read time: 10 minutes | Updated on: 1 December 2021

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5G network architecture is a vast improvement upon previous architectures. Huge leaps in performance are made possible by large cell-dense networks. One of the features of 5G technology also includes better security compared to 4G LTE (long-term evolution) networks.

For 5G network architecture to support demanding applications, the design will be complex – and thus, so will your base station design. We’re talking about data transmitting over distances, large data volumes or both. 5G network applications range from smart cities to manufacturing – even to smart farming.

5G transition is still in the early stages, however, and will co-exist with previous generations. Why? Implementation of 5G technology will require a sizeable investment for starters. It’s time-consuming as well and will rely on collaboration with providers. But it will happen and in some major cities, it’s already happening.

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. Their overall differences, however, are vast.

4G vs. 5G

Specifications	Details about 4G technology	Details about 5G technology
Data bandwidth	2 Mbps – 1 G	1 Gbps and higher as per need
Latency	10 ms radio	< 1 ms radio
Download speed	1 Gbps	10 Gbps
Spectral efficiency	30 b/s/Hz	120 b/s/Hz
TTI (Transmission Time Interval)	1 ms	Varying: 100 µs (min.) to 4 ms (max.)
Frequency band	2 to 8 GHz	3 to 300 GHz
Primary base stations	Cell towers	Small cells
Connection density	1000/Km2	1000000/Km2
OFDM encoding	20 MHz	100—800 MHz channels
Goal for cell encoding	200—400 users per cell	100 times greater than 4G

Design considerations for a 5G network architecture

5G is designed to run on radio frequencies that range from sub 1 GHz to extremely high frequencies. These are called millimeter wave, or mmWave. The lower the frequency, the farther the signal travels. The higher the frequency, the more data it transmits. 5G core network architecture operates on different frequency bands, but it’s the higher frequencies that deliver the most benefits. To accommodate these higher frequencies, different and more densely distributed base station antenna for mobile communication is needed.

5G overview: frequencies

5G high band (mmWave)	Delivers highest frequencies, from 24 GHz to around 100 GHz Short range – high frequencies can’t travel through obstacles Limited mmWave coverage Requires more cellular infrastructure
5G mid ban	Operates within 2-6 GHz range Designed as a capacity layer Peak data rates in hundreds of Mbps
5G low band	Operates below 2 GHz Enables broad coverage Uses spectrum in use today for 4G LTE

Architecting a 5G base station

Your design should take into account several challenges. Does your application depend more on distance or bandwidth capabilities – or a combination of both? What are your power requirements? 5G base stations typically need more than twice the amount of power of a 4G base station.

In 5G network planning, cellular operators have two options to consider when transitioning from 4G legacy core to 5G: non-standalone (NSA) or standalone (SA) architecture.

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.

Standalone base-station architecture

As already noted, option 1 is 4G, which leaves us with options 2 and 5.

Option 2: gNodeB connects to the 5G Core Network

Ideal for new entrants into the market who don’t have legacy LTE systems already installed. It’s also good for the operator who wants to offer 5G-only service.

Uses New Radio (NR) air-interface and signalling protocols towards the EUD
Connects to an AMF for control plane signalling with 5G Core Network
Connects to a UPF to transfer data
gNodeB are inter-connected using Xn interface

Connecting to AMF

gNodeB can be connected to more than one AMF. The gNodeB selects an initial AMF for each UE.

Connectivity to the AMF is based upon the Next generation – control plane (NG-C) interface, which uses Next Generation Application Protocol (NGAP) to transfer signalling messages between the gNodeB and the AMF
NGAP messages are provided in 3GPP TS 38.413 and transferred using SCTP over IP
These messages are transferred between gNodeB and AMF
UE and AMF signal to each other using Non-Access Stratum (NAS) signalling messages

Connecting to UPF:  

gNodeB can be connected to one or more UPF.

SMF selects UPF for each PDU session
Connectivity to the UPF is based upon the Next Generation-User Plane (NG-U) interface, which uses the GRPS tunnelling protocol - User Plane (GTP-U) to transfer data that belongs to PDU sessions
Each PDU Session has a single GTP-U tunnel
User plane packets are transferred using GTP-U over UDP over IP

5G core network and 5G radio access network

Option 5: Next generation eNodeB (ng-eNodeB)

This is actually a 4G base station, upgraded to connect to the 5G core network, which has transitioned toward the NGC but still uses LTE access.

Fastest and most direct path to a single-core network that supports all access traffic
4G interworking function allows a 4G device to connect into a 5G core
This function allows operators to divert traffic from the 4G core to the 5G core

The interworking function enables operators to make cost savings by switching off legacy appliances not needed. They can also benefit from 5G capabilities such as network slicing, which is vital for meeting emerging enterprise needs. Operators can apply this function to other core network services that need protocol translation, i.e., 3G and WiFi.

Most of the advantages of 5G will derive from moving to a 5G NR access network.

ng-eNodeB uses the 4G air interface and signalling protocols to the EU
The node connects to the 5G-core network using NG-C and NG-U interfaces, enabling it to support network signalling procedures
Node is also capable of transferring application data to and from a User Plane Function (UPF)

Part of your initial designs needs to take into account thermal management to ensure the life of your base station. Take a moment and read 5G base stations and the challenge of thermal management.

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