Evolution of RAN: The Road from 1G to 5G
The evolution of Radio Access Networks (RAN) has witnessed a remarkable journey from the first-generation (1G) to the fifth-generation (5G) mobile networks. This research article aims to explore this evolutionary path, highlighting key milestones, technological advancements, and the impact of each generation. By examining the historical context, technical innovations, and the promising future of 5G, this study provides a concise overview of RAN's transformation and its significance for the telecommunications industry and society.
Evolution of RAN
From 1G to 5G, the evolution of RAN has transformed the telecommunications landscape.
Introduction
RAN is an acronym for Radio Access Network.
RAN has been an integral component of mobile networks from the beginning.
RAN exists in between the user equipment (UE) and core network (CN) (i.e., RAN wirelessly connects UE to a CN).
Different generations of mobile networks use different types of RANs. Examples of varying kinds of RAN include,
GSM RAN (GRAN)
GSM EDGE RAN (GERAN)
UTRAN (UMTS RAN)
E-UTRAN (Evolved UTRAN)
Different components of cellular network
(Source: Lumenci)
A RAN typically comprises radio base stations (BSs) with large antennas.
For example, it is common for handsets to support multiple radio access technologies.
It is also possible for a single UE (mobile/handset) to be connected to multiple RANs simultaneously. Handsets capable of this are sometimes called dual-mode handsets.
A typical cellular network has four major components– UE, Radio Network, CN, and External Networks. The entities/terms involved in each element are listed below.
Key Components of a Typical Cellular Network
Basic RAN Architecture
The basic RAN architecture (shown in the figure below) consists of:
(a) Baseband Unit (BBU):
In general, baseband refers to the range of frequencies occupied by a transmission signal before the modulation process.
BBU is a unit that manages baseband in telecom systems. It manages the whole BS, involving operating maintenance and various signal processing functions, coding, modulation, and FFT.
BBU connects with RRU via fiber optic cable (CPRI).
(b) Radio Unit (RU) or Remote Radio Unit (RRU):
RRU interfaced with an antenna on one side and BBU on another. CPRI is the standardized protocol for communication between BBU and RRU.
RRU is the RF circuitry of a BS enclosed in a small outdoor module. The RRU is typically installed close to the antenna to lower the transmission line losses.
RRU performs the following RF functionalities:
Converts RF signal into the data signal and vice-versa.
Filtering and amplification of RF signal
Components of Remote Radio Unit
Functioning of a Remote Radio Unit
RRU has two parts:
(a) Transmit part
The transmit part typically comprises a DAC, Mixer, PA, and Filters. A digital signal is received via a CPRI interface, converted to analog, upconverted to an RF Frequency, amplified, filtered, and then sent out via an antenna.
(b) Receive part
The receiving part typically comprises a filter, LNA, Mixer, and an ADC. It receives a signal from the antenna, filters it, amplifies it, down-converts it to an IF Frequency, and then converts it to a digital signal before sending it out via the CPRI to a fiber for further processing.
(c) Antennas
Antennas convert electrical signals into RF waves and transmit/receive RF signals.
They are interfaced with cellular phones wirelessly.
(d) Various interfaces
Before proceeding to the discussion on RAN evolution, it is essential to study the difference between C-RAN and D-RAN. In the next section, we will learn the difference between C-RAN and D-RAN.
The difference in properties of
D-RAN and C-RAN
The comparison of D-RAN and C-RAN is provided in the table. (Source: Lumenci)
The D-RAN and C-RAN are better illustrated in the figures below:
RAN Evolution - 1G to 5G
1) Early RAN (1G)
In the 1G cellular network, RAN was not considered an independent unit. The RAN in 1st generation comprises of B.Ss and antennas.
1st generation RAN comprising BS and antennas (Source: Lumenci)
2) 2G RAN- GRAN and GERAN
The RAN in the 2G GSM cellular network is called GRAN and GERAN.
2G cellular network is fully distributed, meaning everything is at the cell site.
2G cellular network defines the term BSS, consisting of BTS and BSC.
RAN in 2G cellular networks comprises a radio BS known as BTS.
The BTS is controlled by an entity known as BSC. BSC performs various functions, such as RRM, mobility management, and data encryptions.
2G GSM networks were initially designed to perform voice calls (by circuit-switching (CS) means); even the SMS part came later. GRAN is the RAN that allows voice calls and SMS services. The data core network in the 2G GSM network is MSC, that is, CS core. In 2.5G GPRS enhancement, the data part was added to the voice part. The RAN that allows performing mobile data services is called 2.5G GERAN via GPRS and EDGE (by packet-switching (PS) means). The PS core was added in 2.5G GPRS, comprising Gateway GPRS Support Node (GGSN) and Serving GPRS Support Node (SSGN).
3) 3G RAN- UTRAN
The RAN in the 3G UMTS cellular network is called UTRAN.
UTRAN consists of two key components: NodeB and RNC.
The RNC is located in between the NodeB and core network.
The BSs in 3G cellular network are termed as NodeB (3GPP term for BS). NodeB comprises Tx and Rx to communicate with the UEs within the cell. NodeB communicates with the UE just like BTS in a GSM cellular network. NodeB is controlled by an entity known as RNC.
RNC in 3G cellular networks performs similar functions just like functions performed by BSC in a GSM cellular network.
In UTRAN, some centralized functions exist in the RNC or centralized controller.
3G RAN Architecture
4) 4G RAN-E-UTRAN
The RAN in 4G LTE is called E-UTRAN.
Similar to 2G, in 4G, everything is distributed at the cell site. In contrast to GRAN and UTRAN, which uses a combination of BS and a controller for RAN functions, E-UTRAN uses eNodeB (eNB) for all radio communication (nearly all parts of RNC are incorporated into eNB). Such architecture is called D-RAN (as defined earlier) architecture (or flat architecture).
4G LTE network only maintains the PS part (doesn’t carry the CS part).
In E-UTRAN, eNodeB is directly associated with 4G CN (MME and S-GW). MME handles the signaling part, while S-GW and P-GW take the data part.
The interface between eNBs is the x2 interface, while the interface used between eNBs and MME/SGW is the S1 interface.
5) 5G RAN- NG-RAN
The RAN in 5G NR is called NG-RAN.
NG-RAN consists of two kinds of BSs: gNodeB (also called gNB) and ng-eNodeB.
gNB is the radio BS for 5G NR networks. ng-eNodeB is an upgraded radio BS for 4G LTE that connects to a 5G CN.
Cloud RAN & vRAN
Typically, there are three significant configurations of centralized RAN.
C-RAN, Configuration type 1
Configuration Type 1
In type 1, BBUs are placed collectively (i.e., centralized) at one location and dedicates each BBU to its own BS (i.e., there is a one-to-one relationship).
This configuration is like a typical D-RAN configuration (except BBUs moved to a centralized location).
C-RAN, Configuration type 2
Configuration Type 2
In type 2, centralized BBUs are connected to form a BBU pool (i.e., there is a many-to-many relationship).
BBU pool can provide service to several towers at a time.
Configuration Type 3-> vRAN
This configuration of C-RAN is known as vRAN.
vRAN is an acronym for Virtualized-RAN.
In vRAN, RU is located on the cel,l site, and BBU is in a centralized location. The functional split options, viz., vDU and vCU, are available for BBU.
This configuration is like a typical C-RAN configuration, but there is no hardware dependency on BBU, i.e., BBU is virtualized/software package provided by a vendor.
BBU (a software package) is located on top of COTS servers.
COTS servers refer to the commercially available servers off the shelf, and these can be bought from a COTS server manufacturer, and BBU software is placed on top of it.
Disadvantage: Close interfaces, still vendor dependency exits (RRH and BBU (vDU and vCU) must be from the same vendor).
C-RAN Benefits
More efficient: C-RAN lets BBU pool collectively manage the data for several BSs, which allows a significant amount of data to be driven by lesser equipment.
Less expensive: C-RAN requires lesser equipment to manage the data, which reduces installation and operational costs. Also, due to the centralized deployment of BBUs, it is comparatively easy to expand and maintain the C-RAN compared to D-RAN.
Reduces inter-cell interference: In C-RAN, BBUs are situated at a centralized location, where they can access high-processing resources. Advanced processing techniques can be easily employed by using these high-processing resources. CoMP processing is an efficient technique to improve SINR, reduce inter-cell interference, and improve UE experience.
Easier to Upgrade: C-RAN forms a simplified, scalable, and adaptable network; hence it is easy to upgrade the C-RAN
Improved Energy Efficiency: the processing functionalities in C-RAN are executed at a centralized remote data center. Therefore, power utilization can be enhanced by dynamically assigning processing capability (viz., several BSs can be allocated a low power or shut down completely depending upon the requirements).
Better Administration and Security: With the centralization of BBUs, it is easier to supervise and secure BBUs, improving network security.
Faster Speeds: centralization of BBUs in C-RAN ensures faster speeds.
Benefits of C-RAN include faster speed, easy upgrade, less expensive. (Source: Lumenci)
O-RAN
The O-RAN environment allows disaggregating RAN into three blocks, namely:
Radio Unit (RU)
Distributed Unit (DU)
Centralized Unit (CU)
The RU is located near the antenna. It supports the transmission, reception, amplification, and digitization of radio frequency signals.
The computation parts of the BS are CU and DU, sending the digitalized radio signal into the network. The DU is physically located at or near the RU, whereas the CU can be near the Core.
As the name implies, the interfaces between RU, DU, and CU are open in O-RAN. No vendor dependency exists, meaning each unit can be from a different vendor.
Summary: The following illustrations summarize Most of the discussion in this section.
Summary of RAN Evolution: 2G to 5G
(Source: Lumenci)
O-RAN Challenges
(i) Operation and Maintenance
In a traditional single vendor RAN, a communication service provider (CSP) uses a “manage service (MS)” agreement and monitors the performance based on a pre-defined Service Level Agreement (SLA). However, it seems challenging for multi-vendor-oriented (different hardware and software suppliers) O-RAN due to the responsibility overlaps.
To solve this challenge, CSPs should define a clear responsibility matrix monitored by CSPs themselves or by a third party assigned to them. This responsibility matrix should be updated regularly for service /supplier addition or update, which and more complexity and responsibility for CSPs [26].
(ii) Software Upgradation
O-RAN brings new challenges, viz., difficulty in integrating and upgrading software from different vendors. O-RAN must be flexible enough to support further upgrades and compatible with the existing devices [27]-[28].
(iii) Interoperability Testing
The development of interoperability testing among O-RAN vendors is the key challenge. A unique set of tests are required to standardize the documentation of software.
Though different vendors employ open interfaces per the standards specifications (3GPP and O-RAN), they may interpret new specifications in various manners. Therefore, once the specifications become stable, verification via interoperability testing to unite different vendors and test each feature and product is challenging.
(iv) Security
The open interfaces, new interfaces, and virtualization create new challenges in terms of security in an O-RAN system. O-RAN must be managed by a new approach, such as containers [28].
(v) Troubleshoot Network Issues
In comparison to a traditional single-vendor network, detecting network issues are challenging in a multi-vendor network environment. To resolve such issues, vendor-independent troubleshooting is required. However, the other associated challenge is who will take ownership of the problems since many vendors are involved in a multi-vendor network environment.
5G RAN Market Trends
5G RAN market with its CAGR, Market value (2022), Estimated Market Value (2032) and its key players. (Source: Lumenci)
Scope of 3GPP Standardization
3GPP standardization has three dedicated work groups (WGs) that produce documents on specifications related to:
Radio Access Networks (RAN)
Services and Systems Aspects (SA)
Core Network and Terminals (CT)
The RAN specifications groups are known as Technical Specification Group (TSG) RAN, divided into six working groups: RAN WG1 to RAN WG6. This WG is responsible for defining the functions, requirements, and interfaces associated with the RAN, i.e., UTRA/E-UTRA, in both FDD and TDD modes.
TSG RAN encompasses both UE and BS functionality addressing areas, including radio performance, physical layer, layer two and layer three radio resource specification in UTRAN/E-UTRAN; specification of RAN interfaces (Iu, Iub, Iur, S1, and X2); definition of the Operation and Maintenance (O&M) requirements in UTRAN/E-UTRAN.
TSG RAN also addresses the conformance testing of both the UE and the BSs to ensure complete interoperability regardless of the manufacturer/designer of the equipment.
Key RAN 3GPP Specifications
Future of RAN
Artificial Intelligence (AI) and Machine Learning (ML) driven RAN Intelligent Controller (RIC) technology is expected to be used in the future RAN for more effective network management and power consumption [23]. The xApps and rApps are two software applications of RIC employed for network automation [24]. It is expected that worldwide spending on RIC platforms (xApps and rApps) will reach $120 Million in 2023 (and $600 Million by the end of 2025) as preliminary operations turn from field experiments to production-grade operations [25].
List of Acronyms
RF: Radio Frequency
RRU: Remote Radio Unit
RRH: Remote Radio Head
eNodeB: Evolved Node B
gNodeB: Next Generation Node B
CPRI: Common Public Radio Interface
DAC: Digital-to-Analog Converter
ADC: Analog-to-Digital Converter
PA: Power Amplifier
LNA: Low Noise Amplifier
EPC: Evolved Packet Core
PDN: Packet Data Network
MME: Mobility Management Entity
S-GW: Serving Gateway
P-GW: PDN Gateway
GGSN: Gateway GPRS Support Node
WG: Work Group
O&M: Operation and Maintenance
CSP: Communication Service Provider
RAN: Radio Access Network
UE: User Equipment
BS: Base Station
CN: Core Network
BTS: Base Transceiver Station
GSM: Global System for Mobile
GRAN: GSM RAN
EDGE: Enhanced Data rates for GSM Evolution
GERAN: GSM EDGE RAN
UMTS: Universal Mobile Telecommunications System
UTRAN: UMTS RAN
LO: Local Oscillator
E-UTRAN: Evolved UTRAN
BBU: Baseband unit
RU: Radio Unit
SSGN: Serving GPRS Support Node
AI: Artificial Intelligence
ML: Machine Learning
RIC: RAN Intelligent Controller
TSG: Technical Specification Group
References
[1] https://www.sdxcentral.com/5g/ran/definitions/radio-access-network/
[2] https://www.trentonsystems.com/blog/radio-access-network-ran
[3] https://www.techtarget.com/searchnetworking/definition/radio-access-network-RAN
[4] https://commsbrief.com/radio-access-network-ran-geran-utran-e-utran-and-ng-ran/
[5]https://www.exfo.com/en/resources/glossary/basebandunit/
[6] https://moniem-tech.com/questions/what-is-the-ran-evolution-from-2g-to-5g/
[7] https://blog.3g4g.co.uk/2021/07/different-types-of-ran-architectures.html
[8] https://moniem-tech.com/questions/what-is-the-difference-between-d-ran-and-c-ran/
[9] https://telecompedia.net/ran/
[10] https://www.sdxcentral.com/5g/ran/definitions/radio-access-network/
[11] https://www.everythingrf.com/community/what-is-a-remote-radio-head
[12] https://www.electronics-notes.com/articles/connectivity/3g-umts/radio-access-network-utra-utran.php
[13] https://www.lambdagain.com/learning-center/chapter-3-c-ran/
[14] https://www.sdxcentral.com/5g/ran/definitions/radio-access-network/
[15] https://stackoverflow.com/questions/56320739/
[16] https://www.rfwireless-world.com/Terminology/Advantages-and-Disadvantages-of-CRAN-Cloud-RAN.html
[17] https://jwcn-eurasipjournals.springeropen.com/articles/10.1186/s13638-018-1142-1
[18] https://telecompedia.net/ran/
[19] https://telcocloudbridge.com/blog/c-ran-vs-cloud-ran-vs-vran-vs-o-ran/
[20] https://www.futuremarketinsights.com/reports/5g-ran-market
[22] https://www.youtube.com/watch?v=16X34zfSxwA
[23] https://telecoms.com/519116/what-will-2023-hold-for-the-telecoms-industry/
[24] https://www.rcrwireless.com/20211123/fundamentals/xapps-vs-rapps-network-automation-fundamentals
[26] https://www.linkedin.com/pulse/open-ran-what-why-challenges-khaled-shakaki/
*Disclaimer: This report is based on information that is publicly available and is considered to be reliable. However, Lumenci cannot be held responsible for the accuracy or reliability of this data.
*Disclaimer: This report is based on information that is publicly available and is considered to be reliable. However, Lumenci cannot be held responsible for the accuracy or reliability of this data.
Author
Reema S Chauhan
Associate at Lumenci
Reema S Chahuan is an Associate at Lumenci. She has been a wireless technology enthusiast since elementary school. She has extensive experience in Wi-Fi and Bluetooth packet capture and analysis and software development with the TCP/IP stack. An avid follower of cellular technologies.