What Are Radio Access Networks?

Radio access networks (RANs) are the segment of a mobile telecommunications system that connects individual user devices, such as smartphones and IoT endpoints, to the core network through wireless radio links. A RAN consists of base stations that transmit and receive signals to and from devices in their coverage area, together with the backhaul links, interfaces, and control protocols that route traffic between those base stations and the mobile core. The RAN is the wireless edge of the telecommunications infrastructure and is responsible for managing the radio resource allocation, scheduling, handover between cells, and the physical-layer signal processing that converts digital data into radio waveforms.

The architecture and capabilities of RANs have evolved through successive generations of mobile standards, each introducing new radio access technologies, frequency bands, and network architectures to meet increasing demands for data throughput, capacity, and latency. The 3rd Generation Partnership Project (3GPP) defines the technical specifications for RAN interfaces and protocols across all modern mobile generations.

RAN Architecture

A mobile network divides its territory into cells, each served by a base station. In 3G UMTS networks, the base station is called a Node B, controlled by a radio network controller (RNC) that manages handover and resource allocation across multiple Node Bs. In 4G LTE, the base station is called an evolved Node B (eNB); the RNC function was eliminated, and control functions were distributed directly to the eNBs and the evolved packet core (EPC), reducing latency. In 5G NR, the base station is called a gNB. The 5G RAN (NG-RAN) architecture introduced a further functional split, separating the gNB into a central unit (gNB-CU) that handles higher-layer protocols and one or more distributed units (gNB-DU) that manage time-sensitive radio functions, connected via the F1 interface. This disaggregation enables flexible deployment: radio units can be placed close to the antenna while baseband processing is centralized. The 3GPP overview of NG-RAN architecture describes the full set of interfaces and functional entities defined for 5G.

3G Mobile Communication and Standardized Air Interfaces

Third-generation mobile communication, specified in 3GPP Release 99 and subsequent releases, introduced wideband code-division multiple access (WCDMA) as the dominant 3G air interface, replacing the narrowband TDMA and CDMA air interfaces of 2G systems. WCDMA spread each user's signal across a 5 MHz channel using a unique spreading code, allowing multiple users to share the same spectrum simultaneously while using signal processing at the receiver to separate them. 3G networks, branded as UMTS in Europe and CDMA2000 in North America, enabled mobile data services for the first time at practically usable speeds, achieving peak downlink rates of up to 42 Mbps in the HSPA+ variant. The IEEE Xplore publication on 5G radio access network architecture provides context on how 5G NR was designed to coexist with and ultimately replace these legacy 3G systems.

Open RAN and Virtualization

Open RAN (O-RAN) is an industry-driven initiative that defines open interfaces between the functional components of the RAN, allowing operators to source radio units, distributed units, and central units from different vendors rather than relying on a single integrated system. This disaggregation enables the use of commercial off-the-shelf computing hardware for baseband processing and facilitates software-defined and cloud-native RAN implementations. The O-RAN Alliance, whose members include major mobile operators and network equipment vendors, specifies the open interfaces and deployment architectures that make multi-vendor RAN feasible. The technical dimensions of 5G RAN disaggregation are analyzed in the Systems Approach 5G RAN chapter, an open resource covering RAN functional splits and cloud-native deployment models.

Applications

Radio access networks have applications in a range of fields, including:

• Mobile broadband services delivering voice, data, and video to smartphones and tablets
• Telecommunication services for enterprise mobile private networks using licensed or shared spectrum
• Internet of Things connectivity for large-scale sensor deployments in industrial and agricultural settings
• Public safety networks providing mission-critical communications for emergency responders
• Fixed wireless access providing broadband connectivity to homes and businesses without fiber