Understanding Radio Access Network (RAN) in 4G & 5G LTE

A Radio Access Network (RAN) is the part of a telecommunications system that connects individual devices to other parts of a network through radio connections. A RAN resides between user equipment, such as a mobile phone, a computer or any remotely controlled machine, and provides the connection with its core network. The RAN is a major component of wireless telecommunications and has evolved through the generations of mobile networking leading up to 5G.

A RAN provides access and coordinates the management of resources across the radio sites. A handset or other device is wirelessly connected to a backbone, or core network, and the RAN sends its signal to various wireless end points, so it can travel with other networks’ traffic. A single handset/phone could be connected at the same time to multiple RANs, which is sometimes called dual-mode handsets.

The term radio access network (RAN) has been in use since the beginning of cellular technology and has evolved through the generations of mobile communications (from 1G up to 5G today). Components of the RAN include a base station and antennas that cover a given region depending on their capacity, plus required core network items.

What components are used to make up a Radio Access Network?

RAN components include a base station and antennas that cover a specific region depending on their capacity, as well as core network including a RAN Controller.  In modern LTE networks an EPC is required at the core.

Recent evolution of RAN architecture divides the user plane from the control plane into separate elements. User data messages can then be exchanged by the RAN controller through one software-defined networking (SDN) switch and a second set through a control-based interface. This separation allows the RAN to be more flexible, accommodating for network functions virtualization (NFV) techniques such as network slicing and high MIMO that are necessary for 5G

Examples of radio access network types are:

• GRAN: GSM radio access network
• GERAN: essentially the same as GRAN but specifying the inclusion of EDGE packet radio services
• UTRAN: UMTS radio access network
• E-UTRAN: The Long Term Evolution (LTE) high speed and low latency radio access network

RAN Base Stations

In modern 4G networks the Base Station is termed eNodeB (Evolved NodeB).  For 5G networks, the term gNodeB (Next Generation NodeB) is used.  The base station takes digital packets from the network core (typically the EPC) and synthesises the radio signals for transmission.  Modern eNodeB and gNodeB base stations typically use Software Defined Radio (SDR) for this purpose.

The Base Station may comprise of 1 sector (an example being a Small Cell) up to 3 sectors or more (typically a Macro Site) for longer range and higher capacity.  A modern multi-band LTE Base station may transmit on more than one carrier, with the ability of Carrier Aggregation across multiple bands to provide higher user throughput.

Explaining BBU, RRH & Antennas

The Base Station may be split into a Baseband Unit (BBU) plus one or more Remote Radio Heads (RRH) which is a typical design for 4G LTE, or may be combined into a single unit for a Small Cell featuring 1 or 2 sectors only.  The Radio Heads are typically mounted up on the tower next to the Sector Antenna(s) with short RF jumper cables for low signal loss to ensure maximal coverage.

The Remote Radio Heads typically feature MIMO connections to the antennas with 2×2, 4×4, 8×8 or even higher count for Massive MIMO.  Generally, high order MIMO only works effectively at shorter distances in urban environments.  However, 8×8 configurations can also feature beamsteering to enhance range and capacity at the cell edge, making 8×8 MIMO potentially useful for long range & rural broadband applications.

Antennas used for the RAN may vary from an Omnidirectional or patch antenna for single-sector short-range coverage up to a cluster of Sector Antennas which may be designed with 3, 4, 6 or more sectors to create full 360-degree coverage from the base site to users.  Generally, higher gain antennas are used for long range applications, whereas a short-range Omnidirectional or patch antenna has lower gain

The RAN Controller

The RAN controller controls the radio nodes that are connected to it. The network controller performs radio resource management, mobility management, and data encryption. It connects to the circuit-switched core network and the packet-switched core network, depending on the type of RAN.

In a modern 4G network an Evolved Packet Core (EPC) is central to the RAN core network.  The EPC.  For 5G, a Next Generation Core (NG, NextGen core) may be required.   The requirement for an EPC makes LTE more complex than simpler wireless technologies such as WiFi, but brings many benefits such as seamless roaming and advanced user management.  Some vendors such as CableFree offer the option to virtualise an embedded EPC within an eNodeB base station, enabling simpler LTE implementations with fewer boxes, reduced complexity and cost.

Modern RAN architectures separate the user plane from the control plane into different network elements. In this scenario, the RAN controller can exchange user data messages through one software-defined networking (SDN) switch, and a second set with base stations via a second control-based interface. This separation of the control plane and data plane will be an essential aspect of the flexible 5G RAN, as it aligns with SDN and network functions virtualization (NFV) techniques such as service chaining and network slicing.

Evolution of the RAN for 5G and beyond

Radio access networks have evolved significantly since their origins to the point at which today’s RANs support multiple-input, multiple-output (MIMO) antennas, wider spectrum bandwidths, multi-band carrier aggregation, and so on — with many increases and enhancements for today with 5G and for the future.

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