A radio access network (RAN) is defined as the combination of telecommunication network elements used to establish communication between user equipment and the core network. Traditionally, this has included base station components, radios, and antennas that provide cell coverage within a specific area. With the advent of 5G, RAN architecture has been transformed by network function virtualization (NFV) as more intelligence moves from the core to the edge.
5G RAN innovation is centered around the vastly improved speed and reliability of millimeter wave (mmWave) transmission. Massive MIMO antenna arrays, beamforming, and network slicing are among the innovations enabling the high capacity, low latency use cases associated with 5G new radio (NR). At the same time, RAN disaggregation and virtualization have made deployment options more flexible and amenable to these emerging 5G services.
- Virtualized RAN (vRAN) allows conventional baseband functions to be performed using software on standard servers rather than proprietary hardware. Virtualized RAN 5G architecture separates the control and user planes, enabling high levels of automation, visibility, and scalability that cannot be achieved with hardware-based RAN.
- Open RAN (O-RAN) architecture is based on the interoperability of 5G RAN elements using open-source software, white-box hardware, and open interfaces. The traditional, single-source RAN model is transforming into a disaggregated, multi-vendor landscape as 5G Open RAN promises improved efficiency, innovation, and competition. The O-RAN Alliance was founded in 2018 by a diverse consortium of operators with the common goal of evolving RAN networks worldwide.
Virtualization of traditional RAN elements and antenna propagation through Massive MIMO and small cell deployment are among the more visible features of 5G RAN architecture. Logical and physical splits between the user plane (UP) and control plane (CP) also make 5G RAN more adaptive to service requirements. The 3rd Generation Partnership Project (3GPP) continues to develop specifications, core, and transport network architecture standardizing refining new 5G RAN interfaces.
- 5G Spectrum
In addition to millimeter wave frequencies between 30 GHz and 300 GHz, underused frequencies between 300 MHz 3 GHz and Mid-band (C-band) frequencies between 3.3 and 4.2 GHz are also being repurposed for 5G. This assortment of available frequencies enables 5G RAN architecture to meet performance requirements for a broad range of use cases.
- Network Slicing
Network slicing and 5G RAN slicing use NFV technology to allow multiple logical networks to run simultaneously and independently over a shared physical network. Use cases with differing throughput, latency, and coverage requirements can be managed more effectively by partitioning resources between verticals and users.
Beamforming technology uses signal processing algorithms to determine the most effective data transmission path to each device from a massive MIMO array. The phase and amplitude of each individual antenna is optimized to produce a higher gain directional overall. Combining multiple signals constructively also improves bandwidth and coverage.
- 5G Non-standalone (NSA)
5G non-standalone mode is an important incremental step between 4G and 5G architecture. As defined by 3GPP release 15, NSA mode utilizes existing LTE infrastructure to “anchor” new 5G RAN elements. Non-standalone mode does not enable full 5G performance but does increase bandwidth by tapping into millimeter wave frequencies. NSA architecture also focuses on maintaining LTE to 5G mobility and minimizing interrupt time.
With Open RAN, Massive MIMO, network slicing, and 5G vRAN architecture adding complexity and diversity to the RAN landscape, the test tools and processes of the past no longer suffice. Flexible RAN enabling enhanced mobile broadband, (eMBB), ultra-reliable low latency communications (URLLC), and massive machine type communications (MMTC) use cases to successfully co-exist also produces a much larger set of test cases. The same holds true for an Open RAN ecosystem with a seemingly limitless combination of vendors and RAN components. 5G antenna arrays increase fiber and connection density, making testing imperative to identify fiber defects or loss locations. Millimeter wave frequencies enabling high capacity, low latency verticals also drive higher dynamic range and signal-to-noise (SNR) requirements for spectrum analysis. While innovative beamforming techniques overcome radio access network 5G limitations to improve coverage and QoS, a high level of test sophistication is needed to perform accurate beam tracking and channel aggregation at high frequencies.
5G RAN Test Challenges
By combining cutting edge hardware and software advancements, 5G RAN has introduced a new architectural model capable of meeting aggressive use case performance standards. This unique combination also introduces challenging new test conditions.
- Massive MIMO has increased antenna array density to a level where connector ports and traditional cabled testing are no longer feasible. This has brought about new standards for 5G RAN over-the-air (OTA) testing.
- O-RAN has reduced the barrier to entry for dozens of new 5G RAN vendors, although this diversity also creates interoperability and integration challenges. VIAVI is actively engaged in O-RAN Alliance working groups contributing to interoperability test specifications, Open Fronthaul, PlugFest, and other important initiatives.
- Timing and Synchronization are fundamental building blocks for all wireless networks. With 5G RAN interfaces relying on time division duplex (TDD) communication at high frequencies, precise OTA testing is needed to validate TDD frame format and avoid intercell interference.
- Multi-Access Edge Computing (MEC) brings applications from centralized data centers to the network edge, closer to end users and their devices. The fiber networks, computing power, and virtualization that enable MEC also decentralize hardware and software functions, which complicates test, maintenance, and monitoring practices.
- 4G/5G Interactions introduce test complexity as the transition between wireless generations slowly evolves. Coexistence with 4G in non-standalone mode creates potential interference and handoff issues that need to be emulated in the lab. The interaction and synchronization between 4G and 5G layers must also be thoroughly tested and monitored in the field.
- Massive IoT, eMBB, and V2X are among the numerous 5G use cases with unique performance requirements for latency, densification, bandwidth, and speed. While network slicing and NFV allow these verticals to operate independently, they must also be tested and monitored end-to-end to verify SLA conformance.
Achieving optimum performance requires real-time data collection and analysis to verify QoE expectations are consistently met. Vo5G will continue to supplant both VoLTE and Wi-Fi, and uRLLC applications such as vehicle-to-vehicle communication make stringent latency standards pivotal for SLA compliance. As 5G RAN architecture evolves and small cells, 5G standalone, and private 5G deployments multiply, the long list of test challenges and opportunities will continue to grow. By developing scalable, cloud-enabled, 5G RAN test tools designed to adapt to the latest 3GPP standards and RAN architecture, VIAVI has charted a future-proof path toward 5G RAN testing and assurance.
5G RAN Slicing
The concept of network slicing, with multiple virtualized networks created on top of a common physical infrastructure, is a central pillar of 5G architecture. With each new use case having its own performance requirements, a one-size-fits-all approach to RAN is no longer valid.
Much like a modern transportation system, network slicing architecture utilizes common lanes of traffic along with specialized lanes tailored to the speed, capacity, and budget constraints of the user. An end-to-end (E2) approach that extends to the RAN is needed to realize the full potential of network slicing.
5G RAN slicing applies the virtualization, AI-powered orchestration, and resource optimization used to build network slices in the Core to the RAN. To accomplish this, virtualized, disaggregated RAN architecture with open APIs and intelligence embedded within every layer of the RAN must be implemented to bring intelligence closer to the user. Completing this E2E transition will allow advanced new 5G use cases to be delivered more efficiently.
As a prerequisite for radio access network 5G slicing, virtualized RAN (vRAN) is gaining momentum among OEMs, service providers, and system integrators in the telecom industry. As RAN becomes more software-centric, the ability to emulate virtualized 5G RAN and core behavior in the lab becomes invaluable.
The TeraVM core emulator gives vRAN developers a reliable method to perform 3GPP standards testing quickly and streamline validation. TeraVM-Virtualization is a software only solution with an elastic test bed for virtualized products. The platform features include web-based configuration templates to simplify test delivery and a centralized test library that is accessible to all users.
How VIAVI Supports 5G RAN
5G RAN has redefined the familiar “all-in-one” radio access network by disaggregating and virtualizing RAN elements and unleashing the power of millimeter wave radio transmission through Massive MIMO and beamforming.
VIAVI provides comprehensive 5G RAN testing and assurance solutions from the lab to the field, including scalable real-world emulation, end-user experience testing, large-scale deployment support, and advanced RAN intelligence management platforms.