Tools and Techniques for Effective 5G Network Testing

Tools and Techniques for Effective 5G Network Testing

Key takeaways:

• MIMO and beamforming are key to 5G's high-throughput capabilities.
• 5G can coexist with 4G in non-standalone deployments to enable the gradual transition from 4G to 5G.
• Network slicing allows resources to be dynamically allocated based on application requirements.

The phrase "wireless fiber" is often used to describe 5G's high data speeds. Many crucial use cases like global connectivity and autonomous driving rely on 5G technology's latency and reliability promises.

To ensure those promises, effective 5G network testing is crucial. This article explores various aspects of 5G network testing and the equipment and software used for it.

What is the purpose of 5G network testing?

5G testing is performed with the goal of:

• satisfying quality of service requirements by prioritizing certain application traffic
• measuring the average and maximum traffic capacity of the network
• checking network coverage in different areas, especially areas with poor connectivity
• measuring data throughputs for media and virtual reality use cases
• verifying 5G network performance for voice and data use cases

What deployment options are checked during 5G network testing?

In the sections below, we explain the two 5G deployments that must be checked during 5G network testing.

Non-standalone 5G deployment

Non-standalone (NSA) 5G architectures enable established network operators to set up 5G alongside their existing 4G infrastructure and provide both services simultaneously to their subscribers. A user can gradually transition their devices and subscription plans from 4G to 5G services without disruption, falling back on 4G in areas where 5G is not yet available.

The infrastructure can comply with either the 5G new radio (NR) or the latest 5G-advanced specifications (release 18 and later). The 4G infrastructure can comply with long-term evolution (LTE) or LTE-advanced (LTE-A) specifications.

The mix of standards complicates all aspects of the 5G network testing - functionality, performance, reliability, conformance, and regulatory compliance. For example:

• The testing must ensure that all the features and key performance indicators (KPIs) are satisfied or exceeded despite the mix of new and old standards.
• Mobility between 5G and 4G cells must be seamless.

Standalone 5G deployment

Standalone (SA) 5G is suitable for a network operator that is newly stepping into a market to provide 5G services either to the public or to businesses that want private 5G networks (like oil and gas, logistics, or airports).

From a testing perspective, operators must comply with the relevant 5G NR conformance standards based on the nature of their services.

Which radio access network configurations must be tested?

The 5G NR specifications enable network operators to deploy the 5G portions of their radio access networks (RANs) in different ways according to their business, expansion, and financial plans.

1. Distributed RAN

Fig 1. Distributed RAN architecture

In a traditional distributed RAN (D-RAN) deployment, a 5G base station - called a gNodeB (gNB) - is a logical subsystem consisting of these components colocated on each cell tower:

• Advanced antenna system (AAS): These are the antennas that receive the modulated analog radio signals from user equipment (UE) like smartphones and IoT sensors. They also transmit the return signals back to the UE.
• Remote radio unit or head (RRU/RRH): This device is placed very close to the AAS. It digitizes the received radio frequency signals (downlink) to send to the baseband unit (BBU) for processing and converts the processed signals from the BBU (uplink) to radio frequencies for transmission.
• Fronthaul: The RRU sends the digitized data over the fronthaul to the BBU. It consists of fiber optic transmission infrastructure and protocols like the common public radio interface (CPRI).
• Baseband unit: The BBU is responsible for most of the signal processing, decoding, and preparing to send the data to the 5G core network.

2. Cloud or centralized RAN

Fig 2. Centralized RAN

In cloud or centralized RAN (C-RAN) architecture, BBUs are moved away from the cell sites to hubs so that each BBU can serve multiple RRUs. This brings both technical benefits (such as better channel allocation between RRUs) and cost savings due to the reduced number of BBUs.

Fronthaul interfaces and technologies become more important in C-RAN due to the distances. New technologies like enhanced CPRI (eCPRI) and next-generation fronthaul interface (NGFI) are used instead of plain CPRI.

An alternate preferred configuration further splits a BBU's functions into a distributed unit (DU) and a centralized unit (CU), as shown below. This adds more flexibility, allowing the 5G network to satisfy its latency and real-time processing KPIs cost-effectively.

Fig 3. Centralized RAN with DU and CU

The DU is located close to the cell sites and does time-sensitive processing of lower protocols like the radio link control (RLC) layer, the media access control (MAC) layer, and the physical (PHY) layer. It manages aspects like error correction, scheduling, modulation, and demodulation.

The CU manages less time-sensitive control-plane functions like session management, radio resource control, mobility control, and talking to the 5G core. A CU can serve multiple DUs, which again yields technical and financial benefits. The DUs are connected to CUs over high-bandwidth, low-latency fiber networks that form the midhaul. The CUs are connected to the 5G core again over high-bandwidth fiber networks that form the backhaul.

3. Virtual RAN (vRAN)

The vRAN is conceptually the same as C-RAN. Its main difference is that the DU and CU functions are deployed using techniques like network function virtualization (NFV) and containers to achieve more flexible deployments on off-the-shelf hardware and software that can be scaled easily and inexpensively - for example, on public or private cloud services.

4. Open RAN (O-RAN)

The open RAN specifications allow network operators to mix network elements from different vendors in a vRAN architecture. For example, the open radio units (O-RUs) can be from one vendor, the open distributed units (O-DUs) from another, and the open centralized units (O-CUs) from a third vendor.

What is beamforming?

Beamforming concentrates radio transmissions in the direction of a receiver to boost their signal strengths and ranges. It does this by manipulating the elements of a phased array antenna such that all the transmissions constructively interfere with each other in the direction of the receiver.

But why is this needed? The 5G NR standards allow communications over new frequencies in the millimeter wave (mmWave) band, especially in the 24-100 gigahertz (GHz) range. However, these high frequencies are easily blocked in dense urban environments by buildings, trees, vehicles, and other objects. Latency as well as mobility will suffer severely.

Beamforming alleviates this by enabling both the RAN and the user equipment to focus their transmissions carefully toward each other.

How is beamforming tested?

Testing beamforming in the network or user equipment calls for these prerequisites:

• the ability to emulate device transmissions to test the base station
• the ability to emulate the base station's transmissions to test devices
• over-the-air (OTA) testing since the sheer number and variety of transmissions prevent traditional wired testing

What is multiple input multiple output (MIMO)?

Massive MIMO (mMIMO) and multi-user MIMO (MU-MIMO) use a large number of antennas to simultaneously transmit many data streams over the same frequency channel through spatial multiplexing. These multiple data streams greatly bolster the effective throughputs of 5G channels.

Just like beamforming, MIMO requires OTA testing because the number of antennas and transmissions is too high.

How are 5G non-terrestrial networks (NTNs) tested?

A major aspect of 5G is the use of satellites and unmanned aerial vehicles (UAVs) - like balloons, airplanes, and drones - to expand the RAN high up into space for ubiquitous connectivity. However, these new mobile base station platforms introduce Doppler shifts in frequencies due to high orbital speeds and higher latencies due to greater distances between network components.

For NTN and device testing, network operators and 5G device manufacturers need:

• the ability to emulate the orbital motions of satellites and the kinetics of UAVs, including phenomena like Doppler shifts
• the ability to emulate transmissions from user equipment

How are internet-of-things (IoT) networks tested?

Another major feature of 5G is massive machine-type communications (mMTC) that allows a large number of IoT devices to send data over 5G networks efficiently.

Plus, the 5G reduced capability (RedCap) or NR-Lite is a reduced version of the 5G standard specifically designed for IoT use cases.

How is the 5G core tested?

The 5G core communicates with base station components (i.e., BBUs, CUs, or O-CUs) of the RAN over fiber networks. To test the core, the functions of the 5G base stations must be emulated.

What is network slicing?

Network slicing is the dynamic allocation of 5G core functions and resources to suit specific applications. For example, autonomous driving requires ultra-low latency, while data browsing does not. Network slicing dynamically configures and deploys its functions to suit these different applications using NFV.

How is network slicing tested?

To test network slicing, the ability to configure and simulate different use cases is necessary. For example:

• You must be able to create a driving fleet with pre-programmed routes and then simulate their radio transmissions to make the 5G core think it's communicating with actual 5G user equipment aboard autonomous vehicles.
• You must be able to simulate large numbers of user equipment to make the core think it's talking to a transportation fleet's IoT position-reporting network.

What are the key metrics used in 5G network testing?

Some of the key metrics and KPIs measured in 5G network testing include:

• quality of service (QoS) factors like latency, throughput, and bit error rate
• quality of experience (QoE) as perceived by the end users in terms of voice call quality, mobile broadband speeds, mobility, and overall user experience of different 5G services
• service availability
• radio frequency (RF) coverage and metrics like the path loss and spatial correlation
• radio interference
• positioning accuracy
• power efficiency
• security metrics
• supported device density

What are the challenges of 5G network testing?

Some of the bigger challenges of 5G network testing are listed below:

• Testing MIMO and beamforming: These two aspects have major impacts on the QoE. However, it's not easy to emulate the large number of antennas, transmissions, and channels and OTA testing to set up different scenarios. Test automation is crucial here.
• Emulating dense urban environments: These environments affect the signals, resulting in path loss. However, emulating such environments requires software with 3D-mapping capabilities.
• Testing interoperability: Checking whether 4G and 5G components in NSA mode and O-RAN components can interoperate can be challenging. Test automation is essential to simulate these complex test scenarios.

What equipment and software are used for 5G network testing?

Given the complexities of 5G networks, all stakeholders - mobile network operators, device manufacturers, satellite service providers, IoT providers, and various ancillary service providers - have to use several purpose-built equipment and software to effectively test them. In the sections that follow, we look at some of the test equipment and software that are used.

RF signaling platform specializing in 5G

Fig 4. Keysight E7515B UXM 5G wireless test solution

A signaling platform that's aware of the latest Third Generation Partnership Project (3GPP) specifications is essential. The Keysight E7515B UXM 5G wirelesstest solution is one such specialized platform with multi-format stack support, rich processing power, and abundant RF resources.

5G RAN testing

Fig 5. 5G RAN testing software

The 5GRANtesting software can simulate stateful UE traffic at scale for end-to-end 5G RAN validation. It can simulate real-world user activities like voice over NR, voice over LTE, video on demand, and more - scaling up from a few UEs to thousands of UEs.

Over-the-air test chambers

Fig 6. OTA test chamber

The 5G OTA test chambers enable antenna measurements and RF conformance tests. These chambers are configurable with different numbers and positions of probe antennas to support different use cases. For example, they can do performance testing of MIMO and radio resource management under faded conditions.

5G core validation

Fig 7. P8900S 5G core validation software

The P8900S LoadCore software simulates user equipment behavior for network slicing, multi-access edge computing (MEC), low latency, offloading, video optimization, and similar use cases.

5G core simulator

A core simulator allows the emulation of 5G core functions to help test RAN solutions. For example, the P8850S CoreSIM can simulate 4G, NSA 5G, and SA 5G core functions.

User equipment simulator

Fig 8. P8800S UeSIM

A user equipment simulator creates realistic network traffic over the radio as well as fronthaul interfaces. For example, the P8800S UeSIM can generate realistic traffic loads, simulating applications running on thousands of concurrent devices operating real voice and data sessions.

NTN testing software

Several advanced simulators and measurement software are available for validating non-terrestrial network components.

Spectrum analyzers

Fig 9. Keysight 5G signal analysis solution with UXA and PXA signal analyzers

The UXA and PXA signal analyzers (spectrum analyzers) with the PathWave X-Series family of multi-touch applications and PathWave Vector Signal Analysis (89600 VSA) software enable the 5G signal analysis.

How do operators test 5G network security?

The increase in the number and complexity of 5G capabilities exponentially increases their attack surface. For example:

• NTNs add an entirely new dimension of network elements that, if broken into, can have geopolitical implications.
• IoT networks must be protected from turning into botnets.
• Malicious inputs sent to autonomous cars over cellular vehicle-to-everything can lead to major accidents.

To simulate vulnerabilities and attacks, some of the notable security testing tools include:

• Threat Simulator to safely recreate attacks on your live network with breach and attack emulation
• CyPerf to validate the security and performance of hybrid and cloud infrastructures used for 5G architectures
• BreakingPoint to validate the security posture of 5G networks

Streamline 5G network testing with Keysight

In this article, we explored the capabilities of 5G that must be tested and the equipment and tools for doing so.

Contact us for insights into testing your 5G network equipment or devices.

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