Test & measurement: How to simplify 5G device testing
The multiple layers of the 5G standard make testing processes complex to ensure compatibility with mobile devices and networks, says Aytac Kurt.
The R&S CMX500 tester is coupled with the CMQ500 test chamber for detailed analysis of 5G devices and modules
On the long road from prototype to production, mobile devices undergo countless tests of many different types. This is especially true for 5G. The mobile communications industry is therefore looking for user-friendly test and measurement equipment to make testing straightforward to allow users to work efficiently through a high degree of customisation, a short learning curve and uniform look and feel.
Signal generators and signal analysers, radio communication testers have almost the same set of functions, albeit not with the same depth and precision. Nevertheless, they can simulate all the functional diversity of a mobile network for the device under test (DUT). They must initiate, measure and evaluate every possible interaction between a smartphone or other mobile device and the network.
Testing needs to encompass 5G’s entirely different radio communications layers: physical – which must remain within tight tolerances, logical (signalling) – which structures data exchange, and application – which is becoming increasingly important in the internet era. The ideal 5G tester facilitates physical, logical and application layers and makes complex test tasks more manageable.
A uniform user interface allows users to configure exactly the functions and displays they need for the task at hand, including RF parameter measurements, protocol tests, performance analyses, application tests and extensive validation test runs. A consistent look and feel makes it easier to create a homogeneous test landscape along the value chain.
Adding 5G NR (New Radio) capabilities to existing test systems for LTE and legacy standards ensures a seamless evolution. For example, users can add a test platform extension and compatible test chamber. Such a set-up is suitable for testing all 5G NR use cases in the framework of 5G Implementation Guidlines’ 3GPP Option 3x and Option 2 in both non-standalone (NSA) mode, which requires an LTE substructure, and pure 5G standalone (SA) mode in all 5G frequency bands (FR1 and FR2).
5G testers avoid traditional controls, in favour of a browser-based test environment using web technologies. An example is the ‘CMsquares’ interface which supports manual testing in an interactive call‑box mode as well as automatic sequencer‑driven tests. Tools such as CMsequencer support the practical tasks of these programs. Typical functions include configuration of the emulated 5G network, measurement of RF parameters and IP data throughput, plus analysis of protocol stack messages over all layers.
The home screen of the graphical user interface (GUI) is a dashboard with direct access to the key tools and work environments through visual squares (Figure 1). From there users can build a complete test environment in a few steps. The first is creating the 5G network, such as an NSA network with LTE anchor cells or a pure 5G NR network as a virtual network layout in the network square, by using drag‑and‑drop.
Changing to the settings menu of the newly‑created LTE or 5G cells provides access to key parameters such as frequency bands, bandwidths, antenna interconnections and cell transmit power. Typical network data services can then be added and configured in the services square, to perform data tests, simulate IMS VoLTE and VoNR calls, and enable data links to the internet via the integrated DNS server.
Figure 2: The same interface can configure the virtual network and DUT, with data updates and measurement functions
Once the virtual network has been set up, the focus shifts to the DUT (Figure 2). Device‑specific data such as SIM card profiles and antenna configurations can be entered here. The square displays real‑time status of the connection between device and network, together with important information about the 5G device, such as its IP address assigned by the network.
The next step is to access various measurement applications in the workspace window. The presentation can also be customised, with a choice of a graphical or tabular display depending on the required level of detail.
Managing test scenarios and sequences
A popular test scenario is to check all the LTE and 5G bands supported by the device as well as mixed 5G/LTE operation (dual connectivity, EN‑DC). This can be done with a sequencer – a campaign manager that runs predefined test scenarios and enables users to create their own scenarios.
Graphically displayed test sequences can be created from function blocks and can contain user‑defined scripts developed in a Python API environment. User scripts can be named and saved in the sequencer library, and they can be assigned to soft keys for quick access. Automatic and interactive modes are synchronised, making it easy to quickly switch back and forth between script‑driven tests and manually triggered actions.
Whether initiated interactively, controlled by the sequencer or remotely controlled via SCPI, tests can be analysed for errors using the real‑time display of protocol messages exchanged via the air interface. These can be probed down to the bit level, allowing errors in the LTE or 5G protocol stack in any layer to be traced quickly. Messages exchanged between the DUT and the emulated network can be saved for offline analysis.
High‑performance data transmission via the air interface is only possible with devices that have perfect transmit and receive characteristics. Transmit power must remain within defined limits and the signal quality must meet minimum requirements, to ensure the quality of the device connection and avoid interference with other users.
Figure 3: RF transmitter measurements for 5G include modulation quality, transmit power and spectral parameter
Crucial RF transmitter measurements of the 5G standard include modulation quality, transmit power and spectral parameter. These can be performed in all test modes (Figure 3), along with receiver measurements such as BLER. For 3GPP testing, extensive test cases for transmitter and receiver measurements are defined in TS 38.521 sections 6 and 7. These are included ready‑made in the sequencer and can be run there.
With its all‑IP architecture, 5G is perfectly equipped for mobile devices that integrate increasing numbers of internet‑based services and applications. IP services in mobile communications are increasingly being reflected in device test programs and built into end‑to‑end tests.
IPv4/6 configuration, throughput measurements with iPerf and directly deployable web, FTP, DNS and IMS services enable device tests at the IP level. User‑friendly data test solutions are bundled in the services square to reduce test times. Built‑in quality of service (QoS) measurements are important to device manufacturers and network operators, who need confidence in the functionality of devices they market based on their own lab tests.
Passing a series of 3GPP test cases is a requirement for trouble‑free device operation in a real network. But there are also options for fashioning a 5G network (FR1, FR2, NSA, SA) and providing network services. This creates countless functional cross‑links and dependencies that can differ from network to network or country to country. These cannot be dealt with using standardisation. New features and functions may be launched before suitable mandatory 3GPP tests are available, while the growing field of IP applications is not addressed by 5G standardisation.
Network operators must devise their own test plans to cover extensive and specific needs. Device manufacturers that want to sell their products in the large networks subject their devices to these carrier acceptance tests, as do network operators. Typical tests supported by radio communication testers include VoNR, the US emergency call service E911, location‑based services, rich communication services and data throughput measurements with various MIMO configurations.
The requirements of network operators and mobile device manufacturers for basic RF testing call for a comprehensive 5G test solution. Today, all commercially relevant versions of the 5G NR standard, all test dimensions and carrier‑specific special features can be easily tested. The resulting test environment combines a uniform look and feel over a variety of test functions with a high degree of customisation and a short learning curve.
About The Author
Aytac Kurt is a product manager for mobile radio testers, Rohde & Schwarz