While marketing departments for mobile operators around the world extol the seemingly endless benefits that 5G network rollouts enable, the fact is that operators face a glut of new complications to validate, activate and optimize 5G infrastructure.
Since 5G is not simply an incremental update to existing communication standards, 5G test practices are dictated by the inherent complexity of the new technology. The expected enhancements depend upon multiple elements performing seamlessly in tandem, which can only be achieved through innovative and robust 5G testing practices.
Test challenges in 5G NR
Initially 5G networks are being deployed in non-standalone mode (NSA) mode on host LTE networks using a 4G core that eventually will migrate to a 5G core operating in standalone (SA) mode. To achieve gigabit throughput in 5G, operators can deploy wider channel bandwidth by utilizing 5G NR, which enables the aggregation of as many as 16 component carriers (CCs) and up to 1 GHz of spectrum.
5G NR introduces flexible spectrum usage with scalable numerology, dynamic TDD, massive MIMO and beamforming. However, increases in the overall spectral efficiencies from massive MIMO and beamforming impact testing. In the past, most radio functionality could be evaluated independent of antenna systems. But 5G requires associated adaptive antenna system (AAS) technologies, making it impossible to separate radio performance from antenna performance. Additionally, antenna arrays used with the radios makes it impossible to conduct tests for each antenna port, instead requiring over the air (OTA) testing.
As such, OTA testing is required for 5G NR base stations (gNBs) and user equipment (UEs). All UEs and gNBs must pass required conformance tests before being released into the market. Device and base station manufacturers are using OTA testing during design to test a wider set of parameters to ensure quality and sufficient margins, as well as during manufacturing to ensure a UE or base station meets its specification. Test systems and the specific test cases used to perform conformance tests must be validated by independent parties to ensure that the conformance test is both consistent with the standards and repeatable.
Additionally, radiated tests are required to meet the 3GPP (Third Generation Partnership Project) conformance requirements. Radiated tests are necessary for two reasons. First, 5G NR designs use multi-element active antennas in both frequency ranges. The active nature of these antenna arrays makes it impossible to extract end-to-end performance from individual antenna element measurements.
Second, these antenna arrays use narrow beams in frequency band 2 (FR2) that create a spatial 3-dimensional requirement that depends upon OTA testing. The antenna arrays necessary for mmWave frequencies are highly integrated with the amplifier integrated circuits (ICs) in the radio system. As such, there are no probing points for conducted measurements, meaning OTA testing is required.
Test challenges of massive MIMO and beamforming
In the past, lambda wavelength requirements have made it impossible to deploy large chains of antennas. Massive MIMO and antenna beamforming are key to the 5G centralized radio access network (C-RAN), which will change from static cell-centric coverage to dynamic user-based coverage.
Massive MIMO can have more than 256 array elements that require a large number of radio channels. The addition of beamforming enables the array elements that serve the device to dynamically change, which means cable testing isn’t always viable or cost effective.
Beamforming utilizes a larger antenna array by manipulating the phase and amplitude of the signals so energy can be directed to specific service areas. This approach provides a way to avoid obstacles that can interfere with high-frequency transmissions and can also strategically focus transmissions directly to the end user.
However, a number of test challenges accompany beamforming and other mmWave applications. 3D beamforming is proving one of the most difficult technologies to master, as engineers are forced to conduct static tests on devices and antennas in active beamforming environments.
Overcoming 5G test challenges
 The complexity added with massive MIMO and beamforming configurations rely upon proper downlink (DL) testing, which depends upon validation of active antenna beam configurations, as well as channel performance and quality. Performing a comprehensive system verification with network simulation in the lab will enable technicians to identify any DL anomalies, including variability in behavior of gNBs, DL channel power, degraded DL modulation quality and beamforming performance. Doing so saves time by reducing unnecessary manual root cause analysis steps during field validation.
For operators to reap the benefits of beamforming, technicians will need to identify the signal at beam level and test the performance of all algorithms and handoffs, while also validating the signal to interference ratio prior to service activation.
As commercial deployments of 5G infrastructure become reality, operators will need to move beyond lab testing and field trials. Operators must ensure that they can deploy and turn up new 5G infrastructure without negatively impacting current customers. Operators that successfully implement 5G will do so by taking a best practices approach to integrate lab verification with field testing to validate the performance of new network elements and guarantee network quality.
