Although the evolution to 5G has been years in the making, we are now reaching a point where the steady march of progress has become a mad dash to the finish line as communications service providers (CSPs) race to deliver profitable new services. Yet, even as network rollouts gain momentum, an array of new complications needs to be addressed in order to validate, activate and optimize 5G infrastructure.
This evolutionary step is not just an incremental update to existing communication standards — 5G represents a paradigm shift in network technology. The enhancements that 5G is expected to deliver will depend on multiple elements working seamlessly in tandem, which is only attainable through innovative and robust 5G testing practices.
Emerging OTA Testing Needs
Although the first 5G networks were deployed in non-standalone (NSA) mode using a 4G core, networks 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 using 5G New Radio (NR), enabling 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, although massive MIMO and beamforming increase overall spectral efficiencies, these technologies also impact test and measurement processes. In the past, most radio functionality could be evaluated independent of antenna systems. But adaptive antenna system (AAS) technologies used with 5G make it impossible to separate radio performance from antenna performance, necessitating over the air (OTA) testing.
OTA testing is required for both 5G NR base stations (gNBs) and user equipment (UEs), requiring conformance testing to ensure quality and sufficient margins. 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 needed because 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.
Moreover, 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.
Massive Test Challenges
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 uses a larger antenna array by manipulating the phase and amplitude of the signals so energy can be directed to specific service areas. This approach makes it easier 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.
Taming Test Complexity
Due to the complexity added with massive MIMO and beamforming configurations, proper downlink (DL) testing cannot be overlooked, which depends on validation of active antenna beam configurations, as well as channel performance and quality. Performing a comprehensive system verification will enable technicians to identify any DL anomalies, including variability in behavior of gNBs, DL channel power, degraded DL modulation, quality and beamforming performance. For operators to reap the benefits of beamforming, technicians also will need to identify the signal at beam level and test the performance of all algorithms and handoffs, while validating the signal to interference ratio prior to service activation.
As commercial deployments move beyond field trials, CSPs must ensure that they can deploy and turn up new 5G infrastructure without negatively impacting current customers. Successful implementation of 5G requires a best practices approach integrating validation and verification with field testing to optimize performance of new network elements, ensuring that your customers’ first experience with 5G delivers the best possible quality of experience.
About the Author
Kashif Hussain is the Wireless Solutions Director for VIAVI Solutions. He has more than twenty years of experience in mobile networking and wireless technology. For more information, please click here