5G Redefines Drive Testing
2020-05-31 | 5 min read
Fundamental differences in 5G New Radio (NR) technology compared to Long Term Evolution and other predecessors require wholesale changes in test equipment and methodologies. A case in point is user equipment (UE)-based active field testing on the live network, often referred to as drive testing.
5G NR's Frequency Range 1 (410 MHz to 7.125 GHz) and Frequency Range 2 (24.25 to 52.6 GHz) each require changes in radio access techniques and network architecture. Achieving the higher network capacity and data throughputs promised by 5G NR at millimeter-wave (mmWave)) frequencies — Frequency Range 1 — demands massive multiple-input / multiple-output (MIMO) technology with beamforming. Because of these new technologies, 5G NR uses beam coverage rather than the cell coverage used by LTE and previous wireless communications technologies.
Other changes brought by 5G have expanded uptake of software-defined networking and network functions virtualization, which require new tests to optimize the quality of experience (QoE) for different applications.
Massive MIMO requires a vast increase in the number of antennas on a base station, increasing the multi-user MIMO performance and the total cell capacity. However, with MIMO and beamforming, there is no cell-level reference channel from which to measure the coverage of the cell. Instead, synchronization signal block (SSB) beams are used to form a grid of beams covering the area of a cell. The UE measures the beams and maintains a list of candidate beams that are the strongest. In field testing, scanning receivers and test UEs are used to measure the signal power, quality, and signal-to-interference-plus-noise ratio for each of the beams.
Verifying the field performance and capacity gain of a massive MIMO implementation is critical to the overall performance of a 5G NR network. Field testing requires multiple test UEs distributed throughout a cell performing simultaneous active bulk data transfer against a test server. Accurate testing requires that these test UEs be physically spread across the cell area, rather than all bunched in one area. (It is virtually impossible to isolate users to nonoverlapping beams if the UEs are too tightly packed together).
Field testing of a 5G NR network can use both scanners and test UEs. Because a UE is always associated with one particular operator and does not measure all technologies, scanners are best suited to measure the SSB beams, which are the essential coverage measurement of the 5G network. But scanner antennas have different characteristics than mobile UE antennas, a critical point when dealing with massive MIMO. As a result, most live 5G NR network testing uses both scanners and test UEs.
5G NR also implements a new concept called network slicing for both core networks and radio access networks (RANs). This technology allows the creation of multiple virtual networks atop a common shared physical infrastructure. A single physical network can be sliced into various virtual networks that can support different RANs. Since 5G networks can automatically detect the application type, it can apply separate quality of service (QoS) settings for each application.
Thus, active testing at the device end is required to assess end-to-end QoE in 5G NR. Accessibility, retainability, and time to content are measurable only at the device end and are best measured in active tests using real- over-the-top applications.
Testing the latency and peak throughput of the 5G connection is another critical step for identifying points of failure for dropped calls or handover issues. Drive testing at the application layer is crucial for translating the user experience into measurable KPIs and speeding up the verification of use cases.