5G Testing: Drivers and Challenges for Real-World Performance Channel Emulation
2020-04-30 | 6 min read
Real network environments are complex. Testing in clean channel conditions is not enough to ensure that 5G devices operate as expected in real environments. A signal traveling from a base station to a device in pure line-of-sight (LoS) conditions faces no interference or distractions from other users. But most mobile devices are used in city environments with rich multipath and interference. Testing complex environments is critical to ensuring a positive user experience. It requires thorough knowledge about radio channels.
A radio channel is the propagation path between transceivers. It consists of the transmitter and receiver antennas, multipath propagation, and mobility and interference. Several factors affect signal propagation and reception. Path loss, shadowing from obstacles, and fast fading caused by multipath propagation impact signal propagation. Signal reception is affected by noise sources like thermal noise and broadband noise from power amplifiers, and interfering signals from adjacent cells/users and modulated waveforms.
Radio channels are a part of the physical environment. The industry has developed channel models to describe different propagation environments because the radio channel itself is physical property and cannot be engineered. With continuous evolution in cellular technology, telecommunications system complexity is growing significantly. Channel model complexity increases proportionally as a result. Continuing this trend, 5G requires more advanced channel models. The industry is moving toward spatial models with testing that must involve the antennas.
The move to millimeter-wave (mmWave) frequencies and highly dynamic fading channels with 5G create new challenges. Base stations and devices need to operate seamlessly on beam refinement and change and, eventually, handovers to the next cell and/or fallback to 4G. High blocking channel conditions prevent seamless interoperability, which will likely cause the link to collapse requiring mitigation.
Figure 1. Significant amount of beam changes over time
Even at sub-6 GHz, the effects of channel models are very different. With multi-user multiple-input multiple output (MU-MIMO) base stations with beam scanning over the sphere, for example, radio channel angular dispersion makes it more challenging to achieve isolation between devices. There is also movement even in static conditions because of multiple, non-correlated fading clusters.
Figure 2. Example of LoS channel model at sub-6 GHz
Figure 3. Example of non-line-of-sight (NLoS) channel model at sub-6 GHz
The 3rd Generation Partnership Project (3GPP) has developed channel models to evaluate 5G physical layer performance. You can find them in TR 38.901. They are extensions of existing sub-6 GHz channel models and defined up to 100 GHz to support all the 5G frequency bands. The model properties also include bandwidth support for up to 10% of the center frequency (but not larger than 2 GHz) to address wide signal carrier aggregated scenarios, and spatial consistency. 3GPP channel scenarios include urban microcell (UMi), which mounts the base station below the rooftop, and urban macrocell (UMa), where the base station is mounted above the rooftop. These scenarios enable testing device and base station performance in massive MIMO implementations.
Beam management is an important aspect when evaluating the performance of 5Gdevices at mmWave frequencies. However, there is no test plan for beam management or end-to-end performance testing in 3GPP. 3GPP only defines channel models for radio resource management (RRM) testing of user equipment (UE) and demodulation testing for UEs and base stations, all at both frequency range 1 (FR1) and frequency range 2 (FR2). Beam management testing is defined by the industry outside of 3GPP.
High-density environments require 3D spatial beamforming, MU-MIMO, and more advanced spectrum utilization to increase wireless RF propagation channel effectiveness between devices and base stations. User experience with 5G devices highly depends on the performance of the device in harsh mobile environments. These factors drive the need for expertise in channel models and innovative channel emulation solutions to accelerate testing under complex RF channel conditions. This step in the device and base station workflow is critical to meeting user expectations.
Learn more about 5G channel models and channel emulation in the following webinars available on demand available on the Keysight's Engineering Webinar Series webpage:
- From LTE to 5G MIMO Over-the-Air Testing: Challenges and Solutions
- 5G NR Massive MIMO Testing with Channel Emulation
- 5G Non-Terrestrial Networks — Overview & Focus on Satellite Link Simulation
Our recent Virtual 5G Innovations event also featured a demonstration on 5G radio channel emulation. View it here.
More information on 5G challenges and solutions is also available at www.keysight.com/find/5G.