Putting 5G to the Test
As the 3GPP standardization body moves toward finalizing the first 5G specifications in December of this year, several challenges lie ahead on the road to making 5G the transformative catalyst industry experts have been predicting. 5G proposes faster data rates, lower latency, and increased capacity while addressing new use cases. Unlike prior wireless evolutions, 5G proposes radically different architectures to meet these objectives. Perhaps overlooked in the 5G excitement are the daunting challenges instrumentation companies face to meet the commercialization timelines.
Test and measurement solutions will be a key link in the commercialization cycle. The initial 3GPP specification drafts for release 15 introduce new antenna concepts with controllable/steerable beams, new spectrum in the mmWave frequency bands, and very wide bandwidths compared to LTE today. How will these new technologies be tested? It is important to note that solutions for test not only have to test the important parameters of a device, but they must also be cost effective.
The 3GPP is proposing new phased array antenna technologies for mmWave mobile access using techniques such as hybrid beamforming. In hybrid beamforming systems, test engineers must characterize the antennas to ensure repeatable performance and that this analysis extends to individual beams. In addition, companies like Intel have introduced early phased array antenna modules where the antenna is attached directly to the RF front end to minimize the system losses. The test equipment must not only step up in frequency to the mmWave bands, but key performance metrics must also be characterized beam-by-beam because of the directional nature of transmission and reception at these frequencies. After all, using these directional high gain antennas are the fundamental system element underpinning the mmWave mobile access architecture.
Taking all of this into consideration, it’s clear that mmWave test systems must differ from previous generation architectures in at least three important aspects: beam control, test time and access. mmWave test systems must include a beam control function alongside standard measurement and signal generation capabilities. This integration must be seamless or test time will suffer. Beam characterization will increase the number of measurements and test scenarios by an order of magnitude putting pressure to minimize test time. And lastly there is a question of access. mmWave RF front ends include the antenna and will be packaged as a monolithic unit. Unlike LTE devices, there is no cable or connector access. Possible solutions proposed by the 3GPP RAN4 working group include over-the-air (OTA) testing, which presents its own set of challenges.
With OTA testing, the environment for which the test equipment and the device under test must coexist for a specific test. Because the air is an unpredictable medium with interferers from different sources and noise, the channel itself varies over time and environmental conditions. The test engineer must isolate the channel in the OTA scenario, and control the device on a per beam basis in order to effectively “test” the device.
Additionally, while bandwidth is a familiar test challenge, the tested bandwidth with 5G may increase by 50x over a standard LTE channel. At these bandwidths, the test systems must not only generate and acquire these wider bandwidth waveforms but must also have the processing capacity to process all of that data. And to make things even more complicated, in an OTA scenario, these samples must be processed in real-time.
While there has been much focus and excitement regarding 5G, the challenges that test instrument vendors face delivering solutions to the 5G ecosystem have perhaps been overlooked. These challenges must be solved before 5G can go mainstream and prime time is just around the corner. Test equipment vendors must develop cost effective, flexible solutions that are software configurable to address the challenges presented by 5G. It seems clear that FPGAs must certainly be a part of these systems due in part to their software programmability and immense processing capability. With 5G getting closer, it’s the test and measurement industry’s turn to innovate.