The almost addictive reliance on wireless communications devices such as smartphones has spurred the planning and development of Fifth Generation (5G) wireless networks, so as to support the constantly increasing need for additional wireless data. Part of building those networks will be testing and characterizing them, and this will mean the evaluation of components and systems with many new technologies, including multiple-input, multiple-output (MIMO) antenna arrays and the use of millimeter-wave frequencies.
Lead by Kate Remley, Dylan Williams, and associates, the National Institute of Standards and Technology (NIST) at Boulder, Co. has launched a new Communications Technology Laboratory with a mission of identifying new measurement requirements and solutions related to the expected operational needs of 5G wireless communications networks. Since 5G networks and equipment are still in their formative stages, NIST faces a wide open challenge of preparing for high-frequency systems and technologies that may or may not be applied in the future.
What appears to be an inevitable extension of the technology in current 4G and 4G LTE networks will be the use of signal frequencies at millimeter-wave bands. NIST is developing a traceability path to millimeter-wave modulated communications signals through at least 70 GHz in frequency, with the need for test solutions capable of fully characterizing such signals in terms of amplitude, phase, and frequency using S-parameters. NIST strives to develop such measurements with the highest levels of accuracy possible, correcting or calibrating out measurement errors. Current research is evaluating calibrating methods for sampling oscilloscopes and vector network analyzers (VNAs) at 50 GHz and beyond.
The NIST traceability plan applies not only to the test equipment, but also to the measurement techniques and types of measurements—including for S-parameter measurements and error-vector-magnitude (EVM) measurements. For example, based on an arbitrary waveform generator (AWG), NIST has developed low-EVM source for calibrating vector receivers. By using predistortion, the EVM of the AWG can be minimized, with levels of 0.5% EVM already having been recorded at 44 GHz.
Robots are helping with these new levels of measurement precision for 5G systems. NIST has developed a robotic antenna range called the Configurable Robotic Millimeter-Wave Antenna (CROMMA) facility that combined robotic control with optical spatial metrology for antenna positioning accuracy of better than ±25 μm for alignment and tracking within a 1.5-m radius spherical volume. The positioner is part of an antenna measurement facility with frequency range to 500 GHz.
These are just a few examples of the NIST measurement capabilities in the new facility, with a great deal of attention paid to measurements at millimeter-wave frequencies. NIST works closely with industry and has been deeply involved in the development of channel-sounding models, so that the performance of emerging 5G wireless systems can be simulated in terms of propagation effects, no matter the operating frequency.
See “Measurement Challenges for 5G and Beyond,” IEEE Microwave Magazine, Vol. 18, No. 5, July/August 2017, p. 41.