Statistical Methods in Millimeter-Wave Wireless Metrology

Summary

The goal of the millimeter-wave wireless metrology project is to develop the metrology for the next-generation mobile communications at millimeter-wave frequencies. The project was motivated by a unique combination of events: the national need for increased utilization of the communication spectrum has reached a fever pitch and the FCChas recently allocated spectrum at frequencies in the 70, 80 and 90 GHz range that is thirty times the total cellular bandwidth available today.Concurrently, semiconductor processing advancements have, for the first time,enabled inexpensive silicon radio chips that operate above 50 GHz. This combination of spectrum allocation, technological advancement, and national need represents a unique opportunity for NIST to have a significant impact on both the state of the art in telecommunications and also on the national economy as a whole. Since electrical metrology for broadband modulated wireless communication links at millimeter-wave frequencies is nonexistent, NIST will develop fundamental metrology in this frequency range. The Statistical Engineering Division has developed statistical methods to support this effort.

Description

DESCRIPTION:

One of the measurement solutions is the use of reverberation chambers for free-field testing of wireless devices. A reverberation chamber is an environment for electromagnetic compatibility testing and other investigations. Quantities of interest that have been studied for wireless testing in the reverberation chamber include total radiated power, total isotropic sensitivity, bit error rate, and other wireless device metrics. The study of antenna parameters is common as well. The fields within the chamber can be manipulated through the use of radio-frequency absorber to replicate various real-world environments, exposing a wireless device to desired conditions. The reverberation chamber is highly reflective and needs to be characterized statistically.

We have studied the effect of various aspects of chamber testing configurations. For example, we proposed a measurement-based approach that allows users to verify that the reduction in received power, due to antenna proximity to lossy objects, is no more significant than variation in received power due to the lack of spatial uniformity in the chamber. We developed a new estimation method for the Rician K-factor of reverberation chambers. The Rician K-factor is defined as the ratio between the invariant components and the components that are randomly scattered from one measurement to the next. This is an important characteristic parameter for a wireless fading channel, since it is a measure of the distribution of the components of the received signal resulting from various interactions with the surrounding environment. Reverberation chamber setups with low K-factors enable low measurement uncertainty for over-the-air tests such as total radiated power.

Major Accomplishments

A list of recent joint work:

• "A compact millimeter-wave comb generator for calibrating broadband vector receivers," 85th ARFTG Conference, May 22, 2015, Phoenix, AZ. 
• "Using the amplitude variation of a reverberation chamber channel to predict the synchronization of a wireless digital communication test system," 2015 Joint IEEE International Symposium on Electromagnetic Compatibility and EMC Europe, August 16-22, Dresden, Germany. 
• "Uncertainty from choice of mode-stirring technique in reverberation-chamber measurements," IEEE Transactions on Electromagnetic Compatibility, 55, pp. 1022-1030, 2013. 
• "Parameter estimation and uncertainty evaluation in a low Rician K-factor reverberation chamber," IEEE Transactions on Electromagnetic Compatibility, 56, pp. 1002-1012, 2014.
• "Modulated-signal measurements and uncertainty in error vector magnitude at millimeter-wave frequency," IEEE Transactions on Microwave Theory and Techniques, in press, 2015. 
• "Proximity-effect test for lossy wireless-device measurements in reverberation chambers," IET Science, Measurement and Technology,in press, 2015.