An Architecture for Monitoring Humidity Using Signals

Mike Barts, Asokam Ram, Koichiro Takamizawa, Shruthi Soora Research Center

Mark Weber, Dusan Zrnic, Alexander Ryzhkov, Danny Wasielewski NOAA OAR National Severe Storm Laboratory

Keith Brewster Center for Analysis and Prediction of Storms, University of Oklahoma

Presented to the AMS 100th Annual Meeting, Boston, MA January 16, 2020

A Non Profit 501(C)(3) Wireless Research Hub Problem Statement/Goal  Near ground humidity measurements are sparsely sampled

 More dense (spatial and temporal) humidity measurements can produce better quality inputs for numerical weather forecasts

 Widespread deployment of base stations, will provide an opportunity for passive, opportunistic measurements using them as a reference source

 Goal: Develop a technique to use /5G signals to derive integrated humidity between base stations and sensors

A Non Profit 501(C)(3) Wireless Research Hub 2 Cellular Signals (4G/5G)  Current (4G LTE) frequency bands extend to 2.7 GHz; soon will include 3-6 GHz

 5G will use the same frequency bands but will also include mm Wave bands at 26, 28, 36-40 GHz and higher

 Cellular base stations provide a fixed, reliable signal source with 24/7/365 availability

 Measurements can be single point-to-point or point-to-multipoint for additional data and covering a wider area  Greater density of sampling using mesh topology can provide finer resolution of data over an area vs point sampling

 Proposed technique uses a channel calibration/ synchronization signal  No issues with user privacy

A Non Profit 501(C)(3) Wireless Research Hub 3 4G/5G Signals  4G LTE  Adaptive signal with of 1.4 – 20 MHz  4G signal protocol includes a Cell Specific Reference Signal (CRS) transmitted every 1 ms  Channel Estimation to measure amplitude and phase of CRS

 5G protocol is similar to 4G  Instead of CRS, use Demodulation Reference Signal (DM- RS)

A Non Profit 501(C)(3) Wireless Research Hub 4 Experimental Testbed

Anritsu MT8821 NI 5644R VST Base Station Simulator

LTE User Equipment (UE)

Directional Coupler

A Non Profit 501(C)(3) Wireless Research Hub 5 LTE Signal Decoding Results

Verizon eNB

WRC Office

1.07 mile

Software correctly decoded LTE signal for eNB information

A Non Profit 501(C)(3) Wireless Research Hub Channel Estimation “C”  Channel Estimation for one sample over LTE 10 MHz bandwidth and 1 subframe (5 ms) is shown  Phase needs unwrapping due to difference in wavelength over 10 MHz bandwidth  The channel estimate is noisy  Interference from other LTE signals  Fast fade due to changes in scattering environment (cars, people)  We will require some averaging to obtain stable channel estimation

Amplitude Estimate Phase Estimate

A Non Profit 501(C)(3) Wireless Research Hub Amplitude Measurements  Previous work has shown that amplitude variations on fixed microwave links follow humidity  Need to monitor pressure and temperature as well to derive humidity

“Humidity Measurements using Commercial Microwave Links,” David, Alpert, & Messer, Advanced Trends in Microwave Communications, pp 65-78

A Non Profit 501(C)(3) Wireless Research Hub 8 Phase Measurements  Phase change is extracted from measurements of CRS (DMRS)  By tracking phase change, we measure change in RF path length  From geodesy: = R – electrical path length S – physical path length n – index of refraction

 Phase shifts → n variaon  n ∝ , ,  Derive humidity () from n variation

A Non Profit 501(C)(3) Wireless Research Hub 9 Distributed Measurements

Elevated transmitters help define the humidity above the ground as well as the horizontal distribution

Base Station

Base Station

Monitor Monitor

With multiple monitors looking at multiple base stations, the result is a mesh of humidity measurements covering a larger area than point samples

A Non Profit 501(C)(3) Wireless Research Hub 10 Monitoring Station Concept  Station should be compact, low power, low cost  Deployment on rooftops, light poles, etc  SDR based to cover multiple bands, carriers  Need flexibility in RF coverage for different locations  Pressure and temperature monitors  Can use the cellular network to report data back to central monitoring

A Non Profit 501(C)(3) Wireless Research Hub 11 Conclusion  Current Status  Software for decoding 4G LTE and extracting CRS completed  Making over-the-air (OTA) measurements on 4G cell towers  Developing algorithms to extract humidity from OTA measurements  Live demonstration of system planned for Spring 2020

A Non Profit 501(C)(3) Wireless Research Hub 12