An Architecture for Monitoring Humidity Using Cellular Network Signals
Mike Barts, Asokam Ram, Koichiro Takamizawa, Shruthi Soora Wireless 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 5G base stations, will provide an opportunity for passive, opportunistic measurements using them as a reference source
Goal: Develop a technique to use 4G/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 bandwidth 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 varia on 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