Signals Research Group (SRG) for a long time has been known for its drive tests and benchmark studies, but now it’s taken to the skies, evaluating U.S. carriers’ LTE coverage for drones.
SRG looked at commercial LTE systems from Sprint, AT&T, T-Mobile and Verizon Wireless to see what their coverage is like for the most basic functions of a drone—command and control (C2). Terrestrial cellular networks are designed to provide coverage from zero to 10 feet above ground, not 400 feet, but the analysts noted that several network operators are touting their network performance for drone coverage and they wanted to see for themselves how well the networks could support unmanned aerial systems (UAS).
“Suffice it to say, there were significant differences between operators but no one operator really stood out in all cases,” SRG President and founder Michael Thelander told FierceWirelessTech. “Operators haven’t done much/any optimization for UAS-based traffic so any differences we observe are due to other factors, including frequency band and pure luck.”
“Put another way, there isn’t any one operator LTE network that we think will be adequate to provide ubiquitous C2 for drones, which is not to say that LTE isn’t a good technology for drones, it just requires a little TLC first,” he said.
SRG is making an executive summary of the “Keeping Up With the Jetsons” study available as part of its Signals Ahead report, but details about exactly how each carrier performed are reserved for the full and final report, which is available for purchase here. The researchers said they believe their study represents one of the most comprehensive independent evaluations of LTE for UAS.
The analysts used equipment from Rohde & Schwarz, which provided its TSMA Autonomous Mobile Network Scanner, allowing SRG to evaluate simultaneously eight bands in 10 LTE channels from 700-2100 MHz. UAS Colorado and 3DVistas also participated in the flight portions of the testing, which was conducted in Boulder, Colorado.
And lest anyone think flying drones sounds like day at the park, there’s a lot of rules to follow. 3DVistas conducted a pre-flight check list of 140+ items before commencing with each flight, and liability insurance to the tune of $3.4 million was in place for each flight. No crew or third party was allowed to stand at any time under the expected and actual flight path of the multirotor.
Specifically, a redundant coaxial octocopter with 17-inch propellers was used to carry out the tests, which meant fitting the TSMA below the main body of the octocopter and centered for balance. A GPS antenna was placed on the top side of the drone and an RF antenna was affixed to the device.
“From the data we collected, the networks performed better than we initially thought for some bands but there are significant design considerations for both the eNB antenna system and the UAS antenna system,” the executive summary said. “Further, there are likely changes to the standard that are required to ensure optimal and reliable performance while not degrading the terrestrial cellular network.”
Getting data from 10 LTE bands simultaneously and logging multiple parameters with the added dimension of altitude create a lot of data; the analysts said they viewed and reviewed the data using the R&S ROMES post processing platform. Signal quality analysis was performed by looking at the spectrum analyzer output and correlating that information to reported parameters such as Signal to Interference Plus Noise Ratio (SINR).
“It should be noted that SRG testing was limited since we tested with only one device antenna configuration and from a few select locations,” the analysts said. “Testing across multiple locations and with additional device antenna configurations could have provided a different set of results. We look forward to doing further drone testing using these tools and some test phones, or better yet drone LTE modems.”