Summary

SRG just completed its 48th 5G benchmark study. For this endeavor we collaborated with Accuver Americas and Rohde & Schwarz to conduct a benchmark study of the T-Mobile – Starlink text messaging service and how it performs relative to a terrestrial-based text messaging service.

Highlights of the Report include the following:

Our Thanks.  We did this study with the support of Accuver Americas and Rohde & Schwarz.  Accuver provided us with its XCAL5 drive test software and XCAP post-processing software to execute the tests and to capture the corresponding metrics, including signaling, radio conditions, and various milestones associated with the sending/receiving of the messages.  We used the TSMA6 scanner from Rohde & Schwarz to measure LTE and 5G signals with a particular focus of bands between 1.7 and 2.2 GHz, including neighboring cells.  SRG is responsible for all analysis and commentary provided in this report.

The Methodology.  We tested in very rural Minnesota where there was little to no terrestrial coverage on the T-Mobile network.  We also tested the service at SRG HQ where there happens to be excellent LTE and 5G coverage, including in the same channel used by Starlink.  Each test lasted 60 minutes with 1 message sent per minute.  We used NAS and SIP signaling to precisely measure how long it took to send/receive the message, including the time from “tap to send” to sent as well as the total time.  We sent messages in both directions.  We also captured and analyzed RACH signaling and radio parameters to understand the radio conditions when the messages were being sent.

The Results.  The messaging service worked as promised, albeit generally slower than a pure terrestrial service.  In fact, the service even worked in places where it shouldn’t have worked, including deep inside SRG HQ and in the presence of a very good Band n25 signal.  We show results with lots of detail and analysis.

Opportunities Exist.  The current service leverages basic LTE protocols with no changes.  Advancing to basic data services and voice could requirement enhancements, including 5G NTN.  We believe, and hopefully prove, that any issues we experienced with text message delivery was not due to poor RF (low RSRP).