Yesterday, CableLabs, the cable industry’s non-profit research and development consortium, published a blog that highlighted an important question that many in the tech policy community are talking about: Does the lack of effective politeness protocols in LTE-U technology risk disrupting consumer Wi-Fi and other devices that rely on unlicensed spectrum?
In short, the conclusion was yes. As the blog makes clear, the LTE-U “specification” provides only a limited, half-page discussion of potential approaches to testing sharing but no actual sharing requirements. If this is LTE-U’s answer to coexistence, it is cold comfort to the millions of current users who rely on consensus-based sharing protocols that currently promote fair use of a scarce resource.
“The FCC has granted limited bandwidth for use by a wide array of critical technologies. If politeness breaks down, consumers will suffer.”
We’ve detailed on past blogs the importance of what we call effective “politeness protocols” when using unlicensed spectrum. After all, the FCC has granted limited bandwidth for use by a wide array of critical technologies that use the unlicensed bands. If politeness breaks down, consumers will suffer.
It’s extremely important that technologies that rely on unlicensed spectrum share this precious resource and respect each other’s signals by following basic standards like “listen-before-talk.” Listen-before-talk, as the name implies, means devices do not transmit data while there is another active nearby signal in the band. Politeness protocols are not merely clever features – they’re fundamental to fair coexistence in unlicensed bands. LTE-U, as CableLabs has confirmed, does not use these protocols, leading to significant interference risk to Wi-Fi and other unlicensed signals.
CableLabs’ blog details how LTE-U protocol differs, stating:
“[LTE-U] is taking an entirely different approach to coexistence, using a carrier-controlled on/off switch known as “duty cycling” instead of reliably fair listen-before-talk. Here, LTE turns on to transmit for some time determined by the wireless carrier, then switches off for some period of time, again determined by the carrier. It is during this “off” period that other users such as Wi-Fi can have the chance to access the channel.”
In other words, rather than listening-before-talking, LTE-U can be set to constantly talk without listening – even on top of an active Wi-Fi user – disrupting the foundation of shared spectrum behavior.
So what is the fix? LTE-U proponents should follow the lead of international standards bodies that have presided over these technical issues for years. These groups use established collaborative processes that provide stakeholders and technicians a forum for developing sharing protocols and other solutions.
For a much deeper dive into exactly how LTE-U can disrupt Wi-Fi and other unlicensed spectrum signals and how LTE-U proponents have failed to build adequate fairness or politeness into their spectrum sharing protocols, you can read the full CableLabs blog here.