A Milestone in Wi-Fi / LTE-U Coexistence

Rob Alderfer
VP, Technology Policy

Sep 21, 2016

Today is an important milestone for unlicensed spectrum coexistence - the Wi-Fi Alliance (WFA) has released its plan for testing how well LTE-Unlicensed coexists with Wi-Fi.

This culminates many months of work by many expert engineers within the WFA and its membership, including CableLabs staff. The outcome is that we now have a definitive set of tests, based on real-world consumer data, against which to judge LTE-U – and we can move past the competing technical studies that were the hallmark of 2015.

The WFA and its staff are to be commended for bringing all sides to the table on this issue of such importance for broadband consumers everywhere. The test plan, developed in record-time, is a product of compromise by all sides, and LTE-U proponents participated robustly in the process. There are a number of tests that CableLabs supported as important that ultimately were not adopted. But the final product is nevertheless essential – both in validating coexistence performance of any LTE-U device proposed for deployment, and as a sign that diverse industry interests can work toward solutions as wireless access becomes ever more important for consumers.

CableLabs will continue to be engaged as the WFA moves to implement this plan with authorized test labs. We look forward to a transparent process with results reported publicly by the WFA. As we move to this implementation phase, it is worth describing what the test plan does, in order to understand why it is so important.

At a high level, the test plan does the following:

  1. Checks that LTE-U devices select the most lightly used channel, as LTE-U proponents say they will do;
  2. Ensures that new Wi-Fi networks can access the channel when LTE-U is active;
  3. Measures the impact to Wi-Fi throughput and latency from LTE-U; and,
  4. Ensures that LTE-U adapts its use of the spectrum in response to variation in consumer use of Wi-Fi, as occurs in the real world, in real time.

And it does all of this at signal levels that have been shown with real-world data to be reflective of consumer use of Wi-Fi hotspots. These tests are necessary due to the well-documented shortcomings in the LTE-U Forum coexistence specification, and the lack of standardized test procedures to date, which has yielded vastly different coexistence conclusions. For more information on our views of the test procedures, see Jennifer Andreoli-Fang’s contribution to the August workshop of the WFA, which is available here.

Reasonable compromises have been made by all sides in developing this test plan. It is time to move forward using the outcome of this process, in full, as the sole source of reliable determinations of LTE-U coexistence.