New LTE-U, Wi-Fi coexistence tests show promise, but controversy continues
Dueling test results for LTE-Unlicensed/Wi-Fi coexistence continue with a newly released data set from Qualcomm developed with input from CableLabs, which Qualcomm says confirm fair coexistence between LTE-U and Wi-Fi.
However, CableLabs described the interaction as merely a “brief technical engagement” and continues to press for LTE-U to be vetted via a standards process. The specification for LTE-U, which was recently updated to address some of the coexistence concerns expressed by the Wi-Fi community, was privately developed by a group of vendors and carriers (including Qualcomm, Verizon Communications and others) via the LTE-U Forum. Meanwhile, the standards process for the license assisted access version – which also uses LTE-over-unlicensed spectrum and a listen-before-talk coexistence mechanism – is still being finalized by 3GPP.
The Wi-Fi Alliance held a workshop on coexistence recently, with Qualcomm (which is a member of both the LTE-U Forum and the Wi-Fi Alliance) and other industry players in attendance. CableLabs presented work that showed significant concerns over the impact LTE-U can have on Wi-Fi – which Qualcomm has taken issue with, saying that the test scenario CableLabs used violated the principals laid out in the LTE-U specification.
Qualcomm followed up this week with the release of the test results from its own work with CableLabs, which it described as a “three-week trial with CableLabs” and said it followed CableLabs’ guidance on scenarios to test, including density of nodes, different equipment vendors and the combinations that were analyzed, although it said time constraints allowed only a subset of the agreed-upon tests to be run.
As in past tests, the Wi-Fi coexistence scenarios run by Qualcomm showed Wi-Fi throughput improves when a second, interfering Wi-Fi access point gets replaced by LTE-U equipment – which is why one of the arguments used by supporters of LTE-U is that the technology is a “better neighbor to Wi-Fi than Wi-Fi is to itself.”
In this scenario, Qualcomm used the same Wi-Fi vendor for the test and interfering APs, distributed 15 user devices over three locations and tested both data and voice-over-IP services for throughput and delay. Qualcomm said the “testing also showed that the average one-way delay is substantially reduced when the second Wi-Fi AP is replaced by an LTE-U small cell. These latest test results are thus fully consistent with all prior tests that were performed in accordance with the LTE-U specifications.”
Qualcomm emphasized in a blog entry it is “cooperating openly with the Wi-Fi industry and will support the test development effort jointly with Wi-Fi Alliance, who agrees with us on focusing on LTE-U behavior as much as possible rather than Wi-Fi performance.”
Test results that support arguments on either side have emerged over the past year, particularly in comments to the Federal Communications Commission, with companies ranging from Google to Broadcom and others weighing in with a variety of test results. However, the LTE-U spec does rely on some proprietary technology from Qualcomm for coexistence, and also depends on any given operator following the LTE-U’s guidelines for implementation – and many in the Wi-Fi community are reluctant to rely solely on a wireless operator’s good intentions to protect enterprise and consumer Wi-Fi implementations. In addition, testing has been hampered by the fact there is no commercially available LTE-U equipment that can be used for testing, so tests have typically been conducted with LTE signal generators.
In part because LTE-U has formed outside the typical standards process, what constitutes terms such as “collaboration” and “coordination” has also been a hotly debated topic on both sides, with some on the Wi-Fi side claiming LTE-U proponents have made minimal information sharing sound like closer cooperation than is actually happening. The working group of the Wi-Fi Alliance is supposed to help address that since many companies of the LTE-U Forum are also Wi-Fi Alliance members.
CableLabs, for its part, said it continues to have concerns about LTE-U/Wi-Fi coexistence and certainly did not back down from its previous results. In regards to Qualcomm’s newest results, the organization responded to RCR Wireless News’ request for comment by saying:
“CableLabs has done extensive research and shares the concern of the Wi-Fi community that LTE-U will significantly interfere with Wi-Fi. We continue to hold that view after a brief technical engagement at Qualcomm’s facilities, and we continue to believe that the best path toward solutions is an inclusive, collaborative standards process,” said Rob Alferder, VP technology policy at CableLabs.
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