LTE-U as currently contemplated would be a disaster for Wi-Fi, and any type of co-channel LTE, including LAA, is likely to significantly reduce Wi-Fi coverage area unless specific coexistence mechanisms are adopted, according to a presentation Broadcom delivered to the FCC last week.
Based on a variety of tests and simulations using publicly available information, Broadcom and others in the Wi-Fi industry believe Wi-Fi links will be severely degraded by interference from neighboring co-channel LTE-U based networks. That in part is what prompted Christopher Szymanski, director of product marketing and government affairs at Broadcom, to meet with advisors to FCC Chairman Tom Wheeler, as well as advisors to Commissioners Jessica Rosenworcel, Michael O'Rielly and Ajit Pai.
Other FCC staff were also present during the meetings, where Szymanski discussed the results of laboratory tests that Broadcom conducted based on the draft test plan published by the Wi-Fi Alliance, which is in the processing of finalizing a co-existence test regime for LTE-U and Wi-Fi.
Given the current installed base of Wi-Fi users and the ever-increasing demand for Wi-Fi, Broadcom engineers want to highlight the impact on users – rather than framing the issue as a technology vs. technology debate or cable vs. carrier dispute as it has been characterized.
"Our focus is ensuring this public resource, the unlicensed spectrum, isn't a race to the bottom," where you get more and more interference, Szymanski told FierceWirelessTech. "We want to drive to the library type of environment -- quieter and more polite is going to ensure better traffic rather than a noisy bar room environment."
The noisy bar type of environment is what some see happening when LTE-U is introduced in unlicensed spectrum where Wi-Fi has grown and flourished. And since so many people have deployed Wi-Fi based on current technology – including municipalities and real libraries – that creates a problem if the environment changes.
According to Szymanski's presentation filed with the FCC, the most harmful impact to the user experience will be on Wi-Fi signal strengths below -62 dBm. Measurements in the field for enterprise and outdoor deployments have demonstrated that ~90 percent of Wi-Fi links are below -62 dBm and ~50 percent of Wi-Fi links are below -80 dBm.
Clint Brown, director of product marketing at Broadcom, said Wi-Fi by design is polite; it "listens before talk" to avoid interference in the unlicensed bands. LTE doesn't have that mechanism because it was designed for licensed spectrum where there's typically only one user. To ensure fairness to deployed Wi-Fi, Broadcom recommends mandatory neighbor detection level of at least -82 dBm, consistent with Wi-Fi preamble detect levels.
Qualcomm (NASDAQ:QCOM), a big proponent of LTE-U, has pointed out that it also has a substantial vested interest in Wi-Fi, and it's collaborating with stakeholders to make sure LTE-U and Wi-Fi will coexist successfully. It expects the test plan developed through the Wi-Fi Alliance will validate that LTE-U will not adversely impact Wi-Fi. The developers of LTE-U have said they're not just taking LTE and plunking it into unlicensed spectrum; they developed a certain type of LTE so that it would co-exist in unlicensed bands.
While Broadcom did get out of the LTE baseband business for handsets in 2014, it still has a lot of LTE expertise in house and continues to work on carrier-grade equipment based on LTE.
For more:
- see this FCC filing
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